Schuyler, Nebraska Platte River and Shell Creek –
Section 205 Flood Risk Management
Feasibility Report and Environmental Assessment with Finding of No Significant Impact
SEPTEMBER 2011
EXECUTIVE SUMMARY
The project area is located along a reach of the Platte River near Schuyler, Nebraska, which is the county seat for Colfax County. The Platte River is located approximately 1.5 miles south of the city. Lost Creek, a minor tributary of the Platte River, runs along the southern edge of the community. Another tributary to the Platte River, Shell Creek, lies to the north and east of Schuyler. Most of the land surrounding Schuyler is used for agricultural purposes.
Schuyler is subject to flooding from the Platte River / Lost Creek and Shell Creek. A major Shell Creek flood did extensive damage to property in northeastern Schuyler in May 2008 and a smaller flood did significant damage again in 2010, just as residents were completing repairs from the earlier flood. Southern Schuyler was also impacted by flooding from Lost Creek, a tributary to the Platte River during the 2010 Shell Creek flood.
The current FEMA Flood Insurance Rate Map for Schuyler notes that portions of the city are within the 100-year (1% annual chance of exceedance) floodplains of both Shell Creek and the Platte River. A draft flood insurance rate map developed by the Corps for FEMA now indicates that the Platte River 100-year floodplain will extend well into heavily developed areas of Schuyler – areas which had not previously been designated as lying within the 100-year floodplain. The new area includes the downtown section. According to recent analysis, 684 residential structures lie within the 100-year floodplain and 830 residences lie within the 500- year floodplain at Schuyler.
A thorough Feasibility study has been conducted to determine the recommended plan for addressing the flooding problem in Schuyler. The study evaluated structural and nonstructural measures including a detailed analysis of four different levee alternatives along Shell Creek and three different Platte River/Lost Creek levee alternatives. The analysis examined flood risk reduction measures over a range of flood frequencies for both threats. Pursuant to NEPA and USACE planning guidance, formulation of plans must considered environmental effects (EQ account) including avoidance, minimization, and mitigation of environmental impacts. Results from this feasibility study indicate that levees to protect Schuyler from both Shell Creek and the Platte River are economically feasible.
Based on the feasibility study analysis Shell Creek levee Alternative SC-C and Platte River/Lost Creek levee Alternative PR-A were selected as the recommended plans. The plans once implemented would include 5.6 miles of levees and some channel shaping /cleanout. The combined plan provides flood risk management at the 1% annual exceedance level to 207 structures in northeast Schuyler and 559 structures in the southern portion of Schuyler that are within the 100-year floodplain, resulting in an expected reduction in annual damages of $1,900,000. The cost of construction, including real estate is estimated at $9,868,000, which will be cost shared 65/35 with the local sponsor. The preferred plan has an estimated net annual benefit to the nation of $1,386,290 and a benefit to cost ratio of approximately 3.7 to 1. An environmental assessment was conducted, which resulted in a finding of no significant impact (FONSI), resulting in a conclusion that no environmental impact statement will be needed.
TABLE OF CONTENTS
Table of Contents 1. STUDY BACKGROUND ...... 1 1.1 STUDY AUTHORITY AND PURPOSES ...... 1 1.1.1 Authority ...... 1 1.1.2 Sponsorship and Cost Sharing ...... 1 1.1.3 Purpose and Need ...... 1 1.2 PROJECT LOCATION...... 1 1.2.1 Study Area Location and Description ...... 1 1.2.2 Congressional District ...... 5 1.3 STUDY BACKGROUND ...... 5 1.3.1 Physical Setting ...... 5 1.3.2 History of Flooding ...... 5 1.3.3 Study History ...... 11 1.3.4 Relationship to Prior Studies and Existing Water Projects ...... 11 2. EXISTING CONDITIONS ...... 15 2.1 EXISTING CONDITIONS FOR FLOODING ...... 15 2.1.1 Hydrology ...... 15 2.1.2 Existing Conditions Hydraulic Model ...... 24 2.1.3 Platte River / Lost Creek Structure ...... 31 2.1.4 Floodplain Issues and Regulation ...... 32 2.2 GENERAL ENGINEERING EXISTING CONDITIONS ...... 37 2.2.1 Soils and Geotechnical Engineering Existing Conditions ...... 38 2.2.2 Hazardous, Toxic and Radiological Waste (HTRW) ...... 41 2.3 ENVIRONMENTAL EXISTING CONDITIONS ...... 41 2.3.1 Climate ...... 41 2.3.2 Physiography, Soil Conditions and General Land Use ...... 42 2.3.3 Water Quality ...... 43 2.3.4 Vegetation and Terrestrial Habitat ...... 44 2.3.5 Wetlands ...... 44 2.3.6 Fish and Wildlife...... 48 2.3.7 Threatened and Endangered Species and State-Listed Species of Concern ...... 49 2.4 COMMUNITY EXISTING CONDITIONS ...... 50
Platte River and Shell Creek Section 205 i Flood Risk Management Schuyler, Nebraska 2.4.1 Economic Existing Conditions ...... 50 2.4.2 Cultural Resources ...... 52 2.4.3 Recreational Resources ...... 55 2.4.4 Real Estate and Utilities ...... 57 2.4.5 Relationship of this Project to Other Community Projects and Plans ...... 58 3. FUTURE WITHOUT-PROJECT CONDITIONS ...... 60 3.1 FUTURE FLOODING CONDITIONS ...... 60 3.1.1 Hydrology and Flood Frequency ...... 60 3.1.2 Hydraulics and Channel Stability ...... 60 3.1.3 Floodplain Management ...... 62 3.1.4 Embankments and Agricultural Levees ...... 62 3.2 ENVIRONMENTAL FUTURE CONDTIONS ...... 63 3.2.1 Climate Change ...... 63 3.2.2 Ecosystem ...... 63 3.3 FUTURE COMMUNITY CONDITIONS ...... 64 3.3.1 Future Without-Project Condition Economic Analysis ...... 64 3.3.2 Impacts of Future Flooding on Community Stability ...... 68 3.3.3 Recreational Outlook under Future Without-Project Conditions ...... 68 4. PLANNING, PROBLEMS, OPPORTUNITIES, CONSTRAINTS, GOALS AND OBJECTIVES ...... 70 4.1 PROBLEMS ...... 70 4.1.1 Overall Project ...... 70 4.1.2 Shell Creek ...... 71 4.1.3 Platte River...... 72 4.2 PLANNING OPPORTUNITIES ...... 72 4.3 PLANNING CONSTRAINTS ...... 72 4.3.1 Overall Project ...... 73 4.3.2 Shell Creek ...... 74 4.3.3 Platte River...... 74 4.4 PLANNING OBJECTIVES ...... 74 4.4.1 Reduce the Number of Structures in the Floodplain ...... 75 4.4.2 Lower the Evacuation, Road Closure and Recovery Costs to the City and County 75 4.4.3 Reduce the Risk of Flood Damages to Property ...... 75 4.4.4 Minimize the Operation and Maintenance Cost ...... 75 4.4.5 Restore or Build Effective Wetlands Where Opportunities Permit ...... 75
Platte River and Shell Creek Section 205 ii Flood Risk Management Schuyler, Nebraska 4.4.6 Replace Invasive Species with Native Species Where Possible ...... 76 4.4.7 Protect and Promote Recreational Opportunities ...... 76 4.4.8 Improve Safety ...... 76 4.4.9 Minimize Erosion and Sediment Impacts during Construction ...... 76 4.4.10 Provide for the Restoration of Community Vitality ...... 76 5. ALTERNATIVE FORMULATION ...... 77 5.1 NONSTRUCTURAL FLOOD DAMAGE REDUCTION MEASURES ...... 77 5.1.1 Flood Proofing Measure for Shell Creek Floodplain Structures ...... 78 5.1.2 Flood Proofing Measure for Platte River Floodplain Structures ...... 78 5.1.3 Flood Warning ...... 79 5.1.4 Other Nonstructural Measures ...... 80 5.1.5 Relocation ...... 80 5.2 SHELL CREEK STRUCTURAL MEASURES ...... 80 5.2.1 Improving Conveyance through the Railroad Embankment ...... 80 5.2.2 Diversion of Water from Shell Creek Upstream of Highway 30 ...... 81 5.2.3 Improvement of the Shell Creek Channel Downstream of Schuyler ...... 82 5.2.4 Levee Measures ...... 82 5.2.5 Other Structural Flood Risk Reduction Measures Considered for Shell Creek ...... 82 5.2.6 Shell Creek Alternatives Formulated ...... 83 5.2.7 Consolidation of Shell Creek Alternatives ...... 87 5.2.8 Shell Creek Alternatives Comparison ...... 92 5.2.9 Selection of Shell Creek NED Plan ...... 96 5.3 PLATTE RIVER STRUCTURAL MEASURES ...... 97 5.3.1 Reconnaissance Study Alternatives ...... 97 5.3.2 Construct a Dam Upstream of Schuyler ...... 98 5.3.3 Build a Levee near the North Bank of the Platte River ...... 98 5.3.4 Improve the Conveyance of Lost Creek South of Schuyler ...... 98 5.3.5 Remove the Abandoned Railroad Embankment South of Schuyler ...... 98 5.3.6 Levee Measures ...... 98 5.3.7 Consolidation of Platte River Alternatives ...... 101 5.3.8 Optimum Platte River Levee Height ...... 102 5.3.9 Platte River Alternatives Comparison ...... 104 5.4 SUPPLEMENTAL LEVEE INFORMATION ...... 107 5.4.1 Impervious Fill ...... 107
Platte River and Shell Creek Section 205 iii Flood Risk Management Schuyler, Nebraska 5.4.2 Random Fill ...... 108 5.4.3 Topsoil ...... 108 5.4.4 Disposal of Clearing and Grubbing Materials, Excess Excavated Soils and Refuse 108 6. ALTERNATIVE PLANS EVALUATION AND COMPARISON ...... 109 6.1 METHODS OF EVALUATING A SUCCESSFUL FLOOD RISK MANAGEMENT PLAN 109 6.1.1 The NED Account ...... 109 6.1.2 EQ, RED and OSE Accounts ...... 109 6.2 COMPARISON OF ALTERNATIVE PLANS ...... 110 6.2.1 Nonstructural Flood Damage Reduction Alternative ...... 110 6.2.2 Screening Structural Flood Damage Reduction Alternatives ...... 110 6.3 ENVIRONMENTAL QUALITY (EQ) CONSIDERATIONS ...... 113 6.4 OTHER SOCIAL EFFECTS (OSE) CONSIDERATIONS ...... 115 6.5 MITIGATION OF IMPACTS FROM PROJECT ALTERNATIVES ...... 115 6.5.1 Base Flood Elevations...... 115 6.5.2 Environmental Mitigation Considerations ...... 116 6.6 PLAN SELECTION PROCESS ...... 116 6.6.1 Shell Creek Plan Selection ...... 116 6.6.2 Platte River Plan Selection...... 116 7. RECOMMENDED PLAN ...... 117 7.1 PLAN DESCRIPTION ...... 117 7.1.1 Shell Creek Plan Description ...... 117 7.1.2 Platte River Plan Description ...... 117 7.2 COMPLIANCE OF SELECTED PLAN WITH THE PRINCIPLES AND GUIDELINES (P&G) ...... 118 7.2.1 Flood Risk Management Principles and Guidelines ...... 118 7.2.2 Application to Recommended Plans for Schuyler ...... 119 7.3 OPERATION AND MAINTENANCE (O&M) CONSIDERATIONS ...... 121 7.4 ENVIRONMENTAL FEATURES AND MITIGATION ...... 121 7.5 RECREATIONAL FEATURES ...... 122 7.6 REAL ESTATE AND LERRD CONSIDERATIONS ...... 122 7.7 COST SHARING AND SPONSORSHIP...... 123 7.8 DESIGN AND CONSTRUCTION CONSIDERATIONS ...... 124 7.8.1 Design ...... 124
Platte River and Shell Creek Section 205 iv Flood Risk Management Schuyler, Nebraska 7.8.2 Construction ...... 125 7.9 POST PROJECT COMPLETION ACTIVITIES AND RESPONSIBILITIES ...... 125 7.10 LEGAL OR POLICY ISSUES, OPTIONS CONSIDERED AND COMPLIANCE 125 7.11 QUALITY REVIEWS ...... 125 7.11.1 Levels of Review ...... 125 7.11.2 Independent External Peer Review (IEPR) ...... 126 7.12 RISK AND UNCERTAINTY ...... 127 7.13 PLAN IMPLEMENTATION AND SCHEDULE ...... 128 8. ENVIRONMENTAL IMPACTS, REVIEWS AND COMPLIANCE ...... 130 8.1 ENVIRONMENTAL CONSEQUENCES ...... 130 8.1.1 Water Quality ...... 130 8.1.2 Wetlands ...... 131 8.1.3 Trees and Shrubs ...... 133 8.1.4 Fish and Wildlife...... 134 8.1.5 Threatened and Endangered Species ...... 134 8.1.6 Physiographic and Soil Conditions ...... 135 8.1.7 Cumulative Effects ...... 136 8.1.8 Irreversible and Irretrievable Commitment of Resources ...... 137 8.2 SUMMARY OF COORDINATION, PUBLIC VIEWS AND COMMENTS ...... 137 8.2.1 SPONSOR – STAKEHOLDER MEETINGS ...... 137 8.2.2 GOVERNMENT AND ENVIRONMENTAL AGENCY COORDINATION MEETINGS ...... 140 8.2.3 GENERAL PUBLIC INVOLVEMENT MEETINGS ...... 142 8.3 OTHER ENVIRONMENTAL ACTS, COORDINATION AND COMPLIANCE .... 145 8.3.1 Endangered Species Act ...... 145 8.3.2 Fish and Wildlife Coordination Act ...... 146 8.3.3 Clean Water Act (CWA) ...... 147 8.3.4 Migratory Bird Treaty Act ...... 147 8.3.5 Prime Farmlands ...... 148 8.3.6 National Environmental Policy Act ...... 148 8.3.7 CULTURAL RESOURCES ...... 148 8.3.8 Executive Order 11988 Floodplain Management ...... 148 9. RECOMMENDATIONS ...... 150 9.1 OMAHA DISTRICT ...... 150 9.2 LOCAL SPONSOR...... 151
Platte River and Shell Creek Section 205 v Flood Risk Management Schuyler, Nebraska 10. REFERENCES ...... 152
LIST OF TABLES Table 2-1 Shell Creek Peak Flood Flow Frequency ...... 17 Table 2-2 Shell Creek at Schuyler Duration Frequency ...... 19 Table 2-3 Shell Creek near Schuyler (Highway 15) Balanced Hydrographs ...... 19 Table 2-4 Discharge-Frequency Results Platte River North Bend, NE ...... 23 Table 2-5 Comparison of Platte River Water Surfaces ...... 28 Table 2-6 Average Maximum and Minimum Temperature, Precipitation, and Snowfall Values for 1970-2007 for Columbus and Schuyler, Nebraska ...... 42 Table 2-7 Shell Creek, Existing Conditions Expected Annual Damages ...... 52 Table 4-1 Planning Problems ...... 70 Table 4-2 Planning Constraints ...... 73 Table 4-3 Planning Objectives ...... 75 Table 5-1 Summary of Initial Screening Shell Creek Measures ...... 83 Table 5-2 Summary of Initial Screening Platte River Measures ...... 99 Table 6-1 NED Account: Benefits and Cost Summary, With-Shell-Creek Project Alternatives 112 Table 6-2 NED Account: Benefits and Cost Summary for With-Project Alternatives ...... 113 Table 6-3 Impacts to Upland and Wetland Vegetation ...... 114 Table 6-4 Impacts to Prime Farmland ...... 115 Table 7-1 Implementation Schedule ...... 129 Table 8-1 Impacts to Trees and Shrubs ...... 133 Table 8-2 Impacts to Prime Farmland ...... 135
Platte River and Shell Creek Section 205 vi Flood Risk Management Schuyler, Nebraska LIST OF FIGURES Figure 1-1 Location of Schuyler along the Platte River in Nebraska ...... 2 Figure 1-2 Major Waterways and Levee Alignments (USGS topographic image) ...... 4 Figure 1-3 Aerial Photo of Schuyler Flooding taken on June 13th, 2010 Fire Station along Old Highway 30 in foreground (State of Nebraska Photo) ...... 7 Figure 1-4 Aerial Photo of Shell Creek Flood taken on May 31, 2008 Looking Northwestward from near Confluence with Platte River ...... 7 Figure 1-5 Photo of June 2010 Lost Creek Flooding in Schuyler Golf Course ...... 9 Figure 1-6 Platte River Flood at Schuyler, NE 1967 ...... 10 Figure 2-1 Plot of the Discharge – Probability Distribution for Shell Creek near Columbus ...... 18 Figure 2-2 Shell Creek Balanced Flood Hydrographs used in HEC-HMS Analysis at Schuyler 20 Figure 2-3 Schematic of Shell Creek HEC-HMS Model ...... 21 Figure 2-4 Shell Creek Ponding Areas during Flooding at Schuyler ...... 22 Figure 2-5 Platte River at North Bend - Updated Discharge Frequency Curve ...... 24 Figure 2-6 Shell Creek Economic Damage Reaches ...... 26 Figure 2-7 Platte River Cross Sections used in the Analysis ...... 29 Figure 2-8 Typical Floodway Cross Section ...... 33 Figure 2-9 Effective and Draft 100-year (1% annual chance of exceedance) floodplain boundaries ...... 35 Figure 2-10 Typical Pattern of Soils and Parent Material near Schuyler, Nebraska ...... 39 Figure 2-11 Drainage Pattern and Wetlands near Schuyler, NE ...... 45 Figure 2-12 View of Shell Creek Channel north of UPRR line. Photo is oriented southeast...... 46 Figure 2-13 View of Lost Creek in western portion of golf course. Photo is oriented southwest 47 Figure 2-14 Interior of the Oak Ballroom in Schuyler, NE ...... 54 Figure 3-1 50 Years of Stage-Discharge Trends on the Platte River at North Bend ...... 62 Figure 4-1 Debris Removal at UPRR Bridge over Shell Creek During flood on May 30, 2008 . 71 Figure 5-1 Temporary Platte River Gage at Schuyler, NE (March 2010) ...... 79 Figure 8-1 Notice of Public Involvement Meeting in Spanish ...... 143
Platte River and Shell Creek Section 205 vii Flood Risk Management Schuyler, Nebraska LIST OF PLATES
PLATE 1: Shell Creek Drainage PLATE 2: Alignment SC-A PLATE 3: Alignment SC-B PLATE 4: Alignment SC-C PLATE 5: Alignment SC-D PLATE 6: Alignment SC-E PLATE 7: Alignment PR-A PLATE 8: Alignment PR-B-1 PLATE 9: Alignment PR-B-2 PLATE 10: Typical Section Earthen Levee PLATE 11: Downstream Shell Creek Channel Cleanout PLATE 12: Alignment SC-B-1 PLATE 13: Alignment SC-E Final PLATE 14: Alignment SC-C Final
LIST OF APPENDICES
Appendix A: BIOLOGY Appendix B: COST ENGINEERING Appendix C: CULTURAL RESOURCES Appendix D: ECONOMICS Appendix E FLOOD RISK AND FLOOD PLAIN MANAGEMENT Appendix F: GEOTECHNICAL Appendix G: GIS & SURVEYS (Placeholder for E. files) Appendix H: HTRW Appendix I: HYDRAULICS Appendix J: HYDROLOGY AND INTERIOR DRAINAGE Appendix K: MODEL PPA Appendix L: PREVIOUS STUDIES (Placeholder for E. files) Appendix M: PUBLIC INVOLVEMENT Appendix N: REAL ESTATE Appendix O: RECREATION
Platte River and Shell Creek Section 205 viii Flood Risk Management Schuyler, Nebraska LIST OF ABBREVIATIONS
ATR – Agency Technical Review (USACE) BA – Biological Assessment BCR – Benefit-Cost Ratio BOD – Biological Oxygen Demand cfs – cubic feet per second CLOMR – Conditional Letter of Map Revision (FEMA) CWA – Clean Water Act CY – Cubic Yard D&I – Design and Implementation (USACE) EA – Environmental Assessment (USACE) EC – Engineering Circular (USACE) EAD – Expected Annual Damages (USACE) EGM – Economic Guidance Memorandum (USACE) EM – Engineer Manual (USACE) EQ – Environmental Quality (Account) ER – Ecosystem Restoration (USACE) ER – Engineer Regulation (USACE) ESA – Endangered Species Act FCSA – Feasibility Cost Share Agreement (USACE) FEMA – Federal Emergency Management Agency FIRM – Flood Insurance Rate Map FIS – Flood Insurance Study (FEMA) FONSI – Finding of No Significant Impact FPMP – Floodplain Management Plan FS/EA – Feasibility Study/Environmental Assessment (USACE) FWCA – Fish and Wildlife Coordination Act FY – Fiscal Year GIS – Geographic Information System HEC – Hydrologic Engineering Center (USACE) HEC-FDA – Hydrologic Engineering Center – Flood Damage Reduction Analysis (USACE) HEC-HMS – Hydrologic Engineering Center – Hydrologic Modeling System (USACE) HEC-RAS – Hydrologic Engineering Center – River Analysis System (USACE) HEC-SSP – Hydrologic Engineering Center – Statistical Software Package (USACE) HEC-TD – Hydrologic Engineering Center – Technical Document (USACE) HQUSACE – Headquarters, U.S. Army Corps of Engineers HTRW- Hazardous Toxic and Radiological Waste IBI – Index of Biotic Integrity IEPR – Independent External Peer Review (USACE) LERRD – Lands, Easements, Relocations, Rights-of-way and Disposal areas (USACE) LOB – Left Over Bank LPNNRD – Lower Platte North Natural Resources District M-CACES – Micro-Computer Assisted Cost Estimating System (USACE) NDEQ – Nebraska Department of Environmental Quality NDOR – Nebraska Department of Roads
Platte River and Shell Creek Section 205 ix Flood Risk Management Schuyler, Nebraska NED – National Economic Development (Account) NEPA – National Environmental Policy Act NER – National Ecosystem Restoration (USACE) NFIP – National Flood Insurance Program (FEMA) NGPC – Nebraska Game and Parks Commission NPDES – National Pollutant Discharge Elimination System (permit) NWI – National Wetlands Inventory NRCS – Natural Resources Conservation Service NRHP – National Register of Historic Places O&M – Operation and Maintenance OMRR&R – Operation, Maintenance, Repair, Replacement and Rehabilitation OSE – Other Social Effects (Account) P&G – Principles and Guidelines (USACE) PCA – Project Cooperation Agreement (USACE) PM – Project Manager PMP – Project Management Plan (USACE) PPA—Project Partnership Agreement (USACE) RAS – River Analysis System (USACE) RED – Regional Economic Development (Account) ROB – Right Over Bank SF – Square Foot SFHA – Special Flood Hazard Area (FEMA) SHPO – State Historic Preservation Officer SWPPP – Stormwater Pollution Prevention Plan SY – Square Yard T&E – Threatened and Endangered TMDL – Total Maximum Daily Load T—Tons UDV – Unit Day Value (USACE) USACE – U.S. Army Corps of Engineers (noting acronyms common to agency) USDA – U.S. Department of Agriculture USFWS – U.S. Fish and Wildlife Service USGS – U.S. Geological Survey WQI – Water Quality Index WRDA – Water Resources Development Act WY – Water Year (October 1st – September 30th)
Platte River and Shell Creek Section 205 x Flood Risk Management Schuyler, Nebraska 1. STUDY BACKGROUND
1.1 STUDY AUTHORITY AND PURPOSES
1.1.1 Authority This study is being conducted under the authority of Section 205 of the Flood Control Act of 1948, as amended. The purpose of the Section 205 program is to implement flood risk reduction measures (structural or nonstructural) to reduce damages caused by flooding. The program focuses on solving local flood problems that are of limited scope and complexity. Projects implemented under Section 205 authority are formulated for flood risk management in accordance with current policies and procedures governing projects of the same type that are specifically authorized by Congress.
1.1.2 Sponsorship and Cost Sharing The local sponsor for this study is the Lower Platte North Natural Resources District (LPNNRD). The LPNNRD, in turn, has an inter-local cooperation agreement with the City of Schuyler. A special relationship exists between the LPNNRD and the state of Nebraska, Department of Natural Resources allowing the LPNNRD to obtain technical services under the guidelines set by the Nebraska Unicameral when the Natural Resources Districts were established. The Lower Platte North Natural Resources District (LPNNRD) requested that the Omaha District initiate a study to evaluate the flood problem and to analyze potential solutions to reduce flood damages at Schuyler, Nebraska.
1.1.3 Purpose and Need The purpose of the study is to determine if there is a feasible flood risk management project at Schuyler that will protect the community against the dual flood threat presented by the Platte River and by Shell Creek. The study results will detail the “Federal Interest” in an economically viable project and define any impacts to the environment, which could occur, as a result of project construction. The primary purpose of a flood risk management project is to reduce the risk of flood damage, injury and death from flooding. As flooding at Schuyler is not high risk in terms of threats to life or potential to directly cause injury to people, the central goal is protecting a vulnerable community from frequent and destructive floods. Northeastern Schuyler has been hit with damaging floods from Shell Creek in 1990, 2008, and 2010. In addition, the Platte River and Lost Creek remain a flood threat to southern Schuyler, as demonstrated by damages from Lost Creek in 2010 and “near misses” in the past 20 years from Platte River floods. This report serves as a combined report of project feasibility and includes an integrated environmental assessment.
1.2 PROJECT LOCATION
1.2.1 Study Area Location and Description The study includes the city and its environs which are adversely impacted by flooding from the Platte River and its tributaries. The study area is located about one mile north of the Platte River near Schuyler, Nebraska, which is the county seat for Colfax County. Schuyler is located
1 approximately 70 miles west-northwest of Omaha in the broad Platte River floodplain as shown on Figures 1-1 and 1-2.
Figure 1-1 Location of Schuyler Along the Platte River in Nebraska
The Platte River is located approximately 1.5 miles south of the city. Lost Creek, a minor tributary of the Platte River, runs along the southern edge of the community and enters the Platte
2 River about three miles downstream. Shell Creek, a much larger tributary to the Platte River, flows eastward to the north of the city before turning south and flowing adjacent to northeastern Schuyler. Shell Creek turns eastward at the Union Pacific rail line which bisects Schuyler before entering the Platte River 3 miles downstream.
Two highways intersect at Schuyler; U. S. Highway 30 runs east and west and state Highway 15 runs north and south through Schuyler. Highway 30 was rerouted north of the community and improved to a 4-lane expressway in 2004 and includes new bridges over Shell Creek and Nieman Ditch. Farming is the main land use around Schuyler, with some sand and gravel pit operations located along the Platte River south of the city. A major meat packing plant is located 1 mile west of the city and is not in the 100-year (1% annual chance exceedance) floodplain. The location of Schuyler and nearby floodplain features are shown in Figure 1-2.
Schuyler, Nebraska had a 2010 population of 6,211, which is a 15.6 percent increase from the 2000 population of 5,371 and a 53.3 percent increase from the 1990 population of 4,052 (32.6 percent increase from 1990-2000). This population growth has led to increases in housing units between 1990 (1,729 units) and 2000 (1,856 units), and an increase to 1,972 units in 2010. The average household size also increased in each of the decennial census years from 1990-2010 with figures of 2.42, 3.03, and 3.37, respectively (U.S. Census Bureau, 1990; 2000; and 2011).
Educational attainment in Schuyler is relatively low, with 25.2 percent of the population age 25 years or older having graduated high school and 7.6 percent having obtained a bachelor’s degree or higher in 2005-2009. In 2005-2009, the major industries employing Schuyler residents were: manufacturing, 51.6 percent; services, 23.0 percent; construction, 7.7 percent; finance and insurance, 5.3 percent; wholesale and retail trade, 4.9 percent; and others, 7.5 percent. Schuyler had an estimated 2005-2009 median household income of $43,580, and in this same time period the percentage of the population living below the poverty level was 16.3. By comparison, median household income and poverty level in the state of Nebraska are $47,995 and 11.8 percent, while the U.S. has figures of $51,425 and 13.5 percent for the same time period (U.S. Census Bureau, 2010).
In 2010, persons of Hispanic or Latino origin (who may be of any race) comprised 65.4 percent of the total population of Schuyler, compared to 9.2 percent of the Nebraska population and 16.3 percent of the U.S. population. In 2010, Schuyler’s racial composition consisted of the following: White, 56.7 percent; Black, 1.3 percent; American Indian and Alaska Native, 1.7 percent; Asian, 0.2 percent; some other race, 37.0 percent; and two or more races, 3.0 percent (U.S. Census Bureau, 2011).
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Figure 1-2 Major Waterways and Levee Alignments (USGS Topographic Image)
4 1.2.2 Congressional District Schuyler is located in Nebraska’s First Congressional District. This study area is represented by Congressman Jeff Fortenberry in the House of Representatives. Senators Ben Nelson and Mike Johanns represent the state of Nebraska in the Senate.
1.3 STUDY BACKGROUND
1.3.1 Physical Setting Schuyler is located in the broad alluvial floodplain of the Platte River in east-central Nebraska. The Platte River is a braided river that drains the eastern Rocky Mountains in its North and South Platte River tributary headwaters. The Platte River begins at North Platte with the confluence of the headwater-rivers and receives drainage from agricultural land in western and central Nebraska. The Loup River with its relatively steady groundwater-supported Sandhills drainage joins the Platte River roughly 15 miles upstream of Schuyler. The Platte River enters the Missouri River at Plattsmouth, roughly 80 miles downstream of Schuyler.
Shell Creek joins the Platte River roughly 3 miles downstream of Schuyler and is adjacent to the city on its northeastern side. Shell Creek transitions from a stream occupying its own valley to a floodplain stream that flows through alluvium shaped by the Platte River in its final 7 miles above its confluence with the Platte. Shell Creek is constrained in a drainage channel adjacent to the Union Pacific Railroad tracks for over two of those miles. Plate 1 of Appendix I (Hydraulics) shows the Shell Creek complexities in the lower 7 miles. Lost Creek rises in the floodplain of the Platte River near Columbus and enters the Platte River near the mouth of Shell Creek, about 3 miles east of Schuyler.
1.3.2 History of Flooding
1.3.2.1 OVERVIEW Schuyler is subject to periodic flooding from the Platte River and Shell Creek. Additionally, Lost Creek and its tributaries can cause flooding to the city of Schuyler’s South Park and surrounding properties within the overall Platte River floodplain. Lost Creek is also subject to “capture” by the Platte River in larger flood events. Platte River flooding is typically due to rainstorms and/or snowmelt that are sometimes augmented by ice-jams. The Platte River flood threat is greatest from late winter into mid-summer. Shell Creek flooding results from heavy rainfall runoff during the thunderstorm season. Protection from the flood threat caused by Shell Creek is the most urgent concern. Shell Creek has flooded northeastern Schuyler in 1990, 2008 and again in 2010 causing extensive damage each time. Flooding from the Platte River threatened southern Schuyler and the downtown area in 1967 and again in 1993. Lost Creek most recently caused damage in 2010.
The general flood damage areas impacted by Shell Creek and by Platte River / Lost Creek flooding are separated by the Union Pacific Railroad embankment that bisects the city, running roughly from east to west just north of the main downtown area. While the two areas can be generally considered separate for floods up to the 100-year (1% annual chance of exceedance) event, extreme events on the Platte River may have the potential of seeping through the railroad
5 embankment or even overtopping it, causing some shallow flooding north of the tracks. Extreme Shell Creek floods historically flow over the rail embankment to the east of Schuyler first and have washed out the railroad embankment before flooding in the city can seep through or flow across the tracks from north to south.
There currently is no comprehensive flood protection system for the community. Channel improvements and spoil bank levees have also been constructed along lower Shell Creek, some with federal technical assistance. While some are effective in protecting individual properties against small and frequent floods, they are subject to flanking and overtopping by medium and larger flood events. Additionally, a revetment was built in 1970, on the left bank of the Platte River, 3.5 miles southwest of Schuyler to prevent Platte River overflows from entering Lost Creek at a point where Lost Creek approaches within a few hundred feet of the Platte River. Although it does reduce some urban and agricultural flood damages in the Schuyler area, the principal purpose of the revetment is not direct flood protection to Schuyler, but to provide for channel separation that prevents the “capture” of the Lost Creek channel by the Platte River during major floods.
1.3.2.2 SHELL CREEK FLOODING Shell Creek presents the most frequent flood threat to Schuyler in recent years. Three times in 20 years, northeastern Schuyler has been heavily damaged by flooding from Shell Creek. Lesser flooding was also reported in 1993 when a crest of 3,600 cfs was recorded at the Columbus gage. Solutions to flooding from this large tributary watershed are the most important flood protection goal for the citizens of Schuyler at the time of this feasibility study.
● Flood of 2010 Very heavy rain occurred over the Shell Creek basin between June 5th and June 12th. As much as 12 inches fell over parts of the western and central parts of the Shell Creek basin during that period. Floodwaters surged overbank from Newman Grove near the headwaters to Schuyler at the mouth. A peak discharge of approximately 5,000 cfs occurred at the Shell Creek near Columbus gaging station, which is between a 10 and 20-year (10% to 5% chance of annual exceedance) event at that site.
Similar to the 2008 event, when Shell Creek emerged from the bluff line north of Schuyler, a minor amount of flow exited the channel to the Rawhide Creek basin, as shallow flow across farmland to the east and down the Hughes-Payzant Ditch, but the majority of the flood pushed southward through the channel and floodplain into Schuyler flowing through the Nieman Ditch and Shell Creek bridges under Highway 30. Flooding entered northeastern Schuyler first from the Nieman Ditch overflow. Extensive flooding hit the same areas of northeastern Schuyler on June 12, 2010 that had been hit hard in May 2008. Stages in Schuyler were less than a foot below elevations reached during the May 2008 flood and caused major property damage as noted in Figure 1-3. Storm sewer manholes connecting to a sewage lift station also collapsed adding to the damages to Schuyler.
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Figure 1-3 Aerial Photo of Schuyler Flooding Taken on June 13th, 2010 - Fire Station Along Old Highway 30 in Foreground (state of Nebraska Photo)
Figure 1-4 Aerial Photo of Shell Creek Flood Taken on May 31, 2008 Looking Northwestward From Near Confluence with Platte River
7 ● Flood of 2008 Thunderstorms in late May caused extensive flooding on Shell Creek and in northeastern Schuyler. Two to three inches of rain fell over the entire Shell Creek basin over a short period of time on the night of May 29 - 30th. Larger rainfall amounts (from 4 to 6 inches) were noted by weather radar over the central part of the watershed, with 3 to 4 inch amounts extending into the Loseke Creek sub-basin. The peak flow recorded at the Shell Creek at Columbus gage was 11,200 cfs on May 30th, which was the flood of record for the gage which dates back to 1947. The flood was likely greater than a 100-year (1% chance of annual exceedance) event at Schuyler, and approached the 200-year (0.5% chance of annual exceedance) event at the gaging station near Columbus. When the Shell Creek flood emerged from its valley northeast of Schuyler on the afternoon of May 30th, some of the flood flow continued eastward into the Rawhide Creek basin, as shallow flow across farmland to the east and down the Hughes-Payzant Ditch, but the majority of the flood pushed southward through the channel and floodplain into Schuyler flowing through the Nieman Ditch and Shell Creek bridges under Highway 30. Flooding became severe in Schuyler early in the morning of May 31st.
Most of northeastern Schuyler was inundated to a depth of 1 to 2 feet. Water 6 to 8-inches deep flowed across Highway 15 (from east to west in the central part of the city), and water approximately 18-inches deep flowed across old Highway 30 northeast of Schuyler. Water reached half-wheel height on trailers at the trucking company in Schuyler adjacent to old Highway 30. The apartments at 18th and E St. were evacuated at 12:30 AM the night of May 30 - 31st. Over 200 homes were inundated and the Union Pacific rail road track ballasts southeast of Schuyler were washed out as much as 4-feet deep in some places. According to Union Pacific, the Shell Creek flooding at Schuyler caused the tracks to be shut down for 5-6 hours before they were repaired at the location of the washout at Schuyler. An approximately 90-foot long breach in the Shell Creek spoil bank north of the UPRR tracks and upstream of the confluence with Nieman Ditch was observed after the flooding. The extent of flooding from Shell Creek is shown in Figure 1-4.
● Flood of 1990 Heavy thunderstorms from June 12th to June 16th caused flooding on Shell Creek, Maple Creek, Pebble Creek, Union Creek, and many other smaller streams in Northeast Nebraska. The heaviest rainfall occurred on June 15th and 16th over soil that was already saturated nearly 100 percent. Rainfall totals over the 5-day period for the basin varied between 7 and 15 inches. The peak streamflow for the Shell Creek near Columbus gage on June 17th, 1990 was 8,000 cfs, the second highest flow on record. Water depths over old Highway 30 were approximately 2 inches.
1.3.2.3 PLATTE RIVER FLOODING Flooding on the lower Platte River is usually long in duration and involves a large contributing area and large volumes of water. Platte River flooding in the vicinity of Schuyler is predominately the result of rainfall and/or snowmelt runoff, with ice jams providing higher flood stages during some snowmelt floods. Historically, there are limited occurrences where Platte River floodwaters have inundated areas of the community. Conversation with representatives of the city of Schuyler indicate that in recent history flooding from the Platte River has not extended north of the immediate vicinity of Lost Creek. Also, there is no indication that Lost
8 Creek, by itself has ever flooded the main residential and business neighborhoods of Schuyler. Lost Creek is capable of conveying larger Platte River floods that spill into the Lost Creek channel upstream of Schuyler. This information is in agreement with the historical reports of flooding that are provided below.
● Flood of June 2010 Lowland flooding along the Platte River and Lost Creek occurred after several very heavy rainstorms between June 5th and June 12th over much of the lower Platte and Loup River basins. Local rainfall on the Lost Creek watershed, including its tributaries Shonka and Ehrenberg Ditches, likely exceeded 8 inches over a 6-day period in early June. Flooding damaged homes southwest of Schuyler, and extensive damage was done to the city golf course and South Park when Lost Creek crested on June 13th. Flooding in the Schuyler golf course is shown in Figure 1-5. Minor Platte River overflows also occurred along the river south of Schuyler, and high groundwater blocked roads in subdivisions located around overflowing sandpits along Highway 15, south of Schuyler.
Figure 1-5 Photo of June 2010 Lost Creek Flooding in Schuyler Golf Course
(Chris Langemeier, 2010)
● Flood of March 1993 Platte River snowmelt runoff flooding, which also included ice action, from March 8th to 11th, 1993 overtopped the Corps’ revetment project constructed in 1970 3.5 miles southwest of
9 Schuyler, and entered the Lost Creek channel. The peak discharge for this flood was 97,800 cfs at the North Bend gage on March 10th, which exceeded the design flood for the revetment which is 68,000 cfs. The flood was approximately a 50-year (2% chance of annual exceedance) event based upon the combined rainfall and snowmelt frequencies. This flood caused damages of $900 to streets and $2,500 to public facilities in Schuyler. Damages in the Schuyler area also included $50,000 to residences, $95,000 to state and federal highways, and $150,000 to county roads in Colfax County. Revetment repair costs were $500. Water 3-feet deep covered 400 to 500 feet of Highway 15 north of the Platte River Bridge, resulting in closure of the bridge for 5 days. During this time, traffic crossing the Platte had to detour to North Bend or west of Columbus (where the bridge was also closed).
● Floods of 1983 and 1984 The Platte River reportedly flooded in the Schuyler area in June of 1983 and 1984. No additional information on extent of flooding was found. Peaks of 59,500 and 65,200 cfs respectively, were recorded at the North Bend gage.
● Flood of 1978 In March 1978 ice jams backed up floodwaters resulting in the overtopping and failure of numerous levees in the lower Platte River basin. This included the major failure of levees near North Bend. Extensive ice jam flooding occurred south of Schuyler and a peak discharge of 80,000 cfs was recorded at North Bend on March 19th, along with an ice jam stage of 15.55 feet, which was the highest stage of record at that gage.
Figure 1-6 Platte River Flood at Schuyler, NE 1967
● Flood of 1967 Repeated rainfalls in the Platte River basin during early June 1967 saturated the ground. On June 13th, rainfall in excess of 7 inches occurred west of Grand Island, and flooding occurred in the basin. On June 16th, the Platte River overtopped the divide between the river and Lost Creek
10 upstream of Schuyler. Schuyler’s city park, golf course, roads, and agricultural lands in the area sustained damage during this event. A discharge of 75,200 cfs was recorded at the North Bend gage, 15 miles downstream on that date. This flood is shown in Figure 1-6.
● Flood of 1966 Extensive rainfall occurred over the Loup River basin on August 12th, 1966. A maximum of 16 inches of rain occurred at the storm center. Schuyler’s city park, the golf course, Highway 15, and agricultural lands in the area sustained damage during this event. A discharge of 72,500 cfs was recorded at North Bend on August 14th from this event.
● Flood of 1960 Climatic conditions in mid-March changed rapidly from record breaking cold to above freezing temperatures, which resulted in rapid snowmelt and ice jams. Major flooding on the Platte River downstream from Columbus began on March 28th and continued for more than one week. The communities of North Bend and Valley experienced major damage and a discharge of 112,000 cfs was recorded at North Bend on March 29th. That was the highest discharge of record at that gage to date.
● Flood of 1949 Snow melt runoff caused flooding in the area from March 6th to 15th, 1949. Highway 15, which was overtopped and sustained damage, was closed for 7 days. Record keeping at the gage at the Platte River at North Bend began later that year.
● Flood of 1947 On June 21st and 22nd, 1947, a severe rainstorm occurred over the Loup River basin. Rainfall averaging 6 inches occurred over much of the basin, and rainfall in excess of 8 inches was reported at several locations. Severe flooding occurred on the Platte River from Columbus downstream. Near Schuyler, Platte River floodwaters entered Lost Creek and damaged agricultural lands and the city park. The park was inundated for 7 days.
● Flood of 1881 Extensive ice jam flooding occurred on the lower Loup at Columbus in April 1881. Flooding downstream at Schuyler may have been associated with this spring ice breakup event. Floodwaters entered Schuyler and damaged several houses.
1.3.3 Study History The initial assessment of the feasibility began with a Letter of Request, which was received in January 2002. The initial assessment was completed in April 2004. A Feasibility Cost Share Agreement (FCSA) was signed in September 2005.
1.3.4 Relationship to Prior Studies and Existing Water Projects
1.3.4.1 EXISTING WATER PROJECTS As discussed in Section 2.1.3 “Platte River Lost Creek Structure,” a levee and revetment system was constructed about 3.5 miles upstream from Schuyler by the Corps of Engineers in 1946 and
11 reinforced in 1970 to prevent the Platte River from flowing into Lost Creek and capturing it as a Platte River channel. This project is limited in scale and provides limited protection to Schuyler from Platte River flooding. This project is a grade control structure of relatively short length, which can be flanked as well as overtopped by large floods. The project was in good condition when last inspected by the Corps of Engineers in 2009. No other federal flood damage reduction projects are located in the Schuyler area.
1.3.4.2 CORPS STUDIES
● Flood Hazard Mitigation Plan for Schuyler, Nebraska (2004) This study was prepared for the city of Schuyler, NE by the Omaha District as part of the Lower Platte River and Tributaries General Investigation Feasibility Study. The report was, in part, an outgrowth of the Lower Platte River Flood Insurance Study of 1998 and supported Schuyler’s participation in the Community Rating System (CRS) of the FEMA Flood Insurance Program. In the report, the known hazards from the Platte River, Lost Creek and Shell Creek were outlined, along with a preliminary assessment of flood risk management measures that could be employed to reduce flood damage. It is noteworthy that the report recommended the removal of the abandoned railroad embankment downstream of Highway 15 to reduce the floodway in the vicinity. At that time, the focus was on Platte River flooding and increased flood threat from Shell Creek was still poorly understood. It was also noted that any CRS-based activities would need to be bilingual at Schuyler.
● Initial Assessment Report Platte River at Schuyler, Nebraska Feasibility Study (2003) At the request of the Lower Platte North Natural Resources District, the Omaha District conducted an initial assessment of Platte River flooding at Schuyler, Nebraska under the authority of Section 205 of the Flood Control Act of 1948, as amended. The focus of this report was Platte River flooding and 3 potential levee alignments along the southern end of Schuyler were evaluated. It was determined that one or more of the concept levee designs may be economically feasible and recommended that a comprehensive feasibility study be initiated.
● Lower Platte River and Tributaries, Reconnaissance Report (1996) The Omaha District completed a reconnaissance level study of the lower Platte River basin in 1996. The area encompassed by the study extended from Grand Island, Nebraska to the mouth of the Platte River and included tributaries to the river. The report evaluated the flood threat and flood damage reduction measures for numerous communities within this reach.
The report notes that the Platte River floods portions of south Schuyler by cutting across its left overbank and spilling into the Lost Creek drainage way. The report concluded that the existing project southwest of Schuyler (the revetment) was constructed to keep such an event from occurring, but it has been flanked and/or overtopped on several occasions. No additional discussion of the flooding problem or the potential for a flood damage reduction project at Schuyler was specifically addressed in this report.
● Lower Platte River, Ice Jam Flooding (1994) The Omaha District and the Cold Regions Research and Engineering Laboratory conducted an assessment of ice-jam flooding on the Lower Platte River from Columbus to its confluence with
12 the Missouri River. Within this study area, several sites were evaluated in detail including state Highway 79 at North Bend, west channel at Leshara, and Big Island at Fremont. The report did not specifically discuss ice-jam related flooding in the Schuyler area.
●The “Great Flood of 1993” Post Flood Report, Appendix D (1993) This report, prepared by the Omaha District, Corps of Engineers, summarized the hydrology and hydraulic conditions before, during, and after the flood and presented high-water marks and flooded-area mapping. It also listed flood damages and estimated damages prevented by existing flood control structures.
● Platte River and Tributaries, Draft Summary (1986) The Omaha District published a reconnaissance level study in 1986 that reevaluated flood problems and opportunities within the multi-state Platte River basin. This study relied heavily on previous studies completed by the Corps of Engineers. The flooding problem and the potential for a flood damage reduction project at Schuyler were not specifically addressed in this report.
● Platte River and Tributaries, Draft Summary (1982) In 1982, the Corps of Engineers published a draft report that reevaluated flood problems in the lower Platte River basin after severe ice-jam flooding in March 1978. The flooding problem and the potential for a flood damage reduction project at Schuyler were not specifically addressed in this report.
● Review Report, Platte River and Tributaries, Nebraska (1971) The Corps of Engineers completed a study of the flood and related land and water resources problems within the Platte River basin in 1971. Details of the flooding problem and the potential for a flood damage reduction project at Schuyler were not specifically addressed in this report.
● Detailed Project Report, Platte River and Lost Creek, Schuyler, Nebraska (1967) The Corps of Engineers completed a study of a flood problem on the left bank of the Platte River in the vicinity of Schuyler in 1967. The purpose of this project was to prevent the Platte River from capturing Lost Creek and making it its main channel upstream from Schuyler. This project, which was constructed in 1970, does not prevent all Platte River flooding in Schuyler, as it was designed to be overtopped by discharges greater than 68,000 cfs.
● Review Report, Platte River in the Vicinity of Schuyler, Nebraska (1938) This report recommended the construction of about 3,600 feet of lumber mattress and riprap on the left bank of the Platte River about 3.5 miles southwest of Schuyler. The Corps of Engineers completed this work in 1946.
● Preliminary Examination Report on Flood Control, Platte River in the Vicinity of Schuyler (1938) A study by the Corps of Engineers found that damages from floods in the vicinity of Schuyler had been nominal, but that the Platte River threatened to pirate the channel of Lost Creek. Local interests favored a plan for deepening and straightening the Platte River and raising its banks. This plan was found impractical and infeasible. The report found that bank protection consisting
13 of a lumber mattress and riprap would be feasible and recommended additional studies should be conducted.
1.3.4.3 STUDIES BY OTHER AGENCIES
● Lower Platte River, Nebraska Flood Insurance Study (1998) An updated flood study was produced by FEMA for the Platte River from approximately Columbus to the confluence with the Missouri River. The study was prepared in cooperation with the Omaha District, Corps of Engineers and the Nebraska Department of Natural Resources. Flood Insurance Rate Maps were prepared for individual counties and communities from the flood study.
● Shell Creek Floodplain Study (1992) The Nebraska Natural Resources Commission published a floodplain study for Shell Creek in 1992. The study delineated maps of the floodway and the 100-year floodplain for much of the Shell Creek basin, including the area around Schuyler. The study report did not address the potential for flood damage reduction projects within the Shell Creek basin.
● FEMA Flood Insurance Study (1990) FEMA published a flood insurance study for Schuyler in 1990. The current flood insurance study and corresponding flood insurance rate map for Schuyler (effective date March 5, 1990) shows that the Platte River 100-year (1% annual chance of exceedance) flood boundary extends into the southern part of Schuyler. This report noted that Shell Creek’s 100-year floodplain encroaches into portions of northern and eastern Schuyler.
● Report on the Platte River Basin, Nebraska Level “B” (1976) The Missouri River Basin Commission published the Report on the Platte River Basin, Level B Study in 1976. This report formulated a comprehensive plan for conservation, development, and management of water and related land resources in the Platte River basin of Nebraska. The report notes that among the principal problem streams noted for flooding were Shell Creek and Lost Creek. However, the flooding problem and the potential for a flood damage reduction project at Schuyler were not specifically addressed in this report.
14 2. EXISTING CONDITIONS The existing conditions are an inventory of conditions at the present time or very recent past. They form a baseline for estimation of future without-project conditions and the evaluation of future-with project conditions, allowing a fair measure of the value of implementing the selected plan. For the purposes of this study, the existing conditions are subdivided into “conditions for flooding,” “general engineering,” “environmental,” and “community.”
2.1 EXISTING CONDITIONS FOR FLOODING The existing conditions for flooding include the watershed hydrology, the hydraulics of the waterways at Schuyler and floodplain management considerations.
2.1.1 Hydrology Schuyler, Nebraska is subject to flooding from the north due to Shell Creek and flooding from the south due to the Platte River. Lost Creek, which rises in the Platte River floodplain near Columbus, is also capable of damaging parks and homes on the southwestern outskirts of Schuyler. More severe flooding can occur from Lost Creek, when overflows from the Platte River spill into Lost Creek, which behaves as an overflow channel to the river and brings the Platte River flood threat directly to Schuyler. Damages from Lost Creek are included with those of the Platte River in this study.
The potential for and impact of coincident flooding from both the Platte River and Shell Creek is small, as the major source of flooding on the Platte River is rapid melt of plains snowpack and ice jams in late winter and for Shell Creek, major floods are caused by late spring through summer severe thunderstorms. The large size difference between the huge Platte River watershed and the much smaller Shell and Lost Creek basins also works against the timing of coincident peak discharges.
While coincident flooding of Shell Creek and Lost Creek are more likely, they are not able to influence the backwater conditions of the other at Schuyler. This is due to the fact that the outlets of Shell and Lost Creeks to the Platte River are several miles downstream of Schuyler. Shell Creek must pass through a bridge under the UPRR and a county road before making its final approach to the Platte. The Platte River would have to be far higher than historically recorded stages to cause a sufficient “tail water” restriction on flow through the UPRR bridge to impact Shell Creek stages near Schuyler. Similarly, flood discharges from both Lost Creek and Shell Creek enter the Platte River well downstream of Schuyler and are not capable of raising Platte River stages at Schuyler due to the difference in elevation.
The principal source of data for this analysis is the streamflow data collected at nearby gaging stations on the Platte River and on Shell Creek. Instantaneous flood peaks and flood volumes were computed from those gaging station records to quantify the flood characteristics of the Platte River and Shell Creek at Schuyler. The results of the computed frequency analysis are presented in tables and graphs. More detailed information on computation methods can be found in Appendix J (Hydrology and Interior Drainage).
15 During a meeting with Schuyler residents after the May 31st, 2008 flood event, it was determined that flood prevention from Shell Creek should be the primary focus. For the feasibility phase of the study, the volume-duration relationships and balanced hydrographs were not updated to include the 2008 and 2010 events. It was determined that the recent flood events would not have a significant enough impact on the daily volume frequency distribution, that was calculated using gaging data up through 2005, to warrant a complete re-calculation of the balanced hydrograph flows during the feasibility phase of the study.
2.1.1.1 SHELL CREEK Shell Creek is a left bank tributary to the Platte River in central Nebraska, with a drainage area of roughly 470 square miles at a point north of Schuyler where Highway 15 crosses the stream. Beyond this point, Shell Creek enters the broad Platte River floodplain, where high flows on Shell Creek can cross over into Rawhide Creek and other smaller drainages serviced by constructed drainage ditches. Shell Creek enters the Platte River about 3 miles downstream of Schuyler. The complexity of the behavior of Shell Creek, as it enters the Platte River valley near Schuyler, presented numerous modeling challenges. Information on those challenges and the solutions employed are summarized in this section, with greater detail provided in Appendix J (Hydrology and Interior Drainage).
● Sources of Data for Analysis Two USGS stream gaging stations have historically operated on Shell Creek – one at Newman Grove and one near Columbus. The Newman Grove gage operated from water year (WY) 1950 – WY1967, while the Columbus gage operated from WY1948 – WY1975 and WY1978 – present. Frequency analysis for each gage was performed using the Hydrologic Engineering Center’s Statistical Software Package (HEC-SSP). The Newman Grove gage was analyzed over the period of record, while the Columbus gage was analyzed over the same period of record as the Newman Grove gage, and the period of record (through WY2006 for daily means, WY2005 for instantaneous peaks).
● Shell Creek Flood Frequency The derivation of the peak flood flow distribution of Shell Creek at Schuyler presented numerous challenges. In addition to the fact that there is no gage at Schuyler, the upstream gaging stations located at Newman Grove and near Columbus revealed an atypical basin. The Shell Creek watershed is unusual in that greater floods occur further upstream in the basin than at the mouth. This results in peak discharges at the upstream Newman Grove gage exceeding those at the downstream Columbus gage for a flood event of a given frequency.
This counterintuitive flood pattern is due primarily to basin shape and to a lesser extent channel slope. The upper portion of the Shell Creek watershed is more rounded and has many contributing sub-watersheds with moderately steep slopes. The Newman Grove gage is located in this portion of the basin. Downstream of Platte Center, the basin is constrained to a narrow valley with negligible tributary streams. The Columbus gaging station is located in this reach. Larger tributaries, such as Loseke Creek, enter downstream of the Columbus gage and their runoff can increase peak flows downstream to around Highway 15. As Shell Creek leaves its tributary valley and enters the broad Platte River plain, peak flood discharges are reduced by
16 overflows to Rawhide Creek and man-made drainage ways, such as the Hughes-Payzant Ditch. Because of these complexities the discharge frequency relationship at Schuyler was developed from the statistical relationship between the Newman Grove and Columbus gages and an assessment of hydraulic conditions in the floodplain at Schuyler.
Details on the computations are provided in Appendix J (Hydrology and Interior Drainage). Results of the analyses in cubic feet per second (cfs) are presented in Table 2-1 and Figure 2-1 as follows:
Table 2-1 Shell Creek Peak Flood Flow Frequency
Table 2-1 Shell Creek Peak Flood Flow Frequency Instantaneous Peaks Derived from Gaging Station Records and Extrapolated to Schuyler Location 2-Yr 5-Yr 10-Yr 20-Yr 50-Yr 100-Yr 500-Yr Newman Grove 1590 4200 6750 9830 14700 19100 31500 Columbus 1590 32504560 5940 7870 9400 13100 Schuyler 2420 43405740 7130 8970 10400 13600 50% ex. 20% ex. 10% ex. 5% ex. 2% ex. 1% ex. 0.2% ex.
17 100000 Legend Computed Original Computed Extended Original Weibull Extended Weibull
10000
)
s
f
c
(
e
g
r
a
h
c
s
i D
1000
100 0.9999 0.999 0.99 0.95 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.05 0.01 0.001 0.0001 Probability of Exceedance
Figure 2-1 Plot of the Discharge – Probability Distribution for Shell Creek near Columbus
● Shell Creek Volume Probability Flooding from Shell Creek at Schuyler is a function of both the instantaneous flood peak and duration of flood flows near the peak. This is because floodplain storage north and east of Schuyler must fill first, before flood waters can back into the town from the east. Sustained peaks beyond the capacity of the Shell Creek channel, that runs eastward along the north side of the Union Pacific Railroad tracks, will overflow into the floodplain. If there is sufficient volume in the flood, eventually the water backs up until it flows across the Union Pacific tracks and makes its way to the Platte River. By that time, much of northeast Schuyler is inundated.
Since volume and instantaneous peak discharge both play a role in determining flood severity at Schuyler, volume probability analysis as well as peak discharge analysis was performed on the Shell Creek gaging records. The volume frequency information was obtained by analyzing the flood history of the Shell Creek at Newman Grove and Columbus gages and translating those results downstream to Schuyler. The results of this analysis are presented in cubic feet per second (cfs) in Table 2-2.
18
Table 2-2 Shell Creek at Schuyler Duration Frequency
Table 2-2 Shell Creek at Schuyler Duration Frequency Return Period 2-Yr 5-Yr 10-Yr 20-Yr 50-Yr 100-Yr 500-Yr 1-Day 2050 36204750 5870 7340 8460 11100 3-Day 1320 22302870 3490 4300 4900 6280 7-Day 806 13101660 1990 2410 2720 3430 15-Day 592 9371170 1380 1660 1860 2310 31-Day 427 657807 946 1120 1250 1530 61-Day 318 476577 670 785 867 1050 91-Day 269 395476 549 639 703 843 121-Day 238 347 415 477 553 607 724 181-Day 203 291 346 395 455 497 589
● Shell Creek Balanced Hydrographs The Shell Creek volume-frequency analysis was used to develop balanced hydrographs, along with hydrographs of actual historical floods recorded at the Columbus gage. After an evaluation of eight significant floods, the records from floods in 1950, 1982, and 2004 were further evaluated for their use in developing the balanced hydrographs. Ultimately, the 2004 flood, though smaller than some of the others, was selected as the template flood for derivation of the balanced hydrographs.
The records of the 2008 and 2010 floods were not available at the time of the volume-probability analysis. Although the 2008 flood peak of 11,200 cfs was the flood of record, with the 1990 flood of 8,000 cfs the second largest event, it was determined that the length of gaging record was adequate to produce balanced hydrographs at Highway 15 north of Schuyler that would be representative of flooding in the Schuyler area for the feasibility analysis. The balanced hydrographs allow the flooding to be analyzed on the basis of total flood volume as well as just the peak discharge. Balanced hydrographs are used as the input to a hydrologic routing model such as the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS). The balanced hydrographs for a range of flood return periods are shown in Table 2-3 and in Figure 2- 2.
Table 2-3 Shell Creek near Schuyler (Highway 15) Balanced Hydrographs
Table 2-3 Shell Creek Near Schuyler (Highway 15) Balanced Hydrographs Return Period Day 1 Day 2 Day 3* Day 4 Day 5 Day 6 Day 7 2-Year 706 840 2050 1070 538 269 168 5-Year 1040 13503620 1720 794 397 248 10-Year 1260 17004750 2160 963 482 301 20-Year 1450 20205870 2580 1110 554 346 50-Year 1670 24507340 3110 1270 635 397 100-Year 1820 2750 8460 3490 1390 694 434 500-Year 2170 341011100 4330 1650 827 517 *Discharges represent mean daily discharges. The instantaneous peak discharge is assumed to occur on Day 3 in the balanced hydrograph.
19 Flood Hydrographs
14000 0.20% 0.50% 1% 12000 2% 5% 10% 10000 20% 50% 80% 90% 8000 95% 99%
6000 Discharge (cfs)
4000
2000
0 4/1/2005 0:00 4/2/2005 0:00 4/3/2005 0:00 4/4/2005 0:00 4/5/2005 0:00 4/6/2005 0:00 4/7/2005 0:00 4/8/2005 0:00 Date & Time
Figure 2-2 Shell Creek Balanced Flood Hydrographs Used in HEC-HMS Analysis at Schuyler
● HEC-HMS Model and Shell Creek Flood Routing There are several locations along Shell Creek where flow from the stream is diverted to other basins by overflowing low watershed divides during floods. Just after Shell Creek passes under Highway 15, flow is diverted to Rawhide Creek during major flood events. Further downstream, flow is diverted to the Hughes-Payzant Ditch. North of Highway 30, flow can break out of the main channel and travel across fields where it eventually ponds along Highway 30, denoted as Ponding Area 1 in Figure 2-3, before draining through Highway 30 using the Nieman Ditch culverts. Once the overbank flow is passed through the Nieman Ditch culverts, it can break out of the ditch and pond along the old Hwy 30 alignment, denoted as Ponding Area 2 in Figure 2-3. The last diversion occurs along the southern edge of Ponding Area 2 where weir flow can overtop the railroad and travel south until it eventually joins the Platte River.
The terrain around Schuyler is flat; therefore, road and railroad embankments serve as low-head dams during a large flood. Each reservoir behind each dam must fill and spill before the following reservoir can be filled. Property damages in Schuyler are related to the flood elevation reached in the reservoir that backs up behind the old Highway 30 embankment, and eventually the Union Pacific Railroad embankment, once the Shell Creek channel capacity has been exceeded. These two ponding areas are shown in Figure 2-4, an aerial photo taken of the flood of 2008. A hydrologic model using HEC-HMS was developed to route the modeled flood volumes from Highway 15 downstream to Schuyler, with appropriate consideration to flood water lost to Rawhide Creek and the Hughes-Payzant Ditch. The loss of flow to those waterways is also evident in Figure 2-4.
20
The hydrologic model was used to route the balanced hydrographs for different exceedance frequencies from Shell Creek at Highway 15 downstream to the confluence with the Platte River. Both the hydrologic and hydraulic models were calibrated using observed high water marks taken in the field after the May 31st, 2008 flood event. The hydrologic model used begins at the Shell Creek at the Columbus gage and is configured to route flows to Highway 15 using the Modified Puls routing method. The storage-discharge curves for the reaches were developed from an existing HEC-RAS hydraulic model and include overbank storage. The model was used to determine ponding elevations at different frequencies using the balanced hydrographs. A schematic of the HEC-HMS model from the Columbus gage to the Platte River that was used in the calibration is shown in Figure 2-3. Details of the data collected and the calibration effort are presented in Appendix I (Hydraulics) and Appendix J (Hydrology and Interior Drainage).
Figure 2-3 Schematic of Shell Creek HEC-HMS Model
21
Figure 2-4 Shell Creek Ponding Areas during Flooding at Schuyler
2.1.1.2 PLATTE RIVER The Platte River is a major right bank tributary to the Missouri River that drains large portions of Nebraska, Wyoming, and Colorado. Schuyler is located roughly 80 miles upstream from the mouth of the Platte River, which joins the Missouri River at Plattsmouth, Nebraska. Schuyler is located nearly 2 miles north of the Platte River; however Lost Creek flows through the city park and golf course and is capable of receiving Platte River overflows from larger floods and conveying them directly towards southern Schuyler.
● Sources of Data for Analysis The primary source of hydrologic and hydraulic data used in the analysis of the Platte River at Schuyler comes from the Platte River at North Bend gaging station, which is located approximately 15 miles downstream of Schuyler. The period of record for the North Bend gage is from April 1949 to present. During the snowmelt and rainfall flooding of 2010, stage data were also available from a temporary Platte River gage installed at Schuyler. There are no gaging records for Lost Creek.
22 ●Discharge-Frequency Analysis for Flood Insurance Study The Corps of Engineers developed discharge-frequency relationships for various gaging stations along the Platte River for the Lower Platte River, Nebraska, Flood Insurance Study (1998). For the Schuyler FIS revision, the discharge-frequency relationships at the North Bend gaging station were utilized because this is the closest long-term gaging station to Schuyler. The discharge frequency distribution for the Feasibility Study was updated to take advantage of the additional years of gaging record. The additional length of record improves the accuracy of the analysis and reduces the uncertainty which is used in defining the freeboard.
●North Bend Gage Discharge-Frequency Update The initial discharge-frequency curves for the Platte River at North Bend were developed as part of the Lower Platte River, Nebraska Flood Insurance Study in 1998 as noted previously in this report. The period of record used from the North Bend gage for that analysis was 1950-1994. The updated discharge-frequency curves, explained in the following paragraphs, were used for Platte River hydraulic analysis in this study.
Two separate discharge-frequency curves were developed for the snowmelt and rainfall seasons. The snowmelt season was defined as December 15th through March 31st, and the rainfall season was defined as April 1st through December 14th. Annual peak flow values from 1950-2008 were classified as either snowmelt or rainfall. The snowmelt and rainfall season discharge-frequency curves were combined into a composite season curve. It was determined that the composite curve was the best discharge-frequency representation for the North Bend gage. The results are shown in Table 2-4 and Figure 2-5.
Table 2-4 Discharge-Frequency Results Platte River North Bend, NE
Table 2-4. Discharge-Frequency Results Platte River North Bend, NE Return Exceedance Snowmelt Season Rainfall Season Combined (cfs) Period (yrs) Frequency (%) (cfs) (cfs) (HEC-TD 17) 2 50 17200 22700 28500 5 20 30500 36500 44900 10 10 42800 47200 58300 20 5 57700 58700 73600 50 2 82500 75500 98900 100 1 106000 89600 123000 200 0.5 135000 105000 150000 500 0.2 183000 128000 198000 Years of Record 59 (1950-2008) 59 (1950-2008) 59 (1950-2008) Mean 4.2631 4.3648 4.4265 Standard Deviation 0.2770 0.2376 0.2604 Adopted Skew 0.6000 0.2000 0.2000
23 1E+006 Legend Snowmelt Computed Rainfall Computed Combined (TD 17) Snowmelt Weibull Rainfall Weibull
100000
)
s
f
c
(
e
g
r
a
h
c
s
i D
10000
1000 0.9999 0.999 0.99 0.95 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.05 0.01 0.001 0.0001 Probability of Exceedance
Figure 2-5 Platte River at North Bend - Updated Discharge Frequency Curve
Concern was expressed about updating the Platte River at North Bend discharge-frequency curve without updating the rest of the discharge-frequency curves established in the Lower Platte River, Nebraska Flood Insurance Study (1998). That study was completed to create uniform discharge-frequency curves for that entire stretch of the Platte River. The uniformity evaluation took into account the dissimilar periods of record at the gages in the study, and statistical adjustments were made accordingly to provide consistent discharge-frequency values for a river reach. Uniform discharge-frequency curves provide a consistent base for determining and explaining the need for different projects to the public in the numerous communities along the river. Updating the North Bend frequency curve detracts from the consistency established in the earlier study, but it was deemed necessary to do the best possible analysis of current flood conditions at Schuyler. Extending the record for the North Bend discharge-frequency curve added 14 years of data to the analysis, improving the discharge-frequency information for levee design and lowering the uncertainty for the economic analysis.
2.1.2 Existing Conditions Hydraulic Model The hydraulic analysis was performed to define the water surfaces that can be expected from floods of various frequencies in and around Schuyler. The hydraulic modeling was completed using the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) Version 4.1.0
24 (January 2010). Hydraulic modeling was completed to evaluate water surface elevations for existing conditions. The computed water surface profiles were used to develop stage-discharge relationships for use in the economic models.
2.1.2.1 SHELL CREEK This section describes the hydraulic analysis conducted on Shell Creek for the Schuyler, NE, and Section 205 Feasibility Study. It also includes a description of the hydraulic analysis necessary to develop and run the Hydrologic Engineering Center – Flood Damage Reduction Analysis (HEC-FDA) model for economic analysis.
● Model Overview Upstream of Schuyler, Shell Creek transitions from a stream channel bounded by hills to a channel flowing in the floodplain of the Platte River. As Shell Creek upstream from Schuyler approaches the Platte River confluence, flow may split into several different areas (See Figure 2- 4). First, just east of Highway 15, flow can leave Shell Creek on the left bank and enter the remnants of the old Rawhide Creek channel that has been converted to farmland. Second, flow can leave on the right bank and flow through what is referred to as the Shell Creek Right Overbank (ROB). At about the same location as flow leaves to the ROB; it can also leave on the left bank and flow into the Hughes-Payzant Ditch. Plate 1 depicts this complex flow system.
Flow leaving Shell Creek and entering Rawhide Creek or the Hughes-Payzant Ditch does not return to Shell Creek. Flow entering the ROB reach either returns to Shell Creek near the Union Pacific Railroad (UPRR) or flows over the UPRR tracks and enters the Platte River without returning to Shell Creek. Flow entering the Hughes-Payzant Ditch enters the Platte River downstream from the Shell Creek-Platte River confluence.
While a number of reaches were used to model the river system, the main reach of interest for this study is the Shell Creek Right Overbank. The only reaches used in the economic analysis are the ROB and a short reach of the Shell Creek main channel just downstream from Highway 30.
● Modeling Considerations Two HEC-2 models developed for the 2002 Flood Insurance Study (FIS) were combined into a HEC-RAS model. Additionally, several previously un-modeled reaches were added to evaluate the complex split flow situation. A lateral structure representing the UPRR embankment and two diversion rating curves reflecting flow attenuation were also added to the model.
New bridge data were incorporated into the model. The Highway 30 bypass, constructed since the FIS, included two new bridges (one on Shell Creek, the other on Nieman Ditch). The old Highway 30 bridge from the FIS model and a county bridge (where the new Highway 30 bypass is) were deleted and as-built bridge plans received from the Nebraska Department of Roads (NDOR) were used to code in the new bridges. Following the Shell Creek flood of May 30th, 2008, the HEC-RAS model was calibrated to high water marks obtained during and after the flood. More details of the model development and calibration are provided in Appendix I (Hydraulics).
25
● HEC-FDA Modeling The Corps’ HEC-FDA model evaluates hydraulic and economic data and allows estimates of the frequency of flood damages in a community. In accordance with current USACE guidelines, an uncertainty analysis was completed to better define flood damages. The Hydrologic Engineering Center’s Flood Damage Reduction Analysis (HEC-FDA) Version 1.2.4 (November 2008) was used in the analysis. The HEC-FDA model runs were executed by the project economist. However, input from the hydrologic and hydraulic sections were employed in model setup.
► Model Overview Damage reaches used in the HEC-FDA model are summarized in Figure 2-6.
Figure 2-6 Shell Creek Economic Damage Reaches
►Exceedance Probability Shell Creek and the Shell Creek ROB reach were modeled using a graphical stage-probability function. Analysis based purely on discharge-probability is not appropriate for the exceedance function because of the multiple flow splits upstream from the damage reaches of interest. Additionally, the multiple hydraulic controls in the damage reach result in perched floods at certain frequencies, as damaging floods may back up behind old Highway 30 due to floods
26 entering the city from Nieman Ditch, prior to the onset of floods controlled by the conveyance of lower Shell Creek and the railroad embankment.
►Hydraulic Uncertainty The stage-discharge relationship for each reach is based on the water surface profiles computed with the HEC-RAS model at the index station. Input to HEC-FDA requires the description of stage uncertainty of the computed water surface profiles. Uncertainty in computed stage profiles reflects modeling assumptions, numerical errors, parameter estimation and natural uncertainty. Uncertainty was estimated for the entire study reach by performing a sensitivity analysis with the HEC-RAS model and also by comparing model results with observed high water marks. A value of 1.0 ft is employed in the HEC-FDA model. Refer to Appendix I (Hydraulics) for details.
2.1.2.2 PLATTE RIVER
● Model Overview The most severe Platte River flooding in the Schuyler area generally results from ice jam flooding and high runoff from melting snow. Very heavy rains over the Lost Creek basin by itself also are capable of inundating the Schuyler City Park and golf course and homes on the outskirts of southern Schuyler.
Hydraulic modeling of the Platte River was completed using the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) Version 4.1.0 (January 2010). The HEC-2 computer model used in the development of the draft flood insurance rate map was utilized in this study and as such, no additional survey information was obtained. The HEC-2 model was converted to HEC-RAS and georeferenced. Topographic mapping of the community, dated 1984, with one-foot contours, was obtained from the Nebraska Department of Natural Resources and was used for plotting water surface outlines within the community where necessary. The only major change to the HEC-RAS model from the flood insurance rate map HEC-2 model pertains to the area around the old railroad embankment east of Highway 15. Ineffective flow areas were added to the HEC-RAS model to correct an instability in effective flow area near the embankment. This correction led to an increase in the existing conditions water surface elevation of up to 0.7 feet.
● Modeling Considerations Ice–affected flows have occurred frequently in the study reach. When the flows are ice-affected, the stages for a given Platte River discharge may be significantly higher than the stages for the same discharge during open flow conditions. Ice-affected flow conditions may be the result of floating ice cover, floating ice jams or grounded ice jams. To account for the effect of ice cover on stage-frequency and the fact that ice-affected floods do not occur every year, composite water surface elevations had to be derived from three flood scenarios which included:
► Rainfall season discharges with open water ► Snowmelt season discharges with open water ► Snowmelt season discharges with ice cover
27 For the 100-year return period (1% annual chance of exceedance) discharges, the new computed stages were generally higher in Schuyler than they were projected to be with the FIS Study. Table 2-5 shows that stages in Schuyler ranged up to more than ½ foot higher in the new analysis. Locations of the cross sections (yellow) and damage reaches (red) are depicted in Figure 2-7. More details on the computation of the new existing conditions water surface, including the derivation of the composite water surface elevations are provided in the Hydraulic Appendix.
Table 2-5 Comparison of Platte River Water Surfaces
TABLE 2-5 COMPARISON OF PLATTE RIVER WATER SURFACES (For the 1% annual chance of exceedance flood)
CROSS SECTION LOCATION CROSS SEC. # FIS COMPOSITE WSEL WSEL East Schuyler and north sewage lagoon 460400 1345.2 1345.1 East Schuyler and upstream side of soccer fields 463600 1348.1 1348.1 Downstream of old railroad embankment 465900 1350.1 1350.8 Upstream of old railroad embankment 466500 1351.3 1351.7 Upstream of Highway 15 468600 1352.9 1353.4 Upstream of Lake Socorro and west Schuyler 470350 1355 1354.9
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Figure 2-7 Platte River Damage Reaches and Cross Sections Used in the Analysis
● Analysis of the Downtown Ridge A flood insurance study was performed on the Lower Platte River in December 2002. In the 2002 study, a subtle ridge was identified that passes through the city of Schuyler and restricts the flow of flood waters during large discharges from the Platte River into the downtown area. Modeling performed for the FIS study indicated that during the 100-year (1% annual chance of exceedance) flood, floodwaters cross this ridge and flow to the north into the downtown area.
An initial task was identified for the Section 205 study to verify the results of the FIS modeling and to provide a baseline from which to evaluate the severity of flooding in downtown Schuyler. Survey data were obtained and the flood flow was modeled using the FIS HEC-2 Hydraulic Model. Changes were made to the model, to allow for the extraction of flow from the Platte River across the ridge and the model was upgraded to HEC-RAS.
Based upon the results of the split flow modeling, the minimum flow that crosses the
29 ridge during a 100-year event is 2,200 cfs. A lack of definitive flow patterns for the water as it crosses the ridge makes it difficult to quantify the impacts resulting from the flows. It appears that three of the major flow paths through the area are by way of 10th, 11th, and 12th Streets. Rating curves were developed for the flow paths and used to evaluate flow depths for various flood events in downtown Schuyler. The rating curves indicated that for a discharge of 400 cfs, there are water depths greater than 1 foot up against the surrounding structures. Assuming 400 cfs is carried through each of these drainage ways this only accounts for 1,200 cfs of the total minimum value of 2,200 cfs computed crossing the ridge. The remaining water may be assumed to flow through the other streets and alleys or increase the discharges in the identified drainage ways, thus increasing the depths of flow against downtown buildings.
From the analysis of the downtown ridge, it was concluded that:
1. The ridge separating southern Schuyler from the downtown area runs west to east from 7th to 8th Streets. This ridge does not prevent Platte River flooding from reaching downtown Schuyler during the 100-year (1% annual chance of exceedance) event. 2. Quantifying the magnitude of the discharges crossing the ridge is greatly dependent upon the initial assumptions made in the analysis. Dependent upon those assumptions, discharges may vary from 2,200 to 10,600 cfs. Using a conservative modeling approach, a minimum value of 2,200 cfs has been assumed for this analysis. 3. There are no definitive drainage patterns once flow crosses the ridge and flows to the north and east. However, based upon a normal depth analysis of the surveyed cross sections, flow depths greater than one foot would be anticipated in many areas throughout the downtown area for the 100-year event. 4. The initial assumptions used in the FIS study for the cross sections appear to be valid based upon the comparison with the recently surveyed cross sections. When using the new channel cross sections in the old FIS model, minimal changes in water surface elevation were noted.
In summary, the conclusion of the Flood Insurance Study, showing downtown Schuyler inundated by the 100-year event, appears valid upon reexamination.
● HEC-FDA Modeling As noted in the Shell Creek discussion of HEC-FDA modeling, the Corps’ HEC-FDA model evaluates hydraulic and economic data and allows estimates of the frequency of flood damages in a community and is used in defining the hydraulic model uncertainty for economic analysis.
► Model Overview The HEC-FDA model runs were executed by the Omaha District economist. However, input from the Hydrologic and Hydraulic Sections of the District was used in model setup. For the Platte River analysis, the Hydrologic Engineering Center’s Flood Damage Reduction Analysis (HEC-FDA) Version 1.2.4 (November 2008) was used in the model setup. Refer to Appendix D (Economics) for additional details of the HEC-FDA model analysis.
30 ►Stage Probability and the Exceedance Function The computed combined season discharges do not precisely fit the Log-Pearson Type III distribution. Therefore, a graphical discharge-probability curve was used to define the exceedance probability. Discharges provided by the Omaha District Hydrology Section were used. In addition to the frequencies listed in Table 2.4, the 0.9999 (approximate 1-year) and 0.0010 (1000-year) frequency discharges were entered. These two discharges, 5,000 cfs and 233,000 cfs, are included because the statistics, including the uncertainty of the graphical exceedance-probability function, are influenced by the entire sample. An equivalent record length of 59 years was used.
►Hydraulic Uncertainty The stage-discharge function for each reach is based on the water surface profiles computed with the HEC-RAS model at the index station. Input to HEC-FDA requires the description of stage uncertainty of the computed water surface profiles.
Uncertainty in computed stage profiles reflects modeling assumptions, numerical errors, and parameter estimation. Natural variations in the stage discharge relationship also must be considered. Model uncertainty was estimated for the entire study reach by performing sensitivity analyses with the HEC-RAS model. The total uncertainty used in HEC-FDA was 1.3 feet. Details of the uncertainty analysis can be found in Appendix I (Hydraulics).
2.1.3 Platte River / Lost Creek Structure Lost Creek comes within a few hundred feet of the Platte River about 3.5 miles upstream of Schuyler. Historically, Platte River flood flows in excess of 40,000 cfs were able to overtop the small ridge and flow directly towards Schuyler along Lost Creek. In 1946 a project consisting of a stone fill dike and revetment was built to prevent Platte River flows from washing out the ridge. This structure was reinforced in 1970 and is designed to not be overtopped by flows of less than 68,000 cfs, which is between a 10 and 20-year (10% and 20% annual chance of exceedance) flood. Were the ridge to be eroded out, much of the Platte River flow could suddenly be redirected towards Schuyler during the course of a major flood. This structure if maintained, has lessened, but not eliminated, the historical Platte River flood threat to Schuyler.
As discussed in Section 1.3.4 “Corps Studies”, a levee and revetment system was constructed about 3.5 miles upstream from Schuyler by the Corps of Engineers in 1970 to prevent the Platte River from overtaking Lost Creek as its main channel where the waterways are at their closest point. This project is limited in scale and provides limited protection to Schuyler from Platte River flooding. The project was in good condition when last inspected by the Corps of Engineers in 2009. No other federal flood damage reduction projects are located in the Schuyler area.
The Corps of Engineers completed a study of a flood problem on the left bank of the Platte River in the vicinity of Schuyler in 1967. Selected excerpts from this report are provided below.
“The most critical point is located about 3.5 miles southwest of the city where Lost Creek approaches within a few hundred feet of the Platte River. A natural divide between the river
31 and the creek, which formerly contained flows of up to 40,000 cfs on the Platte River, has been overtopped by greater flows, and in recent years, has been reduced in height.”
“Future overflow from the Platte River could further reduce the natural divide between the river and Lost Creek. As Lost Creek is lower than the Platte River, such erosion could permit the Platte River to capture Lost Creek for its main channel. If this should happen, approximately 1,500 acres of highly productive farmland would be destroyed in formation of the new channel, county and state highways would be breached, and the railroad at Schuyler would be threatened.”
“The recommended project would provide protection against a flood with a discharge of 68,000 cfs, or a 10 percent chance of annual occurrence and would consist of a stone-fill dike and revetment 3,000 feet long, and of two levee segments having lengths of 3,820 feet and 5,110 feet as shown on [Figure 2].”
As noted above, the purpose of this project was to prevent the Platte River from capturing Lost Creek as its main channel upstream from Schuyler. This project, which was constructed in 1946 and improved in 1970, does not prevent all Platte River flooding in Schuyler.
2.1.4 Floodplain Issues and Regulation Regulation of floodplains is the responsibility of local, state, and Tribal governments. Some federal programs require communities to enact floodplain regulations that meet certain standards to participate.
2.1.4.1 GENERAL The Federal Emergency Management Agency (FEMA) has published a flood insurance study (FIS) for the city of Schuyler. In this study, FEMA utilizes the 100-year flood as the base flood to define flood hazard areas. A 100-year flood is a flood that occurs on average once every 100 years or has a 1% chance of occurring in any given year. FEMA also uses the concept of a floodway to assist local communities in the aspect of floodplain management. Under this concept, the area of the 100-year flood is divided into a floodway and a floodway fringe. The floodway is the channel of a stream plus any adjacent floodplain areas that must be kept free of encroachment in order that the 100-year flood may be carried without substantial increases in flood heights. Minimum federal standards limit such increases in flood heights to 1.0 foot, provided that hazardous velocities are not produced. Individual state requirements may be more stringent. Currently, the state of Nebraska also limits the increase to 1.0 foot.
The area between the floodway and the boundary of the 100-year flood is termed the floodway fringe. The floodway fringe thus encompasses the portion of the floodplain that could be completely obstructed without increasing the water-surface elevation of the 100-year flood more than 1.0 foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to floodplain development are shown in Figure 2-8.
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Figure 2-8 Typical Floodway Cross Section
2.1.4.2 FLOOD INSURANCE STUDIES FEMA published a flood insurance study for Schuyler in 1990. The current flood insurance study and corresponding flood insurance rate map for Schuyler (effective date March 5, 1990) shows that the Platte River 100-year (1% annual chance of exceedance) flood boundary extends into the southern part of Schuyler. Shell Creek’s 100-year floodplain encroaches into portions of northern and eastern Schuyler. A change in the Flood Insurance Rate Maps is currently underway, and the new maps are expected to become effective in the fall of 2012. The revised maps will show additional areas within the 100-year floodplain in and around Schuyler.
The current effective Schuyler Flood Insurance Study for the Platte River is referred to as a limited detail study. This study had only 3 cross sections in the Schuyler area, with the sections an average of about 10,000 feet apart. The effects of the Nebraska Highway 15 bridge and its approach embankments were not considered. The starting water surface elevation at the downstream study limit was based on an estimate using the average valley slope.
The flood insurance study specifically for Schuyler is currently being revised. This revision study for the Platte River through the Schuyler area is a full detailed study. Cross sections were obtained by aerial photogrammetry at approximately 2,000- to 3,000-foot intervals and sometimes at closer spacing. These additional cross sections pick up the effects of terrain not included in the current effective study hydraulic model. The FIS revision also includes the Highway 15 bridge as well as the effects of the embankments from the abandoned railroad grade located downstream. The revised floodplain mapping for the Platte River at Schuyler will be
33 included in new county-wide mapping for Colfax County. The new mapping is expected to be effective sometime in the fall of 2012.
A floating ice cover was used in the Schuyler reach of the Platte River for the revised Flood Insurance Study. Ice jams could potentially be a problem in this reach, but not enough information was available on the location and severity of past ice jams to include them in the hydraulic analysis at specific cross sections. Because of the wide floodplain around Schuyler, the floating ice cover resulted in 100-year (1% annual chance of exceedance) stages only about 0.5 feet higher than the 100-year open water stages. With combined probability stage frequency analysis, there were only small differences between the 100-year open water to the 100-year composite probability stages.
A draft flood boundary map that was prepared by the Corps for the FIS revision indicates a greater flood threat to Schuyler from the Platte River than had previously been projected. This draft flood boundary map indicates that the 100-year floodplain now extends to the Union Pacific Railroad tracks in central Schuyler as shown on Figure 2-9. In that figure, the dark blue area represents the land recently added to the 100-year floodplain, while the light blue area represents the flood fringe that is considered high enough to remain outside of the 100-year flood plain. Grey zones are those areas that have previously been included in the 100-year floodplain. An area of slightly higher ground shown on this map was a focus of evaluation early in this feasibility study, as questions were raised as to whether that area, known as the “Downtown Ridge,” was high enough to prevent flooding at the 1% annual chance of exceedance event. Surveys and subsequent hydraulic modeling determined that it was not in fact high enough. The flood threats to downtown Schuyler, as well as the ridge, are discussed in Sections 2.2.1.4 and 4.1.3.4.
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Draft limits of expanded Draft limits 100-Year Floodplain Effective 100-Year Floodplain Platte River Platte River Effective 100-Year Floodplain
k Lost Cree HWY 15 No Scale Railroad Tracks
FigureFigure 2-9 2-9 Effective Effective and and Draft Draft 100-year100-year (1% annualAnnual chance Chance of of exceedance) Exceedance) floodplain Floodplain boundaries Boundaries for forthe the downtown portion of Schuyler, NE Downtown Portion of Schuyler, NE
35 2.1.4.3 LOCAL FLOODPLAIN REGULATIONS The city of Schuyler and Colfax County both participate in the National Flood Insurance Program (NFIP). The NFIP is administered by the Federal Emergency Management Agency (FEMA). The NFIP makes flood insurance available to all property owners in participating communities. In return, participating communities must enact floodplain management regulations that meet the minimum standards of the NFIP. States and local communities may enact regulations that are stricter than NFIP minimum standards.
As required by the NFIP, the city of Schuyler and Colfax County have enacted local floodplain management regulations that meet the minimum standards of the NFIP. In the designated Special Flood Hazard Area (SFHA) zones (the 100-year floodplain), floodplain development permits are required for new building construction or other significant development, which has to meet certain requirements, such as elevation of the lowest floor above the base (100-year) flood. In the part of the SFHA zones that are designated as the regulatory floodway, new development is severely restricted and must not cause adverse impacts by increasing the 100-year (1% annual chance of exceedance) flood elevations.
2.1.4.4 STATE FLOODPLAIN REGULATIONS The state of Nebraska has enacted “Minimum Standards for Floodplain Management Programs” (Nebraska Administrative Code, Title 455, Chapter 1). These regulations are administered by the Nebraska Department of Natural Resources. Some Nebraska floodplain regulations are stricter than the minimum required by the NFIP, such as the requirement for new construction in the 100-year floodplain to be elevated to one foot above the 100-year (1% annual chance of exceedance) flood elevation.
2.1.4.5 FEMA FLOODPLAIN REGULATIONS FEMA publishes official floodplain maps for communities participating in the NFIP to be used for flood insurance purposes and for floodplain management. The current effective FEMA floodplain maps for the city of Schuyler and its extra-territorial jurisdiction were published on March 5th, 1990 based on studies completed for FEMA by the Omaha District in 1988. This date is also that of the initial Flood Insurance Rate Map (FIRM) for Schuyler that is used to differentiate pre-FIRM and post-FIRM construction and development. The current effective FIRM for Colfax County was published on August 6th, 2002. The initial FIRM for Colfax County dates from February 1st, 1987.
The current effective floodplain mapping for Schuyler was from a limited detailed study of the Platte River and Shell Creek. The study was based on a small number of surveyed cross sections and previously developed topographic mapping with a two-foot contour interval. The study provided only the 100-year (1% annual chance of exceedance) flood profiles and did not delineate floodways.
In 2003, the Omaha District completed the Lower Platte River, Nebraska, Flood Insurance Study for FEMA which included the entire reach of the river through Colfax County and Schuyler. This study used numerous cross sections developed from aerial and ground surveys and developed profiles for the Platte River 10-, 50-, 100- and 500-year (10%, 2%, 1% and 0.2%
36 annual chance of exceedance) flood events. A one-foot-rise floodway was delineated along the river. This study did not update the previous study for Shell Creek at Schuyler.
The Lower Platte River FIS was done in coordination with the Corps’ Lower Platte River and Tributaries General Investigations Feasibility Study. As part of the feasibility study, a flood hazard mitigation study was developed for Schuyler. The flood hazard mitigation study investigated structural and nonstructural measures to reduce the flood hazard but did not have the level of detail for the alternatives of this Section 205 feasibility study.
As of the date of this report, the effective FEMA studies for the city of Schuyler and Colfax County have not yet been revised to include the information developed for the Lower Platte FIS, although it has been used to update adjacent counties. The draft floodplain maps developed by the Corps were presented to the city of Schuyler and Colfax County as the best available data. The potential flood damages and an increase in the Platte River 100-year floodplain affecting the city of Schuyler were factors that resulted in the sponsors partnering in this Section 205 feasibility study.
2.1.4.6 POTENTIAL LETTER OF MAP REVISION INVESTIGATED The construction of the U.S. Highway 30 expressway immediately north of Schuyler in the late 1990’s resulted in a substantial embankment crossing the floodplain of Shell Creek northeast of the city. This embankment had the potential to divert floodwaters from Shell Creek away from the city. As part of this study, hydraulic analyses were planned to determine if the 100-year floodplain of Shell Creek shown on the current effective FIRM would be reduced by the effects of the U.S. 30 Expressway embankment, which was not included in the 1988 study of Shell Creek. If the analyses indicated a reduction in the 100-year floodplain of Shell Creek was warranted, an application for a Letter of Map Revision was to be submitted to FEMA to have the floodplain of Shell Creek officially changed.
Before the hydraulic analyses of the effects on the 100-year (1% annual chance of exceedance) floodplain with the expressway in place could be completed, the flood event of May 30-31, 2008 occurred. This flood showed that the expressway did not significantly reduce the floodplain from Shell Creek. The expressway embankment did block floodwaters on the right bank of Shell Creek, but the bridge for the Nieman Ditch allowed sufficient flow into northeast Schuyler to inundate the floodplain area shown on the current effective FIRM.
2.2 GENERAL ENGINEERING EXISTING CONDITIONS The general engineering existing conditions include the subsurface (soil) conditions and the existence (or nonexistence) of pollutants that could impact the construction of flood risk reduction solutions.
37 2.2.1 Soils and Geotechnical Engineering Existing Conditions
2.2.1.1 PHYSIOGRAPY, RELIEF AND DRAINAGE The physiography, topography and drainage in the Schuyler area is described in the Soil Survey of Colfax County, Nebraska (NRCS, 1982). Portions of this description are reiterated below.
“Colfax County is in the Great Plains physiographic province. The strongest relief is in the breaks adjacent to the Shell Creek and Platte River Valleys. Relief between ridge tops and bottoms of the adjacent drainage ways ranges to a maximum of about 100 feet.”
“About 60 percent of Colfax County is an upland landscape. This landscape consists of ridge tops, side slopes, and narrow valleys. The ridge tops are rounded and commonly gently sloping. The side slopes range from gently sloping to steep.”
“The Platte River Valley is nearly level except for a few hummocky areas of sandy soils. Small drainage ways transect the valley. A stream terrace borders the valley on the north side. This terrace is about 1 mile wide at the western end of the county, just north of Richland, and tapers to a point about 2 miles north of Schuyler. Stream terraces constitute about 5 percent of the county, and bottom lands about 35 percent of the county.”
“Colfax County is drained by the Platte River and its tributaries, including Shell Creek and Lost Creek. The Platte River flows to the east and northeast. Shell Creek and Lost Creek flow into the Platte River from the west and northwest. The Platte River and its major tributaries flow continuously except during periods of extended drought.”
2.2.1.2 GEOLOGY The geology in the Platte River Valley in the Schuyler area is described in Detailed Project Report, Platte River and Lost Creek, Schuyler, Nebraska (1967) as follows: “The uplands bordering the Platte River are dissected, loess-covered, glacial drift hills. Geologic information for the Platte River Valley indicates that about 70 feet of sand, gravel, and clay overlie the Graneros shale.”
In addition, the Soil Survey of Colfax County (NRCS 1982) provides a cross section of soil patterns that are to be expected in the Platte River Valley. The Platte River alignments would be in the area of Association 9 and the Shell Creek alignments would be in Association 7 as depicted in Figure 2-10. The soil characteristics of the upper 5 feet of soils from the Soil Survey of Colfax County are summarized in Section 2.2.1.3 and are separated into Shell Creek and Platte River associations.
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Figure 2-10 Typical Pattern of Soils and Parent Material near Schuyler, Nebraska
2.2.1.3 SOIL SURVEY AND BORING INFORMATION IN THE PROJECT AREA No new borings were conducted as part of this feasibility study. Soil surveys conducted by the NRCS and boring information obtained from the Nebraska Department of Natural Resources (NDNR) Registered Groundwater Wells Data Retrieval website (http://dnrdata.dnr.ne.gov/wellscs/Menu.aspx) from wells in the area of evaluated alternatives for this study are summarized in the following paragraphs.
● Shell Creek Alignment Soils According to the soil surveys, the upper 5 feet of soils are predominantly the Blendon Association. This association generally consists of CL, ML, CL-ML, SM, and SC soils as classified by the Unified Soils Classification System (USCS). Below the upper layer of soils is mostly loamy and sandy alluvium classified as SM, SC, SP-SM, etc at shallower depths and stratified sand and gravel classified as SP, GP, and to a lesser extent SM at deeper depths. According to several borings, two clay layers may exist at a depth of 40-50 feet and 60-70 feet, although it is unknown if they are continuous. Bedrock is expected to be encountered anywhere between 77 and 90 feet of depth.
39 ● Platte River Alignment Soils The upper 5 feet of soils along the Platte River alignment consist of predominantly Alda-Ord Associations. The Alda soils are fine sandy loam, generally classified as SM, SM-SC, SP-SM, and SP by the USCS and are mostly non-plastic. The Ord soils are fine sandy loam, generally classified as ML, SM, SP-SM, and SM-SC and are mostly non-plastic. Below the upper 5 feet are mostly stratified sands and gravels generally classified as SP, GP, and to a lesser extent SP- SM and SM. Clay stringers have been noted in various borings. These lower depth soils are also non-plastic. Bedrock, presumably Graneros Shale, is expected to be encountered between 55 and 65 feet in depth.
● General Soils Consideration Based on standard design practices in the area, it is generally assumed that any levees built as part of a flood control project will consist of a thick impervious blanket on the riverside face and a thinner impervious blanket on the landside face and seepage berm (if required), with random fill material comprising the rest of the levee section.
Potential impervious borrow areas include an abandoned section of Highway 30 located south of the existing Highway 30 and just west of Shell Creek; an abandoned railroad embankment south of Lost Creek and just east of the city of Schuyler; and areas in the hills north of the city of Schuyler. Exact locations of impervious borrow areas north of the city of Schuyler have not been located. Random fill material mostly comprised of sands and/or silty-sands can be obtained from any excavations required for the project, e.g. storm water detention basins and channel cleanouts. Sources of any additional random fill necessary have not been identified. The engineering properties of potential borrow sources have not been thoroughly evaluated and geotechnical soils testing should be conducted during the design after exact borrow sources are identified.
2.2.1.4 AVAILABLE SURVEY / TOPOGRAPHIC DATA Some topographic information in the form of GIS data defining 2-foot contours was obtained from the Nebraska Department of Natural Resources at the start of the feasibility study. Additional surveying was done to define the ridge near downtown Schuyler in the hopes of finding protection from floods of greater than 100-year (1% annual chance of exceedance) frequency, early in the study.
2.2.1.5 EXISTING SHELL CREEK LEVEES A spoil bank levee exists along both banks of Shell Creek between Highway 30 and the Union Pacific Railroad embankment to the south. This levee was constructed by the local landowners to protect agricultural land from Shell Creek flooding during minor flood events. It is uncertain how the levee was constructed and therefore has been discounted as a flood control measure. It was documented to have breached during the spring 2008 flood, but it is unknown if it was a failure from overtopping or a structural failure.
40 2.2.1.6 EXISTING PLATTE RIVER LEVEES No levees are present on the southern end of Schuyler that provide significant flood risk management of Platte River flooding. To prevent Platte River flows from cutting a new channel along Lost Creek, a federal levee was constructed approximately 3.5 miles southwest of Schuyler. This project was built primarily to prevent Platte River flooding through Lost Creek and does not directly provide significant flood risk management for Platte River flooding.
2.2.2 Hazardous, Toxic and Radiological Waste (HTRW) An Environmental Condition of Property (ECP) Phase 1 evaluation was performed for both the proposed Shell Creek and Platte River levee alignments in May and June 2011. As part of this evaluation, environmental data bases were queried, a site visit was conducted and knowledgeable city personnel were interviewed. No evidence of contaminants was found during this investigation. According to the investigation, no limits or restrictions due to contaminants apply to the lands considered for levee construction at Schuyler. Documentation of this investigation is provided in Appendix H (HTRW).
2.3 ENVIRONMENTAL EXISTING CONDITIONS The environmental existing conditions include those ambient conditions that can impact or be impacted by construction of flood risk reduction solutions. They include climate, land forms and land use, water quality, vegetation, fish, wildlife and the presence or absence of threatened and endangered species near the proposed project.
2.3.1 Climate Colfax County has a continental climate, with cold winters and hot summers (Bartlett et al. 1982). Average monthly minimum temperatures range between a low of 12.8°F in January to a high of 66.3°F in July and average monthly maximum temperatures range between a low of 31.2°F in January to a high of 87.4°F in July (Table 2-6).
Precipitation during the winter frequently occurs as snowstorms (Bartlett et al. 1982). The average monthly snowfall, which occurs from October through April, ranges from 0.9 to 6.6 inches, with the greatest amounts typically falling in February (Table 2-6). Precipitation during the warm months is mainly in the form of showers, often heavy, that occur when warm moist air moves in from the south (Bartlett et al. 1982). Precipitation is typically highest in May and June (Table 2-6).
41 Table 2-6 Average Maximum and Minimum Temperature, Precipitation, and Snowfall Values for 1970-2007 for Columbus and Schuyler, Nebraska
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Avg. Max. 31.2 36.5 48.3 62.2 73.0 83.2 87.4 84.6 76.5 63.0 46.0 34.3 60.5 Temperature (°F)* Avg. Min. 12.8 17.7 28.1 39.9 51.7 61.6 66.3 64.3 54.1 41.5 27.5 16.8 40.2 Temperature (°F)* Avg. Total 0.60 0.72 2.02 2.78 4.12 3.94 3.26 3.60 2.92 1.92 1.51 0.74 28.12 Precipitation (inches) Avg. Total 6.3 6.6 5.5 1.0 0 0 0 0 0 0.9 3.5 5.8 29.5 Snowfall (inches) * Temperature values are from the Columbus weather station, 19 miles to the west of Schuyler, since the Schuyler weather station records precipitation but not temperature data. Source: National Climatic Data Center, http://www.ncdc.noaa.gov/oa/ncdc.html
2.3.2 Physiography, Soil Conditions and General Land Use The land use in Colfax County is predominantly agrarian. Of the 268,256 acres in the county, 73% is in cropland and 21% is in rangeland (CALMIT 2007). The remaining land use in the county is classified as riparian forest and woodlands (3.7%), urban land (1.2%), open water (1.1%), wetlands (0.3%), and roads (0.2%) (CALMIT 2007).
2.3.2.1 PHYSIOGRAPHY / TOPOGRAPHY Colfax County is located in the Great Plains physiographic province. A physiographic province is a region that is classified based on its terrain texture, rock type, and geologic structure and history. The strongest relief in Colfax County is in the breaks adjacent to Shell Creek and the Platte River. Relief between ridge tops and bottoms of the adjacent drainage ways ranges to a maximum of about 100 feet. Schuyler is at an elevation of about 1,350 feet (Bartlett et al. 1982).
The terrain in the Platte River Valley is nearly level except for a few hummocky areas of sandy soils. Small drainage ways transect the valley. The study area is drained by the Platte River and its tributaries; Shell Creek and Lost Creek. Several local drainage ditches, most notably Hughes- Payzant Ditch, Shonka Ditch and the Nieman Ditch drain into the Platte River, Shell Creek, and Lost Creek at various locations in the study area.
2.3.2.2 SOILS The study area is located within the Platte River Valley, which covers the southern two-fifths of Colfax County (Bartlett et al. 1982). The major soils in the Platte River Valley developed in silty or clayey alluvium. Soils that formed in sandy alluvium range from deep to shallow over sand and gravelly sand. The principal limitation of these soils for most uses is wetness from the seasonal high water table (Bartlett et al. 1982). The sand and gravel deposits are mined using open pit operations near the Platte River. Flooding, which is rare to frequent, depending upon local topography, is the principal hazard (Bartlett et al. 1982).
42 2.3.2.3 PRIME FARMLAND The town of Schuyler is built on a concentration of soils mapped as Prime Farmland. Prime Farmland map units that are in crop production are located primarily east and west of the town of Schuyler. Soils classified as Prime Farmland in the project area include Euroda loam, Blendon fine sandy loam, and Shell silt loam (digital soils data obtained from USDA Soil Data Mart).
2.3.2.4 GEOLOGY Loess, till, and alluvium are at or near the land surface in Colfax County. The bedrock is of Cretaceous age and lies 60 to 400 feet below the land surface. There are no known outcrops of bedrock in Colfax County. Deposits of sand and gravel or of glacial till overlie the bedrock. Till is present beneath most of the uplands, but is absent or very thin beneath the Platte River Valley (Bartlett et al. 1982).
The land surface in Colfax County was relatively stable before agricultural disturbance. There was little movement of surface materials by water and very little movement or shifting by wind. Cultivated crops have replaced the native grasses, and the soil surface is no longer well protected from erosion. The nearly level and gently sloping silty areas remain relatively stable; however, considerable erosion occurs on hill slopes if left unprotected during tillage.
2.3.3 Water Quality Water quality management of the Platte River and Shell Creek is under the jurisdiction of the state of Nebraska. As required by Section 303(d) of the Clean Water Act, in even-numbered years the Nebraska Department of Environmental Quality (NDEQ) must submit a list of lakes, wetlands, streams, rivers, and portions of rivers that do not meet state water quality standards (40 CFR 130.7). These are considered “impaired water bodies” and states are required to calculate total maximum daily loads (TMDLs) for pollutants causing impairments in these waters. A TMDL is a calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards (EPA 2007).
The Platte River, Lost Creek, Shell Creek, and Shonka Ditch are all classified by the NDEQ Title 117 Anti-degradation Clause. Class A resources are surface waters which constitute an outstanding state or national resource. The existing quality of Class A surface waters must be maintained and protected. Class B waters possess an existing quality which exceeds levels necessary to maintain recreational and/or aquatic life uses. The existing water quality of these surface waters shall be maintained and protected. However, the state may choose to allow lower water quality as a result of important and necessary economic or social development in the area.
2.3.3.1 SHELL CREEK In 2004, 2006, and 2008, NDEQ placed the section of Shell Creek that is within the project area in Category 3, water bodies where there is insufficient data to determine if any beneficial uses are being met and therefore if the water body is impaired.
The Newman Grove Field Study and Ecology class at Newman Grove High School has been studying the water quality of Shell Creek since 2002 (Newman Grove 2008). Each year, five or six sites are tested two days a month from May through August. The closest monitoring site to
43 Schuyler, Site 5, is located approximately 30 miles northwest of Schuyler. Chemical tests of the water are conducted using the Water Quality Index (WQI) System developed by the National Sanitation Federation (1970). The WQI incorporates measurements of dissolved oxygen, fecal coliform, pH, biological oxygen demand (BOD), temperature, total phosphate, nitrates, turbidity, and total solids. Between 2004 and 2008, the WQI at Site 5 ranged from approximately 47-56, or between bad and medium water quality on the WQI scale used in the study.
Beneficial uses assigned to the sections of Shell Creek within the project area include: recreation, warm water aquatic life, agriculture water supply, and aesthetics. Currently, none of these beneficial uses are listed as impaired.
2.3.3.2 PLATTE RIVER In 2004, 2006, and 2008, NDEQ placed the section of the Platte River that is within the project study area in Category 4A, which consists of water bodies that are impaired but have a completed TMDL for the impairments (NDEQ 2004, 2006, 2008). This section of the Platte River is impaired for E. coli and fecal coliform even though a fecal coliform TMDL was completed in 2003.
Beneficial uses assigned to the reach of the Platte River south of the project area include: recreation, warmwater aquatic life, public drinking water, agricultural supply, and aesthetics. Currently, recreation, warmwater aquatic Life, public drinking water, agriculture water suply, industrial water supply, and aesthetics. Recreation, aquatic life, and public drinking water are listed as impaired. The parameters of concern include: E. coli and atrazine.
2.3.3.3 LOST CREEK and SHONKA DITCH Beneficial uses assigned to Lost Creek and Shonka Ditch within the project area include: warm water aquatic life, agriculture water supply, and aesthetics. None of these beneficial uses are listed as impaired.
2.3.4 Vegetation and Terrestrial Habitat Lost Creek and Shell Creek are both bordered by a riparian corridor consisting primarily of white mulberry (Morus alba), honey locust (Gleditsia triacanthos), black walnut (Juglans nigra), green ash (Fraxinus pennsylvanica), elms (Ulmus spp.), and a few mature cottonwoods (Populus deltoids) and willows (Salix spp.) Shrubs consist primarily of gray dogwood (Cornus drumondii) and box elder (Acer negundo). The 2.5 miles of Shell Creek in the vicinity of the project area supports approximately 45 acres of riparian trees and shrubs. The 3 miles of Lost Creek in the vicinity of the project area supports approximately 46 acres of riparian trees and shrubs. The 2.5-mile section of Nieman Ditch in the vicinity of the project area supports approximately 6.75 acres of riparian trees and shrubs. Grasslands in the vicinity of the proposed project are dominated primarily by smooth brome (Bromus inermis) and reed canarygrass (Phalaris arundinacea).
2.3.5 Wetlands The National Wetland Inventory (NWI) depicts several wetland areas associated with the Platte River, Lost Creek, Shell Creek, and a roadside drainage ditch that drains to Shell Creek (see
44 Figure 2-11). The NWI uses the Cowardin System of wetland classification (Cowardin et al. 1979).
Figure 2-11 Drainage Pattern and Wetlands Near Schuyler, NE
Corps biologists visited the site on August 6th, 2010 to conduct a vegetation survey, verify the presence or absence of NWI-mapped wetlands, and identify other areas of potential environmental concern. The site visit was focused on potential levee alignments along Lost Creek south of Schuyler and along Nieman Ditch and Shell Creek east of Schuyler. Wetlands were delineated using methods described in the Great Plains Regional Supplement to the Corps of Engineers’ Wetland Delineation Manual. Sample points were taken to determine the upland/wetland boundary, and wetland boundaries were surveyed in the field using a sub-meter accuracy GPS unit.
2.3.5.1 SHELL CREEK The NWI depicts forested, scrub/shrub, and emergent wetlands just north of the intersection of Shell Creek and the Union Pacific Railroad (UPRR) line. Shell Creek diverts sharply to the east along the north side of the UPRR line at this location. See Figure 2-12. In addition to these wetlands, the NWI maps a roadside drainage ditch that drains to Shell Creek as an emergent wetland.
45
Figure 2-12 View of Shell Creek Channel North of UPRR Line. Photo is Oriented Southeast.
On-site observations of Nieman Ditch located east of Schuyler and west of Shell Creek, were consistent with the NWI depiction of an emergent wetland. Nieman Ditch supports an approximately 20- to 25-footwide corridor of wetland vegetation from Highway 30 to roughly 3,000 feet upstream of its confluence with Shell Creek. Dominant vegetation includes: river bulrush (Scirpus fluviatilis), smartweed (Polygonum spp.), barnyard grass (Echinochloa crusgalli), prairie cordgrass (Spartina pectinata), and swamp milkweed (Asclepias incarnate). There is a notable lack of cattails (Typha spp.) and reed canarygrass (Phalaris arundinacea) which often dominate disturbed wetlands. A roadside drainage ditch that connects to Nieman Ditch just south of Highway 30 supports a wetland dominated by cattails (Typha spp.). Roughly 2.5 miles of Nieman Ditch (including the roadside ditch portion) is located within the project area. Nieman Ditch supports approximately 3.25 acres of wetlands within the project area.
Contrary to the NWI depiction, Shell Creek does not appear to support a large concentration of wetlands near the UPRR line. A wetland fringe, however, is present in several locations on the lower embankments of Shell Creek. The wetland fringe consists primarily of barnyard grass (Echinochloa crusgalli) and reed canarygrass (Phalaris arundinacea). Near its diversion along the north side of the UPRR line, the embankments are steep and there appears to be little
46 connectivity between the creek and its floodplain due to head cutting. Dominant vegetation in this area includes white mulberry (Morus alba), box elder (Acer negundo), dogwoods (Cornus spp.), and a few mature cottonwoods (Populus deltoides) and willows (Salix spp.). Herbaceous vegetation includes barnyard grass (Echinochloa crusgalli) and reed canarygrass (Phalaris arundinacea) on lower lying areas adjacent to the stream and smooth brome on the embankments. Approximately 2.5 miles of Shell Creek are located in the vicinity of the project area. This portion of Shell Creek supports approximately 5.73 acres of fringe wetlands.
2.3.5.2 PLATTE RIVER The NWI maps the Platte River as a riverine (R2UBH) wetland. In addition to riverine wetlands, the NWI depicts areas of forested, scrub/shrub, and emergent wetlands in the Platte River floodplain. Typically, in the Platte River floodplain, forested wetlands consist of mature cottonwoods (Populus deltoides) and willows (Salix spp.); scrub/shrub wetlands consist of willow and cottonwood saplings; and emergent wetlands consist of grasses, forbs, and emergent macrophytes such as reed canarygrass (Phalaris arundinacea), smartweeds (Polygonum spp.), cattails (Typha spp.), and rushes (Juncus spp.).
The NWI classifies several old gravel pits along Lost Creek as lacustrine wetlands. It is common for former gravel pits to have a fringe of emergent macrophytes such as cattails (Typha spp.). According to the NWI, Lost Creek itself does not appear to support a significant amount of riparian wetlands.
Figure 2-13 View of Lost Creek in Western Portion of Golf Course. Photo is Oriented Southwest.
47 Dominant herbaceous vegetation along Lost Creek includes a narrow (3-4 foot) fringe of reed canarygrass (Phalaris arundinacea) along the edge of the creek with smooth brome (Bromus inermis) dominating the embankments (see Figure 2-13). A wider riparian corridor is present along Lost Creek east of Highway 15. Woody riparian vegetation along Lost Creek consists primarily of white mulberry (Morus alba), locust (Gleditsia spp.), green ash (Fraxinus pennsylvanicum), elms (Ulmus spp.), and a few mature cottonwoods (Populus deltoides). Roughly 3 miles of Lost Creek is located within the project area. This portion of Lost Creek supports approximately 1.5 acres of wetlands.
2.3.6 Fish and Wildlife
2.3.6.1 FISH Fish collected by Newman Grove within Shell Creek in 2007 include fathead minnow (Pimephales promelas), sand shiner (Notropis stramineus), red shiner (Cyprinella lutrensis), river shiner (Notropis blennius), black bullhead (Ameiurus melas), yellow bullhead (Ameiurus natalis), green sunfish (Lepomis cyanellus), and carp (Cyprinus carpio) (Newman Grove 2008). Possibly because of poor water quality, Newman Grove has had a hard time finding aquatic macroinvertebrates in recent years (Newman Grove 2008). A site on Shell Creek was sampled as part of the USGS National Water Quality Assessment Program in 1993-1994. An index of biotic integrity (IBI) determined from fish community data was developed for nine sites on streams in the Platte River basin. Of the nine sites, Shell Creek had the lowest IBI score (25 miles from the Platte River confluence) due to low number of native species and high percentage of pollution tolerant species (Frenzel and Swanson, 1994).
According to the initial Planning Aid Letter from the U.S. Fish and Wildlife Service (USFWS) in 2003, the Nebraska Game and Parks Commission (NGPC) 1978 Stream Evaluation Map rates the Platte River as a Highest-Valued fishery resource and the segment of Lost Creek, located upstream from the west edge of the Schuyler golf course as a Substantial fishery resource. Channel catfish (Ictalurus punctatus), freshwater drum (Aplodinotus grunniens), flathead catfish (Pylodictis olivaris), shovelnose sturgeon (Scaphirhynchus platorynchus), carp (Cyprinus carpio), and goldeye (Hiodon alosoides) are typical fish species found in the Platte River south of the project area.
The NDEQ lists the Platte River, Shell Creek, and Lost Creek as Class A warm water surface waters in the vicinity of the project area. Shonka Ditch is listed as a Class B warm water aquatic resource. Key species noted for the Platte River include sturgeon chub, walleye, flathead catfish, and channel catfish. Channel catfish are also listed as the key species for Shell Creek and Lost Creek.
2.3.6.2 MAMMALS Mammals that may typically be found in the vicinity of waterways in eastern Nebraska like Shell Creek and the Platte River include Virginia opossum (Didelphis virginiana), masked shrew (Sorex cinereus), least shrew (Cryptotis parva), eastern red bat (Lasiurus borealis), woodchuck (Marmota monax), white-footed mouse (Peromysus leucopus), northern grasshopper mouse (Onychomys leucogaster), southern bog lemming (Synaptomys cooperi), meadow vole (Microtus
48 pennsylvanicus), common porcupine (Erethizon dorsatum), least weasel (Mustela nivalis), gray fox (Urocyon cinereoargenteus), and bobcat (Lynx rufus) (Benedict et al. 2000).
2.3.6.3 BIRDS Common breeding birds in eastern Nebraska in the vicinity of floodplain forests that may be found along the Platte River or Shell Creek include the Cooper’s hawk (Accipiter cooperii), great horned owl (Bubo virginianus), Northern flicker (Colaptes auratus), red-headed woodpecker (Melanerpes erythrocephalus), great crested flycatcher (Myiarchus crinitus), blue jay (Cyanocitta cristata), black-capped chickadee (Poecile atricapilla), house wren (Troglodytes aedon), eastern bluebird (Sialia sialis), American robin (Turdus migratorius), red-eyed vireo (Vireo olivaceus), yellow warbler (Dendroica dominica), Baltimore oriole (Icterus galbula), and Northern cardinal (Cardinalis cardinalis) (Sharpe et al. 2001).
2.3.6.4 AMPHIBIANS Amphibians that may be found in Colfax County include the American toad (Bufo americanus), bullfrog (Rana catesbeiana), Great Plains toad (Bufo cognatus), Northern cricket frog (Acris crepitans), Northern leopard frog (Rana pipiens), Plains leopard frog (Rana blairi), Plains spadefoot (Spea bombifrons), Western gray treefrog (Hyla chrysoscelis), Western striped chorus frog (Pseudacris triseriata), and Woodhouse’s toad (Bufo woodhousii) (UNL 2008).
2.3.6.5 REPTILES Turtles that can be found in Colfax county include Blanding’s turtle (Emydoidea blandingii), painted turtle (Chrysemys picta), smooth softshell turtle (Apalone muticus), snapping turtle (Chelydra serpentina), and spiny softshell turtle (Apalone spiniferus) (UNL 2008). Snakes that may be found in Colfax County include bullsnake (Pituophis catenifer), eastern hognose snake (Heterodon platyrhinos), fox snake (Elaphe vulpina), lined snake (Tropidoclonion lineatum), massasauga (Sistrurus catenatus), milk snake (Lampropeltis triangulum), Northern watersnake (Nerodia sipedon), Plains garter snake (Thamnophis radix), racer (Coluber constrictor), red- sided garter snake (Thamnophis sirtalis), ringneck snake (Diadophis punctatus), and smooth green snake (Opheodrys vernalis).
2.3.7 Threatened and Endangered Species and State-Listed Species of Concern In a preliminary Planning Aid Letter dated February 26th, 2003, the U.S. Fish and Wildlife Service (USFWS) stated that critical habitat for the interior least tern (Sternula antillarum), piping plover (Charadrius melodus), and pallid sturgeon (Scaphirhychus albus) occurred within the portion of the project area that is along the Platte River. Supplemental letters from the USFWS and Nebraska Game and Parks Commission (NGPC) in 2009 indicated that the project also lies within the range of the western prairie fringed orchid (Platanthera praeclara) and small white lady’s slipper (Cypridpedium candidum), both of which are typically found in high quality prairies or wet meadows. Site visits did not reveal any high quality prairie or wet meadow areas in the project area. Grasslands in the project area are dominated almost entirely by smooth brome (Bromus inermis) and reed canarygrass (Phalaris arundinacea). Informal Endangered Species Act consultation is ongoing with the USFWS and a Biological Assessment is being prepared in conjunction with this project.
49 2.4 COMMUNITY EXISTING CONDITIONS Community existing conditions are those factors that make up the economic, social, cultural, recreational and real estate structure of the community at the present time. These factors will impact the implementation of a project and be implemented by the proposed project. The economic baseline factors, in particular, are important in evaluating the positive impact of a flood risk reduction project.
Schuyler has a population of 6,211, as of the 2010 Census (U.S Census Bureau, 2011). It is a rapidly growing county seat and important regional population center with an active central business district. From 1990 to 2000, Schuyler grew by 32.6% and from 2000 to 2010, the community increased by 15.6% (U.S. Census Bureau, 1990, 2000, and 2011).
2.4.1 Economic Existing Conditions The purpose of the without-project economic analysis is to evaluate the potential economic justification for a flood risk management project at Schuyler, Nebraska for both the Shell Creek and the Platte River floodplains. Additional detail about the economic analysis may be found in Appendix D (Economics).
The economic analysis was performed using the Hydrologic Engineering Center’s Flood Damage Reduction Analysis (HEC-FDA) Version 1.2.4 Risk Analysis model (November 2008). Annualized estimates of damages in this analysis assume the FY 2011 federal interest rate of 4.125% and a period of analysis of 50 years based on official guidance for evaluation of federal projects. All estimates are expressed in FY 2011 price levels.
2.4.1.1 ECONOMIC DAMAGE PARAMETERS A land use file for Schuyler was created which contained all structures in the Federal Emergency Management Agency (FEMA) 500-year floodplain (0.2% chance of annual exceedance) to determine expected annual flood damages under existing without- project conditions. All structures with the potential for damage from flooding within the areas considered were included in the land use file.
In this analysis, the economic database for the existing condition is also used to characterize the existing and future conditions. According to the November 2004 Comprehensive Development Plan for Schuyler, Nebraska, it is unlikely that there will be major changes to the land use within the city of Schuyler’s floodplain area over the next 25 years. Rather, the plan suggests development will primarily concentrate on the fringe and outlying areas of the community outside of the flood plain. Ultimately, while there could be potential development projects on the horizon as this study is completed, none met the criteria for inclusion into future conditions: (a) high likelihood of implementation, (b) firm identification of a location, and (c) availability of information on industrial classification and estimated investment. Thus, for purposes of this analysis it is assumed that existing level of development will remain the same for the next 50 years under future without-project conditions, as there are no evident drivers for significant change beyond the period covered in the comprehensive plan (25 years). Therefore, the economic database used for the existing conditions analysis is carried through to the future conditions without change.
50 2.4.1.2 NATIONAL FLOOD INSURANCE PROGRAM SAVINGS The City of Schuyler is a participant in the National Flood Insurance Program (NFIP). As part of this program, the City has adopted and enforces strict land use controls, including building codes, zoning regulations, and subdivision regulations designed to limit flood damage to future construction within the Federal Emergency Management Agency (FEMA) specified Special Flood Hazard Area (SFHA). This area comprises the 100-year (1% chance of annual exceedance) floodplain. The city has statutory authority to enforce land use regulations in the city and within an extraterritorial zoning jurisdiction. As a result of the City’s participation in this program, property owners and renters in the area are eligible to purchase flood insurance. These policies provide coverage for eligible damages in the event of a flood.
Savings which accrue to the government as a result of the implementation of a flood risk management project are considered national economic development (NED) benefits. The savings in policy premiums are not considered, because to do so would result in double counting flood damages that are reflective of the policy premiums. The savings of flood insurance policy administration costs are not reflected as flood damages and would constitute a benefit. Those cost savings would occur to the extent present and future policyholders are removed from the SFHA and NFIP policies are no longer required and would not be purchased.
The most current NFIP administrative costs for existing structures in the 100-year (1% annual chance of exceedance) floodplain are $192 for FY 2011, according to Economic Guidance Memorandum 06-04, National Flood Insurance Program Operating Costs, dated April 6th, 2006, the most recent one available. An estimated 87.5% of structures in the current 100-year (1% chance of annual exceedance) floodplain have federally-subsidized flood insurance coverage for the depreciated replacement value of structures and contents. It is assumed that 87.5% of owners of structures in newly designated 100-year (1% chance of annual exceedance) floodplain areas expected to become effective in 2012 would purchase flood insurance. In accordance with paragraph E-19, ER 1105-2-100, it is assumed that if a flood risk management project reduces the risk of damages from a 100-year event from occurring by 90%, then structures will consequently no longer be in the 100-year (1% chance of annual exceedance) floodplain and will no longer be insured under the NFIP. For this analysis, 87.5% of structures removed from the 100-year (1% chance of annual exceedance) floodplain due to the project improvement, multiplied by the most current administrative cost per policy, constitutes the annual cost avoidance benefits for reductions in NFIP administrative costs. As displayed in Tables 10a and 10b of Appendix D (Economics), HEC-FDA shows 207 and 559 structures in the Schuyler study area in the 100-year (1% chance of annual exceedance) floodplain of Shell Creek and the Platte River, respectively; 87,5% of these structures are 181 and 489 structures, respectively. Thus a potential of approximately $34,800 and $93,900 in annual flood insurance administrative costs could be avoided with a project providing flood damage risk reduction for a 100-year (1% chance of annual exceedance) floodplain on Shell Creek or on the Platte River.
2.4.1.3 EXPECTED ANNUAL DAMAGES, EXISTING CONDITIONS For Shell Creek, expected annual flood damages (EAD) derived from HEC-FDA under existing conditions are $851,400. Reach ROB5 accounts for 60% of the damages, followed by Reach ROB4 with almost 25% of the damages (See Table 2-7 and Figure 2-6).
51 Table 2-7 Shell Creek, Existing Conditions Expected Annual Damages
Table 2-7. Shell Creek, Existing Conditions Expected Annual Damages (in thousands, FY 2011 prices) Reach C CRP DIS EMG I P R STR Subtotal NFIP Total EAD % of EAD ROB1 $0.00 $0.56 $0.00 $2.37 $30.51 $0.00 $0.00 $3.96 $37.41 $0.17 $37.57 4.41% ROB2 $0.00 $0.61 $0.61 $0.10 $0.00 $0.00 $6.57 $0.17 $8.06 $0.50 $8.56 1.01% ROB3 $0.00 $1.34 $1.28 $1.11 $14.09 $0.00 $24.50 $1.86 $44.18 $2.69 $46.87 5.50% ROB4 $1.99 $1.34 $9.57 $3.37 $4.29 $0.00 $171.18 $5.61 $197.34 $12.94 $210.27 24.70% ROB5 $276.16 $2.46 $10.74 $8.19 $61.94 $0.00 $137.55 $13.65 $510.70 $0.17 $510.87 60.00% ROB6 $0.00 $1.27 $0.14 $0.04 $0.00 $0.00 $2.24 $0.07 $3.76 $18.14 $21.90 2.57% Shell1 $0.00 $0.62 $0.43 $0.81 $0.00 $0.00 $12.00 $1.34 $15.19 $0.17 $15.35 1.80% Total $278.15 $8.19 $22.76 $15.99 $110.83 $0.00 $354.04 $26.66 $816.62 $34.78 $851.40 100.00% C = commercial, CRP = crop, DIS = disaster, EMG = emergency I = industrial, P = public, R = residential, STR = street, NFIP = insurance administrative costs
For the Platte River, expected annual flood damages (EAD) derived from HEC-FDA under existing conditions are $1,093,230. Reach P2 accounts for over 54% of the damages, followed by Reach P3 with nearly 44% of the damages (See Table 2-8). Damages from Lost Creek are included with Platte River damages, as gaging records are not available for Lost Creek.
Table 2-8 Platte River, Existing Conditions Expected Annual Damages
Table 2-8. Platte River, Existing Conditions Expected Annual Damages (in thousands, FY 2011 prices) Reach C CRP DIS EMG I P R STR Subtotal NFIP Total EAD % of EAD P1 $0.19 $1.25 $0.74 $0.11 $0.82 $0.60 $8.05 $1.00 $12.77 $8.90 $21.67 2.0% P2 $178.29 $1.58 $19.22 $7.36 $6.44 $24.69 $255.35 $52.76 $545.69 $49.22 $594.91 54.4% P3 $16.30 $8.35 $8.01 $7.23 $9.83 $130.32 $220.00 $40.83 $440.87 $35.78 $476.65 43.6% Total $194.78 $11.18 $27.97 $14.70 $17.09 $155.61 $483.40 $94.59 $999.33 $93.91 $1,093.23 100.0% C = commercial, CRP = crop, DIS = disaster, EMG = emergency I = industrial, P = public, R = residential, STR = street, NFIP = insurance administrative costs
2.4.1.4 RISK ANALYSIS The risk analysis was performed using the Hydrologic Engineering Center Flood Damage Analysis (HEC-FDA) Version 1.2.4 (November 2008). The basic assumptions underlying the risk analysis program are that the field data in flood risk management studies are based on imperfect knowledge and those key variables for which median or most likely values are specified could, in reality, take on a range of values above and below the specified values. Under the risk-based analysis condition, the model uses the expected probability function along with the stage-discharge and damage-stage functions with uncertainty to compute expected annual damage (EAD). Further details on how HEC-FDA performs the risk analysis may be found in Appendix D (Economics).
2.4.2 Cultural Resources
2.4.2.1 BACKGROUND Various indigenous peoples inhabited Nebraska as early as 8000 BC. During proto-historic and historic times, semi-sedentary Indian tribes, notably the Ponca, Omaha, Otoe, and Pawnee, lived in eastern and central Nebraska. Schuyler is located along the Platte River, downstream from the Loup River, and corresponds to an area of proto-historic (Lower Loup phase) and historic
52 Pawnee villages that have been identified as Pawnee by the Pawnee Nation and archeologists. The Loup River area was settled by the Skidi Pawnee, one of four Pawnee bands, by 1700. Skidi Pawnee sites are identified in historic documents dating as early as 1718, and they remained the primary Pawnee band in the area for the next century. By 1857, all four Pawnee bands coalesced along the Loup River after disease, warfare and land cessions resulted in a restriction of Pawnee lands. By 1875, the Pawnee left the Loup River and settled on a tract of land in Oklahoma. Today they are known as the Pawnee Nation of Oklahoma.
The Mormon Trail, over which thousands traveled from Winter Camp near Florence to Utah starting in 1847, ran along the south edge of what later became Schuyler. The Military Road, commissioned in 1859, used the same general path.
Moses Shinn’s ferry across the Platte near the mouth of Shell Creek allowed travelers from Omaha to use the south side of the river, where there were fewer streams to cross. The Union Pacific Railroad’s route across Nebraska in 1866 also chose the Platte Valley but stayed on the north side of the river, establishing a depot called Shell Creek Station.
The city of Schuyler was originally known as Shell Creek Station in Nebraska territory. In 1866 the Union Pacific Railroad (UPRR) reached Schuyler and in 1867 Nebraska became a state of the United States. In 1869 the legislature divided the over-sized Platte County into three smaller ones. The eastern portion was named Colfax County with Shell Creek Station (designated as county seat) renamed Schuyler in 1870 honoring U.S. Vice President Schuyler Colfax. There was only a depot, a section house, a water tower, and a fuel storage area until the Smith brothers opened a small general store.
Soon other businesses set up shop, and in 1870 Schuyler was incorporated. This was the year that Texas cattlemen started driving large herds to the stockyards at Schuyler. This caused the town to grow to over 600 people with more than 100 businesses, including a brewery, livery stables, and other establishments to serve the cowboys.
The Oak Ballroom, listed on the National Register of Historic Places (NRHP), is located at the entrance to the city’s South Park and is situated on the old Mormon Trail. The building was built by the Works Progress Administration (WPA) and completed in 1937. Its name was derived from the huge natural timbers and beams cut from native oak trees. Its interior is shown in Figure 2-14.
53
Figure 2-14 Interior of the Oak Ballroom in Schuyler, NE
In the latter part of the 20th century, Schuyler became host to an important regional meat packing center for east-central Nebraska. Many migrants came from Mexico, Guatemala and other parts of Central America in pursuit of jobs. Over time, Hispanics started many businesses in Schuyler, effectively revitalizing the downtown core area. Residential occupancy increased sharply and new homes and businesses have been built. The relative youth of the population has resulted in a huge growth in enrollment in the Schuyler public schools. According to the 2010 U.S. Census, people of Hispanic descent account for 65.4% of the population of Schuyler (U.S. Census Bureau, 2011). Even more recent immigrants include natives of Sudan and nearby African nations.
2.4.2.2 CULTURAL RESOURCE ACTIVITIES IN THE INITIAL ASSESSMENT Formal coordination with the Nebraska State Historic Preservation Office (SHPO), Tribes, and other interested parties was initiated during February of 2003. Response letters were received from State Historic Preservation Office (SHPO) and the Pawnee Nation of Oklahoma. A file search was conducted by the Nebraska State Historical Society in February of 2003. No recorded historic properties or surveys were discovered for the alignments, and survey of the proposed levee routes was recommended by the SHPO. Communication from the Pawnee Nation of Oklahoma identified two sites affiliated with their Tribe in the vicinity of Schuyler. Copies of these letters are provided in Appendix C (Cultural Resources).
54 A second site file search was completed at the Nebraska State Historical Society in January 2004. In addition to the Oak Ballroom, two historic properties were identified within the city of Schuyler.
Site 25CX504 was a steam-powered roller mill built in 1881 and owned by the Wells, Abbot & and Nieman Co. This plant produced “Puritan Flour,” marketed worldwide. On October 7th, 1933, the milling plant was completely destroyed by fire. It is located on the south side of the Union Pacific Railroad track (UPRR), at the intersection of Wyoming and the railroad tracks. Site 25CX509 is the Schuyler Milling Company, a 1930s-era oil-powered roller mill which replaced the earlier mill. The building still exists and is in use for livestock feed. It is located on the south side of UPRR and on the west side of the new overpass. Neither site has been evaluated for National Register eligibility.
2.4.2.3 CULTURAL RESOURCE ACTIVITIES IN THE FEASIBILITY STUDY PHASE Several additional NRHP-listed structures were identified within the City of Schuyler. These include the Colfax County Courthouse, Schuyler City Hall, the John Janicek House, the Schuyler Carnegie Library, and the Schuyler United States Post Office, known for its WPA-era mural. The above-named property sites would benefit from the flood risk management measures and are not in the Area of Potential Effect (APE).
The two sites known to the Pawnee Nation were identified as the Wolfe site, 25CX02, and Grey (aka Schuyler) site, 25CX01. These two adjacent sites overlook Shell Creek near Schuyler. These villages apparently date from A.D. 1500-1650, and they were probably occupied by ancestors of the Skidi Band of the Pawnee. They are not located in the APE.
2.4.3 Recreational Resources Schuyler, Nebraska currently offers a variety of different recreational opportunities at several parks in various areas of the city to meet community needs.
The largest recreational facility is the Schuyler Golf Club, a scenic, public nine-hole golf course with a new club house addition (City of Schuyler, 2010a). The golf course is part of South Park and is located south of Lost Creek and adjacent to the Oak Ballroom and other city recreational facilities. The golf club has 180 members who pay membership dues, and non-members can pay greens fees to play golf. Total visits to the golf course and club house are not available. However, visitation was lower in 2010 than in 2009 because the golf course was closed for 2 weeks in June 2010 after Lost Creek flood waters inundated and killed much of the grass, and it was closed for the season the second week in September 2010 for reseeding (Peschel, pers. comm., 2010b, 2010c, 2010d).
The Oak Ballroom was constructed in 1937 with Works Progress Administration (WPA) funding at the entrance to South Park, which opened the same year. Oak trees from the Linwood, NE area were used in its construction. The Lawrence Welk Band was the first band to play at the Oak Ballroom, which was a popular dance hall through the 1950s (City of Schuyler, 2010b). The Oak Ballroom is listed on the National Register of Historic Places. It is the site of wedding
55 receptions, anniversary parties, and many events sponsored by community groups such as dances, chili feeds, fish fries, and banquets. In 2009, 13,701 persons attended events at the Oak Ballroom (Peschel, pers. comm., 2010a, 2010b).
A swimming pool is located on a knoll in South Park just north of Lost Creek, and a bathhouse abuts the pool. The knoll is high enough that the pool has never been flooded. In 2009, the pool received approximately 8,525 daytime visits (Peschel, pers. comm., 2010a, 2010b). There are two lighted tennis courts west of the pool area (City of Schuyler, 2010c). Two group picnic areas (each of which has a group shelter, tables, grills, trash can, and playground) and a restroom serving both picnic areas are located between the golf course and Highway 15. A campground and fishing lake are located east of Highway 15. There were 1,918 camping nights recorded at the campground in 2009 (Peschel, pers. comm., 2010a, 2010b). Along the north side of the fishing lake is a 10-foot-wide concrete trail that runs west to the crosswalk on Highway 15; this constitutes Phase I of a three-phase trail construction project. A 35-foot-long footbridge over Lost Creek was located west of Highway 15, near the Oak Ballroom, pool bathhouse, and Group Picnic Area 1 playground; it was damaged by the 2010 flood on Lost Creek and was removed. Consequently, people are currently walking, jogging, bicycling, and pushing strollers on the shoulders of Highway 15 so they can use the Highway 15 bridge for access between the north and south portions of South Park. There are also many recreational walkers along South Park Road and Higgins Road, in the vicinity of the golf course. These walkers, hikers, and joggers view birds and other wildlife, especially ducks, geese, herons, woodpeckers, mourning doves, and songbirds (Peschel, pers. comm., 2010a, 2010c, 2010d).
Public fishing occurs at the following locations: the fishing lake near the campground; along Lost Creek; and in the “lagoon” (pond) east of the golf course, which has just undergone restoration that included dredging sediment. Another lake is located within a subdivision south of the golf course and is used by residents of the subdivision for boating and fishing. Adjacent landowners can fish in Shell Creek, but it has no public fishing access. The Nebraska Department of Roads (NDOR) does not allow fishing off the Highway 30 bridge (Peschel, pers. comm., 2010a).
Eagles, deer, and a variety of other wildlife are found in the mature woodlands along Shell Creek. Many adjacent landowners hunt deer in the woods along Shell Creek, but members of the general public can hunt there only with the landowner’s permission. No hunting is allowed on Lost Creek within the city limits. Public hunting is allowed at the Whitetail Reserve, which is managed by the Nebraska Game and Parks Commission (NGPC) and is located along the Platte River, about 1 mile west of Highway 15 (Peschel, pers. comm., 2010a).
Two American Legion baseball teams, for youths 15-16 and 17-18 years old, use the baseball field at Merchant’s Park, which is located north of the swimming pool in South Park. Merchant’s Park has a well-manicured field and excellent grandstands (City of Schuyler, 2010d). It is estimated that there are approximately 3,600 visits per year to Merchant’s Park to practice, play, coach, umpire, and attend (as spectator or concession stand volunteer) American Legion baseball games (Meister, pers. comm., 2010).
56 North Park, located in the northeast part of Schuyler, contains three baseball fields, a half-court basketball court, a small tennis court, and a sand volleyball area. A group picnic shelter and a small playground are located in the southwest corner of North Park (Peschel, pers. comm., 2010a). A fourth ball field at North Park consists of a grassy area with an adjacent sandy area for parking and is used for five tee-ball teams, three for baseball and two for softball (Gilson, pers. comm., 2010). There are 9 or 10 Schuyler teams practicing and playing baseball at North Park, from tee-ball through age 14. It is estimated that there are approximately 8,400 visits per year to North Park to practice, play, coach, umpire, and attend (as a spectator or concession stand volunteer) baseball games (Meister, pers. comm., 2010). It is estimated that there are approximately 900 visits per year to practice, play, coach, umpire, and attend Schuyler tee-ball games (Inselman, pers. comm., 2010).
There are four Schuyler softball teams above the tee-ball level, from 10 and under through 18 and under, who use the softball field in South Park west of the tennis courts. It is estimated that there are approximately 2,300 visits per year to practice, play, coach, umpire, and attend (as a spectator or concession stand volunteer) softball games in South Park. Development of a second softball field north of the existing softball field at South Park began in 2010. When this second field is completed, the tee-ball teams will practice and play games at South Park instead of North Park (Inselman, pers. comm., 2010).
A 28-acre soccer complex with 4 large and 2 small soccer fields is located on the site of the old landfill in the southeast area of Schuyler (Gilson, pers. comm., 2010). The landfill was closed in the late 1980s under a formal process involving the Nebraska Department of Environmental Quality. Monitoring wells are located along the perimeter of the old landfill site. The landfill was crowned and designed for soccer fields. A well that supplies water for the irrigation system is located in the middle of the northern boundary of the soccer complex, and concrete drainage ways were installed between the soccer fields. A parking lot and portable restrooms are located in the northeast corner of the soccer complex. A road from the parking lot accesses a yard waste site for grass clippings and tree branches located southeast of the soccer fields; and a guard shack for the yard waste attendant is located south of the soccer fields. East of this road is a detention cell for storm water. On the southwest side of the soccer fields is a small former sandpit lake, which is not accessible to the public (Peschel, pers. comm., 2010a).
2.4.4 Real Estate and Utilities Any structural flood damage reduction project, such as a levee, will require real estate acquisitions. Depending on the selected type of project and alignment, it is possible that some homes or other structures will need to be removed and other properties adversely impacted.
2.4.4.1 REAL ESTATE ACTIVITIES IN THE INITIAL ASSESSMENT STUDY PHASE A levee along the southern end of the community and north of Lost Creek was discussed in the Initial Assessment Study (Corps, 2003). The alignment proposed that would closely follow the north bank of Lost Creek would impact a historical building (Oak Ballroom), significant groves of mature trees, residential developments, agricultural areas, commercial land, and public property. In contrast, another levee alignment proposed in the Initial Assessment Study, proposed to be located south of the park and golf course, would predominantly impact agricultural lands. Although no detailed cost estimates for real estate acquisitions were
57 developed for this assessment, a levee along the southern edge of the community could incur much greater real estate unit costs than a levee along a more southern alignment. It was noted that in addition to real estate impacts, any levee within the community will likely incur substantial costs for relocation or modification of electrical, phone, cable, sewer, and other utilities.
2.4.4.2 REAL ESTATE ACTIVITIES IN THE FEASIBILITY STUDY PHASE Several possible project areas lie within the city of Schuyler and adjacent Colfax County, Nebraska because of flooding to northern Schuyler from Shell Creek and to southern Schuyler from the Platte River with some additional impacts from Lost Creek. A major factor in existing conditions is the footprint of the Union Pacific Railroad (UPRR) traversing from generally east to west across the county of Colfax and through the city of Schuyler.
Several possible variations in the project area are within the city of Schuyler and Colfax County, Nebraska in response to flooding to northern Schuyler from Shell Creek and to southern Schuyler from the Platte River with some additional impacts from Lost Creek. Recent flooding events in Schuyler dictate consideration of impacts to residential, recreational, commercial and industrial structures, and agricultural uses. Real estate considerations from site visits and consultations with sponsor representatives to date are as follows:
1) Navigational Servitude, if applicable, needs to be considered within the report. 2) Recommended estates require Fee Title, Permanent Levee Easement, Licenses or Permits (for the streets or roads that may be impacted), Temporary Construction Easement, and possibly a Flowage Easement. 3) Some sponsor-owned lands including a public golf course, a park, a recreational area (with public swimming pool) and the Oak Ball Room, a historical building, which abut an area that is under consideration as a part of the possible project. 4) Some agricultural lands will be necessary as a part of any preferred design footprint. 5) There appears to be no federal-owned lands within the likely project design footprint.
2.4.5 Relationship of this Project to Other Community Projects and Plans The city of Schuyler has expressed a vision for revitalizing its urban area; particularly its downtown area. This vision is expressed in its “Downtown Schuyler Revitalization Plan” (DSRP) from July, 2010. The plan notes that the population in Schuyler has been increasing since the 1990s, particularly the Hispanic community. This cultural shift has brought new life to the downtown area which has led to a need for additional parking and retail space. Additionally, “construction trends have not responded to the city’s population growth, driving up rental rates and causing overcrowding” (DSRP, pg. 6, 2010). Community response has cited these reasons, along with dilapidated structures, run down storefronts, and poor signage, as major liabilities to the future of Schuyler. These challenges are also noted in the 2004 Comprehensive Plan; which the DSRP discusses in the context of the continuing struggle to achieve cohesiveness among businesses and in the overall look and feel of the district.
The DSRP lists several specific projects and plans as part of its overall development plan. Some of the plans listed in the DSRP document include:
58 ► A public gathering space that is interactive and brings life and energy to the downtown, connecting the Colfax County Courthouse lawn to the south and parking to the north.
► A reinvigorated B Street retail and civic core anchored by a stronger 12th and B Street intersection and improved street environment.
► An improved Railside Green, bringing a community green space into the downtown with defined pathways and additional parking.
► A major downtown entrance at the intersection of 11th and Colfax Streets. The entrance should proudly speak to the energy and history of the district. Signage and the main amenities should be replicated at the 16th and B Street entrance, directing travelers to the district.
► Commercial and mixed-use developments, including residential, on major sites that surround downtown. These should be amenity-driven sites, with parking and landscaping that make the sites inviting and elevate the quality of the downtown area.
► Capitalizing on existing opportunity sites in the downtown area for new and exciting uses. These include the currently occupied police station and library but also the vacant Carnegie Library.
It is noted in the DSRP that accomplishing all of these objectives would be ambitious, yet realistic. The future of these plans is not known with enough certainty to merit changing the future condition HEC-FDA analysis. However, it should be noted that the flood reduction plans recommended in this report would serve to enhance the probability that the vision of increasing community cohesion and revitalization would come to fruition.
59 3. FUTURE WITHOUT-PROJECT CONDITIONS
The future without-project conditions are an estimate of what the community will be like, up to 50 years in the future. Current trends and the potential for change, as expressed by other development plans on the books, are a basis for estimating this future condition. For the purpose of this analysis the future conditions are subdivided into future flooding conditions, future environmental conditions, and future community conditions.
3.1 FUTURE FLOODING CONDITIONS
3.1.1 Hydrology and Flood Frequency Absent climate change (discussed in Section 3.2.1), or some large water project being built on lower Shell Creek or on the Platte or Loup Rivers, the discharge frequency relationship should closely resemble the discharge frequency relationships derived from recent records of the Platte River and Shell Creek gaging stations. Both cost and environmental regulations appear to preclude a large reservoir being built upstream of Schuyler on the lower Platte, Loup or Shell Creeks.
Based on work in progress, improvements in drainage ditches upstream of Schuyler can be anticipated. The Hughes-Payzant Ditch improvement efforts, occurring in the same time frame as the Schuyler levee project, has the potential to reduce the flood peak at Schuyler by 1 to 2% of the 100-year (1% annual chance of exceedance) peak.
Flood peaks recorded at the Shell Creek near Columbus gaging station since 1990 include the two largest floods among records dating back to 1947. Data indicate that these floods were caused by rainfall events that were similarly exceptional. There is presently no evidence to indicate that the recent large rains and resulting Shell Creek floods are outside the expected statistical variation for the watershed.
3.1.2 Hydraulics and Channel Stability The other part of the future stage and discharge relationship at Schuyler is local channel and floodplain hydraulics. Presently, there does not appear to be a general trend in floodplain use which would change the floodplain stage-discharge rating for either Shell Creek or the Platte River at Schuyler.
3.1.2.1 SHELL CREEK Over time, Shell Creek has had considerable scour, and head cutting continues in the upper Shell Creek watershed. However, in the reach of Shell Creek near Schuyler, the stream is on a flat gradient, and the channel stability of the downstream end of the Shell Creek reach is constrained by the bridge under the UPRR embankment at low and moderate flows and by the embankment and railroad tracks themselves at high flows. There are no plans by the UPRR to abandon that main line or significantly alter that structure.
Periodic track maintenance activities by the UPRR have added height to the ballast since the transcontinental railroad was completed in 1869. Track maintenance will continue in the future,
60 but is not expected to add significant height to the current ballast without offsetting efforts to balance the stage increase via greater conveyance given greater scrutiny by the Colfax County Floodplain Administrator and state floodplain regulations.
Following the 1990 Shell Creek flood, landowners to the east of Schuyler have constructed or improved spoil bank levees along Shell Creek. While the agricultural levees are subject to overtopping or breaching during major flood events, they are capable of containing lesser floods. It is expected that the levees will be maintained in the future to meet the ever-present flood threat and will largely resemble the spoil bank levees in place, absent a project along that reach of Shell Creek.
Bank erosion will continue to degrade the Shell Creek riparian corridor, especially portions of Shell Creek near the UPRR line. The long-term effect of channel modification, including straightening, on channels and their tributaries initiates headward-progressing degradation in small tributary channels and ditches, which causes channel widening by bank failure (USGS, 2003). Degradation and head cutting are somewhat limited in the lower portion of the Shell Creek channel, due to the grade-stabilizing effect of the railroad and highway bridges and the erosion control measures taken over time to protect those structures. Upstream of the study reach, Shell Creek features active head cutting on its channel and tributaries. Future bank erosion in the study reach, unless managed, could further isolate the creek from its floodplain and any remaining patches of wetland and riparian vegetation, lessening the value of the Shell Creek corridor for fish and wildlife.
3.1.2.2 PLATTE RIVER Changes in a large river basin, such as the Platte, can be subtle and are only detected using hydrologic and hydraulic data analysis or a combination of aerial photography and Geographic Information Systems (GIS). Rainfall and runoff characteristics can change due to development and flood storage. Rivers can develop trends in scour and fill over time, which can impact the stage-discharge and stage-damage relationships. If there is a trend in such relationships, then forecasts of future conditions, different than existing conditions can be made.
Future conditions in regard to Platte River flood discharges and stages are anticipated to be similar to the current conditions at Schuyler. As part of the Platte River at Fremont, NE Section 205 Study, an evaluation of trends in peak discharge, stage discharge and sediment ratings, land use and channel configuration extracted from GIS databases in the lower Platte River was conducted (Physical Channel Changes Over Time and Implications to Flood Risk Reduction Plans for Fremont, USACE 2011). The reach covered in the analysis included the Platte River at Schuyler. It was determined that there appears to be no current trends, though the river changed in every respect from the late 1800s through the mid- 20th century. Following the middle of the last century, the Platte River appears to have entered a new equilibrium. It is evident that following the mid-20th century, the river has established a new equilibrium, with essentially stable stage and discharge relationships. An example of the trend analysis, and the current stability, is provided in Figure 3-1 for the Platte River at North Bend.
61 Platte River at Northbend Stage Trends
9.00
8.00
7.00
3,000 cfs 6.00 5,000 cfs 10,000 cfs 15,000 cfs Stage (ft) 5.00 20,000 cfs 35,000 cfs
4.00 *Based on annual peak values instead of daily values.
3.00
2.00 1950 1960 1970 1980 1990 2000 2010 Year
Figure 3-1 50 Years of Stage-Discharge Trends on the Platte River at North Bend
3.1.3 Floodplain Management The city of Schuyler and Colfax County will continue to participate in the National Flood Insurance Program and continue to enforce floodplain regulations. It is likely that the official floodplain mapping for Schuyler and Colfax County will be updated. While the areas shown inundated by the 100-year flood are not likely to change significantly, future remapping will certainly delineate floodways along the Platte River and Shell Creek.
With or without a project, enforcement of the floodplain regulations will inhibit growth from occurring in the designated Special Flood Hazard Areas (SFHA) along Shell Creek and the Platte River. The SFHA zone outside the floodway would not be a favored area for development unless a particular land parcel is raised with fill to above the base flood elevation and a Letter of Map Amendment is obtained from FEMA. The potential exists for more restrictive floodplain regulations to be enacted, either due to new NFIP requirements or from decisions by the state or city.
3.1.4 Embankments and Agricultural Levees It is assumed that the type and distribution of levees at Schuyler will change little absent a project. While there may be repairs and additions to existing agricultural spoil bank levees near Shell Creek, neither the alignment, or the construction of those levees is likely to significantly change in the absence of the proposed project. As a result, the current flood threat from Shell Creek to the city of Schuyler would also be expected to remain unchanged. On the Platte River
62 side there are currently no levees, and absent a project, it is unlikely that levees would be built. While it is possible that the city may remove the old railroad embankment that lies perpendicular to the floodplain downstream of Highway 15 at some point in the future, there are no current plans outside of the project to remove this blockage. Also, its removal would not provide 100- year (1% annual chance of exceedance) flood risk management to downtown Schuyler in the absence of other flood risk reduction measures.
3.2 ENVIRONMENTAL FUTURE CONDTIONS
3.2.1 Climate Change At the present time, it is not possible to quantify the potential impact of future climate change on project formulation over the projected 50-year economic life, as many of the potential impacts of climate change on the peak flow regime at Schuyler tend to be oppositional, particularly for the Platte River near Schuyler.
On the large Platte River Basin, a continued trend towards warmer and drier conditions is more likely to reduce mountain snowpack runoff peaks from the headwaters of the North and South Platte Rivers in the spring. Additionally, a general trend towards a warmer climate would tend to lessen the frequency of ice jam floods near Schuyler. At the same time, the trend towards higher temperatures also allows more atmospheric heating, and thus potentially more total moisture in the air. This change could support larger thunderstorms and heavier rainfall events for the more rare storms (i.e. 100-year rainstorm) even as it results in drier summers on the average. Drier summers could result in a downward trend in the base flow produced by the very permeable Sandhills region of the upper Loup River basin, but have little impact on the distribution of the peaks produced by larger thunderstorms falling on the less pervious ground of the lower Platte River and tributary watersheds. Since both ice jams and large rainfall events define the stage- frequency relationship of the Platte River at Schuyler, the net effect may be a stage-damage relationship at the city which is little changed from the current distribution over the economic life of the project.
The smaller Shell Creek Watershed lies entirely within the lower Platte River sub basin and is characterized by cropland on clay-type soils. A trend towards a warmer climate could result in less frequent but larger thunderstorms featuring heavier rainfall, especially given the impact of periodic strong mid-level moisture inflows from the Gulf of Mexico during the spring and summer. Similar to the larger Platte Basin, warming could produce oppositional impacts on the discharge-frequency relationship. Additionally, the stage frequency relationship flattens for the less frequent events due to loss of flow from Shell Creek to Rawhide Creek and drainways connected to the Platte River well downstream of Schuyler, thus the stage-damage relationship is likely to be little altered by climatic change over the economic life of the project.
3.2.2 Ecosystem In the absence of a project, the physical and biological structure of the Platte River, Shell Creek, and Lost Creek communities would continue to develop through natural succession. Early successional species (pioneer species) would colonize newly disturbed areas and would slowly be replaced by mid to late successional species. In the absence of any disturbance, the plant communities will continue to be dominated by late successional species. Continued pressure
63 from invasive species, such as phragmites, purple loosestrife and salt cedar, is expected along the Platte River and its tributaries will continue to pose management challenges. The water quality in Shell Creek, Lost Creek, and the Platte River would continue to be impacted by contaminants typical of watersheds dominated by agricultural use.
3.3 FUTURE COMMUNITY CONDITIONS
3.3.1 Future Without-Project Condition Economic Analysis The future without-project condition economic analysis is the same as the “no action alternative analysis.” The resources consulted in establishing the current and future without-project conditions included maps, aerial photos, topographic and hydrographic surveys, soils data, previous studies, and data and consultation with other agencies. It is assumed that minimal channel encroachments (urbanization and commercialization) will continue. Periodic flooding will continue to plague portions of the floodplain and will continue to damage property in the floodplain. This will continue to create economic and social hardships to the properties affected, as well as to others not directly impacted by flooding. Economic and social revitalization along Shell Creek will be impeded due to the floodplain development restrictions that currently exist. In addition, Shell Creek bank degradation due to high-velocity flood flows would continue to impact the creek and riparian wildlife corridors. The projects developed out of this effort will strive to greatly improve the economic and social conditions in the Schuyler study area. A “no action” condition would have negative impacts on the national economic development (NED), regional economic development (RED), and other social effects (OSE) accounts, as detailed below.
3.3.1.1 NED EFFECTS OF NO ACTION Losses to national economic output can be quantified to a considerable extent by reference to the equivalent annual damages estimated for this study. Equivalent annual damage is the average damage expected annually over the long term if existing conditions are maintained. The flood damage analysis model discounts the expected annual damage stream to the base year. As noted in the “Analysis Years and Period of Analysis” section, the data used in the existing conditions analysis were carried through to the future conditions without change. As computed in the HEC- FDA risk analysis model, equivalent annual damage totals an estimated $851,400 in the Shell Creek study area and $1,093,230 in the Platte River study area based on fiscal year 2011 price levels, an interest rate of 4.125 percent, and a 50-year project life. This is only an average annual total; little or no damage might occur in some years, while other years would bring flood events causing several million dollars in damages. Listed below are several aspects of these losses.
● Residential - Many residents in the study area would sustain heavy personal losses from flooding. A 500-year flood (0.2% annual chance of exceedance) could damage nearly 650 homes in the Platte River study area and over 180 homes in the Shell Creek floodplain. A 100- year (1% annual chance of exceedance) flood could damage over 510 homes in the Platte River study area and over 170 homes in the Shell Creek study area.
● Businesses - Many businesses and public facilities, large and small, would be damaged by flooding and possibly driven out of business. A 500-year (0.2% annual chance of exceedance)
64 flood could damage more than 60 businesses and public facilities in the Platte River study area; and nearly 40 in the Shell Creek study area. A smaller 100-year (1% annual chance of exceedance) flood is estimated to damage nearly 50 businesses and public facilities in the Platte River study area and over 30 in Shell Creek study area.
● Public sector - Public sector losses could be severe: (a) Highways and streets would require costly repairs. (b) Police and fire-fighting services employed in flood fights, along with other emergency personnel and their equipment and temporary offices, could cost the city millions of dollars in significant floods. (c) Relocation and reoccupation assistance to residents forced from their homes by flooding would be required for thousands of residents at an average of $3,000 per home.
Additional effects that are likely NED losses, but are not included in the equivalent annual damage cited above because they were not calculated for this study, include the following:
Traffic interruptions – Periodic closures during flooding (threatened and actual flooding) could interrupt traffic and commerce along key transportation arteries such as U.S. Highway 15, Old Highway 30, county roads, and the Union Pacific Railroad. Road closures could result in detours and time-consuming delays on these routes. Old Highway 30 would be under water for approximately 2.5 days during the 100-year (1% annual chance of exceedance) event on Shell Creek. Much of this traffic could use new Highway 30 as a detour route because it would not be overtopped by flood waters even at the 500-year (0.2% annual chance of exceedance) event. The 100-year event on Shell Creek would also overtop Highway 15 at the low spot between 16th and 17th Streets for about 2 days, and Highway 15 traffic would need to detour for several blocks during that period of time. Public safety may be a concern if some vehicles try to drive around road barricades when flood waters are still at low depths above the road surface, but deep enough to result in loss of vehicular traction with the road. The Highway 15 bridge approaches would be overtopped by Platte River flood waters, but the proposed levees would not affect the frequency or duration of Highway 15 overtopping. Traffic needing to cross the Platte River would have to detour at least 15 miles east to the Highway 79 bridge at North Bend or at least 16 miles west to the Highway 81 bridge at Columbus, and even longer if either of the highway approaches to these bridge crossings are also overtopped by Platte River flooding. Flood-related detours result in extra vehicular operating expenses as well as the opportunity costs of lost time, and these costs can be substantial when busy routes or lengthy detours are involved.
Business income and recreational benefit losses from shutdowns – Business shutdowns can last for weeks in large floods, causing sizable and even ruinous production losses. Usually, production can be replaced by facilities at other locations of the company or companies in the same industry, so costs of business interruptions are generally considered economic transfers rather than losses to total output and are not counted as NED damages. However, some income losses are not able to be transferred and are losses to NED.
65 For example, during flooding experienced in 2010, the Schuyler public golf course was shut down for two weeks during the summer and was closed early for the season in order to repair flood damages. The nearest course, located 15 miles away, was closed as well. Revenue loss was estimated at over $20,000. Many of the people who use the course are full time members, league players and senior citizens. These people will not golf elsewhere when the course is closed; instead they will not golf at all (Benson, pers. comm., 2011), which results in lost recreation benefits. This type of income (and recreational benefit) loss is not just a regional effect, but represents an NED loss.
3.3.1.2 RED EFFECTS OF NO ACTION Regional Economic Development (RED) considerations are factors affecting the Schuyler regional economy while not necessarily affecting national economic outputs. Several such effects in this study would occur if no action was taken to reduce the flood threat. This action would loom large in the area’s business climate. RED effects resulting from this and other factors would include the following:
Residential flood insurance premium costs (probable adverse income impact) - Residents would continue to face onerous flood insurance requirements. In addition, an increasing number of residents would be required to obtain flood insurance when the new FEMA Flood Insurance Rate Maps with an expanded 100-year (1% annual chance of exceedance) floodplain become effective; the effective date is expected to be in 2012.
Threats to existing local/regional businesses (probable adverse income and jobs impacts) - Schuyler businesses in and around the study area would be threatened by multiple factors related to flood risk, including (a) catastrophic periodic flood damage; (b) business closures or scale backs; (c) employee safety problems during flood events; (d) the cost of flood insurance requirements; and (e) stiff building codes, that would work against firms that are located in the floodplain and need to expand. Particularly affected would be manufacturing jobs, which are declining nationally but have been a strong part of the Schuyler jobs base, and which are concentrated in floodplain locations.
Threats to economic development prospects (probable adverse income and jobs impacts) - The same considerations listed above would also discourage new development and growth in the form of businesses migrating into Schuyler or elsewhere in the region, or could stifle the development of new areas. Large companies considering moving into the study area, bringing job concentrations with them, may decide not to move into a flood-prone area, with the attendant regulatory environment. The impact of the two recent floods, in 2008 and 2010, may have created a climate of negative economic development, where businesses and residents may leave rather than face another flood without hope of resolving the flood threat.
3.3.1.3 OTHER SOCIAL EFFECTS OF NO ACTION Public safety (probable adverse impacts on human life) - The chance of a major flood in the next 10 years, on average, is greater than 1 in 2 in the Shell Creek study area. At risk are more than 600 residents in over 180 homes in the 500-year (0.2% annual chance of exceedance) floodplain. At risk in the Platte River study area are more nearly 2,200
66 residents in nearly 650 homes in the 500-year (0.2% annual chance of exceedance) floodplain. Danger could take the form of drowning, electrocution, and illness from exposure to contaminated flood waters. Due to the long flood warning time and shallow flood depths, the public safety risks are greatest from secondary causes, such as electrocution or injuries resulting from flood fighting efforts, rather than from the floodwaters themselves.
Public health (probable adverse impacts on health) - Many homes and businesses in Schuyler have been flooded twice in the past 3 years. Consequently, residents living in the 100-year (1%-annual chance of exceedance) floodplain may suffer from chronic stress due to worrying about future flooding and how a flood could affect their finances and daily activities. Chronic stress can affect mental, emotional, and physical health and quality of life.
Low income residents suffer flood risk (probable adverse socioeconomic impacts) - The census block groups located within the Shell Creek study area on average had a poverty rate of 16.5% in 1999. This rate was 47% higher than the poverty rate of 11.2% for Schuyler as a whole, and 70.0% higher than the state rate, as well as 33.4% higher than the national rates. By 2005-2009, 16.3% of all Schuyler residents were living below the poverty level, compared to 11.8% in the entire state of Nebraska. The 2000 average unemployment rate of 4.2% for the Shell Creek study area block groups was 18% greater than the state rate of 3.5%. Average per capita income for the block groups in 2000 was $13,824, which was 96.2% of the overall Schuyler per capita income, 70.5% of Nebraska’s average per capita income, and 64% of the national figure (U.S. Census Bureau, 2000 and 2010).
Minority residents suffer greater flood risk (probable adverse socioeconomic impacts) - According to the 2010 Census, Hispanics account for over 65% of the population of Schuyler (4,060 of 6,211). These percentages are over four times the national percentage of 16.3% and over 7 times the state percentage of 9.2% (U.S. Census Bureau, 2011).
Threats to redevelopment (possible adverse cultural, historical and aesthetic impacts) - Also touched on above under RED impacts; if redevelopment is indeed hampered, it would negatively affect aesthetic values (removal of blight followed by orderly, planned redevelopment) and historical values.
Effects on recreational opportunities (probable adverse effects on golfing, camping, fishing, bird watching, and group picnicking opportunities) - Facilities open to the general public for these activities are located in South Park, which is in the 100-year (1% annual chance of exceedance) floodplain of the Platte River. If these facilities in South Park are flooded, it may be a long time before some of the facilities are clean and functional; especially toilet facilities and the lake which the city has just dredged and is renovating the fishery.
67 Effects on historic and cultural properties (possible adverse effects to a historically significant center of community activities that could affect community cohesion and quality of life) – The Oak Ballroom, located in South Park on the Platte River side, is on the National Register of Historic Places (NRHP). It is the site for many community-wide events as well as wedding receptions, family reunions, etc. It also lies in the 100-year (1% annual chance of exceedance) floodplain of the Platte River. If it is flooded, some damage may be done to the exterior and/or interior of the structure that can never be completely repaired to its original condition due to lack of period-authentic materials, etc. Even if repaired, the community of Schuyler would have lost the traditional “heart” of many of its social functions for the period of time during which repairs were made. As a result, there may be temporary and, to some extent, permanent losses in social cohesion among some Schuyler residents.
3.3.2 Impacts of Future Flooding on Community Stability The impact of frequent floods on Shell Creek and recent Lost Creek flooding has been devastating. Following the 2008 Shell Creek flood, citizens rallied to repair damage to their homes and to the community. In many cases, citizens had just completed repairs to their homes, including basement repairs, re-carpeting and drywall installation, only to have it all destroyed a short two years later in 2010. That flood was also accompanied by Lost Creek flooding and a groundwater surge that flooded basements that had not been hit during the 2008 flood. The very real threat of relatively frequent flooding has resulted in a condition where many people would like to move out of Schuyler if something cannot be done to alleviate the flood threat. The future without-project condition may reflect a once vibrant community going into a period of decline, which would threaten to destroy the fabric of community stability and resulting impacts to Regional Economic Development.
3.3.3 Recreational Outlook under Future Without-Project Conditions The trail along the north side of the fishing lake at the campground will be extended completely around the lake in 2011 as Phase II of a trail construction project, with funding received in 2010 from the NGPC. For Phase III of the trail, the city of Schuyler has applied to NDOR for a Surface Transportation Fund grant to construct a 6-inch-thick, 10-foot-wide concrete trail from the west side of the Highway 15 crosswalk northward, paralleling Highway 15 and crossing Lost Creek on a new pedestrian bridge adjacent to Highway 15 to provide access between the northern and southern portions of South Park. The city of Schuyler plans to replace a small wooden bridge with wood pilings across Shonka Ditch, a tributary of Lost Creek, with a concrete box culvert or a bridge with concrete decking at the intersection of Higgins Road, South Park Road, and Gold Street at the northwest corner of the golf course (Peschel, pers. comm., 2010a, 2010c, 2010d).
At the campground, it is planned that a modern restroom will replace the pit toilet without showers that was constructed in the 1960s with a Land and Water Conservation Fund Act grant. By 2015, it is expected that additional camp pads, with water and electric hookups, will be developed at the campground (Peschel, pers. comm., 2010a).
It is anticipated that the renovated lagoon east of the golf course will be further rehabilitated and stocked with fish by 2015 (Peschel, pers. comm., 2010a).
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It is expected that the construction of the new softball field north of the existing softball field will be completed in the near future, and that later some additional facilities such as dugouts, a batting cage, bleachers, and a concession stand will be added (Peschel, pers. comm., 2010a).
Many recreational facilities/areas in Schuyler are subject to flooding. Under without-project conditions, the flood risk to these recreational facilities would not be reduced. Consequently, the residents of Schuyler will continue to live with the threat that flooding could reduce the variety of their local outdoor recreation opportunities, either temporarily or permanently.
69 4. PLANNING, PROBLEMS, OPPORTUNITIES, CONSTRAINTS, GOALS AND OBJECTIVES 4.1 PROBLEMS The problems are derived from the purpose and need for this project, which were outlined in Section 1.1.3. The entire community of Schuyler has been severely impacted by floods and its future depends upon successfully solving the flood risk problems. A significant portion of Schuyler is at risk of flooding that has been highlighted by recent events. Planning problems are summarized in Table 4-1.
Table 4-1 Planning Problems
SEC. PROBLEM NO. Overall Project 4.1.1.1 Most of Schuyler is located in the 100-year floodplain Schuyler will continue with same susceptibility to 4.1.1.2 flooding as currently exists with no action Shell Creek The new Highway 30 Expressway did not prevent 4.1.2.1 flooding
4.1.2.2 Flooding in northeastern Schuyler is made worse by downstream flow constrictions Platte River 4.1.3.1 Ice jam flooding 4.1.3.2 Lost Creek can convey Platte River floodwaters towards Schuyler 4.1.3.3 Lost Creek can flood from heavy rainstorm Downtown "ridge" does not stop the Platte River 100- 4.1.3.4 year flood
4.1.1 Overall Project
4.1.1.1 MOST OF SCHUYLER IS LOCATED IN THE 100-YEAR FLOODPLAIN Much of southern Schuyler is in the Platte River 100-year (1% annual chance of exceedance) floodplain and most of northeastern Schuyler is located in the Shell Creek 100-year floodplain. Many property owners must pay high premium costs for flood insurance.
4.1.1.2 SCHUYLER WILL CONTINUE WITH SAME SUSCEPTIBILITY TO FLOODING AS CURRENTLY EXISTS WITH NO ACTION A significant portion of Schuyler is at risk of flooding which has been highlighted by recent events. Three major floods, one in 1990 and another in 2008, followed by a third in 2010 demonstrate the vulnerability of Schuyler to repeated damaging floods from Shell Creek. Damaging floods occur more frequently than the 20-year (5% annual chance of exceedance) flood. The frequency of the Shell Creek flooding, coupled with the Platte River / Lost Creek flood threat represents a serious problem for the long-term vitality of the city of Schuyler.
70 4.1.2 Shell Creek
4.1.2.1 THE NEW HIGHWAY 30 EXPRESSWAY DID NOT PREVENT FLOODING Although the embankment of the new expressway remains above the level of a major flood, the bridges over Shell Creek and Nieman Ditch are large enough to convey a damaging flood into northeastern Schuyler. The capacity of the new Highway 30 bridge over Nieman Ditch is much larger than the bridge on old Highway 30 and conveys flood flows into northeastern Schuyler as its capacity is much larger than the downstream channel or the Nieman Ditch culverts under old Highway 30.
4.1.2.2 FLOODING IN NORTHEASTERN SCHUYLER IS MADE WORSE BY DOWNSTREAM FLOW CONSTRICTIONS Flood waters are not able to flow directly into the Platte River due to the Union Pacific Railroad embankment and a constricted Shell Creek channel downstream of Schuyler. The combination of these constrictions causes flood waters to back up in Schuyler during a major flood event, until the water reaches sufficient depth to flow over the railroad tracks and ultimately wash out the ballast. The Shell Creek channel, which runs parallel to the railroad embankment for 3 miles to the east of Schuyler, is overgrown with trees for part of that length and does not have enough capacity to carry a major flood. Additionally, the railroad bridge on Shell Creek lacks capacity to efficiently convey an extreme flood of a magnitude similar to the 2008 event, especially if it begins to trap debris on the low steel. See Figure 4-1.
Figure 4-1 Debris Removal at UPRR Bridge over Shell Creek during Flood on May 30, 2008
71 4.1.3 Platte River
4.1.3.1 ICE JAM FLOODING There is a significant threat from ice jam flooding from the Platte River, which can be hard to predict and flood fight, due to sudden shifts in the ice during a major ice jam flood. This is in addition to the open water flood threat that produces warm season flood stages nearly as large.
4.1.3.2 LOST CREEK CAN CONVEY PLATTE RIVER FLOODWATERS TOWARDS SCHUYLER Platte River flooding can enter the Lost Creek drainage, based upon historical flooding patterns. In a major flood there is the danger that the Platte River could migrate into and capture the Lost Creek channel which is lower than the Platte River thalweg, greatly increasing the flood threat to Schuyler, Highway 15 and the Union Pacific Railroad. A channel stabilization project upstream of Schuyler built in 1970 reduced, but did not eliminate this threat, since that project could be flanked and overtopped by a flood exceeding its level of design.
4.1.3.3 LOST CREEK CAN FLOOD FROM HEAVY RAINSTORMS Though it is a low gradient stream flowing across a sandy floodplain, with sufficient rainfall, it too can cause flood damages to the outskirts of southwestern Schuyler, the city golf course and the city’s South Park. Flooding of this nature most recently occurred during June 2010.
4.1.3.4 DOWNTOWN “RIDGE” DOES NOT STOP THE PLATTE RIVER 100- YEAR FLOOD A reevaluation of flooding in Schuyler indicates that the downtown area can flood during infrequent large floods and a low “ridge” is not high enough to provide flood damage reduction for the 100-year (1% annual chance of exceedance) flood. An evaluation indicates that the flood threat begins at about the 50-year (2% annual chance of exceedance) flood.
4.2 PLANNING OPPORTUNITIES The flood risk management opportunities include the potential to reduce developed property damage, injuries and deaths, reduce non-physical losses including emergency and income losses, restore riparian and stream corridor, improve water quality and provide for recreational opportunities. The flood risk management opportunities identified in the feasibility report have been supported by the city of Schuyler, other stakeholders, and the federal partners and will serve to promote a higher quality of life and economic development for this community. Measures envisioned to engage the planning opportunities are described in more detail in Section 4.4.
4.3 PLANNING CONSTRAINTS The constraints are those factors that limit the extent of the implementation of flood risk management solutions at Schuyler. Existing and future without-project constraints are assumed to be the same for this community. Planning constraints are summarized in Table 4-2.
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Table 4-2 Planning Constraints
SEC. CONSTRAINTS NO. Overall Project 4.3.1.1 Railroad must approve solutions that impact its operation 4.3.1.2 Levees can induce flood damages 4.3.1.3 Levee construction can destroy wetlands and trees Shell Creek 4.3.2.1 Levees are not allowed to tie off to transportation features Platte River 4.3.3.1 Maintenance of Lost Creek riparian corridor 4.3.3.2 Complying with applicable environmental laws and policies 4.3.3.3 Historic building and park infrastructure
4.3.1 Overall Project
4.3.1.1 RAILROAD MUST APPROVE SOLUTIONS THAT IMPACT ITS OPERATION The Union Pacific Railroad bisects Schuyler from east to west. It lies within the floodplain of both the Platte River and Shell Creek at Schuyler. Conveyance improvements or levee features, such as closure structures, that would impact railroad operations are subject to approval by the railroad. The cost and time associated with obtaining approval must be factored into the benefit and cost analysis of flood risk solutions that propose to impact the railroad.
4.3.1.2 LEVEES CAN INDUCE FLOOD DAMAGES Given that levees will likely be included in any flood damage reduction plan, it is recognized that they can raise the water surface elevation on nearby properties, particularly if the levee is built in a conveyance zone. Every effort will be made to avoid the primary conveyance zones and mitigate stage increases through improvements in channel conveyance.
4.3.1.3 LEVEE CONSTRUCTION CAN DESTROY WETLANDS AND TREES Construction of levees to protect Schuyler has the potential to damage or destroy isolated wetlands and wood lands along their alignment. Efforts will be made to avoid doing this. Mitigation may be needed where unavoidable.
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4.3.2 Shell Creek
4.3.2.1 LEVEES ARE NOT ALLOWED TO TIE OFF TO TRANSPORTATION FEATURES Requirements by the Corps and other federal agencies do not permit levees to tie off to roadways or railroad embankments, due to the uncertainty of the potential tie off’s performance during a flood. Thus, neither Highway 30 nor the Union Pacific Railroad’s embankment may be used as “high ground” for the purposes of terminating the Shell Creek levee.
4.3.3 Platte River
4.3.3.1 MAINTENANCE OF LOST CREEK RIPARIAN CORRIDOR Since Lost Creek serves as a historic overflow channel of the Platte River, consideration must be given to avoiding, reducing or mitigating impacts on riparian wetlands and species.
4.3.3.2 COMPLYING WITH APPLICABLE ENVIIRONMENTAL LAWS AND POLICIES Any structural solution to Schuyler’s flood problems must comply with national and state laws and policies. Among policies which constrain construction activity are the Endangered Species Act (ESA), National Environmental Policy Act (NEPA), and the National Historic Preservation Act (NHPA).
4.3.3.3 HISTORIC BUILDING AND PARK INFRASTRUCTURE The Oak Ballroom and other facilities in the City Park are important to the current quality of life and historical continuity. The Oak Ballroom is on the National Register of Historic Places and activities that would damage the structure are governed under the NHPA. The locations of these facilities next to Lost Creek preclude building a levee between them and the water. Options in dealing with this constraint may include construction of a length of floodwall or rerouting Lost Creek, neither of which are inexpensive.
4.4 PLANNING OBJECTIVES The objectives are the statements that describe how the goals of the completed project would solve the problems within the project constraints. Objectives also expand on how the opportunities for improvement can be realized. The federal objective of water and related land resources project planning is to provide contributions to National Economic Development (NED) consistent with protecting the nation's environment, pursuant to national environmental statutes, applicable executive orders and other federal planning requirements. Planning objectives are summarized in Table 4-3.
The primary goal of a flood risk management project is to reduce the risk of flood damage, injury and death from flooding. As flooding in Schuyler is not high risk, in terms of threats to life or potential to directly cause injury to people, the central goal is protecting a vulnerable community
74 from frequent and destructive floods. Additional goals include protecting the environment and improving recreational opportunities where possible within the general scope of the flood risk solution.
Table 4-3 Planning Objectives
SEC. OBJECTIVES NO. 4.4.1 Reduce the number of structures in the floodplain 4.4.2 Lower the evacuation, road closure and recovery costs to the city and county 4.4.3 Reduce the risk of flood damages to property 4.4.4 Minimize the operation and maintenance cost 4.4.5 Restore or build effective wetlands where opportunities permit 4.4.6 Replace invasive species with native species where possible 4.4.7 Protect and promote recreational opportunities 4.4.8 Improve safety Minimize erosion and sediment impacts during 4.4.9 construction 4.4.10 Provide for the restoration of community vitality
4.4.1 Reduce the Number of Structures in the Floodplain A goal of the citizens of Schuyler and this study is to develop flood damage reduction measures that will reduce the number of structures subject to inundation from the 100-year (1% annual chance of exceedance) flood and remove them from the designated floodplain.
4.4.2 Lower the Evacuation, Road Closure and Recovery Costs to the City and County A goal of the flood damage reduction plan will be to greatly lessen the large and frequent cost of flood fighting, the post-flood cleanup, and public structure repair expense in the area covered by the project.
4.4.3 Reduce the Risk of Flood Damages to Property The central goal of this study is to formulate an economically-feasible solution to remedy Schuyler’s frequent and damaging flood threat.
4.4.4 Minimize the Operation and Maintenance Cost A goal of the flood damage reduction plan will be to use structures and flood risk reduction methods that are not difficult and expensive to operate and maintain, once the project has been turned over to local control at the end of the project.
4.4.5 Restore or Build Effective Wetlands Where Opportunities Permit If replacing impacted wetlands becomes necessary, a goal will be to establish replacement wetlands that are effective in assisting the survival of migratory, threatened and endangered and
75 state-listed species. In the design of the project, opportunities may present themselves for creating riparian wetland habitat in the configuration of altered channel shapes.
4.4.6 Replace Invasive Species with Native Species Where Possible When possible, a project goal is to increase diversity of native plant species on all lands reshaped by the project as well as reduce or eliminate invasive plant species found on lands impacted by the project. Reduction of invasive species and replacement with native plant communities that enhance the riparian ecosystem and transitional buffers will support this goal.
4.4.7 Protect and Promote Recreational Opportunities Wherever possible, another project goal is to provide connectivity between existing recreational facilities within the framework of the flood risk management project.
4.4.8 Improve Safety Though Shell Creek and the Platte River floods present only a minimal threat to life, due to the long time to reach flood stage on each waterway and relatively shallow depths, design steps should be taken to provide a safe project and minimize the risk to life from any residual flood threats. Reduction in the flood threat will reduce the number of potential accidents and injury that can result when people respond to a flood threat. Safety issues that should be greatly improved include those related to lifting, electric shock, motor vehicle operation and water-borne diseases.
4.4.9 Minimize Erosion and Sediment Impacts during Construction Employ construction methods that minimize the impact on the environment while the project is being built.
4.4.10 Provide for the Restoration of Community Vitality Following disastrous Shell Creek floods in 2008 and 2010 and the Lost Creek flood of 2010, community vitality has been hit hard, with residents and individuals uncertain about the future of Schuyler.
76 5. ALTERNATIVE FORMULATION The following section provides an overview of the alternative formulation process. The steps in alternative formulation include the identification of measures (components of plans), development of alternatives (composed of measures), evaluation and comparison of alternatives and ultimately plan selection. The formulation of alternatives in this study drew upon earlier efforts to find a solution to the flood threat at Schuyler. Three alternatives were formulated to protect against Platte River flooding during the initial assessment phase. At that time, the threat from Shell Creek was undefined, due to recent changes to the transportation network at Schuyler.
5.1 NONSTRUCTURAL FLOOD DAMAGE REDUCTION MEASURES Nonstructural flood mitigation measures were considered for reducing flood damages and flood risk at Schuyler. Nonstructural measures reduce flood risk by changing the characteristics of the population and property at risk rather than changing the characteristics of the flooding and can be divided between physical and non-physical flood nonstructural measures.
Physical nonstructural measures include wet and dry floodproofing of buildings, levees and floodwalls protecting individual buildings, raising elevations of buildings, relocation of buildings and buy-outs and removal of buildings in flood-prone areas. These measures result in physical modifications to buildings in flood hazard areas that make them less vulnerable to flood damages or removal of the buildings from the flood hazard area entirely. As these measures are mostly done to privately-owned buildings on a voluntary basis, they require the permission and active participation of the property owners.
Non-physical nonstructural measures consist of programs, systems or activities such as flood insurance, flood warning, floodplain regulations, and flood preparedness planning. The adverse effects of flooding are reduced by providing compensation for flood damages incurred, alerting the population to imminent flooding, preventing unsuitable development in flood hazard areas and providing recommendations for actions by public officials and citizens before, during and after flooding. These measures do not physically reduce the vulnerability to flood damages of existing property in flood hazard areas.
Separate physical nonstructural plans were developed for buildings in the areas of Schuyler subject to 100-year (1% annual chance of exceedance) flooding by Shell Creek and the Platte River. (There were no buildings that were common to the two plans.) The non-physical nonstructural measures evaluated included both Shell Creek and the Platte River.
Nonstructural flood damage reduction measures are applied to individual buildings or to several adjacent buildings. The nonstructural measures include dry flood proofing, wet flood proofing, elevation on fill, elevation on posts, pillars or walls, localized levees or floodwalls and relocation of the building from the floodplain. Based on field investigations, the instances where nonstructural flood damage reduction has been implemented at Schuyler are the elevation of post-FIRM buildings on fill to above the 100-year flood elevation.
Large areas of undeveloped land remain in the SFHA of the Platte River and Shell Creek. The city’s regulations will require that nonstructural measures be used to reduce the potential future
77 flood damages to any new building to be built in the SFHA. The nonstructural practice likely to be most beneficial is construction of new residential buildings to at least one foot above the 100- year (1% annual chance of exceedance) flood elevation, either on raised foundations or on fill. Commercial buildings could be flood proofed to the elevation requirement. Because of the requirements for construction in the SFHA, the area of Schuyler west of Nebraska Highway 15 and north of the Union Pacific Railroad may be favored for new development since it is outside the 100-year floodplains of both Shell Creek and the Platte River.
5.1.1 Flood Proofing Measure for Shell Creek Floodplain Structures A flood proofing and elevation measure for buildings determined to be damaged by the 100-year (1% annual chance of exceedance) flood event from Shell Creek was evaluated. Flood proofing was considered for all buildings that had a first floor or basement that were subject to flooding for the Shell Creek 100-year flood event. This measure would result in all residential buildings having a lowest floor elevation above the 100-year flood elevation. Having the lowest floor of residences above the 100-year flood elevation could result in lower flood insurance premiums as well as reduced flood damages. Commercial buildings would be wet or dry flood proofed to one foot above the 100-year flood elevation.
The cost to elevate or flood proof the approximately 210 buildings in the 100-year (1% annual chance of exceedance) floodplain was estimated at approximately $10,575,000. While damages to the buildings and contents from floods through the 100-year event would be reduced or eliminated, other damages to the properties, such as to vehicles and landscaping, would remain. More details on the evaluation of nonstructural flood risk reduction measures may be found in Appendix E, Flood Risk and Floodplain Management, Section 6.1.
5.1.2 Flood Proofing Measure for Platte River Floodplain Structures A flood proofing and elevation measure for buildings determined to be damaged by the 100-year (1% annual chance of exceedance) flood event from the Platte River was evaluated. Flood proofing was considered for all buildings that had a first floor or basement that were subject to flooding for the Platte River 100-year flood event. This measure would result in all residential buildings having a lowest floor elevation above the 100-year flood elevation. Having the lowest floor of residences above the 100-year flood elevation could result in lower flood insurance premiums as well as reduced flood damages. Commercial buildings would be wet or dry flood proofed to one foot above the 100-year flood elevation.
According to the structure inventory, there were approximately 560 residential and non- residential buildings in or near Schuyler in the Platte River floodplain that are flooded by the 100-year (1% annual chance of exceedance) flood. Of these about 448 had flood elevations greater than the adjacent ground elevation for that flood event. The total estimated cost for floodproofing these buildings would be approximately $35,169,000. The high school complex and the downtown business district are in the Platte River floodplain. These buildings would be complicated to flood proof, so costs will be significantly higher. More details on the assumptions and the estimation of costs for nonstructural risk reduction measures may be found in Appendix E, Flood Risk and Floodplain Management, Section 6.1.
78 5.1.3 Flood Warning Flood warning was considered for both the Platte River and Shell Creek flooding early in the study. In both cases, the local community felt that it had sufficient warning time of impending large floods, based upon contact with upstream communities and the U.S. Geological Survey (USGS) gage located on Shell Creek near Columbus upstream of Loseke Creek. Features provided by the USGS on its Nebraska website permit citizens to be contacted by the agency in the event that preset stages are exceeded at the gage. During ice-jam breakup floods on the Platte River, the USGS also installs temporary gaging stations which can be used to alert citizens. The gages use ultrasonic transducers to measure the river stage and transmit data to the USGS (and ultimately to citizens over the Internet) via a satellite downlink. The temporary Platte River gage at Schuyler, used in the 2010 ice breakup flood, is shown in Figure 5-1.
Figure 5-1 Temporary Platte River Gage at Schuyler, NE (March 2010)
The potential for installing flood warning gages on Shell Creek, downstream of Loseke Creek, was also considered during public meetings and stakeholder discussions. The Corps offered to provide a low tech flood warning system gage as part of the project. One site discussed was Shell Creek at Highway 15. Given the fact that there is not a large risk to life from Shell Creek floods, the community determined that this extra feature was not needed.
The potential need for flood warning will be revisited as the study draws to a close and in the preparation of the operation and maintenance manual, if needed. If only the Shell Creek levee is
79 built, there may be a need for automated flood warning on Lost Creek to warn of Platte River floods that could breach or bypass the channel block revetment southwest of Schuyler.
5.1.4 Other Nonstructural Measures Other nonstructural measures such as flood insurance and flood preparedness planning were considered. Since Schuyler participates in the NFIP, flood insurance is currently available in the community. In the wake of the Shell Creek floods in 2008 and 2010, Schuyler had considerable experience about what to do during flood events. It is recommended that the city develop a formal flood preparedness plan for both Shell Creek and Platte River flooding.
5.1.5 Relocation Given the size of Schuyler, it is not practical to relocate the entire community. Relocation of the parts of the community from the floodplain is also not practical given the large number of dwellings and businesses (over 900 in the 500-year floodplain) and the investment in infrastructure in those areas. Relocation and removal of the dwellings within the 100-year floodplain would result in the relocation of the central business district, including the municipal and county government buildings, which, in addition to the expense, would negatively alter the character of the community. Relocation is a measure however, that can be applied selectively to individual structures for which other measures cannot be economically applied. Candidates for relocation are often structures that are isolated and which may be negatively impacted by flood risk management measures applied to other sections of the community.
5.2 SHELL CREEK STRUCTURAL MEASURES When work began on the feasibility study in 2006, the flood threat from Shell Creek remained undefined. Although there had been a destructive flood in 1990, the Highway 30 Expressway had been built north (upstream) of the community with a much higher driving surface. At the outset of the study, it was not certain whether this new roadway decreased risk of flood damages. The May 2008 flood proved beyond the shadow of a doubt that a serious flood threat still existed from Shell Creek. Following that damaging flood, Schuyler made it clear that solving the Shell Creek flood problem was the leading focus of this project.
Multiple levee alignments, nonstructural features and channel improvement features were looked at before five alignments were selected for further evaluation. Since the 2008 flood had shown that the Highway 30 Expressway did not help protect Schuyler, and in fact, the configuration of the Nieman Ditch bridge opening and downstream channel appeared to increase the flood threat to residential northeastern Schuyler, levee formulation efforts focused on diverting that water away from the community.
5.2.1 Improving Conveyance through the Railroad Embankment Given that the 2008 flood backed up behind the Union Pacific Railroad (UPRR) grade before ultimately overtopping and washing out the rail bed, solutions that improved downstream conveyance were also evaluated. Initially, the impact of the UPRR bridge over Shell Creek was examined. It was determined, that while the bridge did back up water from the 2008 event, that backwater did not extend upstream to Schuyler and impacted property closer to the structure.
80 The Shell Creek channel itself, between the Schuyler COOP and the UPRR bridge was also found to greatly restrict downstream movement of floodwater.
Attention then focused on whether additional conveyance could be achieved by providing more openings in the UPRR embankment near Schuyler. A small bridge, already in existence, carried considerable flow during the 2008 flood, so consideration was given to adding capacity near that structure to carry additional flow through the embankment, lessening the stages upstream. It was determined that costs associated with obtaining real estate and constructing a downstream channel added to the cost of building culverts “under traffic” would be a very significant cost. Due to the nature of Shell Creek flooding, unless the culverts and the downstream channel which would have to be constructed were very large, a damaging residual flood would still hit northeastern Schuyler, which would negate any potential cost savings by placing culverts under the railroad embankment. In addition, obtaining permission from the UPRR would require time and that would slow down implementation of a solution to Shell Creek flooding.
5.2.2 Diversion of Water from Shell Creek Upstream of Highway 30 One method of flood risk reduction is diversion. If enough water can be removed from the channel before it reaches Schuyler, then flooding would be reduced. Given the long history of Shell Creek flooding, several diversions have been constructed over time, including the Byrne (Burns) Ditch which was built in 1912 and the Hughes-Payzant Ditch which was built in 1905. The ditches also serve to drain fields during times when the local water table is high.
The Hughes-Payzant Ditch exits Shell Creek upstream of Schuyler and north of Highway 30 (see Plate 1). A separate study funded by Colfax County and the Lower Platte North NRD evaluated improvements to the Hughes-Payzant Ditch which would improve its ability to drain water away from Schuyler. An evaluation of the current capacity of this ditch indicated that it was well under its designed capacity of 300 cfs. Given that the peak discharge of the 100-year (1% annual chance of exceedance) flood was calculated to be 10,400 cfs, restoration of the Hughes-Payzant Ditch to original capacity would result in less than 3% of the peak flow at Schuyler being diverted when complete. The ditch improvement could potentially double the capacity from its current 1 to 2% of the 100-year peak discharge by increasing the channel cross sectional area to fill its property easement. Given the very flat slopes, real estate and bridge costs, it was determined that diversion of peak flood flows upstream of Schuyler could not provide significant flood risk reduction, thus for the small amount of the peak flows that could be diverted, it would not be economical to add this measure to the project.
While the importance of an improved Hughes-Payzant Ditch is small during a major flood, it becomes more significant during lesser floods, including those in the 10 to 20-year frequency range (5,980 to 7,590 cfs), which is the range where damages begin in northeastern Schuyler. The Hughes-Payzant Ditch improvement efforts, occurring in the same time frame as the Schuyler flood risk management project, may reduce stages in the nearby floodplain that may result from efforts to protect the city. Work on the ditch, coupled with channel cleanout on Shell Creek downstream of Schuyler, can be used to reduce or eliminate potential post-project flood stage increases adjacent to the community.
81 The capability of upstream diversion of flow is also limited by the channel capacities and bridge openings of the waterways directed to convey any increased flow. If the flow diverted upstream of Schuyler was to exceed the ability of the receiving waterways to safely convey the flood flows to the Platte River, excess flow would induce additional damages on downstream landowners, potentially including the village of Rogers and city of North Bend.
5.2.3 Improvement of the Shell Creek Channel Downstream of Schuyler As an option to a levee, widening the existing Shell Creek channel between Schuyler and the UPRR bridge was considered. A hydraulic analysis of this potential measure was performed and it was determined that a channel width of more than 400 feet would be required to convey flows from Schuyler to the UPRR bridge in sufficient quantity that additional measures at Schuyler would no longer be needed to protect the city from the 100-year (1% annual chance of exceedance) flood. It became evident that in addition to the considerable real estate and earth moving expense of constructing nearly 3 miles of very wide channel, that the replacement of at least one county road bridge would be required with a structure spanning 400 feet. Other problems requiring a solution, such as the need to mitigate the increased flooding on property just upstream of the UPRR bridge or increase the capacity of that bridge and the county road bridge just downstream, would result from conveying a much larger flood to areas downstream of Schuyler.
Channel improvements in that shorter reach of Shell Creek can reduce flood stages somewhat at Schuyler and offset small increases in stage caused by flood risk reduction measures at Schuyler on nearby properties located in the Shell Creek floodplain.
5.2.4 Levee Measures Given the areal extent of the inhabited floodplain at Schuyler and the quantity of properties at risk, levees are an attractive flood risk reduction measure. Additionally, most of the properties at risk are located in compact areas where the potential levee lengths are not daunting. Both the Platte River and Shell Creek produce floods that are not very deep, even at the 100-year (1% annual chance of exceedance) event. On the Platte River side, the floodplain is so wide that stages are not extremely deep even for the largest historical floods. On the Shell Creek side, flood crests above a certain magnitude tend to escape Shell Creek altogether and divert to other basins, bypassing Schuyler. The fact that the levees would not need to be that high reduces the potential cost of levee construction, adding to the potential attractiveness of this measure.
From a safety standpoint, Platte River and Shell Creek floods have historically been damaging, not life-threatening. This is because even the major events produce relatively shallow flood stages that occur with relatively long flood warning time. Therefore the residual risk, if levees are to be constructed, would not be excessive for portions of Schuyler located in either the Shell Creek or Platte River floodplains.
5.2.5 Other Structural Flood Risk Reduction Measures Considered for Shell Creek As part of the plan formulation process, many potential flood risk measures were discussed by the team. Some were discarded due to lack of practicality and high cost. Among those discussed and evaluated for consideration were:
82
Construct a dam upstream of Schuyler. Although flooding could be greatly reduced by building a dam on Shell Creek, this measure was not further considered due to high real estate costs, environmental impacts, construction costs and the long lead time required to build a dam. Build a levee and weir upstream of the Highway 30 Expressway. Given that Shell Creek floodwaters pour through the Nieman Ditch bridge in amounts far greater than the channel capacity or culvert capacity under old Highway 30, the potential of diverting water away from the Nieman Ditch opening and back to the Shell Creek channel was considered. While it was determined that this measure could reduce, or possibly eliminate flooding for threshold events, such as the 2010 flood, it would not provide effective flood risk management for larger events, including the 50 and 100-year floods. An evaluation of this measure did not indicate that it could be combined with other measures to protect against large floods, due to the nature of the floodplain hydraulics. For example, a levee or very large channel would still be needed to protect against larger floods backing up behind the UPRR embankment and slowed by the restrictive channel capacity on Shell Creek downstream. Improve Nieman Ditch between the Highway 30 Expressway and the UPRR embankment. While it was determined that this measure could reduce damages to northeastern Schuyler from more frequent events, it would not provide effective flood risk management for larger events, including the 50 and 100-year (2% and 1% annual chance of exceedance) floods. A levee or very large Shell Creek channel cleanout would still be needed to reduce risk of damage from floods backing up behind the UPRR embankment and slowed by the restrictive channel capacity on Shell Creek downstream.
Flood risk management measures were screened according to the four Corps of Engineers planning criteria; completeness, effectiveness, efficiency and acceptability for addressing Shell Creek flood issues. The results of the initial screening are provided in Table 5-1 below:
Table 5-1 Summary of Initial Screening Shell Creek Measures
MEASURE STAND-ALONE MEASURE SCREENING Flood Warning Not complete, not effective Relocation Not efficient, not acceptable Flood Proofing Not efficient Channel Improvement Not complete, not effective, not efficient Upstream Diversion Not acceptable, not efficient, not complete Upstream Dam Not efficient, not acceptable Removal of Floodplain Obstructions Not complete Levees Complete, effective, efficient and acceptable
5.2.6 Shell Creek Alternatives Formulated Once it was determined that there was no effective non-levee plan to protect northeastern Schuyler from a major flood event, plan formulation efforts were directed towards formulating levee alternatives for the area between the UPRR and the Highway 30 Expressway. The formulation process was a multi-disciplinary task for the team, with floodplain regulations, hydraulics, interior drainage hydrology, real estate and utilities, geotechnical considerations and construction cost and the realization of economic benefits among the major factors considered by
83 the team. Several levee routes were evaluated, some of which included closure structures across the UPRR and channel cleanout features. The formulated levee alternatives are listed below and are detailed on Plates 2 through 6.
Locations of the levee alignments for both the Platte River and Shell Creek flood risk reduction were selected based on their ability to protect the greatest areas of Schuyler from damage with minimal impacts to the community. The U.S. Fish and Wildlife Service and the Union Pacific Railroad were consulted early in the study to try to avoid impacts to and conflicts with the interests of those organizations.
In addition, alignments were placed as far north from the Platte River as possible to avoid impacts to Platte River wildlife and encroachment on the delineated Platte River floodway. To ensure alignments avoided the delineated Platte River floodway, the removal of the abandoned railroad embankment was identified as necessary by the team as a component of all Platte River alternatives. Due to FEMA and Federal Highway Administration guidelines, it was identified that a levee would not be tied into any railroad or highway embankments and either had to tie into natural high ground or trail far enough downstream such that the flood waters could no longer flank the levee and flood the city.
A typical levee cross section depicting the higher parts of the Shell Creek and Platte River levees is shown on Plate 10. The preliminary design cross section consists of a 10-foot crest with side slopes of 1 vertical (1V) on 3 horizontal (3H). Due to the presence of sands, silty-sands, and gravels at relatively shallow depths, it can be reasonably assumed that under seepage control measures will be required. To address this possibility, a 15-foot berm was included on the land side of the levee. Based on standard design practices in the area, the riverside of slope of the levee will consist of a 6-inch topsoil layer and an impervious clay blanket. The landside of the levee will include a 12-inch layer of top soil, with the remainder of the section consisting of random fill. A mixture of native grasses will be used on the slopes and berms to ensure the development of a grass cover for protection against erosion. A 6-inch layer of rock surfacing will be placed on the crest as wearing surface for any required inspection and maintenance traffic.
A description of the major levee alternatives that were initially formulated are described in the sections that follow.
5.2.6.1 SHELL CREEK ALTERNATIVE A (SC-A) This levee alternative, shown on Plate 2, features a levee route that would begin as a tie-off levee near the QC Supply farm store at the junction of Expressway 30 and Highway 15 north of Schuyler and proceed eastward along the south side of the expressway to near Nieman Ditch. A borrow pit near the junction was included on the inside of the levee, due to its depth and hydraulic connection to a Schuyler municipal well located west of Highway 15. The levee would then turn southward and would cross old Highway 30 west of the current Nieman Ditch culverts. The culverts would be replaced with larger 60-inch RCP culverts and old Highway 30 would be raised to cross the levee. An interior drainage ditch and gatewell structure would be needed inside the levee to collect rainwater and safely convey the flow to the exterior of the
84 levee. Interior drainage from north of the UPRR could be run to an exit south of the tracks to take advantage of the difference in elevation. The levee would then extend southward to Husker COOP where it would turn westward to tie off to high ground and run parallel to the UPRR grade. At the COOP, buildings near the tracks would be torn down or moved, or a floodwall would be required (floodwall assumed for now).
Except for the shorter tie-off portions, most of the levee would range from 5 to 7 feet high. The unused portion of the old Highway 30 embankment nearest to the Highway 30 Expressway would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made.
5.2.6.2 SHELL CREEK ALTERNATIVE B (SC-B) This levee alternative, shown on Plate 3, features a levee route that would begin as a tie-off levee near the QC Supply farm store at the junction of Expressway 30 and Highway 15 north of Schuyler. A borrow pit near the junction was included on the inside of the levee, due to its depth and hydraulic connection to a Schuyler municipal well located west of Highway 15. East of the borrow pit, the levee would turn southward to near the residential neighborhood. At that point, it would extend eastward. It would be located as close to the northeast edge of town as possible, yet permit the road raise to conclude so as not to interfere with residential and business traffic. The levee would then cross old Highway 30 and then turn southward along the east edge of the residential portion of town to the UPRR tracks. An interior drainage ditch and gatewell structure would be needed inside the levee to collect rainwater and safely convey the flow to the exterior of the levee. Interior drainage from north of the UPRR could be run to an exit south of the tracks to take advantage of the difference in elevation. A closure structure would be needed at the UPRR to complete the levee. The levee would then extend southward from the UPRR embankment for sufficient distance to serve as a trailing levee.
Except for the shorter tie-off portions, most of the levee would range from 5 to 7 feet high. The unused portion of the old Highway 30 embankment nearest to the Highway 30 Expressway would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made.
5.2.6.3 SHELL CREEK ALTERNATIVE C (SC-C) This levee alternative, shown on Plate 4, features a levee route that would begin as a tie-off levee near the QC Supply farm store at the junction of Expressway 30 and Highway 15 north of Schuyler. East of the borrow pit, the levee would turn southward to near the residential neighborhood. At that point, it would extend eastward. It would be located as close to the northeast edge of town as possible, yet permit the road raise to conclude so as not to interfere with residential and business traffic. The levee would then cross old Highway 30 and then turn southeastward towards Nieman Ditch. The levee would then parallel Nieman Ditch’s right bank until it reached the confluence of the ditch and Shell Creek. An interior drainage ditch and gatewell structure would be needed inside the levee to collect rainwater and safely convey the flow to the exterior of the levee. Over 3,000 feet of Nieman Ditch would be cleared and grubbed
85 above its confluence. The Shell Creek channel eastward to the next county road would be cleared, grubbed and excavated to improve flood conveyance away from Schuyler.
Except for the shorter tie-off portions, most of the levee would range from 5 to 7 feet high. The unused portion of the old Highway 30 embankment nearest to the Highway 30 Expressway would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made.
5.2.6.4 SHELL CREEK ALTERNATIVE D (SC-D) This levee alternative, shown on Plate 5, features a levee route that would begin as a tie-off levee near the QC Supply farm store at the junction of Expressway 30 and Highway 15 north of Schuyler. A borrow pit near the junction was included on the inside of the levee, due to its depth and hydraulic connection to a Schuyler municipal well located west of Highway 15. East of the borrow pit, the levee would turn southward to near the residential neighborhood. At that point, it would extend eastward. It would be located as close to the northeast edge of town as possible, yet permit the road raise to conclude so as not to interfere with residential and business traffic. The levee would then cross old Highway 30, extend eastward to Nieman Ditch and then turn southward, paralleling the ditch and then continuing south to the COOP at the UPRR tracks. An interior drainage ditch and gatewell structure would be needed inside the levee to collect rainwater and safely convey the flow to the exterior of the levee. Interior drainage from north of the UPRR could be run to an exit south of the tracks to take advantage of the difference in elevation. A closure structure would be needed at the UPRR to complete the levee. The levee would then extend southward from the UPRR embankment for sufficient distance to serve as a trailing levee.
Except for the shorter tie-off portions, most of the levee would range from 5 to 7 feet high. The unused portion of the old Highway 30 embankment nearest to the Highway 30 Expressway would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made.
5.2.6.5 SHELL CREEK ALTERNATIVE E (SC-E) This levee alternative, shown on Plate 6, features a levee route that would begin as a tie-off levee near the QC Supply farm store at the junction of Expressway 30 and Highway 15 north of Schuyler. A borrow pit near the junction was included on the inside of the levee, due to its depth and hydraulic connection to a Schuyler municipal well located west of Highway 15. The levee would continue east from the borrow pit and extend to the right bank of Nieman Ditch near the Expressway bridge. At that point, it would extend southeastward along the ditch. The levee would then cross old Highway 30, and continue southeastward along Nieman Ditch to the UPRR tracks. An interior drainage ditch and gatewell structure would be needed inside the levee to collect rainwater and safely convey the flow to the exterior of the levee. The levee would then continue eastward along the UPRR embankment for sufficient distance to serve as a trailing levee. The Shell Creek channel eastward and adjacent to the levee would be cleared, grubbed and excavated to improve flood conveyance away from Schuyler until it reached the next county road downstream.
86 Except for the shorter tie-off portions, most of the levee would range from 5 to 7 feet high. The unused portion of the old Highway 30 embankment nearest to the Highway 30 Expressway would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made.
5.2.6.6 SHELL CREEK CHANNEL IMPROVEMENT For several reasons, improving the Shell Creek channel in the vicinity of the bend to the east for all alternatives, gained the support of both the Corps and sponsor teams. Many years ago, a downstream landowner had improved his channel section to carry additional flow and this had improved local drainage. This section is located about 1 mile downstream of that bend. During the public involvement meetings held in June 2009, considerable support for improving the channel reach from Schuyler to that property had been voiced.
Additionally, channel shaping along Shell Creek offers the opportunity for a local source of borrow, adjacent to the sites of the Shell Creek levee alternatives. The total quantity of borrow to be obtained from this reach will be finalized in design; once site surveys have been obtained and the soil quality and efficiencies of other borrow sites have been determined. The construction sequence will also influence the final total of borrow to be obtained from the channel cleanout. For initial evaluation in the feasibility phase, it is assumed that excess borrow obtained from this reach will be stockpiled and used on the Platte River levee.
The proposed channel shaping reach extends from where Shell Creek approaches the railroad near the COOP to approximately County Road 14, a distance of less than 1.5 miles. The channel shaping would include terraces to be graded to just above the 2-year (50% annual chance of exceedance) water surface profile elevation, to avoid impacts to the existing low flow channel.
The channel shaping concept for Shell Creek had already been incorporated into alternatives SC- C and SC-E. It was determined to regrade the upper portion of the channel between the bend and the previously improved section for the remaining alternatives as well. The proposed channel grading reach is shown on Plate 11. Potentially, the improved channel shape can be used to reintroduce native wetland plant species to lower Shell Creek. Additional advantages of incorporating this feature in all alternatives include offsetting stage increases induced on agricultural lands east of the proposed levee alignments.
5.2.7 Consolidation of Shell Creek Alternatives
5.2.7.1 ADJUSTMENT FOLLOWING INITIAL CONSTRUCTION COST ESTIMATES Following the compilation of quantities for Shell Creek Alternatives A through E and the initial M-CACES Construction Cost Estimates for those alternatives, it was noted that the cost spread (inclusive of design and supervision during construction and construction contingency) between the least costly and most costly Shell Creek levee alternatives was less than 18% of the average alternative cost. (M-CACES 11/22/10). The cost estimates did not include real estate costs.
87 At that point, alternatives SC-B and SC-D were reevaluated as they both contained closure structures across the Union Pacific Railroad’s double track main line. The railroad voiced its concern that the closure structures would have adverse impacts on transportation. Given the stated opposition of the railroad, the real estate cost contingency becomes significant, given the potential cost of adverse property acquisition procedures against an unwilling land owner. The construction of closure structures also add greatly to the complexity of both the design work and to the eventual construction process, and add uncertainty to the cost computations, resulting in a larger cost contingency for alternatives with track closure structures.
Based upon previous experience in constructing closure structures across Union Pacific Railroad lines and more recent consultation with staff from that organization, it was determined that the project real estate costs involved in securing right of way to build the closure structures across a main line of the railroad would be substantial. The railroad has expressed its concern about potential delays to trains that may result from closure panels being installed at stages below that which its trains could operate.
From a formulation standpoint, closure structures present many unusual engineering and construction challenges, so it was determined that the construction cost contingency for the closure was probably higher than the single contingency value applied in the M-CACES computations. Finally, delays associated with obtaining permission to construct and executing the construction of the closure was determined to be substantial, adding both increased time and cost to the Feasibility Study and to the design and construction of the project. All of those factors result in much greater risk and uncertainty for Levee Alternatives SC-B and SC-D. Thus, the Corps study team concluded that the perceived construction cost advantages of Alternatives SC-B and SC-D might be swallowed up in study, design, LERRDs and construction contingency costs. Correspondingly, cost evaluations of alternatives with railroad closure structures would require significantly higher cost contingencies.
Following the initial economic analysis the Corps study team discussed its concerns about the closure structures with the sponsor team. The sponsor team noted that it also had the same concerns regarding the levee alternatives using railroad closure structures and suggested that the Corps team drop or modify alternatives SC-B and SC-D. Based upon the initial economic analysis and discussions with the sponsor, Alternative D was dropped from consideration and Alternative SC-B was altered to remove the railroad closure structure and incorporate the tieback westward along the north side of the tracks.
5.2.7.2 OPTIMUM SHELL CREEK LEVEE HEIGHT Flood risk management plans must be formulated to meet the National Economic Development (NED) criterion, which requires that the plan with the maximum net benefit be selected, all other things being equal. Determining the optimal plan means not only finding the alternative with the optimal combinations of measures, but determining the optimal scale of those measures. After screening out various measures that were found to be impractical, or insufficiently effective or efficient, the principle measure evaluated for this project was various levee configurations, and the scale was levee height. That height above the surrounding ground is determined by evaluating various levee alignments and sizes that would protect the community from a range of
88 flood frequencies. For Shell Creek flooding, estimates of levee costs and benefits were evaluated over a range of floods up to the 500-year (0.2% annual chance of exceedance) flood.
Shell Creek flooding begins to cause significant damage within the residential area of northeastern Schuyler between the 10 to 20-year (10% and 5% annual chance of exceedance) floods. Above the 20-year event, flooding pushes into much of the 100-year floodplain within the northeastern neighborhoods of Schuyler and expands in depth and lateral coverage to around the 100-year flood. For lesser levels of flood risk management, benefits rise faster than costs as levee height is increased, as can be seen in Figure 5.2, in which benefits and approximate costs were charted for the 50, 100, 200, and 500-year flood risk management levels. There is a 6% jump in net annual NED benefits at the 100-year flood risk management level in addition to flood damage reduction benefits, as the removal of property from the flood plain will save the annual federal cost of administering the National Flood Insurance Program policies. The addition of the federal benefit in not administering flood insurance policies forms a localized net benefit optimization point relative to lesser levels of flood risk management.
At flood frequencies approaching the 100-year event, Shell Creek begins to spill into other drainage basins upstream of the city, as it leaves the valley and enters the broad Platte River flood plain north of Schuyler (See Plate 1). Due to the general slope of the Platte River valley, a significant portion of peak discharges above the 100-year flood will head eastward from this point and not southward towards Schuyler. A significant portion of that trans-basin loss goes to Rawhide Creek, which is historically a tributary to the Elkhorn River. Thus, the peak discharge and volume delivered to Schuyler grows more slowly, as the percentage of extreme Shell Creek floods lost to the lower basin increases proportionately to the size of the flood delivered from upstream portions of the watershed. As a result of this loss of flood discharge from Shell Creek above Schuyler, the number of structures determined to be in the Shell Creek floodplain only raises from 173 to 184 between the computed 100-year and 500-year floodplains.
Above the 100-year flood, peak flows that do reach Schuyler presently spill across a wide portion of the UPRR railroad grade, which acts as a very long broad-crested weir. Slight increases in stage are associated with very large increases in discharge across the tracks, thus the elevation of the 500-year Shell Creek flood is only about a tenth of a foot higher than the 100- year flood, and therefore benefits rise very slowly with increases in levee height above the 100- year level.
On the other hand, costs on levee heights greater than the 100-year level begin to rise more quickly, as can be seen in Figure 5.2. Inches above the 100-year flood risk management level, additional lands, easements, rights-of-way, relocations and disposal areas (LERRDs) and fill were required to extend the levee’s end across commercial property. In order to provide 500- year flood risk management to northeastern Schuyler, the Shell Creek levee would have to also reduce risks of flood damages from the Platte River. This would entail extending the Shell Creek levee westward to connect with the Platte River levee to essentially ring the community, requiring a road raise on Highway 15 and additional real estate and utility costs. These costs were ascribed to the Shell Creek Levee.
89 Using information derived from cost estimates for this and other recent projects and studies, annual project costs for constructing a 50-year, 100-year, 200-year and 500-year levee were estimated at $185,000, $193,000, $217,000 and $247,000. The annual benefits for the Shell Creek side were $797,000 for the 50-year event and $829,000 for events higher than the 100- year event. The maximum net annual benefits of $636,000 are realized by the levee providing flood risk management at the 100-year event, which is the optimal (NED) levee height.
Figure 5-2 shows on the upper curve the estimated average annual equivalent benefits that would be realized along with, on the lower curve, the estimated average annual equivalent costs for various levels of flood risk management. The X-axis represents the flood risk management levels, and the Y-axis represents thousands of dollars per year. The distance between these curves represents the Net Annual Economic Benefits.
900 Optimum Levee Height Shell Creek Side
800
700
600
Net Annual NED Benefits 500 Maximized at $636,000 benefits 400 costs
300
200
100
0 0.02 0.01 0.005 0.002
Figure 5-2 Optimum Shell Creek Levee Height Based on the data in Figure 5-2, it was determined that the NED frequency of design for the Shell Creek levees would be the 100-year (1% annual chance of exceedance) flood, the elevation of which included risk and uncertainty. Initial risk computations indicated that the contingent overtopping design margin could be set between 2 and 3 feet. The risk was revised upward to 3 feet, after considering the uncertainty of future Union Pacific Railroad track raises. Incremental raises of a few tenths of a foot have occurred in past decades as a part of routine track maintenance and may occur in the future. This necessitates a conservative approach to risk in
90 regard to levee height, given that the rail embankment serves as part of the floodplain backwater control for Shell Creek adjacent to the levee site.
5.2.7.3 ADJUSTMENT FOR CHANGE IN SHELL CREEK CHANNEL SHAPING An economic review of a large-scale channel improvement project revealed that this effort would not be incrementally justifiable. Therefore, the channel shaping was revised downward in size to become an incidental feature which will yield needed random fill for the Shell Creek levee and local improvements to hydraulic flood conveyance in the vicinity of Shell Creek and lower Nieman Ditch at their confluence. Stockpiling of fill obtained from Shell Creek channel work for use as random fill on the Platte River levee was removed from consideration, due to cost, and the quantities adjusted downward to fit the random fill needs of the individual Shell Creek levee alternatives.
The reason that Shell Creek channel shaping was not found to be an incrementally justifiable project component is that proposed levee heights at Schuyler would not be significantly reduced by greatly increasing channel width, but the channel work would add a very significant cost increase to the project. This is because many floodplain features other than the width of the Shell Creek channel immediately downstream of Schuyler determine the stage discharge relationship in northeastern Schuyler, and that the reduction in flood stage achievable by improving just that reach of Shell Creek was found to be relatively small. Details of the exact configuration of the channel shaping effort will be developed early in design once site surveys are obtained. The 2-foot contour interval elevation data were not sufficient for more than gross estimates during the feasibility phase. For the revised feasibility-level evaluation, the same configuration footprint was retained, but the depth of “cut” reduced so that Shell Creek cut and fill would be closer to balance.
5.2.7.4 ADJUSTMENTS FOLLOWING CONFERENCE WITH SPONSOR Following discussions with the sponsor held in March 2011, it was determined that extending the levee around the highway construction borrow pit located next to the southeast corner of the diamond interchange of Highways 15 and 30 would not be necessary and could allow for a slightly shorter levee length. Originally, during project scoping, there had been the concern that if Shell Creek floodwaters were to enter that borrow pit, that contamination of a Schuyler city drinking water well west of Highway 15 could occur. Subsequent evaluation indicated that the flood duration would likely be insufficient to cause contamination to be drawn into the well. Inclusion of the borrow pit near the southeast edge of the intersection of Highways 30 and 15, shown for Alternatives SC-B and SC-C Plates 3 and 4, were dropped as shown on Plate 12 and Plate 14. Plate 14 shows the final configuration of Alternative SC-C.
Following a meeting between the sponsor and the Corps in early March, an adjustment was made to the alignment of levee Alternative SC-E near old Highway 30. The levee was repositioned so that the road raise would be located between the Nieman Ditch and the intersection of East 22nd Street in order to minimize the impact of the elevated road on both features. Using the new alignment will likely permit the use of the existing twin box culverts under old Highway 30 at Nieman Ditch. In addition, the setback from the Nieman Ditch will also improve the conveyance
91 of flood flows along Nieman Ditch and will reduce potential induced damages on nearby property. The levee was not located closer to East 22nd Street in order to avoid a potential traffic hazard that could result by locating the road raise near the intersection.
In addition, following the meeting it was determined that a floodwall would be extremely difficult to construct between the elevators and the Union Pacific Railroad line on the south side of the Husker COOP. This feature is shown for Alignment SC-A on Plate 2. Chief reasons for the extreme difficulty (and likely high cost) were the need to provide closure structures across the railroad siding which serves the elevator. It was decided to leave the elevators on the outside of the levee and potentially flood proof them. Due to the need for trucks to access the elevators, a floodwall with closure structure for truck access would be incorporated in the levee (SC-A) at the COOP.
Additional changes to levee configuration and construction details were made after discussions with officials of the city of Schuyler and reevaluations by the Corps team. For all levee alignments, the impervious soil blanket thickness was increased from 3 feet to 5 feet, reflecting the need for greater safety against prolonged seepage. The results of those changes are reflected in the alternatives which were compared as described in the following section:
5.2.8 Shell Creek Alternatives Comparison Four levee alternatives survived the initial screening process. The following alternatives, modified after the first round of screening, were compared in greater detail to select the recommended plan using benefit and cost analysis.
5.2.8.1 SHELL CREEK ALTERNATIVE A (SC-A) Alternative SC-A, shown on Plate 2, features a levee route that would begin as a tie-off levee near the QC Supply farm store at the junction of Expressway 30 and Highway 15 north of Schuyler and proceed eastward along the south side of the expressway to near Nieman Ditch. The borrow pit near the junction was included on the inside of the levee. The levee would then turn southward and cross old Highway 30 about midway between the Nieman Ditch and East 22nd Street. The existing Nieman Ditch box culverts would be replaced with two larger 60-inch RCP culverts and old Highway 30 would be raised to cross the levee. An interior drainage ditch and gatewell structure would be needed inside the levee to collect rainwater and safely convey the flow to the exterior of the levee. This structure would be located near the COOP. Interior drainage from north of the UPRR may be run to an exit south of the tracks to take advantage of the difference in elevation. The levee would then extend southward to Husker COOP. At the COOP, a floodwall with gate closure would be used to permit trucks to access the elevators along the UPRR. The levee would return to an alignment parallel to the UPRR property where it would proceed westward to tie off to high ground near Highway 15.
Except for the shorter tie-off portions, most of the levee would range from 5 to 7 feet high. The floodwall at the COOP would be approximately 5 feet high and 150 feet long. The unused portion of the old Highway 30 embankment nearest to the Highway 30 Expressway may be removed and used as random fill in the levee. Over 3,000 feet of Nieman Ditch would be cleared and grubbed above its confluence, also providing a source of random fill. The Shell Creek channel eastward would be shaped to improve flood conveyance away from Schuyler (see Plate
92 11). The channel shaping area will be used as a source of borrow based upon the random fill requirements of Alternative SC-A. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made. General material statistics for Alternative SC-A are noted as follows:
. Stripping for levee 22,900 cubic yards . Impervious fill* 66,900 cubic yards . Random fill** 81,300 cubic yards . Topsoil 32,000 cubic yards . Excavate 8’ x 7’ interior drainage ditch 20,700 cubic yards . Remove old highway embankment 9,630 cubic yards . Clearing and grubbing (channels) 15.0 acres . Seeding 5.00 acres . Rock surfacing 6,400 tons . Flood wall (5’ high) 150 lineal feet . Concrete road raise 6’ with 60” culvert pipe 1 job . RCP gatewell structure for interior drainage (72” RCP) 1 job . Shell Creek channel excavate random fill 50,970 cubic yards
* It is assumed that impervious fill would be acquired from an unknown borrow source north of Schuyler. A haul distance of 3 miles was assumed. ** Random fill would be acquired from the removal of existing floodplain features, channel shaping excavations on Shell Creek and lower Neiman Ditch and from excavations for interior drainage ditches and ponding areas where needed.
5.2.8.2 SHELL CREEK ALTERNATIVE B (SC-B1) Alternative SC-B was modified and a new alternative was developed and denoted as SC-B1. This alternative is depicted on Plate 12. This new alternative protects a similar area to B, but with the following modifications: It runs south of the borrow pit previously noted, and does not protect the borrow pit, which allows for a shorter levee. Similar to Alternative A, it features a levee section running westward just outside of the Union Pacific right-of-way to high ground near Highway 15. This alternative now incorporates the channel cleanout feature.
This levee alternative, shown on Plate 12, features a levee route that would begin at high ground near the QC Supply farm store south of the junction of Expressway 30 and Highway 15 on the north side of Schuyler. The levee would proceed nearly eastward to old Highway 30 between the Nieman Ditch and East 22nd Street. Old Highway 30 would cross the levee as a road raise. Immediately east of Old Highway 30 the levee would make a right turn and head southward, passing east of the residential neighborhood before reaching the Union Pacific Railroad right of way. At that point, it would make a right turn and extend westward to high ground near Highway 15 in central Schuyler.
The northern part of the levee would be located as close to the northeast edge of town as possible, yet permit the Old Highway 30 road raise to conclude so as not to interfere with
93 residential and business traffic. An interior drainage ditch and gatewell structure would be needed inside the levee to collect rainwater and safely convey the flow to the exterior of the levee. Interior drainage from north of the UPRR could be run to an exit south of the tracks to take advantage of the difference in elevation. The Shell Creek channel eastward and adjacent to the levee would be shaped to improve flood conveyance away from Schuyler (see Plate 11). The channel shaping area will be used as a source of borrow based upon the random fill requirements of Levee Alternative SC-B-1.
Except for the shorter tie-off portions near Highway 15, most of the levee would range from 5 to 7 feet high. The unused portion of the old Highway 30 embankment nearest to the Highway 30 Expressway would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made. General material statistics for Alternative SC-B-1 are noted as follows:
. Stripping 17,000 cubic yards . Impervious fill* 43,500 cubic yards . Random fill** 45,300 cubic yards . Topsoil 22,600 cubic yards . Excavate 8’ x 7’ interior drainage ditch 19,320 cubic yards . Remove old highway embankment 9,630 cubic yards . Clearing and grubbing (channels) 15.0 acres . Seeding 5.00 acres . Rock surfacing 4,900 tons . Concrete road raise 7’ with 60” culvert pipe 1 job . RCP gatewell structure for interior drainage 60” RCP 1 job . Shell Creek channel excavate random fill 16,350 cubic yards
* It is assumed that impervious fill would be acquired from an unknown borrow source north of Schuyler. A haul distance of 3 miles was assumed. ** Random fill would be acquired from the removal of existing floodplain features, channel shaping excavations on Shell Creek and lower Neiman Ditch and from excavations for interior drainage ditches and ponding areas where needed.
5.2.8.3 SHELL CREEK ALTERNATIVE C (SC-C) This levee alternative as modified is shown on Plate 14 and features a route that would begin at high ground near the QC Supply farm store south of the junction of Expressway 30 and Highway 15 on the north side of Schuyler and extend eastward to Old Highway 30. It would be located as close to the northeast edge of town as possible, yet permit the road raise to conclude so as not to interfere with residential and business traffic. The levee would then cross old Highway 30 and then turn southeastward towards Nieman Ditch. The levee would then parallel Nieman Ditch’s right bank until it reached the confluence of the ditch and Shell Creek. An interior drainage ditch and gatewell structure would be needed inside the levee to collect rainwater and safely convey the flow to the exterior of the levee. Interior drainage from north of the UPRR could be run to an exit south of the tracks to take advantage of the difference in elevation. The levee would then continue eastward parallel to the UPRR embankment for sufficient distance to serve as a trailing
94 levee. Over 3,000 feet of Nieman Ditch would be cleared and grubbed above its confluence. The Shell Creek channel would be shaped to improve flood conveyance away from Schuyler (see Plate 11). The channel shaping area will be used as a source of borrow based upon the random fill requirements of Alternative SC-C.
Except for the shorter tie-off portions, most of the levee would range from 5 to 7 feet high. The unused portion of the old Highway 30 embankment nearest to the Highway 30 Expressway would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made. General material statistics for Alternative SC-C are noted as follows:
. Stripping 16,600 cubic yards . Impervious Fill* 49,900 cubic yards . Random Fill** 56,600 cubic yards . Topsoil 24,700 cubic yards . Excavate 8’ x 7’ interior drainage ditch 27,140 cubic yards . Remove old highway embankment 9,630 cubic yards . Clearing and grubbing (channels) 15.0 acres . Seeding 5.00 acres . Rock surfacing 5,300 tons . Concrete road raise 9’ with 60” culvert pipe 1 job . RCP gatewell structure for interior drainage (72” RCP) 1 job . Shell Creek channel excavate random fill 19,830 cubic yards
* It is assumed that impervious fill would be acquired from an unknown borrow source north of Schuyler. A haul distance of 3 miles was assumed. ** Random fill would be acquired from the removal of existing floodplain features, channel shaping excavations on Shell Creek and lower Neiman Ditch and from excavations for interior drainage ditches and ponding areas where needed.
5.2.8.4 SHELL CREEK ALTERNATIVE D (SC-D) Alternative SC-D was dropped from consideration, as without the railroad closure structure and the addition of the channel cleanout, it was found to be largely duplicative of other alternatives, especially Alternative SC-A.
5.2.8.5 SHELL CREEK ALTERNATIVE E (SC-E) Following a meeting between the sponsor and the Corps in early March 2011, an adjustment was made to the alignment of Alternative SC-E near old Highway 30. The levee was repositioned so that the road raise would be located between the Nieman Ditch and the intersection of East 22nd Street, to minimize the impact of the elevated road on both features. Using the new alignment will permit the use of the existing twin box culverts under old Highway 30 at Nieman Ditch. In addition, the setback from the Nieman Ditch will also improve the conveyance of flood flows along Nieman Ditch and reduce induced damages.
95 This levee alternative, shown on Plate 13, features a levee route that would begin as a tie-off levee near a borrow pit north of the QC Supply farm store at the junction of Expressway 30 and Highway 15 north of Schuyler. The levee would continue east from the borrow pit south of the Highway 30 right-of-way and extend to the right bank of Nieman Ditch near the expressway bridge. The levee would then turn southward and would cross old Highway 30 about midway between the Nieman Ditch and East 22nd Street. The existing Nieman Ditch box culverts would be replaced with two larger 60-inch RCP culverts and old Highway 30 would be raised to cross the levee. At that point, the levee would continue southeastward to near Nieman Ditch, then southward and southeastward along Nieman Ditch to near the UPRR tracks. An interior drainage ditch and gatewell structure would be needed inside the levee to collect rainwater and safely convey the flow to the exterior of the levee. The levee would then continue eastward along the UPRR embankment for sufficient distance to serve as a trailing levee. The Shell Creek channel eastward and adjacent to the levee would be shaped to improve flood conveyance away from Schuyler (see Plate 11). The channel shaping area will be used as a source of borrow based upon the random fill requirements of Alternative SC-E.
Except for the shorter tie-off portions, most of the levee would range from 5 to 7 feet high. The unused portion of the old Highway 30 embankment nearest to the Highway 30 Expressway would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made. General material statistics for Alternative SC-E are noted as follows:
. Stripping 21,100 cubic yards . Impervious fill* 66,100 cubic yards . Random fill** 77,800 cubic yards . Topsoil 27,400 cubic yards . Excavate 8’ x 7’ interior drainage ditch 28,600 cubic yards . Remove old highway embankment 9,630 cubic yards . Clearing and grubbing 15.0 acres . Seeding 5.00 acres . Rock surfacing 5,300 tons . Concrete road raise with 60” culvert pipe 1 job . RCP gatewell structure for interior drainage 72” RCP 1 job . Shell Creek channel excavate random fill 39,570 cubic yards
* It is assumed that impervious fill would be acquired from an unknown borrow source north of Schuyler. A haul distance of 3 miles was assumed. ** Random fill would be acquired from the removal of existing floodplain features, channel shaping excavations on Shell Creek and lower Neiman Ditch and from excavations for interior drainage ditches and ponding areas where needed.
5.2.9 Selection of Shell Creek NED Plan An economic goal of a flood risk management evaluation is to define the plan with the greatest net benefits to the national economy. This plan is then referred to as the National Economic Development or “NED Plan.” Alternatives SC-B-1, SC- C and SC-E all had very favorable
96 project economics in the initial evaluations, with a relatively small cost and benefit difference separating them.
At meetings with the sponsor, comments were favorable for Alternatives SC-C and SC-E, while much less comments were made regarding Alternatives SC-A, SC-B-1 and SC-D. The sponsor favored Alternative SC-E over Alternative SC-C for two reasons. The main reason was that Alternative SC-E would likely keep groundwater seepage out of storm sewers and basements in northeastern Schuyler during a Shell Creek flood, while seepage with Alternative SC-C was considered more problematic. Additionally, Alternative SC-E would not interfere with the operation of a center pivot, while SC-C would.
Given the relatively close net annual benefits in the initial analysis between Alternative SC-C ($670,080) versus Alternative SC-E ($657,160), the team proposed the selection of Alternative SC-E as the recommended plan, with a supporting discussion using the other three accounts beyond National Economic Development (NED) criteria. Given the sponsor’s support and potential impact of groundwater seepage to public facilities, a reasonable case was built supporting Alternative SC-E based upon the Other Social Effects (OSE) Account.
However, once the Shell Creek channel cleanout was found to not be incrementally justifiable and the grading activities along Shell Creek became more limited in scope for all alternatives, the cost changes for that feature widened the gap between the two alternatives, to more than double what it was before. Under review, it was determined that recommending a plan that was clearly not the NED plan, would be very risky to project schedule and swift implementation.
Therefore SC-C, the NED plan, was selected as the recommended plan. This plan is shown on Plate 14.
5.3 PLATTE RIVER STRUCTURAL MEASURES
5.3.1 Reconnaissance Study Alternatives Platte River levee alternatives were investigated in the initial assessment phase of the study. In that study, three Platte River levee alternatives were examined. “Alternative 1” from that 2003 study extended southward across Lost Creek and Ehrenberg Drain (with water control structures at each crossing) then continued east-northeastward around the southern and eastern city limits before tying off at the closed landfill east of Schuyler. Alternative 2 did not cross Lost Creek and Ehrenberg Ditch and proceeded eastward to the Oak Ballroom along the north bank of Lost Creek where a floodwall was required. After crossing Highway 15 the levee resumed and proceeded east-northeastward around the city to a tie-off at the closed landfill. Alternative 3 also did not cross Lost Creek and left the Oak Ballroom on the wet side of a levee which crossed the parking lot to the east of the Ballroom. In all cases, road closure structures were slated for Highway 15. More details on these initial alternatives can be found in the Section 205 Feasibility Study, Platte River at Schuyler, Nebraska (April 2003).
Plan formulation continued with variations of Alternatives 1 and 2 formulated and updated for additional information and land use. Alternative 3 was dropped from further consideration due
97 to the problems associated with tearing up a parking lot in the City Park to leave a historic structure on the wet side of the levee.
5.3.2 Construct a Dam Upstream of Schuyler Although flooding could be greatly reduced by building a dam on the Platte River, this alternative was not further considered due to high real estate costs, environmental impacts, construction costs and the long lead time required to build a dam.
5.3.3 Build a Levee near the North Bank of the Platte River Although considerable property is located in Colfax County between Schuyler and the Platte River, it was not considered feasible to extend the levee to the banks of the Platte. Principal reasons were the additional cost to extend the levee to capture a much lower density of structures and the environmental impacts of constructing a levee near the Platte River in the floodway. Induced flood damages to property on the south side of the Platte River would result from a levee along the north bank of the Platte, and those damages would require mitigation at considerable cost. Construction of a levee in the floodway has the potential to impact channel forming discharges of the Platte River, with potential negative impacts to threatened and endangered species such as the interior least tern (Sterna antillarum), piping plover (Charadrius melodus), or the pallid sturgeon (Scaphirhynchus albus).
5.3.4 Improve the Conveyance of Lost Creek South of Schuyler This alternative would need to include a much larger bridge at Highway 15. This concept was not pursued due to the very large sized bridge that would be needed to avoid constructing a levee and the likelihood that the extensive channel excavation required would not likely offer sufficient savings over levee construction to offset the large scale wetland mitigation efforts that would be required.
5.3.5 Remove the Abandoned Railroad Embankment South of Schuyler The removal of this feature is noted on Plates 7 through 9. Presently, this abandoned embankment forces the floodway northward towards Schuyler and increases flood depths upstream.
Though the majority of the non-levee alternatives considered for protecting Schuyler from Platte River flooding were not found to be cost effective, the removal of the railroad embankment likely provides sufficient benefits that it could be considered a “stand alone” alternative, particularly since it can be considered a local source of random fill for either the Platte River or Shell Creek levees. It was incorporated in all of the Platte River levee alternatives for further evaluation. The implementation of this alternative, by itself, does not prevent flooding in southern Schuyler, but it would decrease the flood stage there, and in Colfax County, for a given flood event.
5.3.6 Levee Measures Flood risk management measures were screened according to the four Corps of Engineers planning criteria: completeness, effectiveness, efficiency and acceptability for addressing Platte River flood issues. The results of the initial screening are provided in Table 5-2 below:
98 Table 5-2 Summary of Initial Screening Platte River Measures
MEASURE STAND-ALONE MEASURE SCREENING Flood Warning Not complete, not effective Relocation Not efficient, not acceptable Flood Proofing Not efficient Channel Improvement Not complete, not effective, not efficient Upstream Diversion Not acceptable, not efficient, not complete Upstream Dam Not efficient, not acceptable Removal of Floodplain Obstructions Not complete Levees Complete, effective, efficient and acceptable
Once it was determined that there was no effective nonstructural plan to protect southern Schuyler from a major Platte River flood event, plan formulation efforts were directed towards formulating levee alternatives to protect downtown Schuyler and associated residential, business and public structures. The formulation process was a multi-disciplinary effort for the team with floodplain regulations, hydraulics, interior drainage hydrology, real estate and utilities, geotechnical considerations and construction cost and the realization of economic benefits among the significant factors considered by the team. Two major levee routes were looked at with variations dictated by interior and exterior drainage issues. The formulated levee alternatives are listed in the following sections and are detailed on Plates 7 through 9.
5.3.6.1 PLATTE RIVER ALTERNATIVE A (PR-A) This alternative would protect a subdivision south of Schuyler as well as the City Park and golf course. This levee alternative, shown on Plate 7, features a levee route that would begin as a tie- off levee west of Schuyler at West 9th Street east of County Road 10 and proceed southward along County Road 10 until reaching the north side of the Shonka Drainage Ditch. The levee would then proceed southeastward to County Road C1 where a road raise would be required and continue to the left bank of Lost Creek. Shonka Ditch flood flows would be rerouted to enter Lost Creek. Both streams would require water control structures. The water control structures would be designed to allow low flows to pass downstream on Shonka Ditch and Lost Creek, but would not permit flood flows to continue. Flood flows would be rerouted using an exterior drainage ditch to convey the water parallel to the levee. The levee would continue eastward around a subdivision south of the golf course. Highway 15 would be routed over the levee and large culverts would be added adjacent to the levee to convey large exterior drainage flows.
Except for the shorter tie-off portions, most of the levee would range from 3 to 6 feet high. The abandoned railroad embankment downstream of Highway 15 would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made. The gravel inspection road on the levee crest could be used as a hiking and biking trail, resulting in incidental recreational benefits. The inspection road would have locked gates to prevent use by unauthorized vehicles and would have several at-grade accesses from roads (including raised roads) intersected by the levee. At these accesses, pedestrians and bicyclists could enter or exit the trail by an opening next to the gate. The levee-top trail could connect to a revitalized downtown Schuyler as well as to recreation facilities in South Park.
99 5.3.6.2 PLATTE RIVER ALTERNATIVE B1 (PR-B-1) This alternative is shown on Plate 8. It features a line of flood defense along Lost Creek. The defining features of this alternative are a floodwall next to the Oak Ballroom and an interior drainage and storm sewer plan that would make use of a ponding area on the southeast edge of Schuyler, near Lost Creek. This levee alternative features a levee route that would begin as a tie- off levee west of Schuyler at West 9th Street east of County Road 10 and proceed southward along County Road 10 until reaching the north side of the Shonka Drainage Ditch. The levee would then proceed southeastward to County Road C1, where a road raise would be required and continue to the left bank of Lost Creek. The levee would then continue east-northeastward along the left bank of Lost Creek until reaching the Oak Ballroom and nearby structures. A floodwall would then be required from that point, eastward until the floodwall reached Highway 15, where a closure structure would be required. Interior drainage features would be incorporated west of Highway 15 and would include a 10’ x 6’ drainage ditch and a 54-inch RCP gatewell structure. East of Highway 15 the levee section would resume and existing culverts and interior drainage features would be routed to a ponding area on the southeastern edge of Schuyler via a 25’x 6’ drainage ditch. The ponding area would require 48.7 acre feet of storage to handle excess runoff including the city’s existing storm sewer network that currently flows to Lost Creek, east of Highway 15. A 15’ x 6’ drainage ditch would be used to carry off excess flow from the ponding area. The trailing levee would terminate at the city’s sewage lagoons.
Except for the shorter tie-off portions, most of the levee would range from 3 to 6 feet high and the floodwall at the Oak Ballroom would be 5 feet high. The abandoned railroad embankment downstream of Highway 15 would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made.
5.3.6.3 PLATTE RIVER ALTERNATIVE B2 (PR-B-2) This alternative is shown on Plate 9. It features a line of flood defense along Lost Creek. The defining features of this alternative are a floodwall next to the Oak Ballroom and that individual storm sewer drainage areas would discharge directly to Lost Creek via gatewell structures, and would not make use of a general ponding area. This levee alternative features a levee route that would begin as a tie-off levee west of Schuyler at West 9th Street east of County Road 10 and proceed southward along County Road 10 until reaching the north side of the Shonka Drainage Ditch. The levee would then proceed southeastward to County Road C1 where a road raise would be required and continue to the left bank of Lost Creek. The levee would then continue east-northeastward along the left bank of Lost Creek until reaching the Oak Ballroom and nearby structures. A floodwall would then be required from that point, eastward until the floodwall reached Highway 15, where a closure structure would be required. Two interior drainage features would be incorporated west of Highway 15 and would include 48-inch RCP gatewell structures west of the Oak Ballroom. East of Highway 15 the levee section would resume and existing culverts and interior drainage features would be routed directly into Lost Creek via four gatewell structures. The gatewell structures, which would include flap gates on the stream side, would include three 48-inch RCP gatewells and one 66-inch RCP gatewell. The trailing levee would terminate at the city’s sewage lagoons.
100 Except for the shorter tie-off portions, most of the levee would range from 3 to 6 feet high and the floodwall at the Oak Ballroom would be 5 feet high. The abandoned railroad embankment downstream of Highway 15 would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made.
5.3.7 Consolidation of Platte River Alternatives
5.3.7.1 GENERAL Changes were made in Platte River Alternatives PR-A, PR-B-1 and PR-B-2 during the plan formulation process. For all three levees, the impervious blanket layer was increased from 3 to 5 feet in recognition of the need for greater safety, given the long duration of Platte River flood hydrographs (see Plate 10). Seepage concerns also resulted in a need for greater underseepage control for Platte River Alternatives B-1 and B-2, with the addition of driven sheet pile in the vicinity of the Oak Ballroom and Highway 15.
5.3.7.2 CULTURAL RESOURCE CONSIDERATIONS REGARDING THE PLATTE RIVER LEVEE ALTERNATIVES As proposed in the PR-B alternatives, a portion of the levee would be erected less than 20 feet directly behind the Oak Ballroom, which is listed on the National Register of Historic Properties. This close proximity is problematic on two fronts:
The construction method for the levee requires the use of driven sheet piles for soil retention. Sheet piles have a limited cross-sectional area, and the amount of material displaced during installation is lower than other pile types. However, the installation techniques used for sheet piling, including impact and vibro-driving, can induce ground vibrations that damage fragile archaeological materials or adjacent buildings. As vibration from piling installation is likely to be an issue on site, a detailed assessment would need to be made, considering frequency of vibration, ground conditions and the type of building and its foundations.
Under Section 800.5(a) (2) of the National Historic Preservation Act, an adverse visual effect could be caused by the introduction of visual elements that would diminish the integrity of a property’s character-defining features. Visual effects can be caused by a change in current esthetics, setting characteristics, or by an obstruction of views from or toward historic properties. Aesthetic and setting visual effects occur when the proposed construction have an effect upon the perceived beauty or character of a place or structure. Obstructive effects can occur when the proposed project obstructs any part of a historically significant property, or views from the historic property, resulting in a diminishment and identifiable change of the historic property’s character. Generally the introduction of visual changes can diminish a resource’s integrity of setting, location, feeling, and/or association. In this case, the introduction of the proposed levee directly behind the Oak Ballroom would impact the structure’s original park setting along Lost Creek.
The only safe and aesthetically acceptable solution to these issues attached to the B alignments would be to relocate the Lost Creek channel, a proposition that would add substantial cost to the project.
101
5.3.8 Optimum Platte River Levee Height Flood risk management plans must be formulated to meet the National Economic Development (NED) criterion, which requires that the plan with the maximum net benefit be selected, all other things being equal. Determining the optimal plan means not only finding the alternative with the optimal combinations of measures, but determining the optimal scale of those measures. After screening out various measures that were found to be impractical, or insufficiently effective or efficient, the principle measures evaluated for this project were various levee configurations, and the scale used was levee height. That height above the surrounding ground is determined by evaluating various levee alignments and sizes that would protect the community from a range of flood frequencies. For Platte River flooding, estimates of levee costs and benefits were evaluated over a range of floods up to the 500-year (0.2% annual chance of exceedance) flood.
Platte River flooding begins to cause significant damage within the residential and business portions of Schuyler, at about the 50-year (2% annual chance of exceedance) flood, with flooding to municipal park facilities occurring more frequently. The onset of severe damages begins close to the 100-year event (1% annual chance of exceedance), as water can flood the downtown area and the high school. There is also an 11% jump in NED benefits at the 100-year flood frequency in addition to flood damage reduction benefits, as the removal of property from the flood plain will save the annual federal cost of administering the flood insurance policies. The addition of the federal benefit in not administering flood insurance policies forms a localized net benefit optimization point relative to lesser flood risk management levels. For lesser flood risk management levels, benefits rise faster than costs as levee height is increased, as can be seen in Figure 5.3, in which benefits and approximate costs were charted for the 50, 100, 200, and 500-year flood risk management levels.
Most of the city of Schuyler is within the 100-year floodplain, causing the benefit curve to be fairly flat above the 100-year flood risk management level. Due to the very flat topography at Schuyler, extending the levee to a 200-year (0.5% annual chance of exceedance) or 500-year (0.2% annual chance of exceedance) flood risk management level would involve greatly lengthening the levee without improving the flood risk scenario for a significant number of additional buildings. To specifically design for the 500-year flood risk management level would require that Schuyler project measures include a ring levee (requiring an additional 1 mile of levee), or a levee tied off to high ground approximately 1 to 2 miles north of Schuyler. Both the ring levee and high ground tie-off options would require a closure structure across the Union Pacific Railroad grade at an estimated additional cost of at least $300,000, additional raises of paved county roads and a connection to a higher Shell Creek levee extended to just west of Highway 15.
Using information derived from cost estimates for this and other studies, annual project costs for constructing a 50-year, 100-year, 200-year, and 500-year levee were estimated at $296,000, $315,000, $389,000 and $437,000. The annual benefits for the Platte side were $939,000 for the 50-year event, $1,065,000 for the 100-year event, $1,076,000 for the 200-year event and $1,082,000 at the 500-year event. Thus, the maximum net benefits of $750,000 are realized at the 100-year event.
102 Figure 5-3 presents these benefit and cost relationships for Platte River levees at various flood risk management levels (shown on the X-axis). The Y-axis units are thousands of dollars per year. The upper curve represents the average annual equivalent benefits, and the lower curve represents the average annual equivalent costs. The vertical distance between those two curves represents the net annual economic benefits.
1200 Optimum Levee Height Platte River Side
1000
800 Net Annual NED Benefits Maximized at $750,000 600 benefits costs
400
200
0 0.02 0.01 0.005 0.002
Figure 5-3 Optimum Platte River Levee Height Based on the data in Figure 5-3, it was determined that the NED frequency of design for the Platte River levees would be the 100-year (1% annual chance of exceedance) flood, which includes risk and uncertainty. Hydraulic analysis indicated that 3 feet of contingent overtopping design margin was needed, given the influence of ice jams on the stage damage relationship. Fortunately, the risk of higher ice jam stages does not grow at a proportional rate above the 100- year event as the Platte River valley is wide at Schuyler. Platte River floods are able to spread out to the south as well as north to Schuyler as the floodplain at Schuyler is nearly 10 miles wide. Given the very wide Platte River floodplain at Schuyler, the computed levee height essentially offers well above 100-year protection with a high degree of confidence, without the large expense of additional miles of levee construction and real estate.
103 5.3.9 Platte River Alternatives Comparison
5.3.9.1 PLATTE RIVER ALTERNATIVE A (PR-A) This levee alignment is located just south of the city of Schuyler and is noted on Plate 7. Alternative PR-A consists of a levee of approximately 18,500 feet in length. It would run just south of the city of Schuyler golf course and a small lake development on the southern end of town. The levee parallels County Road 10 on the west until it ties into high ground and trails of just short of (but not into) the city operated sewage lagoons south of Lost Creek and east of town.
This alternative would protect a subdivision south of Schuyler as well as the City Park and golf course. This levee alternative, shown on Plate 7, features a levee route that would begin as a tie- off levee west of Schuyler at West 9th Street east of County Road 10, and proceed southward along County Road 10 until reaching the north side of Shonka Drainage Ditch. The levee would then proceed southeastward to County Road C1 where a road raise would be required and continue to the left bank of Lost Creek. Shonka Ditch flood flows would be rerouted to enter Lost Creek via a ditch approximately 7’ wide by 6’ deep. Both streams would require water control structures. The water control structures would be designed to allow low flows to pass downstream on Shonka Ditch and Lost Creek, but would not permit flood flows to continue towards Schuyler. The water control on Shonka Ditch will be a 72-inch RCP gatewell structure and the Lost Creek water control structure will be a 60-inch gatewell structure. Flood flows would be rerouted using an exterior drainage ditch, which will be approximately 8’ wide by 7’ deep, to convey the water parallel to the levee. The levee would continue eastward around a subdivision south of the golf course. Highway 15 would be routed over the levee and a 15’ x 7’ box culvert would be added adjacent to the levee to convey large exterior drainage flows under the road.
Except for the shorter tie-off portions, most of the levee would range from 3 to 6 feet high. The abandoned railroad embankment downstream of Highway 15 would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made.
The gravel inspection road on the 10-foot-wide levee crest could be used as a hiking and biking trail, resulting in incidental recreational benefits. The trail could connect to recreation facilities in South Park as well as to routes leading to revitalized downtown Schuyler. The inspection road would have locked gates to prevent use by unauthorized vehicles and would have several at- grade accesses from roads (including raised roads) intersected by the levee. At these accesses, pedestrians and bicyclists could enter or exit the trail by an opening next to the gate. Potential access points include: West 9th Street (the northwest end of the levee); at the road raise just northeast of the vacant poultry farm; at the gatewell structure at the southwest end of the golf course; and at Highway 15, which has an unofficial trail on its shoulders and links with a concrete trail that runs east to the city campground. The city hopes to receive grants to construct another trail in South Park along the west side of Highway 15 and for a trail bridge over Lost Creek (to replace the one destroyed by the 2010 flood). These could link the levee-top trail, South Park’s picnic areas and fishing lake, and the South Park pool, ballroom, tennis, and ball field facilities north of Lost Creek. Bird watchers currently hiking on Higgins and South Park
104 roads could access the levee-top trail to hike, enjoy rural scenery, and view birds and other wildlife along Lost Creek east of the old railroad embankment.
General material statistics for Alternative PR-A are noted as follows:
. Stripping 32,200 cubic yards . Impervious fill* 102,300 cubic yards . Random fill** 141,100 cubic yards . Topsoil 41,700 cubic yards . Clearing and grubbing 22.0 acres . Seeding 11.0 acres . Rock surfacing 7,300 tons . Shonka Drainage Ditch excavation 7,600 cubic yards . Lost Creek Drainage Ditch excavation 57,500 cubic yards . Remove abandoned railroad embankment 21,600 cubic yards . Concrete surfaced road raise 10’ with 15’ x 7’ box culvert 1 job . Aggregate surfaced road raise 6’ with 14’x 6’ box culvert 1 job . RCP gatewell structure for Shonka Ditch (100’, 72” RCP) 1 job . RCP gatewell structure for Lost Creek (90’, 60” RCP) 1 job
* Impervious fill would be acquired from an unknown borrow source north of Schuyler. A haul distance of 3 miles was assumed. ** Random fill would be acquired from the removal of existing floodplain features, channel excavations and from excavations for interior drainage ditches and ponding areas where needed.
5.3.9.2 PLATTE RIVER ALTERNATIVE B1 (PR-B-1) The defining features of this alternative are a floodwall next to the Oak Ballroom and an interior drainage and storm sewer plan that would make use of a ponding area on the southeast edge of Schuyler, near Lost Creek. This levee alternative which would run approximately 14,700 feet is shown on Plate 8. It features a levee route that would begin as a tie-off levee west of Schuyler at West 9th Street east of County Road 10 and proceed southward along County Road 10 until reaching the north side of Shonka Drainage Ditch. The levee would then proceed southeastward to County Road C1, where a road raise would be required and continue to the left bank of Lost Creek. The levee would then continue east-northeastward along the left bank of Lost Creek until reaching the Oak Ballroom and nearby structures. A floodwall would then be required from that point, eastward until the floodwall reached Highway 15, where a closure structure would be required. Interior drainage features would be incorporated west of Highway 15 and would include a 10’ x 6’ drainage ditch and a 54-inch RCP gatewell structure. East of Highway 15 the levee section would resume and existing culverts and interior drainage features would be routed to a ponding area on the southeastern edge of Schuyler via a 25’x 6’ drainage ditch. The ponding area would require 48.7 acre feet of storage to handle excess runoff including the city’s existing storm sewer network that currently flows to Lost Creek, east of Highway 15. A 15’ x 6’
105 drainage ditch would be used to carry off excess flow from the ponding area. The trailing levee would terminate at the city’s sewage lagoons.
Except for the shorter tie-off portions, most of the levee would range from 3 to 6 feet high and the floodwall at the Oak Ballroom would be roughly 5 feet high. The abandoned railroad embankment downstream of Highway 15 would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made. General material statistics for Alternative PR-B-1 are noted as follows:
. Stripping 20,400 cubic yards . Impervious fill* 65,600 cubic yards . Random fill** 94,000 cubic yards . Topsoil 26,400 cubic yards . Clearing and grubbing 18 acres . Seeding 8 acres . Rock surfacing 5,800 tons . Flood wall (8’ high) 450 lineal feet . Sheet pile 450 lineal feet . Excavate and reroute existing storm drainage 24,150 cubic yards . Excavate 10’ x 6’ drainage ditch 11,500 cubic yards . Excavate 15’ x 6’ drainage ditch 12,637 cubic yards . Excavate ponding area 78,600 cubic yards . Remove abandoned railroad embankment 21,600 cubic yards . Aggregate surfaced road raise 6’ with 60” RCP culvert 1 job . RCP gatewell structure for interior drainage (54” RCP) 1 job . Closure structure and bridge @ Highway 15 1 job
* Impervious fill would be acquired from an unknown borrow source north of Schuyler. A haul distance of 3 miles was assumed. ** Random fill would be acquired from the removal of existing floodplain features, channel excavations and from excavations for interior drainage ditches and ponding areas where needed.
5.3.9.3 PLATTE RIVER ALTERNATIVE B2 (PR-B-2) This alternative is shown on Plate 9. It features a line of flood defense along Lost Creek. The defining features of this alternative are a floodwall next to the Oak Ballroom and that individual storm sewer drainage areas would discharge directly to Lost Creek via gatewell structures, and would not make use of a ponding area. This levee alternative features a levee route that would begin as a tie-off levee west of Schuyler at West 9th Street east of County Road 10 and proceed southward along County Road 10 until reaching the north side of Shonka Drainage Ditch. The levee would then proceed southeastward to County Road C1 where a road raise would be required and continue to the left bank of Lost Creek. The levee would then continue east- northeastward along the left bank of Lost Creek until reaching the Oak Ballroom and nearby structures. A floodwall would then be required from that point, eastward until the floodwall reached Highway 15, where a closure structure would be required. Two interior drainage features would be incorporated west of Highway 15 and would include 48-inch RCP gatewell structures west of the Oak Ballroom. East of Highway 15 the levee section would resume and
106 existing culverts and interior drainage features would be routed directly into Lost Creek via four gatewell structures. The gatewell structures, which would include flap gates on the stream side, would include three 48-inch RCP gatewells and one 66-inch RCP gatewell. The trailing levee would terminate at the city’s sewage lagoons.
Except for the shorter tie-off portions, most of the levee would range from 3 to 6 feet high and the floodwall at the Oak Ballroom would be approximately 5 feet high. The abandoned railroad embankment downstream of Highway 15 would be removed and used as random fill in the levee. Efforts were made to minimize unusable real estate remnants, which must be purchased or other compensation made. General material statistics for Alternative PR-B-2 are noted as follows:
. Stripping 20,400 cubic yards . Impervious fill* 94,000 cubic yards . Random fill** 26,400 cubic yards . Topsoil 26,400 cubic yards . Clearing and grubbing 18 acres . Seeding 8 acres . Rock surfacing 5,800 tons . Flood wall (5’ high) 450 lineal feet . Sheet pile 450 lineal feet . Excavate 10’ x 6’ drainage ditch 5,750 cubic yards . Remove abandoned railroad embankment 21,600 cubic yards . Aggregate surface road raise 6’ with 60” RCP culvert 1 job . RCP gatewell structure for interior drainage (66” RCP) 1 job . RCP gatewell structure for interior drainage (48” RCP) 5 jobs . Closure structure and bridge @ Highway 15 1 job
* Impervious fill would be acquired from an unknown borrow source north of Schuyler. A haul distance of 3 miles was assumed. ** Random fill would be acquired from the removal of existing floodplain features, channel excavations and from excavations for interior drainage ditches and ponding areas where needed.
5.4 SUPPLEMENTAL LEVEE INFORMATION The descriptions of construction materials for the levee alternative are provided in the following sections.
5.4.1 Impervious Fill Potential impervious material borrow areas include an abandoned section of Highway 30 located south of the existing Highway 30 Expressway and just west of Shell Creek; an abandoned railroad embankment south of Lost Creek and just east of the city of Schuyler; and areas in the hills north of the city of Schuyler. Exact locations of impervious borrow areas north the city of Schuyler have not been located.
107 5.4.2 Random Fill Random fill material mostly comprised of sands and/or silty-sands can be obtained from any excavations required for the project, e.g. storm water detention basins, Shell Creek excavations, and other drainage ditch excavations.
5.4.3 Topsoil Topsoil for use on the levee will be extracted from all areas stripped within the levee footprint and any other excavations. The stripped topsoil will be stockpiled on project lands for later use on the levee slopes, channel bottoms and other areas incidental to the levee project. Topsoil placement on the levee surfaces with encouraged growth of grasses and forbs able to resist erosion.
5.4.4 Disposal of Clearing and Grubbing Materials, Excess Excavated Soils and Refuse Suitable materials removed from required excavation areas will be utilized in the formation of the embankments, access ramps, haul roads, and as backfill. Excess suitable excavated soils and unsuitable excavated soils will be disposed of in a disposal area provided by the local sponsor or by the construction contractor.
Debris and refuse materials removed as part of the channel widening work or from other required excavations will be disposed of by the construction contractor. The construction contractor will be required to follow all federal, state, and local regulations when disposing of these materials.
108 6. ALTERNATIVE PLANS EVALUATION AND COMPARISON
6.1 METHODS OF EVALUATING A SUCCESSFUL FLOOD RISK MANAGEMENT PLAN Within the Corps’ planning process, four accounts have been established to facilitate the evaluation of alternative plans. The accounts include:
National Economic Development (NED) Account Environmental Quality (EQ) Account Regional Economic Development (RED) Account Other Social Effects (OSE) Account
6.1.1 The NED Account A candidate for becoming a successful flood risk management plan is one that meets the stated objectives for resolving the flood problem and is economically feasible and has a benefit to cost ratio of greater than 1.0. A successful plan must be affordable to the local sponsor and meet its goals for flood damage reduction. Additionally, it must not create environmental or other problems that cannot be economically mitigated. The Corps is required to define the National Economic Development (NED) Plan when evaluating and comparing alternative plans. The NED Plan has the greatest net economic benefits.
Economic costs and benefits resulting from a project are evaluated in terms of their impacts on national wealth, without regard to where in the United States the impacts may occur. National Economic Development (NED) benefits must result directly from a project and must represent net increases in the economic value of goods and services to the national economy, not simply to a locality. For example, if a flood interrupts auto production at a plant in one community, that community suffers a loss. But if the affected company replaces the interrupted production at another plant in another city, the community’s loss does not represent a net loss to the national economy, and the prevention of such a loss cannot be claimed as a NED benefit.
NED costs represent the costs of diverting resources from other uses in implementing the project, as well as the costs of uncompensated economic losses resulting from detrimental effects of the project. NED benefits, the benefit-cost ratio, and the net NED benefits are calculated during the evaluation process. Net benefits represent the amount by which the NED benefits exceed NED costs, thereby defining the plan’s contribution to the nation’s economic output. The plan with the highest net benefits is often considered to be the recommended plan, assuming technical feasibility, environmental soundness, and public acceptability. Note that the plan with highest net benefits is not necessarily the plan with the highest benefit-cost ratio. The benefit-cost ratio helps identify which plans have likely economic feasibility and can be carried forward for further analysis, but is not decisive in identifying the NED plan from among those plans that are economically feasible.
6.1.2 EQ, RED and OSE Accounts While the NED Account is primary in the plan formulation process for flood risk management studies, the EQ, RED and OSE Accounts must be taken in consideration in quantitatively and qualitatively formulating alternative plans. Projects are required to be formulated with
109 consideration of the environment (EQ) to avoid, minimize or mitigate adverse impacts. Additionally, there are often opportunities for ecosystem restoration, which can be incorporated into a flood risk project, at little additional cost. Regional economic (RED) factors are especially important in less populated states like Nebraska, where facilities such as hospitals and commerce are located at great distances. Other Social Effects (OSE) are important to community acceptance of a project, quality of life and community cohesion once a project is implemented. Additional discussion of the recommended plan and the four accounts is provided in Section 7. Environmental consequences are described in detail in Section 8.
6.2 COMPARISON OF ALTERNATIVE PLANS The principal unit of measure for comparing successful flood risk management plans is the comparison of net benefits. The comparison is performed on alternative plans that have been evaluated based upon meeting project objectives and have been found to be cost effective. Projects that have the largest net benefits are favorable solutions. A locally preferred plan also must be affordable to the project sponsor. The local sponsor may also have additional criteria that may influence the selection of a recommended plan. Plans that preserve the unique nature of the community and do not impinge upon the community “livability” are favored over those that are disruptive, when the estimated net benefits are not significantly different.
One of the criteria stated by the city of Schuyler is that the project alternatives along the Platte River reduce the Special Flood Hazard Area (SFHA) as much as possible, which would require that the levees be certified as meeting the National Flood Insurance Program (NFIP) requirements for providing protection from the base (1% annual chance, or 100-year) flood. The requirements for levees to be recognized by the Federal Emergency Management Agency (FEMA) as providing protection from the base flood are given in the Code of Federal Regulations, Title 44, Section 65.10. The levee alternatives under consideration have been formulated to meet the FEMA certification requirements.
6.2.1 Nonstructural Flood Damage Reduction Alternative In the initial phase of the feasibility study, a site reconnaissance was conducted in combination with the economic analysis to identify areas of potential nonstructural alternatives with frequent flood damages. The cost of implementing nonstructural measures was evaluated using structure detail from Schuyler and estimates of construction costs. The concentration of many structures in the floodplain and the relatively expensive solutions resulted in the nonstructural measures being less adequate than other measures. Specifically, the presence of large high value structures in the central business district and also the local high school would be very expensive to flood proof, or to protect using individual ring levees. In addition to the cost issues relative to the NED Account, the impact on the community of flood proofing many structures or a proliferation of ring levees was determined to be unfavorable based on the OSE Account.
6.2.2 Screening Structural Flood Damage Reduction Alternatives Four Shell Creek structural flood risk management plans and three Platte River structural flood risk management plans advanced to detailed analysis. Since the Platte River and Shell Creek plans are independent for the 100-year flood, and floods less severe, two sets of comparisons were run; one for the Shell Creek alternatives and another for the Platte River alternatives.
110 6.2.2.1 NO ACTION ALTERNATIVE While the “No Action” alternative would not meet the planning objectives of this study, it is considered as part of the USACE planning process. Taking “No Action” would not reduce the potential for loss of human life or the potential for extensive flood damage to Schuyler. The need for subsidized federal flood insurance through the National Flood Insurance Program (NFIP) within the existing floodplain would still be required by residents and business owners. The “No Action” alternative would also rely on volunteerism from the community to combat future flood events. Without the implementation of a federal project the city of Schuyler will continue to have an associated risk of possible high flood damages. The “No Action” alternative is the future- without-project condition, and as such, represents the baseline to which all other alternatives are compared.
6.2.2.2 SHELL CREEK ALTERNATIVES SCREENING The implementation of the Shell Creek project alternatives were found to “solve” the economic problem of damages from Shell Creek flooding to varying degrees of success. While none of the alternatives totally eliminated all potential for the Shell Creek damages, the four final alternatives came close. The results of the analysis are provided in Table 6-1 as follows.
111 Table 6-1 NED Account: Benefits and Cost Summary, With-Shell-Creek Project Alternatives
(FY 2011 Prices, $1,000; 50-year period of analysis; 4.125 percent interest rate) AVERAGE ANNUAL BENEFICIAL IMPACTS SC-A SC-B SC-C SC-E Inundation Reduction Benefits 1. Physical Damages Reduced $733.90 $692.51 $731.47 $733.91 2. Public/Emergency Costs Reduced $62.57 $55.48 $62.47 $62.46 3. NFIP Administrative Costs Reduced $34.78 $34.78 $34.78 $34.78
TOTAL ANNUAL BENEFITS $831.26 $782.77 $828.72 $831.15
PROJECT COSTS: SC-A SC-B SC-C SC-E Project Investment, First Costs: 1. Construction Costs $2,736.87 $1,844.21 $2,089.53 $2,467.80 2. Construction Contingency Costs $745.80 $502.55 $569.40 $672.47 3. Planning, Engineering and Design (PED) Costs $246.32 $165.98 $188.06 $222.10 4. Supervisory and Administrative Costs $164.21 $110.65 $125.37 $148.07 5. Lands and Damages (LERRD) $340.40 $294.65 $291.10 $315.61 6. LERRD Contingency Costs $159.50 $158.60 $157.82 $159.00 7. Habitat Mitigation Costs $25.83 $25.83 $29.04 $29.04 8. Induced Damages Mitigation Costs $283.80 $283.80 $283.80 $283.80
Subtotal, First Costs $4,702.73 $3,386.28 $3,734.12 $4,297.89 Subtotal, IDC $135.18 $100.37 $109.15 $124.18 Total Present Value (PV) Investments $4,837.91 $3,486.65 $3,843.27 $4,422.07
Total Annualized Investment Cost (Total PV Investments, discounted 50 yrs @ 4.125%) $230.05 $165.79 $182.75 $210.27 Annual OMRR&R Cost $10.00 $10.00 $10.00 $10.00
TOTAL ANNUAL PROJECT COSTS $240.05 $175.79 $192.75 $220.27
NET ANNUAL BENEFITS$ 591.21 $ 606.97 $ 635.96 $ 610.88 Benefit Cost (B/C) RATIO 3.46 4.45 4.30 3.77
6.2.2.3 PLATTE RIVER ALTERNTIVES SCREENING The implementation of the Platte River project alternatives were found to “solve” the economic problem of damages from Platte River and Lost Creek flooding to varying degrees of success. While none of the alternatives totally eliminated all potential for damages, the three alternatives solved the majority of the flooding problem. The results of the analysis are provided in Table 6- 2 as follows.
112 Table 6-2 NED Account: Benefits and Cost Summary for With-Project Alternatives
Platte River Side, Schuyler, NE (FY 2011 Prices, $1,000; 50-year period of analysis; 4.125 percent interest rate) AVERAGE ANNUAL BENEFICIAL IMPACTS PR-A PR-B1 PR-B2 Innundation Reduction Benefits 1. Physical Damages Reduced $ 836.11 $ 834.67 $ 834.67 2. Public/Emergency Costs Reduced $ 135.08 $ 135.21 $ 135.21 3. NFIP Administrative Costs Reduced $ 93.91 $ 91.03 $ 91.03
TOTAL ANNUAL BENEFITS$ 1,065.10 $ 1,060.91 $ 1,060.91
PROJECT COSTS: PR-A PR-B1 PR-B2 Project Investment, First Costs: 1. Construction Costs:$ 3,846.97 $ 4,287.07 $ 4,127.13 2. Construction Contingency Costs$ 1,048.30 $ 1,169.91 $ 1,126.33 3. Planning, Engineering and Design (PED) Costs$ 346.23 $ 392.58 $ 378.18 4. Supervisory and Administrative Costs$ 230.82 $ 261.72 $ 252.12 5. Lands and Damages (LERRD)$ 473.00 $ 866.63 $ 551.63 6. LERRD Contingency Costs$ 162.93 $ 167.00 $ 160.70 7. Habitat Mitigation Costs$ 25.85 $ 28.24 $ 28.24
Subtotal, First Costs$ 6,134.10 $ 7,173.16 $ 6,624.35 Subtotal, IDC $ 170.38 $ 205.33 $ 184.53 Total Present Value (PV) Investments$ 6,304.48 $ 7,378.49 $ 6,808.88
Total Annualized Investment Cost (Total PV Investments, discounted 50 yrs @ 4.125%)$ 299.78 $ 350.85 $ 323.77 Annual OMRR&R Cost$ 15.00 $ 15.00 $ 15.00
TOTAL ANNUAL PROJECT COSTS$ 314.78 $ 365.85 $ 338.77
NET ANNUAL BENEFITS$ 750.32 $ 695.06 $ 722.14 Benefit Cost (B/C) RATIO 3.38 2.90 3.13
6.3 ENVIRONMENTAL QUALITY (EQ) CONSIDERATIONS The primary EQ considerations related to implementation of the build alternatives include potential effects to Platte River endangered species, impacts to vegetation, particularly trees and shrubs, and potential impacts to wetlands or other waterways. Details regarding the effects of the build alternatives on these and other environmental resources are provided in Section 8 of this report and the Biological Assessment (BA) and Section 404(b) (1) Assessment provided in Appendix A. None of the build alternatives are expected to have significant environmental consequences.
All of the alternatives were designed to avoid impacts to the environmental resources described in this report. Of specific note, impacts to wetlands and other waters of the United States were completely avoided by the Shell Creek Alternatives. Clearing and grubbing of trees along the lower portion of Neiman ditch and removal of an agricultural levee and associated trees and shrubs along Shell Creek would take place outside of the ordinary high water mark. The Shell
113 Creek levee alignments were set back from the upper portions of Neiman ditch to avoid impacts to wetlands associated with Neiman ditch.
Potential negative impacts to listed species associated with the Platte River were avoided by siting the proposed levee alignments outside of the Platte River floodway. Avoidance of construction in the floodway should limit or eliminate the impact on the channel-forming velocity of the river and the sandbar and shallow water habitat critical to threatened and endangered species. The levees would be located approximately 1.5 miles north of the Platte River. Therefore, these structures would have little or no impact on the channel forming velocities of the river during a flood either individually or cumulatively; and therefore impacts to threatened and/or endangered species from implementation of any of the build alternatives would be negligible. See the Biological Assessment in Appendix A for a detailed discussion of impacts to threatened and endangered species.
The Platte River alignments were designed to avoid impacts to the Lost Creek Riparian corridor west of Highway 15. Impacts to trees and shrubs would result from the Shell Creek and Nieman Ditch cleanouts, abandoned railroad embankment removal, and levee alignment encroachment. Removal of trees and shrubs could potentially adversely affect wildlife and the water quality of adjacent streams; however, effects are designed to be minimized by scheduling tree and brush removal to occur outside of the primary nesting season of migratory birds.
Wetland impacts would be avoided by all of the build alternatives with the exception of Alternative PR-A which would impact 0.37 acres of reed canarygrass (Phalaris arundinacea) wetlands. Estimated impacts from implementing the various alternatives are outlined in Table 6- 3 below.
Table 6-3 Impacts to Upland and Wetland Vegetation
Alternative No Action Shell Shell Shell Shell Platte Platte Platte Creek Creek Creek Creek River River River SC-A SC-B SC-C SC-E PR-A PR-B-1 PR-B2 Trees and 5.02 5.02 9.02 9.02 10.88 13.73 13.73 Shrubs 0 acres acres acres acres acres acres acres
Wetlands 0.37 0 0 0 0 0 0 0 acres
Additional EQ considerations included minimizing the amount and length of stream crossings associated with each of the alternatives. Gatewell structures proposed under Platte River Alternative PR-A were designed to minimize impacts to the physical substrate by designing the gatewell structures to maintain the current substrate elevation and to allow the re-establishment of natural substrate in the bottom of the structures. Changes to the physical movement of water in Lost Creek and Shonka ditch were minimized under PR-A by siting the levee crossings at perpendicular angles to the channels, thereby minimizing the length of channel routed under the levee. Gatewell structure design is also intended to maintain passage for fish and other aquatic organisms. Inlets and outlets for the structures would be placed at the existing elevations of the
114 streambed. Sediment would cover the bottom of the structures, maintaining a natural substrate and thereby maintaining connectivity for the movement of fish and other aquatic life. A mitigation plan has been developed (Appendix A) for impacts to resources that could not be avoided.
6.4 OTHER SOCIAL EFFECTS (OSE) CONSIDERATIONS The Platte River B Alignments have greater impacts relative to Alignment A, in the OSE account. Constructing either of the B Alignments would result in the death of many mature trees along Higgins Drive, an entrance to the city park, which are considered part of the character of the community. The Boy Scout cabin, a feature of that portion of the park, would also have been impacted by the “B Alignments.” Additionally, the route of the B Alignment would have the greatest negative impact during construction and upon completion to utilities, city facilities and services. In contrast, Alignment A has positive impacts on recreational opportunities such as preserving mature trees and providing for hiking and bicycling use of the inspection road on the levee crest. Alignment A would also not separate the north and south areas of South Park,
Impacts to prime farmland would result from converting prime farmland to nonfarm land uses through construction of the levee. Impacts from the build alternatives would affect a relatively minor amount of prime farmland compared to the amount of prime farmland existing in the project vicinity (see Table 6-4).
Table 6-4 Impacts to Prime Farmland
Alternative No Action Shell Shell Shell Shell Platte Platte Platte Creek Creek Creek Creek River River River SC-A SC-B SC-C SC-E PR-A PR-B-1 PR-B2 Prime 0 6.52 11.51 14.74 9.61 4.8 10.32 43.79 Farmland acres acres acres acres acres acres acres
6.5 MITIGATION OF IMPACTS FROM PROJECT ALTERNATIVES
6.5.1 Base Flood Elevations In areas where levees are constructed, the flows that previously spread out across the entire floodplain are restricted by the levees into a smaller flow area and the flood elevation profiles for various flood events may increase. These higher project-induced flood stages may result in project-induced flood damages to buildings not protected by the levees. The rules of the NFIP allow induced stages of less than 1 foot for the base flood as the result of development in the 100-year floodplain outside of the regulatory floodway.
The hydraulic model developed for the feasibility study indicates that the amount the increase in the 1-percent annual chance flood elevations on the exterior of the Shell Creek and Platte River Levees should be less than 0.5 feet. During the design phase the pre-project and with-project flood elevations and extent of flooding will be determined for the 1-percent-chance and lesser floods using more detailed topographic data that has become available to review the need for
115 potential mitigation. If mitigation is found to be required, during further review in design, the cost of the mitigation is anticipated to be small in comparison with other costs and will not impact the outcome of the feasibility evaluation nor plan selection.
6.5.2 Environmental Mitigation Considerations Environmental mitigation would be similar in scope for all of the build alternatives. No significant environmental effects would be expected under implementation of any of the build alternatives; therefore, the scope of environmental mitigation that would be required to offset impacts would also be less than significant. All of the build alternatives impact trees and shrubs although tree and shrub impacts are greatest under Alternatives SC-C, SC-E, PR-B1, and PR-B2. Alternative PR-A is the only alternative that would require wetland mitigation. Implementation of this alternative would impact 0.37 acres of reed canarygrass (Phalaris arundinacea) wetlands. Wetland mitigation would be accomplished by lowering the Shell Creek cleanout bench near the Shell Creek and Nieman Ditch confluence to provide wetland hydrology. A detailed mitigation plan is provided in Appendix A. The mitigation required from implementation of any of the build alternatives would be similar in scope and cost.
6.6 PLAN SELECTION PROCESS
6.6.1 Shell Creek Plan Selection The selected Shell Creek flood risk management plan (Alternative SC-C) was found to be the National Economic Development (NED) plan. It had net annual benefits approximately 4% higher than its next challenger, which was Alternative SC-E. Differences between the alternatives, based upon the other three accounts of the Corps’ Planning Guidance, were not determined to be large enough to alter the order of ranking between the Shell Creek plans. Alternative SC-C ranked comparably with the second ranked NED plan, based upon the Environmental Quality (EQ) Account (note Table 8.1) and the Regional Economic Development (RED) Account. The second ranked alternative, SC-E, is likely more favorable based on the Other Social Effects (OSE) Account than is Alternative SC-C. From a local perspective, Alternative SC-E offered greater protection from groundwater infiltration, due to its further setback from utilities and housing and also provided more room for cohesive community expansion. As noted in Table 8-2, Alternative SC-E was also less disruptive to prime farmland, including a current center pivot operation.
6.6.2 Platte River Plan Selection The selected Platte River flood risk management plan (Alternative PR-A) was found to be the NED plan. It had net annual benefits approximately 4% higher than its next challenger, which was Alternative PR-B2. Differences between the alternatives, based upon the other three accounts of the Corps’ Planning Guidance, were not determined to be large enough to alter the order of ranking between the Shell Creek plans. In fact, the OSE Account ranking was deemed less favorable for Alternatives PR-B1 and PR-B2 than for Alternative PR-A, due to the disruptive influence that the PR-B alternatives would have on Schuyler City Park, adjacent areas of the city and a historic building. Additionally, Alternative PR-A was also found to be more favorable from an EQ Account standpoint (Table 8-1) and similar to the PR-B alternatives from an RED Account basis.
116 7. RECOMMENDED PLAN
7.1 PLAN DESCRIPTION 7.1.1 Shell Creek Plan Description
The recommended Shell Creek flood risk management plan is the final configuration of Alternative SC-C, which is shown on Plate 14. This alternative protects northeastern Schuyler from Shell Creek floods, which have been frequent and destructive. Flood damage risk reduction from this alternative extends from near Highways 15 on the north side of Schuyler to east of the Husker COOP near the Union Pacific Railroad tracks. Interior drainage through the levee will be accomplished using one 72-inch RCP gatewell structure located near the downstream end of the levee. Exterior flooding will also be addressed by a reshaping of Shell Creek. The reshaped section of Shell Creek will feature a flood terrace which will be planted to native grasses and forbs.
7.1.2 Platte River Plan Description The recommended Platte River flood risk management plan is Alternative PR-A, which is shown on Plate 7. This plan offers flood risk reduction Schuyler south of the Union Pacific Railroad tracks, including the downtown area from floods greater than the 100-year (1% annual chance of exceedance) event. Flood risk reduction from this alternative also protects northern Schuyler from extreme Platte River floods that significantly exceed the 100-year event that could pass through the railroad embankment and cause shallow flooding in the north part of the city. Flood damage risk reduction extends from County Road 10 on the west to the northern sewage treatment lagoons southeast of Schuyler. Areas with reduced risk of flood damage includes the City Park, golf course and additional residential property in Colfax County outside of the corporate limits.
Lost Creek will be routed through the protected area by means of a gatewell, which will meter the flow of this stream through the community to discharges acceptable to the city during times of flood, yet adequate to nourish existing wetland communities. Control of Lost Creek will also reduce groundwater flooding of basements in southern Schuyler, which presently occur during prolonged periods of high flows on Lost Creek, either from Platte River flooding or from storm runoff within the Lost Creek basin. Interior drainage facilities within the city will continue to discharge storm water runoff to Lost Creek with no change resulting from the project.
Highway 15 may cross the levee as a road raise near Windmill Cove Road, or it may be configured as a closure structure, pending more analysis in the Design Phase. Interior drainage is generally towards Lost Creek along the length of the levee, negating the need for culverts and gatewells for that purpose. Sandy soils limit the ponding of runoff in most areas, but surveys during design will be used to identify and develop measures for any poorly-drained areas within the levee. Exterior flooding near the levee will be mitigated by the removal of much of the old abandoned railroad embankment presently located south of Lost Creek and east of Highway 15. In addition, both Shonka Ditch and Lost Creek flood overflows will be routed along the exterior toe of the levee, eastward under Highway 15 through a 15 foot by 7 foot box culvert. The exterior flood control channel will be planted to native grasses and forbs, appropriate to the
117 hydrologic and hydraulic conditions of the channel. Right-of-way along the exterior ditch will also be planted to native plant varieties. The exterior flood flow will return to Lost Creek near the city sewage lagoons. The final configuration of the trailing levee will be determined early in design once survey data of greater detail is obtained. It is noteworthy that 0.34 acres of reed canarygrass (Phalaris arundinacea) wetlands would be impacted in this area. A conceptual mitigation plan is provided in Appendix A that would be implemented if impacts to these wetlands cannot be avoided in final design.
7.2 COMPLIANCE OF SELECTED PLAN WITH THE PRINCIPLES AND GUIDELINES (P&G)
7.2.1 Flood Risk Management Principles and Guidelines A requirement of the Principles and Guidelines for flood risk management studies is the pursuit of the National Economic Development (NED) Plan. Contributions to NED are the direct net benefits that accrue in the planning area and the rest of the Nation, irrespective of location within the country. The NED plan is the plan with the highest net NED benefits (but not necessarily the highest benefit-cost ratio), which is otherwise “engineeringly feasible,” environmentally-sound and publicly acceptable (IWR, 1988).
Within all flood risk management studies conducted by the Corps of Engineers, alternative flood risk management plans are formulated in consideration of four criteria: completeness, effectiveness, efficiency and acceptability. 1. Completeness is the extent to which a given alternative plan provides and accounts for all necessary investments or other actions to ensure the realization of the planned effects. This may require relating the plan to other types of public or private plans if the other plans are crucial to realization of the contributions to the objective. 2. Effectiveness is the extent to which an alternative plan alleviates the specified problems and achieves the specified opportunities. 3. Efficiency is the extent to which an alternative plan is the most cost-effective means of alleviating the specified problems and realizing the specified opportunities, consistent with protecting the nation’s environment. 4. Acceptability is the workability and viability of the alternative plan with respect to acceptance by state and local entities and the public as well as compatibility with existing laws, regulations and public policies.
Additionally, guidance recognizes other types of potential project effects that stakeholders may view as important for civil works planning. Accordingly, the P&G has established four “accounts” to represent different categories of plan effects, that are described as follows (IWR, 2009): 1. The national economic development (NED) Account displays changes in the economic value of the national output of goods and services that result from a project. 2. The environmental quality (EQ) Account displays non-monetary effects on ecological, cultural and aesthetic resources including the positive and negative aspects of ecosystem restoration plans resulting from a project. 3. The regional economic development (RED) Account displays changes in the distribution of regional economic activity (e.g., income and employment) following project implementation.
118 4. The other social effects (OSE) Account displays plan effects on social aspects, such as community impacts, health and safety, displacement, energy conservation and others.
7.2.2 Application to Recommended Plans for Schuyler
7.2.2.1 SHELL CREEK The recommended plan to combat future flooding from Shell Creek is Alternative SC-C, shown on Plate 14. The recommended alternative for risk management from Shell Creek provides the best overall plan related to the P&G.
The selected Shell Creek alternative meets the planning goals and objectives and captures stated opportunities. By providing 100-year (1% annual chance of exceedance) flood risk management including a contingent overtopping design margin, Shell Creek Levee Alternative SC-C will reduce flooding to northeastern Schuyler and allow this area to be taken out of the regulatory 100-year floodplain. This will remove the need for and the requirement to have flood insurance. The frequent property damage now plaguing northeastern Schuyler will be become much more unlikely, and this will reduce health and safety problems associated with frequent flooding. In addition, the reshaping of the channel downstream of the levee may provide incidental flood damage reduction to the Union Pacific Railroad and a location where native riparian vegetation can be restored.
While residual risk of flooding exists on any completed project, the risk of levee overtopping is extremely unlikely, due to the nature of the adjacent Shell Creek floodplain. Specifically, before flood depths could increase substantially at the levee, discharge will exit the area near Schuyler to the east across the broad floodplain, following the general slope of the valley. In addition, the delivery of substantially larger instantaneous peak discharges to the levee by Shell Creek is precluded by the loss of peak flow to Rawhide Creek and the man-made drainage ways that are located upstream of the Highway 30 Expressway. The inability to deliver significantly larger discharges to the levee, coupled with the inability of water to pond to much greater depths outside of the levee, greatly reduces the residual risk following implementation of the selected plan.
Potentially the largest source of risk during an extended Shell Creek flood would arise from levee maintenance issues, rather than hydrologic overtopping. Good levee maintenance practices, including controlling burrowing animals and tree growth on the levee, can help minimize residual risk.
7.2.2.2 PLATTE RIVER The recommended plan to combat future flooding from the Platte River and adjacent Lost Creek is Alternative PR-A, shown on Plate 7. The recommended plan for risk management from the Platte River provides the best overall plan related to the P&G.
Placement of the levee further south of the residential areas along Lost Creek, and controlling Lost Creek and Shonka Ditch flows reduces the groundwater inflow to basements and the city’s
119 storm sewer system, which result from rapid charging of the shallow groundwater table through the highly permeable soils as demonstrated during the Lost Creek flood of 2010. Even greater damage would likely occur from a long-duration Platte River ice jam flood. Flood stages maintained for more than a day during the 2010 Lost Creek flood did extensive damage to the city’s South Park and other public facilities in southern Schuyler. Providing greater potential protection against subsurface problems, which impact health, safety and community functionality, also demonstrated greater effectiveness and was more acceptable to the community. Additionally, the golf course is a significant source of city revenue, and this facility has been damaged and placed out of service during Platte River and Lost Creek floods.
Placement of the levee further south of the city also improves community cohesion by including the neighborhoods south of South Park Road. The Platte River B Alignments also did very poorly relative to Alignment A, in the OSE Account for community impact. Constructing either of the B Alignments would result in the death of many mature trees along Higgins Drive, an entrance to the city park, which are considered part of the character of the community. The Boy Scout cabin, a feature of that portion of the park, would also have been impacted by the B Alignments.” Additionally, the route of the B Alignment would have the greatest negative impact during and after construction to utilities, city facilities and services. In contrast, Alignment A has positive impacts on recreational opportunities such as preserving mature trees and providing for hiking and bicycling use of the inspection road on the levee crest. Alignment A will also not separate the north and south areas of South Park.
For the Platte River B Alignments, concern about constructability and cost overruns were voiced by the study team and the sponsor due to the potential for large amounts of buried rip-rap near the Oak Ballroom, which would have to be removed prior to driving sheet pile for the floodwall along Lost Creek. From the inception of the initial assessment through the public involvement and stakeholder meetings in feasibility, Alignment A has drawn consistent community support, while the B Alignments have generated no support and significant opposition. Alternative PR-A was selected after consideration of the four criteria and the four accounts. The city of Schuyler also voiced strong support for this plan.
The selected Platte River Plan meets the planning goals and objectives and captures the stated opportunities. By providing much more than 100-year flood risk management using a contingent overtopping design margin, Platte River Levee Alternative PR-A will stop conceivable flooding to southern Schuyler, including the central business district, and allow this area to be taken out of the regulatory 100-year floodplain. This will remove the need for and requirement to have flood insurance. Additionally, removal of much of the old railroad embankment south of Lost Creek, coupled with exterior drainage features along the outside of the levee, will reduce flood stages south of the levee alignment. As low and moderate discharges will continue to flow through the water control structures on Lost Creek and Shonka Ditch, the riparian habitat along this stream can be maintained and improved where opportunities are present.
While residual risk of flooding exists on any completed project, the risk of levee overtopping is not large, due to the width of the adjacent Platte River floodplain. Before flood depths could increase substantially at the levee, a flood discharge would have to fill the entire Platte River valley, deep into Butler County. Potentially the largest source of risk during an extended Platte
120 River flood would arise from levee maintenance issues, rather than hydrologic overtopping. Good levee maintenance practices, including controlling burrowing animals and tree growth on the levee, can help minimize residual risk.
7.3 OPERATION AND MAINTENANCE (O&M) CONSIDERATIONS The selected plans for Shell Creek and Platte River flood risk reduction feature road raises as integral components, rather than closure structures. The advantage of road raises over the closure alternative is less risk and a considerable savings in operations and maintenance costs. O&M costs associated with a road closure structure include the maintenance of the panels, the storage shed, and the mounting facilities in the road and on the road right-of-way themselves. The mounting facilities are a significant O&M cost by themselves, as wear and tear on the road, especially snowplows tend to destroy them after a few years.
Road closure structures involve actions that must be taken before the arrival of a flood to complete the levee’s functional design and may require the installation of a flood warning system, which would add additional O&M costs. Use of a road raise if determined acceptable from a traffic safety standpoint, would reduce the complexity of the flood damage reduction system’s application as well as maintenance costs. The potential changes to O&M are not of sufficient magnitude that they would impact project cost viability, nor would they alter the plan selection.
In general, O&M costs associated with the selected plans will be those associated with the PL- 84-99 Program, and principally consist of mowing, controlling rodents, volunteer trees and reducing erosion. An Operation and Maintenance Manual will be provided to the local sponsor upon completion of the project.
If O&M is performed regularly, annual costs should be much lower. This can entail regular mowing, spraying, replacing gravel, removing trees, eradicating rodents, and repairing burrows. On the Platte River side, there are gatewell structures that will need maintenance, such as lubrication and testing so that they will perform as designed. The performance of O&M activities is contingent on the diligence of the community, the available tax base and follow-up from the Corps. If O&M is not done regularly over the life of the project, the result can be costly repairs. The estimated annual cost for O&M can range from $2,000 - $5,000 per mile. Because of the uncertainty involved, the O&M for Schuyler was estimated on the high end of this range. As such, O&M is estimated at $10,000 for the approximately 2-mile Shell Creek levee and $15,000 for the approximately 3-mile Platte River levee.
7.4 ENVIRONMENTAL FEATURES AND MITIGATION Implementation of the recommended Alternatives PR-A and SC-C would cause impacts to trees and shrubs, grasslands, and wetlands. Impacts to reed canarygrass (Phalaris arundinacea) fringe wetlands and roadside ditch cattail (Typha latifolia) wetlands have been almost completely avoided. Alternative PR-A is the only alternative that would require wetland mitigation. Implementation of this alternative would impact 0.37 acres of reed canarygrass (Phalaris arundinacea) wetlands. Wetland mitigation would be accomplished by lowering the Shell Creek cleanout bench near the Shell Creek and Nieman Ditch confluence to provide wetland hydrology.
121 The wetland mitigation feature is essentially a modification of the already planned Shell Creek cleanout near the Shell Creek Nieman Ditch confluence. This plan is detailed further in Appendix A, Biology.
The levee alignments avoid and minimize impacts to trees and shrubs to the extent practicable. The Shell Creek cleanout, lower Nieman Ditch cleanout, and the removal of the abandoned railroad embankment are designed to improve flow and alleviate flooding. These features have been determined to be necessary components of the project. Combined, these features account for 85% (16.91 acres of the 19.90 acres), of tree and shrub impacts. Because of seepage concerns, trees and shrubs cannot be planted on a levee or a levee right of way. Additionally, the tree and shrub removal along Nieman Ditch and the left bank of Shell Creek north of the UPRR line is designed to improve flow and alleviate flooding. Because of these constraints and the relative availability of in-kind tree and shrub habitat in the vicinity of the impact sites, creation of on-site out-of-kind habitat of a greater floristic quality is proposed.
The Corps proposes to create 12.75 acres of tall-grass prairie buffer along Shell Creek and plant 69.24 acres of native prairie grasses on the levee and levee right-of-way to compensate for vegetation impacts. This equates to a roughly 4:1 mitigation to impact ratio. All impacts would be mitigated within the construction footprint. More details on the mitigation are provided in the Biological Assessment in Appendix A.
7.5 RECREATIONAL FEATURES No separable recreational features are currently incorporated in the feasibility-level project design. The recommended Alternatives SC-C and PR-A may offer incidental recreational benefits, principally in the form of use of a levee project feature (the gravel inspection road on the levee crest) as hike/ bike trails that may be used to connect existing features in Schuyler.
The Platte River levee, in particular, offers the potential for a hiking/biking trail that could be used to connect features in southern Schuyler. At the Lost Creek water control structure, the levee is adjacent to the city golf course. The levee running northwestward from that point will approach the intersection of County Road D and County Road 10. A hike/ bike trail along this levee segment would provide off road access to the city park from the western edge of town. To the east, the levee will run eastward, to the eastern city limits at the sewage lagoons. Before reaching the lagoons, the levee will pass about 0.25 miles south of the soccer fields built upon the old landfill. At some future time after the Corps project is completed, and if the city has the desire and funding, a trail extension north, combined with a pedestrian foot bridge over Lost Creek, could link the city park to the soccer fields. The design requirements for a Lost Creek footbridge in that location would be simplified by the fact that flood flows would be controlled by the levee and water control structure to be located upstream.
7.6 REAL ESTATE AND LERRD CONSIDERATIONS The sponsor will receive credit for the fair market value of the minimum estates identified for the construction, operation, and maintenance for the project. Any proposed project design that impacts property owned by the Union Pacific Railroad (UPRR) will require extensive
122 coordination with UPRR. The project schedule must include a significant amount of time for the sponsor to negotiate the necessary railroad requirements.
Some relocation of utilities (i.e. gas lines, electrical lines, phone lines, and fiber optic cables) may be necessary, depending on the final footprint of the measure selected. It is likely that any footprint will require relocation of power poles.
Preparation of a gross appraisal is required to document the costs of all lands required for the project footprint. The gross appraisal provides the basis for the baseline cost estimate which is included in the real estate plan. The gross appraisal must conform to the Uniform Appraisal Standards for Federal Land Acquisitions. The gross appraisal for this study was initiated in March 2011 and revised and completed in June 2011. The local sponsor will hire an appraiser to conduct the tract appraisals following the completion of the feasibility study and the initiation of the design and implementation phase. The appraiser must be preapproved by the Omaha District Real Estate Division Chief Appraiser.
A preliminary real estate project map will be prepared based on the project design footprint. A real estate project map, clearly delineating each estate required for acquisition and containing the minimum information/criteria is prepared during the feasibility study. The map must define the individual tract ownerships and types of estates. The map will be prepared from the legal descriptions submitted by the sponsor. The final real estate project map will use the legal descriptions of the sponsor’s acquisition deeds to verify the sponsor’s ownership of the required lands for the project.
The sponsor will provide surveys, legal descriptions, and tract appraisals of lands required by the final project design to USACE Omaha District Real Estate Division after the project footprint is established and the Project Partnership Agreement (PPA) has been executed. The sponsor will comply with Public Law 91-646 upon receiving approval of its tract appraisals and notification to proceed with negotiations to acquire the necessary lands.
An Attorney’s Opinion of Compensability is required to determine if the Corps of Engineers, the local sponsor, or the utility owner(s) is responsible for the cost of relocation or alteration of the utility or facility. An Attorney’s Opinion of Sponsor’s Eligibility is required. This document addresses the sponsor’s land acquisition experience and ability to acquire the properties needed (e.g. quick take authority, manpower, resources, etc.). The Office of Counsel addresses the sponsor’s land acquisition experience and ability to acquire (quick take authority, manpower, resources, etc.).
The real estate and LERRDs for completion of the feasibility phase are defined in the Real Estate Plan. More details can be found in Appendix N, Real Estate.
7.7 COST SHARING AND SPONSORSHIP The project sponsor is the Lower Platte North Natural Resources District (LPNNRD). The LPNNRD will pay 35% of the design and construction cost of the project in conjunction with its local partners. LERRD credit can be used as part of the sponsor’s cost share match in place of
123 cash. The LPNNRD has an inter-local agreement with the city of Schuyler, which in turn, has an agreement with Colfax County.
7.8 DESIGN AND CONSTRUCTION CONSIDERATIONS 7.8.1 Design Following the signing of the PPA, additional design will be needed in preparation for construction. Two-foot contour mapping was used in the feasibility study, and site surveys will need to be obtained to refine feasibility-level designs, given the flat topography in the Schuyler area. Among the design activities anticipated are:
7.8.1.1 SURVEYS Accurate surveys will need to be taken along the levee routes, critical channel locations and at borrow sites.
7.8.1.2 GEOTECHNICAL Soil samples and borings will need to be taken along the levee routes and at the borrow sites.
7.8.1.3 HYDROLOGY AND HYDRAULICS An evaluation of the peak discharges of Lost Creek and Shonka Ditch will need to be completed to define the discharge frequency relationship for the design of the two control structures, the exterior drainage ditch, and the box culvert to be placed under Highway 15.
7.8.1.4 ENVIRONMENTAL Once the final levee plans are determined following updated surveys, coordination with Omaha District Regulatory and the Nebraska Department of Environmental Quality (NDEQ) will be finalized to verify coverage under a Clean Water Act Section 404 permit and to obtain Section 401 Water Quality Certification from the NDEQ.
7.8.1.5 ROAD RAISES AND CLOSURES Once accurate survey information has been obtained, road raises, such as the ones to be constructed on old Highway 30 near Shell Creek and the Highway 15 road raise south of Lost Creek, as well as the gravel road raise southwest of Schuyler, will need to be designed according to Federal Highway Administration guidelines governing traffic safety. Consultation and coordination will be needed with the Nebraska Department of Roads (NDOR) as well as Colfax County, in preparation of those designs. The final dimensions of the vertical curves will be determined through that process early in the design phase. Traffic safety issues that surface with the design effort may result in one or more of the road raises being changed to a closure structure. The construction cost of road raises are estimated to be higher than that of closure structures, thus the change to a closure structure would tend to lower overall project costs, and would not change the order of plans selected. On the Shell Creek levee, all competing plans would require the same change. On the Platte River levee, Alternatives PR-B-1 and PR-B-2 already have the lower cost closure, and the most economical plan has the more costly road raise priced in, so PR-A would widen its lead over the competing Alternatives if the change has to be made.
124 7.8.1.6 SHELL CREEK CHANNEL SHAPING Once accurate survey information has replaced the current elevation information consisting of 2- foot contour mapping, the final dimensions and extent of the lower Nieman Ditch and Shell Creek channel shaping, and the eastward extension of the Shell Creek trailing levee parallel to the Union Pacific rail line will be finalized. Considerations will include optimizing flood conveyance and reducing impacts to adjacent landowners and the environment.
7.8.2 Construction Construction of the project will be contracted through an open bidding process. Construction will be overseen by Omaha District construction management specialists with input from the project development team.
7.9 POST PROJECT COMPLETION ACTIVITIES AND RESPONSIBILITIES A full cost accounting will be required following project completion and will involve an audit of federal and sponsor contributions. A final settlement of cost accounts, as defined in the Feasibility Cost Share Agreement (FCSA) and the PPA, will be made to ensure the fair accrual of all costs.
The local sponsor will be responsible for the operation and maintenance of the project. In order to remain in the PL-84-99 program and maintain FEMA certification of the levee, maintenance tasks will need to be performed to guarantee the operation of the levee and its appurtenant structures. An Operation and Maintenance Manual will be provided to the local sponsor upon completion of the project, which will outline the sponsor’s responsibilities following project completion.
7.10 LEGAL OR POLICY ISSUES, OPTIONS CONSIDERED AND COMPLIANCE No known legal issues surfaced during the course of the Feasibility Study.
7.11 QUALITY REVIEWS The quality review process is governed under the guidelines of EC-1165-2-209 and the programmatic review plan model for Section 103 and 205 Projects. Under those guidelines, a review plan was prepared and approved by Northwestern Division on March 16, 2011.
7.11.1 Levels of Review This feasibility report has undergone several levels of review within the Corps of Engineers, the sponsor and stakeholders prior to submittal to the Northwestern Division office for approval.
The first level of review of this report was by the study team and was conducted using the Dr. Checks reviewing software and the track changes feature in Microsoft® Word. Comments were resolved and a new draft report version prepared that incorporated the changes recommended by the team.
125 The next level of review was the supervisor / subject matter expert review. It also was conducted using a combination of Dr. Checks and track changes. The report and its technical appendices are reviewed for technical and policy compliance accuracy.
The Agency Technical Review (ATR) is the third level of review that is conducted. This review is performed by subject matter experts from outside the district that prepared the report. Individuals selected for the review are chosen according to the approved review plan. This level of review is conducted entirely in Dr. Checks. The report and its technical appendices are reviewed for technical and policy compliance accuracy.
The Alternative Formulation Briefing (AFB) is conducted with the Major Subordinate Command or Corps division and the local sponsor. The division experts and the local sponsor team are provided copies of the report in advance of the briefing. The conclusion of the review is the briefing which is typically conducted by webinar or teleconference, and comments received are incorporated into the feasibility report. A major purpose of this review is to prepare the report for review outside of the Corps, including the public and interagency review.
In many cases, an Independent External Peer Review is required, as noted in Engineering Circular (EC)-1165-2-209. This study was excluded from this level, as noted in the following section.
Public review is the final review step prior to submittal of the report to the division office for approval. The public review period lasts 30 days and involves disclosure of the document to the public, other agencies, stakeholders and the media. A final public involvement meeting is held in the community to answer questions and to determine if any revisions are needed prior to submitting the report for approval.
Report approval is the last step in the process. The division office reviews the report one last time to make sure that the comments produced in the AFB have been incorporated. Additionally, prior to review, the division office reviews the resolution of comments raised during the public review period.
7.11.2 Independent External Peer Review (IEPR) According to the guidance in EC-1165-2-209, an Independent External Review is required where there is a significant threat to life before project implementation, and where a residual threat to life could remain, either from locations in the community that remain unprotected, or if the protective measures were to fail. Since the flooding at Schuyler from both Shell Creek and the Platte River has been damaging to property, but has not posed an immediate threat to life, due to unique hydrologic and hydraulic factors involving both the watersheds and community location, the Omaha District applied for and received a waiver of the requirement for IEPR from Northwestern Division (NWD). Specific points addressed in the request included the very long warning times (many hours to days) that the community has to prepare for flooding and the shallow depths of flow that are produced by the flooding. While the floods have historically been very damaging to property and infrastructure, there has been no record of injuries or
126 fatalities from the flood waters. The exclusion was granted to this study in a memorandum from NWD dated February 16, 2011.
7.12 RISK AND UNCERTAINTY A risk and uncertainty analysis is performed on all levees constructed by the Corps to meet the provisions of EC-1110-2-6067. A risk and uncertainty analysis integrates the uncertainty from the hydrology, hydraulics, economics and other aspects of the project into the plan formulation process. Feasibility study team members select their best estimates for hydrologic, hydraulic and economic parameters used in the analysis and determine their related uncertainty. Using a Monte Carlo procedure, the best estimates and uncertainties are integrated into the result.
The analysis proceeded in the following manner: the discharge-frequency curve and confidence limits, the discharge-rating curve with standard deviations, and stage-damage curve with confidence limits are used as input to the program. Using a random number generator, a flood event frequency is calculated by the HEC-FDA program. The best estimate discharge for that frequency is then determined. Using the probability distribution associated with the discharge- frequency curve, another random number is generated and used to determine the error potential for the best estimate. A value for the discharge with error is determined by adding the error (positive or negative) to the best estimate discharge. Next, the discharge with error is used to calculate the best estimate stage. Using the probability distribution for error, a random number is computed and an error (positive or negative) is calculated. The error and best estimate are added to determine the stage with error. The stage with error is used to compute the best estimate of damage. A random number is generated and an error for the damages calculated. The error and best estimate are added to determine the damage with error for this event.
This step (iteration) is repeated numerous times, replicating years of projected record. During the iterations, the damages are accumulated. This process is done for existing conditions and with-project conditions to determine the economics of the selected plan. More information on the risk and uncertainty analysis can be found in Appendix D, Economics.
In accordance with paragraphs 5. b. (2) and 9. f. (1) of EC-1110-2-6067, the selected levee plans were evaluated using the Monte Carlo analysis in HEC-FDA. The assurance (conditional non- exceedance probability (CNP)) of the levees was determined to be greater than 90% with a minimum of three feet of freeboard for the 100-year (1% annual chance exceedance) flood. Additional risk and uncertainty, specifically related to project cost, are covered in detail in Appendix B, Cost Engineering.
Post-project risk is relatively low for this project, due to the flat landscape and the resultant hydraulic and hydrologic characteristics within the Shell Creek and Platte River floodplains at Schuyler. Additionally, the proposed levee project is relatively complete, as it forms a barrier against flooding for this floodplain community for events more rare than the 100-year (1% annual chance of exceedance) event.
For floods more rare than the 100-year event, stages do not increase rapidly, thus the likelihood of overtopping does not increase rapidly. Despite the small risk of overtopping, risk post project
127 can never be zero as levee interiors may flood by means other than overtopping, in addition to the possibility of levee failure at stages lower than top of levee.
At flood frequencies approaching the 100-year event, Shell Creek begins to spill into other drainage basins upstream of the city, as it leaves the valley and enters the broad Platte River flood plain north of Schuyler (see Plate 1). A significant portion of that trans-basin loss goes to Rawhide Creek, which is historically a tributary to the Elkhorn River. Additional flow is lost from Shell Creek eastward following the general slope of the Platte River valley and is unavailable to pile up against a future Shell Creek levee. Thus, the peak discharge and volume delivered to Schuyler grows more slowly with decreasing chance of annual exceedance, as the percentage of extreme Shell Creek floods lost to the lower basin at Schuyler increases proportionately to the size of the flood delivered from upstream portions of the watershed.
The Platte River valley is also very wide at Schuyler, and as a result, large flood flows and even ice jams can spread out laterally in both directions from the river. While the flattening of the stage-discharge rating and resultant stage-frequency rating on the Platte River is not as pronounced as on Shell Creek above the 100-year event, the expected frequency of overtopping would be extremely infrequent and would exceed recorded historical floods.
The risk of additional costs to the projects due to potential induced damages is also not large, due to the relatively unconfined nature of nature of the flooding at Schuyler. The hydraulic model developed for the feasibility study indicates that the amount the increase in the 1-percent annual chance flood elevations on the exterior of the Shell Creek and Platte River Levees should be less than 0.5 feet, which does not require mitigation according to current interpretation of policy. During the design phase the pre-project and with-project flood elevations and extent of flooding will be determined for the 1-percent-chance and lesser floods using more detailed topographic data that has become available to review the need for potential mitigation. As mentioned in the previous section, the potential maximum increase in the 1-percent –chance flood would be less than 0.5 feet, which does not require mitigation according to current interpretation of policy. There are few structures in the areas where the potential increased stages would occur. Most of the potential induced stages would be to agricultural lands and crops that would already be inundated under existing conditions.
If mitigation is found to be required, during further review in design, the cost of the mitigation is anticipated to be small in comparison with other costs and will not impact the outcome of the feasibility evaluation nor plan selection. The lack of impact on plan formulation is due in part to the large Benefit to Cost ratios found for the Shell Creek and Platte River selected alternatives, which were 4.30 and 3.38 respectively. Additionally, the stage range of induced stages was in a similar range (less than 0.5 feet) for all of the competing alternatives.
7.13 PLAN IMPLEMENTATION AND SCHEDULE It is anticipated that the levee design will take 12 to 13 months. It is anticipated that the construction of the levees will take 18 to 24 months. Seasonal issues favor beginning construction in the fall and ending in early summer. Impacts to nesting and cropping seasons can be avoided by starting clearing, grubbing, and initial grading in the late fall. Completion of final grading and seeding prior to the early summer would allow for optimum seeding and erosion
128 control measures to be employed to reduce erosion, runoff and sedimentation. The implementation schedule is shown in Table 7-1.
Table 7-1 Implementation Schedule
SCHUYLER, NE SECTION 205 PROJECT IMPLEMENTATION SCHEDULE
TASK DATE Complete Feasibility and Sign PPA Sep-2011 Initiate design of both levees Sep-2011 Initiate construction of both levees Sep-2012 Shell Creek levee substantially in place Apr-2013 Complete construction of both levees Jun-2014 Provide O&M Manual Sep-2014
129 8. ENVIRONMENTAL IMPACTS, REVIEWS AND COMPLIANCE
All of the alternatives carried forward for detailed analysis were designed to avoid or minimize impacts to the resources described in this section. The primary avoidance and minimization measures considered during the formulation of the alternative plans were previously described in Section 6.3 of this report. The following sections detail the anticipated remaining environmental consequences that would be expected to occur with implementation of the alternatives. 8.1 ENVIRONMENTAL CONSEQUENCES This Section presents the adverse and beneficial environmental effects of the recommended action and alternatives including the No Action Alternative. The Section is organized by resource category, with the effects of all alternatives combined under each resource category. The effects of the build alternatives are nearly the same for most resource categories except where explained otherwise. The effects of the build alternatives are generally presented first under each resource heading followed by a description of the effects of the No Action Alternative. Cumulative impacts and irreversible and irretrievable commitments of resources are provided as separate sections under this Section. The primary issue related to Platte River effects is related to sandbar geomorphology and endangered species. Additional discussion is included in the endangered species section and in the Biological Assessment included in Appendix A. Impacts are quantified whenever possible. Qualitative descriptions of impacts are explained by accompanying text where used.
Qualitative definitions/descriptions of impacts as used in this section of the report include: Intensity o Negligible – effect is not detectable o Minor – detectable impacts to the resource in the project area, but the resource is still mostly functional o Moderate – the resource is impaired, so that it cannot function normally o Major – the resource is severely impaired so that it is no longer functional in the project area Duration o Short term – temporary effects caused by the construction and/or implementation of a selected alternative o Long term – caused by an alternative after the action has been completed and/or after the action is in full and complete operation
8.1.1 Water Quality The quality of water in Shell Creek, Lost Creek, and Shonka Ditch determines, in large part, what type of aquatic species can survive in these environments. Each of these waterways are assigned the beneficial uses of Warmwater Aquatic life, Agriculture Water Supply, and Aesthetics. Additionally, Shell Creek is assigned the beneficial use of Recreation. Potential temporary adverse effects to water quality from the build alternatives could result from clearing vegetation and spillage of contaminants (mainly fuel) from the construction site into waterways; however, none of these effects are anticipated to affect any of the beneficial uses assigned to
130 these waterways. The primary temporary effects to water quality would result from removal of riparian vegetation during construction.
Riparian vegetation slows water runoff, traps sediment, and intercepts pesticides, pathogens, and heavy metals from entering waterways. Clearing riparian vegetation would cause the temporary loss of the streams’ vegetative buffer which could cause increased water temperatures, increased sediment load and turbidity, and increased fertilizer and pesticide runoff from surrounding agricultural fields. All of these effects would be minor and short term. The fish species found in Shell Creek and Lost Creek are tolerant of high sediment conditions and all of the effects previously mentioned would last only until bare soils can be stabilized and vegetation is re- established.
Spillage of contaminants from the construction site into waterways is a potential effect that would be minor and short term. The Clean Water Act requires preparation and submission of a general stormwater permit and preparation of a Stormwater Pollution Prevention Plan (SWPPP) before construction activities can begin. The SWPPP would be based on best management practices such as seeding and mulching bare slopes as soon as practicable and measures to contain spillage of any contaminants into waterways. In the long term there would essentially be no change to the water quality in these creeks from implementation of any of the build alternatives and none of the beneficial uses assigned to Shonka Ditch, Lost Creek, Shell Creek, or the Platte River would be degraded.
The Lower Platte River-Shell Creek watershed is predominantly agricultural. Under the No Action Alternative, fecal coliform, nitrates, low dissolved oxygen, and high turbidity resulting from Agricultural runoff would continue to limit the aquatic life in these waterways to tolerant species; however, it is anticipated that the previously discussed waterways would continue to meet all beneficial uses.
8.1.2 Wetlands Wetlands on the project site are associated with Lost Creek, Shell Creek, Nieman Ditch, and a roadside drainage ditch that drains to Nieman Ditch. The floristic quality of these wetlands is low, though they may serve to provide many of the same beneficial functions as other riparian vegetation such as filtering pollutants, nutrients, pesticides, trapping sediment, and stabilizing soils as well as providing habitat for wetland obligate species including amphibians and turtles. Wetlands were identified through site visits conducted on August 9th, 2010 and November 2nd, 2010. Wetland boundaries and anticipated impacts were digitized on top of NAIP 2009 aerial imagery using GIS software and verified in the field by examination of dominant vegetation, hydric soil indicators, and hydrology indicators.
Wetland impacts would be completely avoided by all of the build alternatives with the exception of Alternative PR-A which would cause an impact of 0.027 acres of reed canarygrass (Phalaris arundinacea) fringe wetlands through placement of gatewell structures on Lost Creek and Shonka Ditch and 0.34 acres of reed canarygrass (Phalaris arundinacea) wetland impacts associated with the easternmost extent of the PR-A Alternative. A 0.37-acre loss of reed canarygrass (Phalaris arundinacea) wetlands represents a minor impact to the wetland resource in the project area. In the final design stage, efforts will be made to avoid potential wetland
131 impacts. If it is determined that wetland impacts in this area are unavoidable then these wetlands would be mitigated at a 2:1 ratio. The conceptual wetland mitigation plan includes lowering the bench along Shell Creek in selected areas to provide wetland hydrology.
Following is a summary of effects to wetlands and associated channels:
Alternative PR-B o Due to the narrow corridor available for siting the Levee north of Lost Creek, approximately 566 feet of Shonka ditch would need to be re-routed west of the Golf Course, and approximately 2,073 feet of Lost Creek would need to be re- routed to accommodate the Levee alignment.
Alternative PR-A (recommended alternative) o Placement of a gatewell structure on Lost Creek to prevent Lost Creek flood flows from entering the City of Schuyler. The levee alignment would intersect with Lost Creek at this Location and 126 feet of stream channel would pass under the levee through a gatewell structure. The channel in this area is approximately 8 feet wide and 2 feet deep with 3:1 side slopes. o Placement of a gatewell structure on Shonka Ditch to prevent Shonka Ditch flood flows from entering the City of Schuyler. The levee alignment would intersect with Shonka Ditch at this Location. Impacts at this location would include 0.027 acres of PEMA wetlands and 140 feet of stream channel would pass under the levee through a gatewell structure. The channel in this area is approximately 10 feet wide and 2 feet deep with 3:1 side slopes. o Placement of the Levee across two drainages near the east end of the Platte River levee. Each drainage supports a PEMA wetland fringe dominated by reed canarygrass. Wetland impacts include 0.34 acre of PEMA wetlands. The west channel is an irrigation ditch and is approximately 6 feet wide and 1 foot deep. The east channel is in a more natural state and is approximately 8 feet wide and 1-2 feet deep. Both drainages have gradual side slopes and low velocity flow. Approximately 259 feet of the west drainage and 347 feet of the east drainage would be diverted into the exterior drainage channel at the toe of the Platte River Levee and re-routed to Lost Creek just downstream of the eastern edge of the trailing levee.
Under the recommended alternative, impacts to 0.37 acre of PEMA wetlands would be mitigated by creating a low-lying bench along Shell Creek to encourage wetland hydrology. Approximately 266 feet of Lost Creek would pass under the levee through gatewell structures and approximately 606 feet of two un-named drainages towards the east end of the recommended alignment would be diverted into the exterior drainage channel. Channel impacts would be offset by the design of the lower portion of the exterior drainage channel (approximately 872 feet above its confluence with Lost Creek) which would include no greater than 3:1 side slopes and
132 would be planted with a minimum 50-foot wide riparian buffer. The conceptual mitigation plan for wetlands is provided in Appendix A.
8.1.3 Trees and Shrubs Impacts to trees and shrubs would result from the Shell Creek and Nieman Ditch cleanouts, from removal of the abandoned railroad embankment, and from encroachment of the levee alignment. Removal of trees and shrubs could potentially adversely affect wildlife and the water quality of adjacent streams. Estimated impacts from implementing the various alternatives are provided in Table 8-1.
Table 8-1 Impacts to Trees and Shrubs
Alternative No Action Shell Shell Shell Shell Platte Platte Platte Creek Creek Creek Creek River River River SC-A SC-B SC-C SC-E PR-A PR-B-1 PR-B2 Trees and 5.02 5.02 9.02 9.02 10.88 13.73 13.73 Shrubs 0 acres acres acres acres acres acres acres
The levee alignments avoid and minimize impacts to trees and shrubs to the extent practicable. The Shell Creek cleanout, lower Nieman Ditch cleanout, and the removal of the abandoned railroad embankment are designed to improve flow and alleviate flooding. These features have been determined to be necessary components of the project. Combined, these features account for 85% (16.91 acres of the 19.90 acres), of tree and shrub impacts. Because of seepage concerns, trees and shrubs cannot be planted on a levee or a levee right of way. Additionally, the tree and shrub removal along Nieman Ditch and the left bank of Shell Creek north of the UPRR line is designed to improve flow and alleviate flooding. Because of these constraints, and because of the relative availability of in-kind tree and shrub habitat in the vicinity of the impact sites, creation of on-site out-of-kind habitat of a greater floristic quality is proposed.
Lost Creek, Shell Creek, and Nieman Ditch support approximately 91 acres of trees and shrubs in the vicinity of the project area. The area of trees and shrubs impacted by the project is proportionately small relative to available like habitat in the vicinity. Consistent with recommendations from USFWS, tree and shrub impacts would be mitigated. Because trees and shrubs cannot be planted on the levee or in the levee right-of-way, it is recommended that substitute habitats be created to mitigate for the loss of trees and shrubs in the project area. Mitigation for impacts to vegetation is further described in the Conceptual Mitigation Plan provided in Appendix A.
The Corps proposes to create 12.75 acres of tall-grass prairie buffer along Shell Creek and plant 67.24 acres of native prairie grasses on the levee and levee right-of-way to compensate for upland vegetation impacts. All impacts would be mitigated within the construction footprint. The tall-grass prairie planting would be located along the left bank of Shell Creek north of the UPRR line. Construction plans call for creation of a low bench along Shell Creek roughly 7,100 feet long by 80 feet wide. This bench would be seeded with a tall-grass prairie mixture. See
133 additional information on proposed plant species mix in the Biological Assessment in Appendix A.
Following the first year after planting, the site should be monitored once annually during the growing season (roughly May 1st to October 31st) and an annual monitoring report should be submitted to the Omaha District Corps of Engineers. Monitoring reports should indicate vegetative communities and dominant plant species on the site. The site would be considered successful if after five growing seasons the site was dominated by native non-invasive species. The local project sponsor will be responsible for monitoring the site, submitting annual reports, and for any subsequent management actions required to consider the site successful.
8.1.4 Fish and Wildlife
8.1.4.1 FISH Impacts to fish in Shell Creek, Lost Creek, and Shonka Ditch from any of the build alternatives would mainly be related to potential water quality impacts resulting from riparian vegetation removal. Clearing riparian vegetation would cause the temporary loss of the streams’ vegetative buffer which could cause increased water temperatures, increased sediment load and turbidity, and increased fertilizer and pesticide runoff from surrounding agricultural fields. All of these effects would be minor and short term. The fish species found in Shell Creek and Lost Creek (including channel catfish) are tolerant of low water quality conditions, and all of the effects previously mentioned would last only until bare soils can be stabilized and vegetation is re- established.
Alternative PR-A includes gatewell structures on Lost Creek and Shonka Ditch. The gatewell structure design would not impede the passage of fish. Inlets and outlets for the structures would be placed at the existing elevations of the streambed. Sediment would cover the bottom of the structures, maintaining a natural substrate and thereby maintaining connectivity for the movement of fish and other aquatic life.
8.1.4.2 WILDLIFE Impacts to birds, mammals, amphibians, and reptiles would mainly be caused by vegetation removal. Long-term operation and maintenance of the levee would not cause ongoing adverse impacts to wildlife species that inhabit the area. Vegetation impacts would be mitigated. Impacts to edge cover around crop fields, mostly smooth brome (Bromus inermis) would be mitigated by planting a native grass mixture on all disturbed areas. Temporary construction impacts to wildlife resulting from noise, disturbance, and displacement would occur during construction of the levee. These impacts would last until construction activities have ceased and vegetation is re-established. Clearing of trees and brush would be scheduled to occur outside of the primary nesting season of migratory birds to minimize impact to nesting birds.
8.1.5 Threatened and Endangered Species No direct effects to threatened or endangered species would result from any of the build alternatives. Initial coordination with USFWS and NGPC in 2003 indicated that the piping plover, least tern, and pallid sturgeon and their critical habitats exist on the Platte River in the
134 vicinity of the project area. USFWS indicated that indirect adverse effects to these species could result from the levee project if the project were to individually or cumulatively cause an increase of flow velocity in the Platte River. USACE, USFWS, and NGPC staff members met onsite in Schuyler the morning of August 10th 2011 to review potential environmental impacts from the recommended levee alignments. USFWS indicated the project is not expected to adversely affect federally listed species or their critical habitats and NGPC indicated that the project is not expected to adversely affect state listed species (see NGPC letter dated September 6, 2011 in Appendix M).
Avoidance of construction in the floodway should limit or eliminate the impact on the channel- forming velocity of the river and the sandbar and shallow water habitat critical to threatened and endangered species. None of the build alternatives are located within the floodway of the Platte River. The levees would be located approximately 1.5 miles north of the Platte River. Therefore, these structures would have little or no impact on the channel forming velocities of the river during a flood either individually or cumulatively; and therefore impacts to threatened and/or endangered species from implementation of any of the build alternatives would be negligible.
The Biological Assessment (BA) included in Appendix A, concludes that the proposed project is not likely to adversely affect the piping plover, the interior least tern, or the pallid sturgeon based on the premise that avoidance of construction in the floodway should limit or eliminate the impact on the channel-forming velocity of the river, and the shallow water and sandbar habitat essential to these species. Additionally, no project related activities are planned to take place in the vicinity of nesting and feeding habitats of least terns and piping plovers. See the Biological Assessment in Appendix A for a detailed discussion of impacts to threatened and endangered species.
8.1.6 Physiographic and Soil Conditions
8.1.6.1 PRIME FARMLAND Impacts to prime farmland would result from converting prime farmland to non-farmland uses through construction of the levee. Impacts from the build alternatives would impact a relatively minor amount of prime farmland compared to the amount of prime farmland existing in the project vicinity (see Table 8-2). During final design, prime farmland will be avoided where possible.
Table 8-2 Impacts to Prime Farmland
Alternative No Action Shell Shell Shell Shell Platte Platte Platte Creek Creek Creek Creek River River River SC-A SC-B SC-C SC-E PR-A PR-B-1 PR-B2 Prime 0 6.52 11.51 14.74 9.61 4.8 10.32 43.79 Farmland acres acres acres acres acres acres acres
135 8.1.6.2 SOIL EROSION Considering the amount of bare soil adjacent to streams, soil erodibility, and the fact that Shell Creek already carries a high sediment load (sand and mud substrate), with application of best management practices the remaining impact to Shell Creek would likely be minimal.
8.1.7 Cumulative Effects Previous studies and analysis of existing conditions have demonstrated there to be historic, cumulative effects in the Platte River near Schuyler. The result of those impacts over time has been a Platte River in eastern Nebraska that is greatly changed from pre-settlement times. The impact of those changes has been detrimental to some species, due to the greatly altered riparian ecosystem. Since the early 1900s, large-scale infrastructure and water storage/diversion projects have transformed the Platte River, both upstream and locally. However, the combined results from analyzing trends in land use, river stage, channel and island formation, and bank line migration seem to indicate that the channel within the study reach today has been relatively stable since the mid-twentieth century.
For the river and floodplain in the Schuyler area, avoidance of new cumulative impacts to those endangered species requires that project features do not adversely impact the river morphology. This can be accomplished by restricting construction of any new project to within the backwater areas of the floodplain (avoiding the floodway) and avoiding construction methods which would impact the water quality. By avoiding the floodway, changes in river hydraulics (including flood stage and velocity) can be minimized. Within the channel of the Platte River, negligible velocity changes are unlikely to exceed the threshold velocities needed to set in motion sediment particles of a given size (Schumm, 1979). Changes in channel velocity in response to future changes in the floodplain can be predicted through detailed hydraulic modeling.
The present-day geomorphic stability of the reach seems to indicate that the river has achieved dynamic equilibrium near the middle of the 20th Century. Biological conditions within the reach may not reflect the stability noted for river morphology, however, due to continued pressure from invasive species and the decline of native ones. The goals of the proposed levee construction would be to allow the river to work within, and to not further impact, this new equilibrium. Efforts were made to formulate levee alternatives in areas which have little or no velocity in the downstream direction. Avoidance of construction in the floodway should limit or eliminate the impact on the channel-forming velocity of the river and the sandbar and shallow water habitat critical to threatened and endangered species.
None of the build alternatives are located within the floodway of the Platte River. The levees would be located approximately 1.5 miles north of the Platte River. Therefore, these structures would have little or no impact on the channel forming velocities of the river during a flood either individually or cumulatively; and therefore impacts to threatened and/or endangered species from implementation of any of the build alternatives would be negligible. Additionally, an old railroad embankment located south of Schuyler and east of Highway 15 will be removed, which will remove a floodplain restriction to flow, reducing upstream flood stages during major flood events.
136 8.1.8 Irreversible and Irretrievable Commitment of Resources Irreversible effects are those caused by the proposal that cannot be reversed. Irretrievable effects are gains and losses of outputs of the lands’ use both in the short term and long term. Irreversible effects would include the conversion of agricultural, riparian, and wetland areas to a levee system. The levee would be a permanent fixture on the landscape. Irretrievable effects would include the short term impacts to natural resources such as wetlands, wildlife, fish, and riparian areas in exchange for long-term flood risk management for the city of Schuyler.
8.1.9 Environmental Justice
Pursuant to Executive Order 12898 of February 1994, Federal Agencies are directed to incorporate environmental justice as part of their missions by addressing, as appropriate, disproportionately high health and environmental effects of programs, policies and activities on minority and low-income populations. The city of Schuyler has a disproportionately high number of individuals of Hispanic or Latino origin and also a median household that is below average, based upon regional and national statistics. The 2010 population statistics for Schuyler show it to be 65.4 percent Hispanic, which compares to 9.2 percent for the state of Nebraska and 16.3 percent of the national population. Statistics for the period 2005 – 2009 show a poverty level of 16.3% for Schuyler, which compares to an average for the period for Nebraska of 11.8 percent and for the United States as a whole of 13.5 percent. Because of the ethnic and income distribution of the city, the 2008 and 2010 floods at Schuyler fell disproportionately on minority and low income residents, relative to flood impacts nation-wide during that timeframe. On the basis of regional and national statistics, a higher priority for flood risk reduction for the community of Schuyler may be justified, based upon compliance with Executive Order 12898. The proposed project is expected to benefit minority and low-income populations by reducing the risk of flooding. No disproportionately high health and environmental effects on low-income and/or minority populations would be associated with implementation of the recommended alternatives.
8.2 SUMMARY OF COORDINATION, PUBLIC VIEWS AND COMMENTS Public comments have been solicited through a variety of public meetings held in Schuyler since the beginning of the project. The format of the meetings has varied, from formal public involvement meetings held at the Oak Ballroom, to open city council briefings and coordination meetings held with the sponsors and stakeholders. The major public meetings are held in both English and Spanish. Details from those meetings, including the Power Point slides presented are provided in Appendix M.
8.2.1 SPONSOR – STAKEHOLDER MEETINGS A series of meeting have been held during the plan formulation phase of project. The meetings helped define the objectives of a successful flood risk reduction project and the levee alternatives to be considered for both the Shell Creek and Platte River flood problems.
● February 2007 Schuyler City Council Study Session The Corps met with the Schuyler City Council on February 20, 2007 to discuss the Section 205 Study progress and goals. The focus was on the Platte River floodplain and the increased portion of southern Schuyler that would be included in the 100-year floodplain in the future. The
137 investigation of the low “ridge” near downtown Schuyler was discussed, including its implications to the remapped floodplain. The results of the Initial Assessment and the alternatives proposed in that phase were also discussed.
● June 2008 Schuyler City Council Study Session The purpose of the meeting was to discuss the impact of the disastrous Shell Creek flood on formulating flood risk management plans for Schuyler. Attendance included officials and employees of the city of Schuyler, Colfax County, Lower Platte North NRD, Corps of Engineers, State Senator Chris Langemeier and interested citizens. The city made it clear that reducing flood damages from Shell Creek was the number one goal following the flood, but still wanted the Platte River flood damages reduced as well. The Corps discussed conceptually what Shell Creek flood risk management could look like and sought additional high water marks and details on the timing of the flood peak, which was considered likely to be near the magnitude of a 100- year (1% annual chance of exceedance) peak flood.
● November 2008 Colfax County Board Meeting A meeting was held at the request of the Colfax County Board to discuss the 2008 flood and issues relative to the Union Pacific tracks and the Corps’ feasibility study. In attendance were officials and employees of the City of Schuyler, Colfax County, Lower Platte North NRD, Union Pacific Railroad (UPRR) and the Corps of Engineers. Discussions included the potential for the UPRR to help share in the cost of flood damage reduction and the progress, scope and schedule of the Corps’ feasibility study.
● December 2008 Schuyler Rotary Meeting The meeting was held in Schuyler at the request of State Senator Chris Langemeier, Unicameral Representative from Schuyler. The project manager presented a progress report on the Feasibility Study. The impact of the 2008 Shell Creek flood on the project scope was discussed, along with a review of the Section 205 Program and scope, schedule and budget issues. Initial Shell Creek alternatives and evaluation were discussed.
● February 2009 Stakeholder Meeting with Union Pacific Railroad (UPRR) A meeting was held in Omaha to discuss engineering, floodplain management and real estate issues impacting the UPRR and Schuyler relative to Shell Creek and Platte River flooding. A significant focus of the meeting was on the 2008 Shell Creek flood and its implications to Shell Creek hydrology (including both flood frequency and duration of flood hydrographs at Schuyler). Discussion also included Platte River and general floodplain issues and data and modeling needs of both organizations.
● July 2009 Meeting with Sponsor A meeting was held at the Schuyler City Hall to discuss the formulation of levee alternatives for Shell Creek and Platte River flood risk reduction. A joint sponsor-Corps field investigation was included to review potential alternative alignments for levees and floodwalls. Attention was focused on real estate issues, tie backs, interior drainage and geotechnical uncertainties.
138 ● December 2009 Meeting with Sponsor A meeting and field investigation was conducted in Schuyler to discuss details of the preliminary levee alternatives proposed for alleviating Shell Creek and Platte River flood threats at Schuyler. In attendance were officials and employees of the city of Schuyler, Lower Platte North NRD and the Corps. Discussions focused on levee alternatives, real estate issues, quality of sources of borrow, and floodplain management issues relative to the recent increase in railroad track elevations. Discussion also included endorsement of the removal of the old railroad embankment south of Schuyler and its use as random fill in any levees.
● February 2010 Stakeholder Meeting with the UPRR A meeting was held in Omaha to further discuss the initial flood risk reduction alternatives proposed by the Corps of Engineers for mitigating Shell Creek and Platte River flooding at Schuyler. Discussions focused primarily on hydrologic and hydraulic modeling and floodplain management issues relative to track height increases during track maintenance. The Corps provided the UPRR the existing HEC-RAS model for Shell Creek, which had been calibrated to the high water marks of the 2008 flood.
● March 2010 Lower Shell Creek Steering Committee Meeting The meeting was held to discuss the progress of efforts to improve the Hughes-Payzant Drainage Ditch and its relationship to the flood damage reduction efforts at Schuyler. In attendance were employees of the city of Schuyler, Colfax County, Lower Platte North NRD and the Corps of Engineers, as well as citizens involved in the Lower Shell Creek Steering Committee. The Corps presented information on the progress of the feasibility study at a general meeting of the organization at the Colfax County Courthouse. The relationship of the Hughes-Payzant Ditch to flooding on Shell Creek was a central focus of the meeting. While an improved Hughes-Payzant Ditch will intercept more of the flood flow of Shell Creek above Schuyler, it was determined that, at best, it might divert about 7% of the 100-year peak flow away from the city.
● October 2010 Meeting with Sponsor A meeting was held with officials of the Lower Platte North NRD in Omaha to discuss the current status of the formulation of the Schuyler alternative levee alignments as well as the project scope, schedule and budget, along with the Fremont and North Bend projects.
● October 2010 Schuyler City Council Meeting Corps project managers and the Lower Platte North NRD attended a Schuyler City Council Meeting and briefed the Schuyler mayor, city council and city staff on the progress of the feasibility study and the delineation of the flood risk reduction alternatives. An important goal of the meeting was to consider whether to implement interim flood damage reduction / flood fight measures ahead of the project implementation. A presentation was made by the City Engineer (JEO Engineering) on potential methods of developing an interim flood damage reduction measure. Cost of the interim flood fight measures was a major factor in the city failing to move forward on the interim measures.
● December 2010 Discussion of Levee Alternatives and Floodplain Issues A meeting was held with Colfax County and city of Schuyler officials in Omaha to discuss levee alternatives and floodplain issues as well as project scope, schedule and budget. Colfax County
139 is a major project stakeholder and may participate financially during design and construction of the project.
● March 2011 Finalizing the Levee Alignments A meeting was held in Schuyler to discuss the near-final Shell Creek and Platte River levee alignments. Included in attendance was the mayor of Schuyler, city council members, Colfax County board members, Lower Platte North NRD representatives, Schuyler city officials, including JEO, serving as the City Engineer, Colfax County officials and Omaha District staff. Following a discussion of alignments, it was determined that Shell Creek Alternative SC-E should be adjusted so that the levee was further from Nieman Ditch to preserve the existing flood patterns along that waterway.
● March 2011 Stakeholder Meeting with UPRR A meeting was held at the Omaha District office to present the recommended feasibility study plans for Platte River and Shell Creek flood risk reduction. Following the screening and elimination of the alternatives with closure structures, there was general agreement on the proposed plans. The UPRR expressed concerns about the additional water that would reach its bridge with the levee and Shell Creek channel cleanout. The Corps noted that the flow was greatly restricted before it reached the bridge, since the improved channel would still end at the next county road bridge upstream. The Corps sought opportunities to improve drainage from Shell Creek flooding through the railroad embankment east of Schuyler. The railroad expressed concern about the costs and impacts of taking any water to the Platte River once it reached the south side of the embankment. The potential for using that water for wetland mitigation east of Schuyler as a joint funded effort was discussed.
● August 2011 Schuyler City Council Meeting The recommended alternative plans for flood risk management were presented to the Schuyler City Council on August 16th, 2011. The City Council reiterated its support for the project at the meeting.
8.2.2 GOVERNMENT AND ENVIRONMENTAL AGENCY COORDINATION MEETINGS
● February 2003 Site Visit Staff members from the U.S. Fish and Wildlife Service, Nebraska Game and Parks Commission, and the Corps conducted a site visit to assess potential impacts of preliminary Platte River alternative levee alignments on February 21st, 2003. The findings and recommendations resulting from the site visit are provided in preliminary Planning Aid Letters from the USFWS and NGPC in Appendix A.
● June 2009 Environmental Coordination Meeting An environmental coordination meeting was held on June 2nd, 2009 in Schuyler to discuss environmental issues and coordination related to a potential flood risk reduction project in Schuyler. No major issues surfaced during the discussions. It was noted by Nebraska Department of Environmental Quality representatives that the flood risk reduction project was
140 worthy of support, as it reduces the flushing of urban pollutants into the streams and rivers. The following agencies and organizations were in attendance:
- Colfax County - City of Schuyler - Nebraska Game and Parks Commission - Lower Platte North Natural Resources District - U.S. Army Corps of Engineers - State Senator Langemeir’s Office - Nebraska Department of Environmental Quality - Union Pacific Railroad Company - JEO Consulting Engineers
● August 2011 Agency Coordination Activities Agency comments were solicited and received during the public review period of August 1st thru August 30th. Letters, e-mails and notes from the consultations are provided in Appendix M.
A project review was conducted on site with the U.S. Fish and Wildlife Service and the Nebraska Game and Parks Commission on August 10th, 2011. Neither agency was opposed to the project but both requested further information as the study proceeds to design and requested that actions and guidelines be followed. Formal Fish and Wildlife Coordination Act work will not be required for this project. Among the requested actions are:
- Provide typical drawings of the gatewell structures proposed for Lost Creek and Shonka Ditch to Game and Parks Commission. - Avoid impacts to wetlands near the east end of the Platte River Levee PR-A. - Clearing and grubbing for the levees should take place outside of the primary nesting season for migratory birds and a migratory bird survey consistent with the Migratory Bird Treaty Act shall be performed. - Borrow sites should be selected with care if in the Platte River Valley, in order to avoid groundwater depletions to the Platte River.
None of the requests made during the field review of August 16th are anticipated to have an impact on project cost, justification or the order of plan selection.
Additional agency comments were received during the agency coordination meeting which was held in Schuyler on August 16th and in communications that followed the meeting. Among the comments received and given consideration were: - Nebraska Department of Natural Resources; A list and location of wells near the levee alignments was provided in written communication. Those wells and locations will be reviewed in design to determine if impacts can be avoided or if compensation will be given for replacement. - Nebraska Department of Roads; It was noted that all modifications to highways within the state highway system will need to be approved by NDOR. There was concern expressed that the road raise on Highway 15 on Levee Alignment PR-A may not have
141 adequate stopping sight distance for intersections with rural roads. The layout of the vertical curve will need to be addressed early in design. Should it be necessary to switch to a closure structure at that location, the estimated cost of Alternative PR-A would likely drop and the net annual benefit increase. Additionally, the closure structure would create less backwater in the floodplain. This change if required, would lower the total project cost but increase the operation and maintenance cost to the community, but would not alter the plan selection. - Village of Rogers: The village of Rogers has conveyed its concern that the Schuyler Shell Creek Levee SC-C and proposed channel work may impact the community, particularly if the existing agricultural levees are removed and not replaced. The Corps will not remove the agricultural levee materials against the wishes of the adjacent land owners and could stockpile that material for the levees to be set back. If this modification is made, and to the extent that the downstream Shell Creek channel is shaped, borrow from that area will be reduced increasing the amount of borrow that will be obtained elsewhere. As the borrow pits were not defined in the Feasibility Study, it cannot be determined if there will be an impact to cost. Any changes in cost would be minor and well within the project contingency.
8.2.3 GENERAL PUBLIC INVOLVEMENT MEETINGS Public involvement meetings are held throughout the project development cycle. Meetings were held during the initial assessment in October 2003. Additional meetings with the city, citizens and stakeholders were held in 2008, as the initial phase of planning was underway. Those meetings included presentations with the city Rotary Club, the Union Pacific Railroad and the Hughes – Payzant Drainage Ditch Improvement Organization. These meetings were followed by a more formal NEPA Coordination meeting in June 2009.
● June 2009 Public Involvement Meeting A public meeting was held on the evening of June 2nd, 2009 in Schuyler as part of the NEPA process for this study. The objectives of this meeting were to provide information on the initial assessment of the flood problems and opportunities at Schuyler and to obtain public comment and input at that phase of the feasibility study effort. Since Schuyler is a bilingual city, efforts were made to publish the meeting notice in Spanish (Figure 8-1) as well as English, and a Spanish language Power Point Presentation was prepared.
The meeting consisted of a Power Point presentation (with English and Spanish versions running) followed by a question and answer period. There were over 80 people in attendance, including those from the cooperating agencies. A large majority of those in attendance were local residents. Several comments were received by mail or e-mail following the meeting. A Spanish language interpreter was present for the meeting. The meeting was also covered by Cable NE (99) Public Information Channel (in Spanish).
All comments were directed towards the Shell Creek flood issue, with none of them directed towards flood issues along the Platte River. Among the comments received was strong support for getting the project built quickly. Residents of farms east of Schuyler expressed concern about potential damages that might be induced by the construction of a levee at Schuyler. Attendees voiced support for cleaning out the Hughes-Payzant Ditch to reduce Shell Creek flooding on those farmlands (including induced flooding), in conjunction with the levee project.
142 Frustration with the role that the Union Pacific rail grade and relatively small bridge plays in the Shell Creek flood problem was noted. Support for cleaning out Shell Creek between Schuyler and the railroad bridge also received support, as it may offset potential induced flooding caused by building a levee.
Figure 8-1 Notice of Public Involvement Meeting in Spanish
● March 2011 Colfax County Flood Insurance Rate Map (FIRM) Review The Corps presented a brief overview of its “Recommended Plans” for the Shell Creek and Platte River Levees at a general public meeting moderated by the Floodplain Administrator of Colfax County. A question and answer period followed. The main purpose of the meeting was to go over the new FIRM Maps and the central presentation was by FEMA. There was considerable interest in the levee plan, as the new FIRM maps might go into effect at approximately the same time that construction begins on the levee projects.
● June 2011 Public Meeting at Oak Ballroom An open public meeting was held with the Mayor and Schuyler City Council and the Lower Platte North NRD. While the central purpose of the meeting was to discuss a revised recommended alternative for Shell Creek and the project budget and schedule, many topics of concern to the public were discussed. Impacts of the current recommended plans on areas outside of the levees were the public discussion focus. In particular, projected stage increases at Lake Socorro and on property along Shell Creek east of the levee were discussed. Discussion of the impacts of changes in Shell Creek, particularly the left bank agricultural levees and impacts
143 to not only adjacent landowners, but even the village of Rogers was discussed. Concern was also noted that Shell Creek Alternative SC-C would not protect northeastern Schuyler from groundwater infiltration as would have been done by SC-E and the operation of a center pivot would now be impaired. It was noted that since final surveys have not been obtained, the final configuration of Shell Creek channel modifications should be done early in design, with the participation of Colfax County officials and the county engineer.
● August 2011 Public Meeting at Oak Ballroom The public review period was published in newspapers and on the Corps Internet site. Notices of the review were published in English and Spanish, given the large number of Schuyler residents more fluent in Spanish than English. Power Point slides detailing the project, comment forms and equivalent references on the web site were also bilingual, and an interpreter was available at the public meetings on August 16th.
Public comments were received from private individuals, units of government and representatives of local companies. Verbal comments were taken at the public and agency involvement meetings on August 16th and the questions and discussion were transcribed by a court reporter from Thomas & Thomas Court Reporters of Omaha, NE. Comments were also received on comment sheets passed out at the public meetings and before and after the meeting via e-mail and regular mail. Those comments and the team’s responses are summarized in the Appendix M Supplement. Comments, transcripts and technical answers provided for specific topics are provided in Appendix M.
Forty-one comments were received, with seven from government and thirty-four from individuals or representatives of local businesses. Some individuals sent in more than one comment during the comment period. Three of the government agency comments were received via site visit or meeting attendance. An initial response was provided to each sender that provided a written comment, by the method of comment receipt (i.e. if e-mail, by e-mail, if letter, by letter). More detailed review of the comments received and the response are provided in Appendix M. Those comments that will need to be addressed in the design phase are noted as follows: - Shell Creek Levee SC-C, West of Old Highway 30: Efforts will be made to avoid a center pivot and associated wells if costs of construction and maintenance would not be increased over the cost of easements and mitigation. The location of the levee termination point near the QC Supply store along Highway 15 will be reevaluated once more accurate elevation data are acquired in design.
- The placement of the Shell Creek Levee SC-C and potential removal of agricultural levees in channel shaping will cause flooding where it has not occurred before: It is evident that the Schuyler Shell Creek levee will result in some changes in the distribution of flow, which may increase flood stages in certain areas. During the feasibility study the impacts of the changes in flow distribution east of Schuyler were determined to be less than 0.5 foot for the 100-year or 1-percent annual chance flood. During the design phase the pre-project and with-project flood elevations and extent of flooding will be determined for the 1-percent-chance and lesser floods using more detailed topographic data that have become available. Any impacts to buildings and cropland east of Schuyler
144 will be determined by these additional analyses, and if necessary, the impacts will be mitigated. The agricultural levees will not be removed against the wishes of the adjacent land owners in order to shape the channel. Working with local government and the landowners, it may be possible to set the levees back and shape the channel. This would reduce the total borrow that could be obtained from that area. As the borrow pits were not defined in the feasibility study, it cannot be determined if there will be an impact to cost. Any changes in cost would be minor and well within the project contingency.
- Removal of all of the old BNSF railroad embankment as part of the Platte River flood risk reduction will increase the flood threat to two subdivisions (Keating Lake and Bobcat Lake) as Platte River overflows, now blocked from those subdivisions, will pour into homes directly from the west: After reviewing that situation, it was determined that the old railroad adjacent to those subdivisions should not be removed, and the embankment removal should focus on the high embankment closer to Schuyler. This change will reduce the random fill that can be obtained from that area and will not lower the water surface elevation quite as much as planned in the Platte River floodway. Given that removal of the entire embankment only lowered the water surface a few tenths, backing off on part of that removal would have negligible impact on the project formulation. Also, there are other sources of random fill nearby and the portion in question has the least volume to offer, so impact on cost is anticipated to be negligible. A minor adjustment to Alternative PR-A is recommended, with final configuration pending surveys and data acquisition in the Design Phase.
8.3 OTHER ENVIRONMENTAL ACTS, COORDINATION AND COMPLIANCE The following text summarizes the major statutory and regulatory environmental compliance requirements and discusses the major Federal and state permits and clearances that would be required for the approval and implementation of the project.
8.3.1 Endangered Species Act Federal agencies are required to determine the effects of their actions on federally listed endangered or threatened species and their critical habitats under ESA [16 USC 1531 et seq.]. Steps must be taken by the federal agency to conserve and protect these species and their habitat, and to avoid or mitigate any potentially adverse impacts resulting from the implementation of the proposed project. A Biological Assessment (BA) has been prepared in conjunction with this project and is included in Appendix A. The preparation of a BA is required under ESA to evaluate if a major construction activity is likely to adversely affect a listed species or its habitat. The BA concludes that the proposed project is not likely to adversely affect listed species. USACE, USFWS, and NGPC staff members met onsite in Schuyler on August 10th 2011 to review potential environmental impacts from the recommended levee alignments. USFWS indicated the project is not expected to adversely affect federally listed species or their critical habitats.
145 8.3.2 Fish and Wildlife Coordination Act The Fish and Wildlife Coordination Act (16 U.S.C. 661, et seq.) provides the basic authority for USFWS involvement in evaluating impacts to fish and wildlife from proposed water resource development projects. It requires that fish and wildlife resources receive equal consideration to other project features. It also requires that federal agencies that construct, license or permit water resource development projects must first consult with USFWS (and the National Marine Fisheries Service in some instances) and state fish and wildlife agency regarding the impacts on fish and wildlife resources and measures to mitigate these impacts. Full consideration is to be given to USFWS recommendations.
8.3.2.1 Fish and Wildlife Coordination during the Initial Assessment Formal coordination with the United States Fish and Wildlife Service (USFWS) and the Nebraska Game and Parks Commission (NGPC) was initiated during this assessment. The USFWS and NGPC provided their preliminary views of the likely beneficial and adverse impacts of the potential flood damage reduction project; refer to Appendix A for copies of USFWS and NGPC correspondence.
The USFWS letter indicated that the potential project may have a direct adverse impact on woodlands, grasslands, and wetlands, and the wildlife species associated with these habitats. Any loss of these habitat types should be mitigated. Whenever possible, the levee should be positioned to avoid impacts to trees. It appeared to the USFWS that the project has the potential to adversely impact the hydrologic regime and channel geomorphology of the Platte River. It was recommended that the Corps assess the direct and cumulative effects of existing and potential levee improvement projects on the lower Platte River. An indirect impact may be the increased development of homes on the landward side of the levee. The USFWS letter stated that potential adverse impacts to threatened and endangered species (bald eagle, least tern, piping plover) and other migratory bird species could be minimized by scheduling project activities to avoid the nesting period of these birds. The USFWS indicated that the direct, indirect, and cumulative impact of any changes in channel geomorphology, especially loss of sandbar habitat, should be assessed. Also, the USFWS specifically recommended that the locations and sizes of borrow sites be identified and assessed as to their potential to cause a depletion to instream flows in the Platte River system. As an enhancement measure, the USFWS recommended that only one side of the levee be mowed each year.
The NGPC letter also expressed concern for potential impacts to state and federal threatened and endangered species in the project vicinity: least tern, piping plover, bald eagle, western prairie fringed orchid, and small white lady’s slipper. The NGPC would like to be informed regarding the type of structures that would be proposed on Lost Creek for any alternative that would cross the creek. The agency would not object to the removal of an old railroad bed berm located southeast of Schuyler that is overgrown with woody vegetation. They recommend a survey for western prairie fringed orchid and small white lady’s slipper if high quality prairie sites are identified in the project area.
146 8.3.2.2 Fish and Wildlife Coordination during the Feasibility Phase Coordination with the USFWS took place on August 10th, 2011. Following the coordination, which was done on location near Schuyler, it was determined that a formal Fish and Wildlife Coordination Act (FWCA) report would not be needed as there are no evident threats to endangered species and the mitigation measures proposed by the Corps are the same types of mitigation actions that the USFWS would provide in a FWCA report. Full consideration will be given to recommendations contained in the Planning Aid Letter and more details of this consultation are provided in Appendix M.
8.3.3 Clean Water Act (CWA) Federal limits on the amounts of specific pollutants that could be discharged to surface waters in order to restore and maintain the chemical, physical, and biological integrity of the water are governed by CWA [33 USC 1251 et seq., as amended], National Pollutant Discharge Elimination System (NPDES).
Discharge of storm water resulting from construction activities that would disturb more than one acre of surface area requires a NPDES permit under Section 402 of the CWA. A Stormwater Pollution Prevention Plan (SWPPP) would be prepared prior to commencement of construction activities. The plan would address practices and measures required to control and reduce the amount of pollutants in storm water runoff.
Regulatory requirements for a permit system governing the placement of dredged or fill material into waters of the United States are also mandated by CWA under Section 404. The Corps authorizes this permit. Clearing of trees and shrubs along the lower portions of Nieman Ditch and Shell Creek would not involve discharges of dredged or fill material; removal of soil along left bank of Shell Creek north of the UPRR line would take place above the ordinary high water mark and would not impact fringe wetlands or Shell Creek (a water of the U.S.). Placement of gatewell structures from construction of Alternative PR-A would result in a minor discharge of fill material in Lost Creek and Shonka Ditch. Even though dredge and fill activities are anticipated to be minor, new levee construction projects are not explicitly covered by any of the 2007 nationwide permits or by a general permit; therefore, a 404(b)(1) analysis has been conducted for this project and is provided in Appendix A. Section 401 of the CWA requires state agencies to certify that a project requiring a federal permit to discharge complies with specific provision of the CWA. An individual Water Quality certification will need to be obtained from the Nebraska Department of Environmental Quality (NDEQ) before construction activities can commence.
8.3.4 Migratory Bird Treaty Act Under the Migratory Bird Treaty Act, construction activities in grassland, wetland, stream and woodland habitats, and those that occur on bridges that would result in the taking of migratory birds; eggs, young, and/or active nests should be avoided. Clearing of vegetation will be scheduled outside of the primary nesting season (April 1st – July 15th in Nebraska) to minimize the taking of migratory birds. A migratory bird survey would be conducted before construction activities would commence in an area. The need for the bird survey was confirmed by the Nebraska Game and Parks Commission and the U.S. Fish and Wildlife Service during their on- site consultation on August 10, 2011.
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8.3.5 Prime Farmlands The Farmland Protection Act [7 CFR 658] minimizes the extent to which federal actions contribute to the unnecessary conversion of prime farmlands to nonagricultural use. The Natural Resources Conservation Service (NRCS) takes steps to ensure that prime farmlands lost to development are documented and provided to Congress in a yearly report. In full compliance with the Farmland Protection Act, Form AD-1006 Farmland Conversion Impact Rating form was submitted to the NRCS for the preferred alternatives (see Appendix A, Biology).
8.3.6 National Environmental Policy Act Federal agencies use NEPA [42 USC 4321 et seq.] to evaluate the environmental impacts of a proposed project. Through the NEPA process, public officials and citizens are given the opportunity to be involved in the environmental review and receive information about environmental impacts before any decisions are made on federal actions regarding the proposed projects. This feasibility report is integrated with an Environmental Assessment (EA) to serve as the documentation necessary to incorporate the NEPA process into the feasibility planning process. If no significant impacts are determined, a Finding of No Significant Impact (FONSI) would be prepared and NEPA compliance would be fulfilled.
8.3.7 CULTURAL RESOURCES In accordance with the National Historic Preservation Act (NHPA) and its implementing regulations, the SHPO, Tribes and other interested parties have been consulted to determine if there are any concerns regarding any proposed actions. Responses were received from both the SHPO and the Pawnee Nation of Oklahoma. Historic properties in the study area that might be affected by the implementation of any proposed project were identified, and the information utilized to assess impacts and make a No Effect determination for the project. SHPO concurrence with this determination was received June 22, 2011. Construction, including borrow areas, of the preferred alignment alternatives would primarily take place in previously disturbed road and railroad rights-of-way, existing levees, modified channels and agricultural land. Undisturbed or minimally disturbed areas of potential construction were examined by a qualified staff archeologist. The Corps believed that the proposed project would have no impact on cultural resources and has received concurrence with a No Effect determination for the project from State Historic Preservation Officer (SHPO).
8.3.8 Executive Order 11988 Floodplain Management
8.3.8.1 Conditional Letter of Map Revision A Conditional Letter of Map Revision (CLOMR) approved by FEMA indicates that a proposed project complies with FEMA regulations and if constructed, FEMA will make the changes to the regulatory floodplain and/or floodway described in the CLOMR application on the official floodplain maps. The CLOMR application would be done when a feasible, locally-preferred alternative is identified.
148 8.3.8.2 Floodplain Management Plan (FPMP) Section 202 of the Water Resources Development Act of 1996 (WRDA 1996) requires the development of a Floodplain Management Plan (FPMP) for federally-constructed flood damage reduction projects. This plan is to be developed and in-place within one year after signing the Project Cooperation Agreement (PCA). The FPMP is a document developed by the non-federal sponsor, with input and guidance from the federal agency. The FPMP assures that the integrity of the federal project will not be diminished during the life of the project and that impacts of future flood events in the project area have been reduced. The FPMP will address potential measures, practices, and policies to reduce loss of life, injuries, damages to property and facilities, public expenditures, and other adverse impacts associated with flooding and to preserve and enhance natural floodplain values. The FPMP is required for either a structural or nonstructural project. An FPMP for a feasible, selected alternative would be developed when a flood reduction project is approved.
149 9. RECOMMENDATIONS 9.1 OMAHA DISTRICT A thorough feasibility study has been conducted regarding flood risk management opportunities along Shell Creek and the Platte River, including Lost Creek, at Schuyler, NE. The study evaluated structural and nonstructural measures including a detailed analysis of four different levee alternatives along Shell Creek and three different Platte River/Lost Creek levee alternatives. The analysis examined flood risk reduction measures over a range of flood frequencies for both threats. Results from this feasibility study indicate that levees to protect Schuyler from both Shell Creek and the Platte River are economically feasible. Repeated and recent flooding have further demonstrated the need for flood damage reduction efforts at Schuyler.
Justified plans have been identified which would greatly reduce the risk of future flooding. The proposed plans would result in the construction of levees to protect the community from Shell Creek and Platte River flooding. The plans have been carefully reviewed regarding the impact of the levees on the environment and adjacent property.
Based on the feasibility study analysis Shell Creek Alternative SC-C and Platte River/Lost Creek Alternative PR-A were selected as the recommended plans. The plans, once implemented, would include 5.6 miles of levees, and some channel shaping. The combined plan provides 100-year flood damage risk reduction to 207 structures in northeast Schuyler and 559 structures in the south end of Schuyler, reducing an estimated $1,900,000 in annual damages. The cost of construction is estimated at $9,868,000, including real estate, which will be cost shared 65/35 with the local sponsor. The preferred plan has an estimated net annual benefit to the nation of $1,386,290 and a benefit to cost ratio of approximately 3.7 to 1.
I have given consideration to all significant aspects in the overall public interest. Those aspects considered include environmental, social, and economic effects; engineering feasibility; the unique capabilities and strengths of the Corps to study, design, and implement such a project; capabilities and interests of the cost-share sponsor; and other elements. The non-federal sponsor, the Lower Platte North Natural Resources District, has stated that prior to implementation it will, through signing of the Project Partnership Agreement, agree to perform the required items of cooperation. I recommend that the plan proposed herein for flood risk management be approved and implemented as a federal project.
This recommendation reflects the information available at this time and current departmental policies governing formulation of individual projects. They do not reflect program and budgeting priorities inherent in the formulation of a national Civil Works construction program nor the perspective of higher review levels within the Executive Branch.
Robert J. Ruch Colonel, Corps of Engineers District Commander
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9.2 LOCAL SPONSOR
151 10. REFERENCES
Alexander, Alice, 2003. Letter from the Pawnee Nation of Oklahoma dated February 19, 2003.
Arps, Mark. 2010. Personal communication. Colfax County Highway Department and Emergency Manager. Information by telephone April 21, 2010, regarding replacement costs of county roads.
Bartlett, P.A., W.H. Saeger, and S.K. Huso. 1982. Soil survey of Colfax County, Nebraska. U.S. Department of Agriculture, Soil Conservation Service.
Benedict, R.A., H.H. Genoways, and P.W. Freeman. 2000. Shifting distributional patterns of mammals in Nebraska. Transactions of the Nebraska Academy of Sciences 26:55-84.
CALMIT (Center for Advanced Land Management Information Technologies). 2007. Delineation of 2005 land use patterns for the state of Nebraska. University of Nebraska-Lincoln.
City of Schuyler. 2004. Comprehensive Development Plan for Schuyler, Nebraska. November 2004.
City of Schuyler. 2010a. Schuyler Golf Club. Accessed March 23, 2010, at the following Web site: http://www.schuylernebraska.net/.
City of Schuyler. 2010b. The Oak Ballroom. Accessed March 23, 2010, at the following Web site: http://www.schuylernebraska.net/.
City of Schuyler. 2010c. Schuyler City Parks. Accessed March 23, 2010, at the following Web site: http://www.schuylernebraska.net/.
City of Schuyler. 2010d. Merchant’s Park. Accessed March 23, 2010, at the following Web site: http://www.schuylernebraska.net/.
Communication with City of Schuyler staff in regard to disaster declaration data, November 2008.
Communication with Colfax County Farm Service Agency, November 2008.
Cowardin, L.M., V.M. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of Wetlands and Deepwater Habitats of the United States. Report FWS/OBS-79/31. U.S. Department of the Interior, Fish and Wildlife Service, Biological Services Program, Washington, DC. Dec 1979.
Downtown Schuyler Revitalization Plan (DSRP). 2010. City of Schuyler, July 2010.
Environmental Protection Agency (EPA). 2007. Introduction to TMDLs. http://www.epa.gov/owow/tmdl/intro.html Accessed July 12, 2007.
152 Federal Emergency Management Agency. 1990. Flood Insurance Study, City of Schuyler, Nebraska, March 1990.
Federal Emergency Management Agency. 2002. “Flood Insurance Study. Colfax County, Nebraska, and Incorporated Areas.” August 6, 2002.
Gilson, Wayne. 2010. Personal communication. Parks Manager, City of Schuyler, NE. Information provided by telephone March 24, 2010, regarding city sports fields and points of contact for the various organizations with teams using these fields.
Inselman, Chris. 2010. Personal communication. Schuyler Women’s Softball Association. Information provided by telephone April 9, 2010, regarding softball teams, fields and parks used, and total person-days of softball use at each park.
Institute for Water Resources, 1988. National Economic Development Procedures Manual, Urban Flood Damage, IWR Report 88-R-2, March 1988.
Institute for Water Resources, 2009. National Economic Development Procedures Manual, Overview, IWR Report 09-R-2.
Interagency Advisory Committee on Water Data. 1981. Guidelines for Determining Flood Flow Frequency – Bulletin 17B. U.S. Department of the Interior, Geological Survey, Reston, Virginia, September 1981.
Marshall and Swift Residential Cost Handbook, 2008. Marshall and Swift/Boeckh, LLC, 2008.
Marshall and Swift Valuation Service, 2008. Marshall and Swift/Boeckh, LLC, 2008.
Meister, Don. 2010. Personal communication. Treasurer, Schuyler Baseball Corporation. Information provided by telephone March 26, 2010, regarding baseball teams, fields and parks used, and total person-days of baseball use at each park.
Missouri River Basin Commission, Platte River Basin, Nebraska, Level B Study, June 1976
National Sanitation Foundation (NSF). 1970. National Sanitation Foundation Water Quality (Eutrophication) Index. http://bcn.boulder.co.us/basin/watershed/wqi_nsf.html
NDEQ (Nebraska Department of Environmental Quality). 2004. Section 303(d) List of Impaired Waterbodies for Nebraska. Nebraska Department of Environmental Quality, Lincoln, NE. http://www.deq.state.ne.us/SurfaceW.nsf/Pages/TMDL Accessed November 25, 2008.
NDEQ. 2006. Section 303(d) List of Impaired Waterbodies for Nebraska. Nebraska Department of Environmental Quality, Lincoln, NE. http://www.deq.state.ne.us/SurfaceW.nsf/Pages/TMDL Accessed November 25, 2008.
153
NDEQ. 2008. 2008 Water Quality Integrated Report. Nebraska Department of Environmental Quality, Lincoln, NE. http://www.deq.state.ne.us/SurfaceW.nsf/Pages/TMDL Accessed November 25, 2008.
Nebraska Incorporated Place Census Populations with Changes and Percent Changes: 1980 to 2010 (2011) Prepared by David Drozd, Center for Public Affairs Research, University of Nebraska at Omaha on March 1, 2011.
Nebraska Natural Resources Commission, Shell Creek Floodplain Study, Volume One: Colfax County, August 1992.
Nebraska Soil and Water Conservation Commission, Missouri River Basin Framework Study, September 1971.
Peschel, Mary. 2010. Personal communication. Administrator and Clerk-Treasurer, City of Schuyler. Information by telephone June 30, 2010, regarding replacement costs of city streets.
Peschel, Mary. 2010a. Personal communication. City of Schuyler Administrator and Clerk- Treasurer. Information provided by telephone March 23, 2010, regarding the Oak Ballroom and facilities for golfing, swimming, picnicking, fishing, camping, and soccer and new and improved recreational facilities planned for the future.
Peschel, Mary. 2010b. Personal communication. City of Schuyler Administrator and Clerk- Treasurer. Information provided by telephone April 19, 2010, regarding the number of persons in 2009 who attended events at the Oak Ballroom, used the city swimming pool or campground, and were golf club members.
Peschel, Mary. 2010c. Personal communication. City of Schuyler Administrator and Clerk- Treasurer. Information provided by telephone June 30, 2010, regarding the recreational facilities that were damaged in the 2010 flood and were being replaced.
Peschel, Mary. 2010d. Personal communication. City of Schuyler Administrator and Clerk- Treasurer. Information provided by telephone November 8, 2010, regarding updates on the recreational facilities that were damaged in the 2010 flood.
Sharpe, R.S., W.R. Silcock, and J.G. Jorgensen. 2001. Birds of Nebraska: their distribution and temporal occurrence. University of Nebraska Press, Lincoln, Nebraska.
UNL (University of Nebraska-Lincoln). 2008. Reptiles and amphibians of Nebraska. http://snrs.unl.edu/herpneb/
USACE, Omaha District 1938. Preliminary Examination Report on Flood Control, Platte River in the Vicinity of Schuyler, Nebraska. 1938.
154 USACE, Omaha District. 1938. Review Report, Platte River in the Vicinity of Schuyler, Nebraska. 1938.
USACE, Omaha District. 1967. Detailed Project Report, Platte River and Lost Creek, Schuyler, Nebraska, December 1967.
USACE, Omaha District. 1971. Review Report, Platte River and Tributaries, Nebraska, March 1971.
USACE, Omaha District. 1982. Draft Summary, Platte River and Tributaries, Nebraska, April 1982.
USACE, Omaha District. 1982. Post-Flood Report, Missouri River and Tributaries, February 1982.
USACE, Omaha District. 1986. Platte River and Tributaries Study, 1986.
USACE, Cold Regions Research and Engineering Laboratory and Omaha District. 1994. Lower Platte River Ice Jam Flooding, July 1994.
USACE. 1994. The Great Flood of 1993: Post-Flood Report. Appendix D, Lower Missouri River Basin. U.S. Army Corps of Engineers, Omaha District, September 1994.
USACE. 1995. Flood Plain Management Assessment of the Upper Mississippi River and Lower Missouri Rivers and Tributaries. U.S. Army Corps of Engineers, June 1995.
USACE, Omaha District, Reconnaissance Report, Lower Platte River and Tributaries, Nebraska, April 1996.
USACE, 1996. EM 1110-2-1619, Risk-based Analysis for Flood-damage-reduction Studies, U.S. Army Corps of Engineers, 1 August 1996.
USACE, 2003. Economic Guidance Memorandum (EGM) 04-01, Generic Depth-Damage Relationships for Residential Structures with Basements, U.S. Army Corps of Engineers, 10 October 2003.
USACE, 2004. Flood Hazard Mitigation Plan, City of Schuyler Colfax County, Nebraska, December 2004.
USACE. 2010. Economic Guidance Memorandum (EGM) 11-02, Current Normalized Prices. U.S. Army Corps of Engineers, November 5, 2010.
USACE, Omaha District. 2011. Physical Channel Changes Over Time and Implications to Flood Risk Reduction Plans for Fremont, Nebraska.
155 U.S. Census Bureau. 1990. 1990 Summary Tape File (STF 1): Schuyler, Nebraska. Accessed July 21, 2011, at the Web site: http://www.factfinder.census.gov/.
U.S. Census Bureau. 2000. Profile of General Demographic Characteristics: 2000. Accessed July 20, 2011, at the Web site: http://www.factfinder.census.gov/.
U.S. Census Bureau. 2010. 2005-2009 American Community Survey. Accessed July 20, 2011 at the Web site: http://www.factfinder.census.gov/.
U.S. Census Bureau. 2011. Profile of General Population and Housing Characteristics: 2010. Accessed July 20, 2011, at the Web site: http://factfinder2.census.gov/.
U.S.G.S. (U.S. Geological Survey). 2008. Physiographic Regions. http://tapestry.usgs.gov/physiogr/physio.html. Accessed October 28, 2008.
U.S.G.S. (U.S. Geological Survey). 2003. Streambed Adjustment and Channel Widening in Eastern Nebraska.
U.S. Water Resources Council. 1983. Economic and Environmental Principles and Guidelines for Water and Related Land Resource Implementation Studies, March 10, 1983.
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