Section 1135 Ecosystem Restoration Study

U.S. Army Corps of Engineers, Omaha District

Integrated Feasibility Report and Environmental Assessment

Southern Platte Valley Denver, Colorado June 2018

South Platte River near Overland Pond Park

TABLE OF CONTENTS 1. INTRODUCTION ...... 1 1.1. STUDY AUTHORITY ...... 1 1.2. STUDY SPONSOR AND CONGRESSIONAL AUTHORIZATION ...... 1 1.3. STUDY AREA AND SCOPE ...... 1 2. PURPOSE, NEED AND SIGNIFICANCE ...... 3 2.1. NEED: PROBLEMS AND OPPORTUNITIES ...... 4 2.2. PURPOSE: OBJECTIVES AND CONSTRAINTS ...... 7 2.3. SIGNIFICANCE ...... 8 3. CURRENT AND FUTURE CONDITIONS ...... 16 3.1. PLANNING HORIZON ...... 16 3.2. EXISTING CONDITIONS ...... 16 3.3. PREVIOUS STUDIES ...... 17 3.4. EXISTING PROJECTS ...... 17 3.5. PHYSICAL SETTING ...... 18 3.6. ECOLOGICAL RESOURCES ...... 22 3.7. HYDROLOGICAL ANALYSIS ...... 30 3.8. HYDRAULIC ANALYSIS ...... 31 3.9. SOCIOECONOMIC SETTING ...... 32 3.10. ECONOMIC SETTING ...... 33 3.11. CULTURAL RESOURCES ...... 36 3.12. RECREATIONAL RESOURCES ...... 36 3.13. FORECASTED FUTURE WITHOUT PROJECT CONDITIONS ...... 37 4. PLAN FORMULATION ...... 40 4.1. SECTION 1135 POLICY ...... 40 4.2. STUDY PROCESS ...... 41 4.3. CONSIDERATION OF PLANNING CRITERIA ...... 41 4.4. QUALITY MANAGEMENT ...... 41 4.5. ALTERNATIVE FORMULATION ...... 42 4.6. ALTERNATIVE EVALUATION ...... 72 4.7. ALTERNATIVE COMPARISON ...... 75 4.8. ANCILLARY RECREATION PLAN FORMULATION ...... 80 5. SELECTED PLAN ...... 81 5.1. ANCILLARY RECREATION PLAN ...... 82 5.1. TOTAL PROJECT COST ...... 83 5.2. COST SHARE ...... 83 5.3. DESIGN AND IMPLEMENTATION ...... 83 5.4. RISK AND UNCERTAINTY ...... 84 5.5. SUMMARY OF PLAN EFFECTS ACROSS FOUR P&G ACCOUNTS...... 87 6. ENVIRONMENTAL COMPLIANCE AND SOCIAL EFFECTS ...... 88 6.1. ENVIRONMENTAL CONSEQUENCES ...... 88 6.2. CUMULATIVE IMPACTS ...... 95 6.3. ENVIRONMENTAL COMPLIANCE ...... 97 6.4. PUBLIC INVOLVEMENT ...... 101 7. MONITORING AND ADAPTIVE MANAGEMENT ...... 103 8. OPERATION AND MAINTENANCE ...... 103

9. RECOMMENDATIONS ...... 104 10. LITERATURE CITED ...... 106

Figures Figure 1. Section 1135 study area. Note Reach 1 (pink) is from West Mississippi Ave upstream (south) to West Florida Ave, Reach 2 (yellow) West Florida Ave upstream to West Evans Ave and Reach 3 (purple) is from West Evans Ave to West Yale Ave...... 2 Figure 2. Comparison of the U.S. Army Corps of Engineers’ (USACE) Six-Step Planning Process and NEPA Process ...... 3 Figure 3. Example cross sections of a non-incised and undisturbed stream (top graphic) and an incised, restricted channel with no ecological floodplain (bottom graphic). Photos derived from Nebraska Stream Condition Assessment Procedure (as cited in Gilbert et al., 2012)...... 4 Figure 4. Aerial view of South Platte River, present day. Left picture: approximately 75 miles downstream of the study area in Kersey, Colorado compared to right picture: approximately 1 mile downstream of study area in Denver, Colorado. The view on the left is resonant with the natural condition of the river and what it once resembled in the study area. Note the meandering, sinuous channel with sandbar formation, side channels and a wide riparian buffer...... 5 Figure 5. Representative vegetation characteristic of Reach 1. Photo taken standing in-stream, oriented upstream looking southwest on the west bank. Note the prevalence of a native sandbar willow understory and invasive Siberian elm overstory as well as desiccated vegetation along river, indicating the normal drift line disturbance ...... 6 Figure 6. A sandbar willow (Salix exigua)/mesic graminoid shrubland community (photo derived from Carsey et al. 2003). This riparian forested community would be typical of habitat historic to the study area prior to upstream water impoundment and urbanization. Communities such as this provide diverse and necessary habitat for migrating birds ...... 9 Figure 7. Left photo: Ute ladies’-tresses (photo credit: Delia Malone, derived from CNHP, Colorado rare plant guide); top right photo: Preble’s meadow jumping mouse (photo derived from the Colorado Observer); bottom right photo: Colorado butterfly plant (photo derived from USFWS, Endangered Species)...... 10 Figure 8. Black rosy-finch (Leucosticte atrata). Colorado species of concern, meaning, they are at risk due to declining population trends, threats to their habitat and have restricted distribution. Photo derived from Montana Field Guide (2010)...... 12 Figure 9. Local environmental and recreational restoration project along the South Platte River in downtown Denver ...... 13 Figure 10. Section 1135 in Colfax, approximately 4 miles downstream of South Platte Valley Section 1135. Top photo is prior to construction. Middle and bottom photos, post construction show widened channel, wetland benching and initial seeding. Connectivity between previously constructed projects provides for improved transportation corridors for wildlife...... Error! Bookmark not defined. Figure 11. NWI map of existing wetlands and water resources in the study area (Source: USFWS Wetlands Data Mapper). Note no NWI wetlands exist adjacent to the South Platte River within the study area. The PUBGx are treatment lagoons at Xcel...... 23 Figure 12. Drop structures within the study area. The Aqua Golf Intake drop structure was modified in 2015 and grade elevation was reduced by placing four additional drop

structures upstream of the existing structure. Overland and Xcel drop structures have not been modified...... 26 Figure 13. Drop structures within the study area currently serving as impediments to fish passage. Left picture is the Overland drop structure in Reach 1 and the right picture is the Xcel drop structure in Reach 3...... 26 Figure 14. Land Use within the Study Area ...... 35 Figure 15. Actual and forecasted future population of Denver County. Figure derived from U.S. Census, Colorado Department of Local Affairs, as appeared in The Denver Post, 2017 . 38 Figure 16. Colorado Forecasted Population Growth Rates ...... 40 Figure 17. Existing Drop Structure in Reach 2 near the Aqua Golf intake pumping house...... 43 Figure 18. Conceptual drawing of Alternative A: Aqua Golf in-fill in Reach 1 to create wetlands in Overland Lake. Top graphic depicts general cross-section while bottom graphic depicts conceptual plan view...... 45 Figure 19. Alternative C in Reach 2 near the Overland Golf Course ...... 46 Figure 20. Conceptual plan view of Alternative D in Reach 2 ...... 47 Figure 21. Reach 1 as relevant to the entire Section 1135 study area...... 50 Figure 22. Location of habitat restoration and pedestrian bridge relocation of Alternative B in Reach 1...... 51 Figure 23. Location of riparian restoration of Alternative T in Reach 1 ...... 52 Figure 24. Schematic of potential in-stream features. Top left: rock vane; top right: J-hook; bottom: cross vane. Note the formation of scour pools created downstream of the structures and the depositional zones that accumulate sediment, creating a localized variety of depths and velocities beneficial to fish and other aquatic organisms (Images Craig Hill, after Rosgen, 2006, NRCS, 2007) ...... 54 Figure 25. Scour pattern around a boulder (derived from Fischenich and Seal, 2000) ...... 55 Figure 26. Conceptual layout of modifications at Overland drop structure. Top graphic (plan view) the auxiliary weir would have boulder clusters strategically placed to allow fish to traverse the drop structure by step-laddering from one boulder cluster to the next in the shelter shadows formed by the clusters. Bottom graphic (cross section) depicts the side profile of the existing structure and auxiliary weir (red) and resting pool that would form between the structures ...... 56 Figure 27. Conceptual modifications of the Overland drop structure. Top graphic (plan view) the auxiliary weir with additional riffle ramp would have boulder clusters strategically placed to allow fish to traverse the drop structure by step-laddering from one boulder cluster to the next. Bottom graphic (cross section) depicts the riffle ramp and resting pool with integrated boulder clusters ...... 57 Figure 28. Reach 2 relevant to the entire Section 1135 study area ...... 58 Figure 29. Location of re-vegetation in the downstream portion of Reach 2 of Alternative O .... 59 Figure 30. Location of riparian habitat restoration in Reach 2 of Alternative S ...... 60 Figure 31. Reach 3 relevant to the entire Section 1135 study area ...... 62 Figure 32. Alternative E at Grant Frontier Park in the downstream end of Reach 3. Left graphic depicts existing condition of Grant Frontier Park (“south” and “west bank”). The right graphic depicts the change to Grant Frontier Park South with restored wetland and riparian areas and a conceptual trail alignment of the Regional Trail. Conditions of Grant Frontier on the west bank retain the existing condition...... 63

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Figure 33. Alternative F at Grant Frontier Park in the downstream end of Reach 3. Left graphic depicts existing condition of Grant Frontier Park (“south” and “west bank”). The right graphic depicts the change to Grant Frontier Park South with restored wetland and riparian areas, an additional channel created from the modification of Harvard Gulch and a conceptual trail alignment of the Regional Trail. Conditions of Grant Frontier on the west bank retain the existing condition...... 64 Figure 34. Alternative H at Grant Frontier Park in the downstream end of Reach 3. Left graphic depicts existing condition of Grant Frontier Park (“south” and “west bank”). The right graphic depicts the change to Grant Frontier Park South with restored wetland and riparian areas, an additional channel created (“north channel”) and a conceptual trail alignment of the Regional Trail. Conditions of Grant Frontier on the west bank retain the existing condition...... 65 Figure 35. Alternative I at Grant Frontier Park in the downstream end of Reach 3. Left graphic depicts existing condition of Grant Frontier Park (“south” and “west bank”). The right graphic depicts the change to Grant Frontier Park South with restored wetland and riparian areas, an additional channel created (“south channel”) and a conceptual trail alignment of the Regional Trail. Conditions of Grant Frontier on the west bank retain the existing condition ...... 66 Figure 36. Alternative J at Grant Frontier Park in the downstream end of Reach 3. Left graphic depicts existing condition of Grant Frontier Park (“south” and “west bank”). The right graphic depicts the change to Grant Frontier Park South with restored wetland and riparian areas, an additional channel created (“south channel” and “north channel”) and a conceptual trail alignment of the Regional Trail. Conditions of Grant Frontier on the west bank retain the existing condition...... 67 Figure 37. Alternative R at Grant Frontier Park in the downstream end of Reach 3. Left graphic depicts existing condition of Grant Frontier Park (“south” and “west bank”). The right graphic depicts the change to Grant Frontier Park South with restored wetland and riparian areas, an additional channel created (“south channel” and Harvard Gulch channel) and a conceptual trail alignment of the Regional Trail. Conditions of Grant Frontier on the west bank retain the existing condition ...... 68 Figure 38. Alternative G on the west bank of Grant Frontier Park in Reach 3. The existing riparian habitat on Grant Frontier Park South is depicted in this graphic; however, an alternative at Grant Frontier Park South (E, F, H, I, J or R) must be selected in order for Alternative G to also be selected...... 69 Figure 39. Conceptual layout of modifications at Excel drop structure. Top graphic (plan view) the auxiliary weir would have boulder clusters strategically placed to allow fish to traverse the drop structure by step-laddering from one boulder cluster to the next in the shelter shadows formed by the clusters. Bottom graphic (cross section) depicts the side profile of the existing structure and auxiliary weir (red) and resting pool that would form between the structures ...... 70 Figure 40. Conceptual layout of modifications at Xcel drop structure. Top graphic (plan view) the auxiliary weir with additional riffle ramp would have boulder clusters strategically placed to allow fish to traverse the drop structure by step-laddering from one boulder cluster to the next. Bottom graphic (cross section) depicts the riffle ramp and resting pool with integrated boulder clusters...... 71

Figure 41. CE/ICA Best Buy Plans (white-boxed numbers). Note that best buy plan 1 is the No Action Alternative. The output along the x-axis describes the AAHUs achieved under each best buy plan while the y-axis describes the incremental cost ...... 75 Figure 43. Riparian (left) and Aquatic (right) Alternatives included in Plan 9 ...... 79 Figure 44. Riparian (left) and Aquatic (right) Alternatives included in Plan 10 ...... 79 Figure 45. Conceptual schematic of Harvard Gulch outfall modification and boardwalk in Grant Frontier Park South...... 80

Tables Table 1. Average Maximum and Minimum Temperature and Precipitation for Denver, Colorado, from 1981 to 2010 ...... 18 Table 2. Fish species observed in the South Platte project area from 2007-2012...... 25 Table 3. Migratory birds of special conservation concern potentially existing within or near the South Platte River of the study area...... 27 Table 4. Discharge-Frequency Values used for HEC-RAS Modeling ...... 30 Table 5. Duration analysis for USGS 06711565 South Platte River at Englewood, Colorado .... 31 Table 6. Median Household Income, Unemployment Rate, and Poverty Rate within the Study Area ...... 32 Table 7. Educational Attainment ...... 32 Table 8. Employment by Industry ...... 33 Table 9. Land Use Distribution ...... 34 Table 10. Sites broken down by section...... 36 Table 11. Study Area Tracts Population ...... 39 Table 12. Population 1970-2015 ...... 39 Table 13. Population Forecast 2015 - 2050 ...... 40 Table 14. Final array of alternatives listed by Reach considered with FACWet and/or FACStream, Cost Estimates and CE/ICA. Note the alternatives with an asterisk (*) are part of the Recommended Plan...... 48 Table 15. Mutually exclusive and dependent alternatives, by reach ...... 49 Table 16. Community habitat units* for existing condition, 50-year FWOP and 50-year FWP for each individual alternative and its associated increase of HU** over the 50-year project life and percent increase...... 73 Table 17. CE/ICA Output for Best Buy Plans ...... 77 Table 18. Recommended Plan contributions to the NER Account ...... 81 Table 19. Summary of Recreation Value Calculations ...... 82 Table 20. Recreation Facilities Cost Estimate (FY2018) ...... 82 Table 21. Benefit-to-Cost Ratio ...... 83 Table 22. Total Project Cost ...... 83 Table 23. Preliminary Design & Implementation Schedule ...... 84

Appendices

Appendix A: Biology Appendix Appendix B: Economics Assessment Appendix C: Hydraulic and Stability Analysis Appendix D: Flood Risk and Floodplain Management Appendix E: Geotechnical Engineering, Soils and Geology Appendix F: Structural Analysis Appendix G: Cost Estimate & Value Engineering Report Appendix H: Real Estate Plan Appendix I: HTRW Analysis & Phase I & Phase II ESAs Appendix J: Cultural Resources Assessment Appendix K: Recreational Analysis Appendix L: Public Involvement

Acronyms

AAHU average annual habitat unit ACE annual chance of exceedance ACS American Community Survey ATR Agency Technical Review BA Biological Assessment BCR benefit to cost ratio bgs below ground surface BNSF Burlington Northern Santa Fe Railroad CAA Clean Air Act CAP Continuing Authorities Program CDOW Colorado Division of Wildlife CDPHE Department of Public Health and Environment CE/ICA Cost Estimate/Incremental Cost Analysis CERCLA Comprehensive Environmental Response, Compensation, and Liability Act cfs cubic feet per second CLOMR Conditional Letter of Map Revision CNHP Colorado National Heritage Program CPW Colorado Parks and Wildlife CRI cultural resources inventory CSDO Colorado State Demography Office CWA Clean Water Act CWQCC Colorado Water Quality Control Commission cy cubic yards DADS Denver Arapahoe Disposal Site DDPHE Denver Department of Public Health and Environment D&I design and implementation DPR detailed project report DQC District Quality Control EA Environmental Assessment ECB Engineering Construction Bulletin EIS Environmental Impact Statement EO Executive Order EPA Environmental Protection Agency EQ Environmental Quality ER Engineering Regulation ESA Endangered Species Act FACStream Functional Assessment of Colorado Streams FACWet Functional Assessment of Colorado Wetlands FCI Functional Capacity Index FCSA Feasibility Cost Share Agreement FEMA Federal Emergency Management Agency FONSI Finding of No Significant Impact FPPA Farmland Protection Policy Act FWOP future without project

FWP future with project GIS Geographic Information System HEC-RAS Hydrologic Engineering Center – River Analysis System HTRW Hazardous, Toxic and Radioactive Waste HU habitat units IPaC Information for Planning and Conservation IWR Institute for Water Resources LERRD lands, easements, relocations, rights-of-way, disposal areas LIDAR light detection and ranging MBTA Migratory Bird Treaty Act MDM Major Decision Milestone NAAQS National Ambient Air Quality Standards NED National Economic Development NEPA National Environmental Policy Act NER National Ecosystem Restoration NFIP National Flood Insurance Program NHPA National Historic Preservation Act NPDES National Pollutant Discharge and Elimination System NPL National Priority List NRCS Natural Resources Conservation Service NRHP National Register of Historic Places NWD Northwestern Division NWI National Wetlands Inventory O&M operation and maintenance OSE Other Social Effects PAH Polycyclic Aromatic Hydrocarbons PAL Planning Aid Letter PDT Project Delivery Team P&G Principles and Guidelines PL Public Law PM particulate matter PMP Project Management Plan PPA Project Partnership Agreement PRF Pollutant Reduction Facilities REC recognized environmental condition RED Regional Economic Development RSL Regional Screening Level SHPO State Historic Preservation Office SOW scope of work SPLRG South Platte Lower River Group SPWFAC South Platte Wetland Focus Area Committee SWPPP Stormwater Pollution Prevention Plan TMDL total maximum daily load TSP tentatively selected plan UDFCD Urban Drainage and Flood Control District UDV unit day value

USC United States Code USFS U.S. Forest Service USFWS U.S. Fish and Wildlife Service USNVC U.S. National Vegetation Classification UWFP Urban Waters Federal Partnership WSE water surface elevation WWE Wright Water Engineers, Inc.

Executive Summary

This ecosystem restoration study is being carried out under Section 1135 of the Water Resources Development Act of 1986 (P.L. 99-662). Under Section 1135, the U.S. Army Corps of Engineers (Corps) is authorized to study, adopt, and construct modifications to existing Corps projects, and areas directly impacted by existing Corps projects, for the improvement of the environment in partnership with state and local governments. The non-federal sponsor for this study is the City and County of Denver, Colorado. In 2010, the City and County of Denver requested planning assistance through Section 1135 to restore and improve fish and wildlife habitat downstream of the Corps Bear Creek and Chatfield Projects. The Chatfield and Bear Creek projects were completed in 1975 and 1982, respectively. While these projects provide flood risk reduction to the Denver area, the altered hydrology due to the impoundment of the river and controlled releases have severely impacted the downstream ecosystem. Lower base flows during spring and increased base flows during summer are released as compared to pre- impoundment condition. Historically, flows along the South Platte River were variable, rising in spring pulses from snow melt in the Rocky Mountains and lowering to almost dry conditions during other times of the year. It is these dredges and deluges of precipitation and runoff that create the dynamic hydrologic and geomorphic regimes that form the biological conditions of a pristine functional watershed. Hydrologic conditions of the study area today result from the artificial management of the water that moves through the impoundment projects as well as complete urbanization of the ecological floodplain. Problems specifically associated with the degraded aquatic environment of the study area include lack of channel sinuosity, loss of riffle pool complexes, reduced shading, woody debris and detritus inputs from lack of vegetation in the riparian corridor, poor depth diversity, poor refuge habitat for fish, and lack of aquatic vegetation. Problems associated with the degraded riparian and wetland habitat adjacent to the river include a lack of natural connection with the ecological floodplain, reduced extent of the riparian corridor vegetative buffer, a vegetative community that is primarily comprised of noxious and invasive species and lack of necessary hydrology to support wetland flora and fauna. The study area for this feasibility study is 2.4 miles of the South Platte River and its floodplain, approximately 200 feet wide on either bank, is located within Denver, Colorado. The federal objective for the Corps during ecosystem restoration planning is to restore structure, function and dynamic processes to degraded ecosystems and contribute to the National Ecosystem Restoration (NER) account. The NER account is also referred to as NER outputs, which are increases in the net quantity and/or quality of desired ecosystem resources. Measurement of NER outputs are based on changes in ecological resource quality as a function of improvement in habitat quality and/or quantity and expressed quantitatively in physical units or indexes; but not monetary units. The need for restoration along the South Platte River within the study area has resulted from these environmental resources being degraded by the construction of two existing Corps multi-purpose flood control dams and reservoirs (Chatfield and Bear Creek) approximately 11 miles upstream of the project area as well as other modification and development of the river corridor. One constraint identified for this study is that ecosystem restoration recommendations must not increase flood risk to the community. Other considerations identified during plan formulation included the existing infrastructure and sewer lines paralleling the river on one or both banks for the extent of the study area and utility and natural gas lines that the traverse the river under three grade control structures as well as the limited opportunity for land acquisitions due to high real estate value.

Ecosystem restoration alternatives were developed collaboratively with input from the City and County of Denver, local and state resource agencies, and the Corps. In-stream restoration alternatives developed centered on habitat structures such as dikes and boulder clusters to increase the complexity of the aquatic environment and modification of existing drop structures to facilitate fish passage. Riparian and wetland restoration alternatives formulated consisted of restoring the quantity and quality of habitat adjacent to the South Platte River. Twenty-two initial measures were preliminary identified and screened before being developed into more detailed alternatives for further consideration. A total of 17 alternatives, and additionally the No Action Alternative, were evaluated and compared based on environmental benefits, in terms of habitat units (HUs), assessed with two hydrogeomorphic environmental assessment models and costs using the cost-effectiveness incremental cost analysis (CE/ICA) planning suite software from the Institute of Water Resources (IWR). CE/ICA determined a total of 11 best buy plans 8,424 different combinations of the alternatives. Following CE/ICA analysis, a recommended plan, Plan 10, was selected for implementation. The Recommended Plan combines nine of the 17 ecosystem restoration alternatives assessed; four alternatives under the recommended plan focus on restoration of the aquatic habitat and the remaining five alternatives focus on restoring the wetland and riparian habitat adjacent to the South Platte River. The Recommended Plan provides 12.91 net total average annual HUs. The average annual cost per unit of habitat is $34,940. The Recommended Plan would result in improvement of 8,196 feet of stream length (approximately 22.4 acres estimated using aerial imagery dated 2015) of low quality aquatic habitat of the South Platte River through the construction of in-stream features such as dikes, cross vanes, riffles and boulder clusters and restore approximately 11.28 acres of riparian habitat and 1.14 acres of palustrine emergent/scrub shrub wetlands across the entire project area in downtown Denver (Table 1 and Figure 1). Other improvements to aquatic habitat include the modification of two drop structures to facilitate fish passage within the study area. Currently, the Overland drop structure is an approximate 3-foot high barrier to fish, while the Xcel Energy drop structure is an approximate 5-foot high barrier to fish. As identified as a formulation consideration, both drop structures sit atop of utility and natural gas lines and cannot be removed or replaced. Modifications include construction of an auxiliary weir and a 1 vertical to 20 horizontal (1:20) riffle ramp downstream of both existing drop structures. Additionally, at Grant Frontier Park “South” (Grant Frontier Park south of the pedestrian bridge), two low-flow side channels will be constructed on the east bank to provide oxbow habitat commensurate with natural conditions of the South Platte River that existed prior to upstream impoundment from the Chatfield and Bear Creek dams. This plan is recommended with full support from the non-federal sponsor. It also carries wide ranging support from federal and state agencies such as U.S. Fish and Wildlife and Colorado Parks and Wildlife, non-profit/grassroots organizations such as Trout Unlimited and the Audubon Society, and the general public.

Table 1. Recommended plan contributions to the NER account 1.

Figure 1. Riparian/wetland (left) and aquatic (right) alternatives included in in the Recommended Plan

Section 1135 permits recreation features to be planned at ecosystem restoration projects. In accordance with Corps policy, recreation at ecosystem restoration projects should be compatible with these types of projects and enhance the visitation experience by taking advantage of natural values. Recreational features must remain ancillary to the primary purpose of the project and cannot diminish

1 Increase in HUs within Table 1 present total net lift each individual measure provides to the overall Reach it occurs in, HUs in this table are raw data and are not average annualized. Net gain HUs and percent increase are the total lift calculated by the difference of the 50-year future without project condition and the 50-year future with project condition

the contributions (HUs) to the NER account which are used to justify the project. Recreation features planned for this project include 1,200 feet of elevated boardwalk at Grant Frontier Park South, which in addition to providing controlled access to the river, will help regulate foot traffic and reduce damage to the restored habitat areas. Other recreation features include interpretive educational signs, and the setback and aesthetic modification of the existing Harvard Gulch outfall where a viewing platform would be constructed, overlooking the restored areas of Grant Frontier Park South. These recreational features provide connectivity to existing recreational facilities in the community. Considering only the costs of recreation features, they will provide recreation benefits to the community with a benefit to cost ratio of approximately 1.04 to 1 and less than 10 percent of the overall project cost, estimated at $830,475 for recreation. The estimated cost-shared total project cost is $10,522,000. Of the total project cost, $1,025,000 is for land, easement, rights-of-way, relocation, and disposal costs, for which credit will be given to the sponsor. Of the total cost, the federal portion is approximately $7,891,000 and the non-federal portion is approximately $2,630,000. Of the total non-federal portion, approximately $1,630,000 will be provided in cash and $1,000,000 will be provided in land, easement, rights-of-way, relocation, and disposal costs. Estimated average annual cost for operations and maintenance is $95,515 for ecosystem restoration.

Finding of No Significant Impact (FONSI) Section 1135 Ecosystem Restoration South Platte Valley, Denver, Colorado Integrated Feasibility Study and Environmental Assessment June 2018

The U.S. Army Corps of Engineers, Omaha District (Corps), has conducted an environmental assessment that has been prepared pursuant to the National Environmental Policy Act (NEPA) in accordance with the Council on Environmental Quality regulations as contained in 40 CFR Parts 1500 to 1508, and the US Army Corps of Engineers (USACE) Department of Army procedures for implementing NEPA found at 33 CFR Part 230. The Corps assessed the effects of the following actions in the Final Feasibility Study and Environmental Assessment, dated XX 2018, for the Section 1135 Ecosystem Restoration Study and that report is incorporated herein by reference.

The Recommended Plan includes the restoration of approximately 11.28 acres of riparian habitat and 1.14 acres of palustrine emergent/scrub shrub wetlands throughout the entire project area in downtown Denver. Additional aquatic improvements include a series of in-stream features as well as the modification of two drop structures and the installation of auxiliary weirs and riffle ramps immediately downstream of these drop structures to restore approximately 22.4 acres of aquatic habitat across 8,196 feet of stream length and improve fish passage within the entire study area of the South Platte River.

In addition to the No Action Alternative, 17 separate alternatives with varying levels of improvement to the ecosystem were evaluated. The recommended plan was identified as the National Ecosystem Restoration (NER) Plan and is the preferred alternative as it meets the project purpose and need and maximizes the ecosystem restoration project for the most effective incremental cost. All practicable means to avoid and minimize natural or human caused adverse environmental effects have been incorporated into the recommended plan. The recommended plan would not result in any impacts to federally-listed threatened or endangered species or their designated critical habitat, would have no impact to sites listed on or eligible for inclusion on the National Register of Historic Places, and would not significantly affect any wetlands or water of the U.S., nor any important wildlife habitat. Therefore, no compensatory mitigation is required.

Technical and economic criteria used in the formulation of alternative plans were those specified in the Water Resource Council’s 1983 Economic and Environmental Principles for Water and Related Land Resources Implementation Studies. All applicable laws, executive orders, regulations, and local government plans were considered in the evaluation of the alternatives. It is my determination that the recommended plan does not constitute a major federal action that would significantly affect the human environment; therefore, preparation of an Environmental Impact Statement is not required.

Date: ______John L. Hudson, P.E. Colonel, Corps of Engineers District Commander

1. INTRODUCTION The South Platte River flows from the Colorado Front Range through the greater Denver Metropolitan Area from southwest to northeast. Within the immediate vicinity of the study location, shown in Figure 1, the river’s floodplain has been heavily urbanized. Furthermore, the U.S. Army Corps of Engineers (Corps) has constructed a series of multi-purpose flood control dams on the South Platte River, known as the Tri-Lakes Projects, to reduce the flood risk within the Denver area. The culmination of these actions has led to degraded riparian and aquatic ecosystems along the South Platte River in Denver, Colorado. In an effort to restore a semblance of this degraded habitat, the City and County of Denver (Denver) sent a letter of request to the Corps, Omaha District to initiate a Section 1135 Ecosystem Restoration Feasibility Study on June 22, 2010. 1.1. STUDY AUTHORITY This feasibility study was conducted under the authority of Section 1135 of the Water Resources Development Act of 1986 (P.L. 99-662). Under Section 1135, the Corps is authorized to study, adopt, and construct modifications to existing Corps projects, and areas directly impacted by existing Corps projects, for the improvement of the environment in partnership with state and local governments. Projects implemented under the Section 1135 authority are formulated in accordance with current policies and procedures governing projects of the same type that are specifically authorized by Congress. Section 1135 projects are typically cost-shared 75 percent federal and 25 percent non- federal, with the federal share limited at $10 million. Exceptions to this cost-share percentage, allowing the non-federal sponsor to cost-share more than 25 percent of the study costs, require a waiver approved by the Corps’ Headquarters. 1.2. STUDY SPONSOR AND CONGRESSIONAL AUTHORIZATION Denver served as the cost-sharing sponsor throughout the feasibility study. The Feasibility Cost Share Agreement (FCSA) for this study was signed on September 30, 2016, providing for the 50/50 cost share of the study between the Corps and Denver. Additionally, the study area is in Colorado’s First Congressional District. Congressional representatives for the study area include U.S. Representative Diana DeGette, and U.S. Senators Michael Bennet and Cory Gardner. 1.3. STUDY AREA AND SCOPE The study area, an approximate 2.4-mile long portion of the South Platte River and its floodplain, is located within Denver, Colorado. The study area includes three reaches, 200 feet on either side of the river, as depicted by the red line in Figure 1. The distance is based on the assumption that ecosystem problems and restoration opportunities are expected to be situated in close proximity to the river, in addition to real estate constraints. The three reaches are identified as follows: Reach 1) South Platte River and its floodplain from West Mississippi Avenue upstream to West Florida Avenue; Reach 2) South Platte River and its floodplain from West Florida Avenue upstream to West Evans Avenue; and Reach 3) South Platte River and its floodplain from West Evans Avenue upstream to West Yale Avenue.

Section 1135 June 2018 South Platte Valley 1

Figure 1. Section 1135 study area. Note Reach 1 (pink) is from West Mississippi Ave upstream (south) to West Florida Ave, Reach 2 (yellow) West Florida Ave upstream to West Evans Ave and Reach 3 (purple) is from West Evans Ave to West Yale Ave.

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The general scope of this study included all investigations and analysis required to prepare an integrated feasibility report and environmental assessment (EA). This included evaluating alternatives and developing the National Ecosystem Restoration (NER) plan to be recommend for implementation. Also included is coordination with the sponsors, state and federal agencies, and other stakeholders, as well as public outreach to ensure that the study adequately considered local concerns and input. Corps feasibility studies follow rigorous planning procedures established in accordance with the “Principles and Guidelines for Water and Related Land Resources Implementation Studies” published by the U.S. Water Resources Council in March 1983 (commonly referred to as the Principles and Guidelines). This report presents integration of both the feasibility analysis following Corps’ current policy, as well as an EA in compliance with the National Environmental Policy Act (NEPA) (42 U.S.C. § 4331 et seq.). Figure 2 presents a side-by-side representation of how the Corps’ six-step planning process aligns with the typical NEPA process.

Figure 2. Comparison of the U.S. Army Corps of Engineers’ (USACE) Six-Step Planning Process and NEPA Process 2. PURPOSE, NEED AND SIGNIFICANCE The purpose of the project is to restore degraded riparian and aquatic ecosystems along the South Platte River in Denver, Colorado within the study area. The need for restoration has resulted from these resources being degraded by the construction of two existing Corps multi-purpose flood control dams and reservoirs (Chatfield and Bear Creek) approximately 11 miles upstream of the project area. The Chatfield and Bear Creek projects were completed in 1975 and 1982, respectively. While both of these projects provide flood risk reduction to the Denver area, the altered hydrology due to the impoundment of the river and controlled releases have severely impacted the downstream ecosystem. The Corps’ project delivery team (PDT) and the non-federal sponsor held a charrette on February 27, 2017 to brainstorm and collaborate on the development of the problems, opportunities, objectives and constraints associated with this study.

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2.1. NEED: PROBLEMS AND OPPORTUNITIES Problems The segment of the South Platte River within the study area has been highly degraded and modified by flood control infrastructure and urbanization throughout the Denver metro. Modification activities include artificially managing hydrology through the existing flood control reservoirs, channelization, armoring the banks, and realigning the river. These impacts have altered the physical structure and function of the system and removed the natural features of the riparian system. More specifically, problems associated with the degraded aquatic environment of the study area include lack of channel sinuosity, loss of riffle pool complexes, reduced shading, woody debris and detritus inputs from lack of vegetation in the riparian corridor, poor depth diversity, poor refuge habitat for fish, and lack of aquatic vegetation. Problems associated with the degraded riparian and wetland habitat adjacent to the river include a lack of natural connection with the ecological floodplain, reduced extent of the riparian corridor vegetative buffer, a vegetative community that is primarily comprised of noxious and invasive species and lack of necessary hydrology to support wetland flora and fauna. Altered Stream Form and Function The flood control features upstream of the project area and intense urbanization of the historic floodplain have effectively cut off the river’s access to its floodplain and confined the South Platte to an approximate 90-foot wide by 15- to 30- foot high trapezoidal, flat-bottomed cross-section throughout the study area (Figure 3). The dynamics of this altered cross-section have contributed to increased velocities, decreased sediment transport and increased water temperatures. Furthermore, the straightened and confined channel along with modifying the slope with artificial drop structures has caused a decrease in the natural meander (sinuosity) which inhibits point bar formation as well as riffle/pool complexes that are important habitat for aquatic species. These components are important for aquatic habitat as they increase the depth diversity of the channel as well as facilitate lateral movement of the water along its floodplain. Alteration of the historic planform morphology has decreased the overall stability and biological resiliency of the South Platte River through this area. Stability is a function of the channel bed and banks’ ability to withstand external forces which act upon them while ecological resilience describes the system’s ability to resist change or to rapidly recover Figure 3. Example cross sections of a non-incised and undisturbed stream (top graphic) and an incised, following an extreme disturbance event. restricted channel with no ecological floodplain (bottom graphic). Photos derived from Nebraska A natural connection with the floodplain does not exist due Stream Condition Assessment Procedure (as cited in to the full entrenchment of the channel with uniform steep Gilbert et al., 2012). side slopes and lack of channel sinuosity. As such, the riparian habitat has become disconnected and altered in structure and species composition. Fill material utilized for channelization of the South Platte River, in conjunction with the altered hydrology, has removed hydric soils and the ability to support transitional wetland flora species natural to a healthy riparian ecosystem.

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Loss of Natural Substrate Like changes in flow regimes as a result of upstream dams, an altered sediment regime may cause a cascade of impacts on stream form and function. Sediment availability within the South Platte River throughout urbanized Denver has been reduced from historic conditions and placed in disequilibrium primarily due to the upstream dams as well as the riprapped banksides and in-stream grade control structures. Sediment is produced within the overall watershed through surface erosion and upstream channel erosion and then transported downstream. Most sediment enters the South Platte River during March through June when snowmelt is occurring and water is moving across the land surface, streets and parking lots (USGS, 1995). Sediment movement throughout the channel is imperative for natural development of aquatic ecosystems through nutrient replenishment, the creation of benthic habitat and spawning areas, and creation of habitat features such as pointbars and sandbars (Figure 4).

Figure 4. Aerial view of South Platte River, present day. Left picture: approximately 75 miles downstream of the study area in Kersey, Colorado compared to right picture: approximately 1 mile downstream of study area in Denver, Colorado. The view on the left is resonant with the natural condition of the river and what it once resembled in the study area. Note the meandering, sinuous channel with sandbar formation, side channels and a wide riparian buffer.

Loss of Streamside Vegetation Historically, the vegetative community that dominated the South Platte River in the study area was a cottonwood (Populus spp.) overstory with a willow (Salix spp.) shrub layer. Plains cottonwood (P. deltoides) stands provide habitat for 82% of all bird species breeding in northeast Colorado (Segelquist et al., 1993). Restricted hydrologic floodplain inundation, competition from non-native vegetation and urbanization have severely reduced cottonwood-willow recruitment in this reach of the South Platte River. The majority of the vegetation along the banks of the South Platte River throughout the study area found today is fairly homogenous and composed of introduced species. A riparian habitat that is a monoculture of undesirable or invasive species outcompetes the native vegetation which is important to native wildlife species. Specifically in Reach 1 (Figure 5), the majority of the overstory is invasive Siberian Elm (Ulmus pumila) while Reach 2 has little wooded vegetation. The herbaceous vegetation along the

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study area is primarily a monoculture of smooth brome (Bromus inermis). The lack of a contiguous streamside vegetative buffer causes a lack of suitable habitat connectivity for wildlife as it does not provide an adequate corridor for faunal movement. Furthermore, a lack of shading from tall woody vegetation along the banksides of the study area increases water temperatures and decreases cover for both aquatic and terrestrial wildlife. Figure 5. Representative vegetation characteristic of Reach 1. Photo taken standing in-stream, oriented upstream looking southwest on the Loss of Aquatic west bank. Note the prevalence of a native sandbar willow understory and invasive Siberian elm overstory as well as desiccated vegetation along Vegetation river, indicating the normal drift line disturbance Channelization and armoring have caused bank incision and steepening therefore impacting the ability of in-stream vegetation to exist along the fringes of the river. Natural shorelines are the undeveloped fringe areas along the edge of waterbody, which connect the shallow aquatic portion of the waterbody with the adjacent upland. In addition to these armoring and stabilization practices reducing riparian succession processes (Fischenich 2003), the lack of shallower in- channel areas as well as natural fringe areas inhibits the ability to support emergent, submergent and floating aquatic vegetation. Aquatic vegetation provides an important role in structuring communities in aquatic environments. These plants provide physical structure, increase habitat complexity and diversity and affect invertebrates, fish and waterbirds (Tomaz and da Cunha, 2010). Loss of Stream Flow The Chatfield and Bear Creek flood control project is authorized for water supply storage, recreation opportunities and fish and wildlife. Withdrawals upstream of the study area due to these projects include surface water diversions and reservoir storage. Prior to this altered hydrology, flows along the South Platte River were variable, rising in the spring from snow melt and lowering to nearly dry conditions during the late summer and fall. Natural geomorphic processes resulted in the river meandering throughout its floodplain, leading to diversity of aquatic habitat features such as natural riffle/pool complexes, point bar formations and areas with varying flow depths and velocities associated with braided, alluvial stream complexes. After construction of the Tri-Lakes project, the natural flows of the South Platte were captured and stored during spring runoff to reduce the impact of downstream flooding. The stored water is then released later in the year over an extended period of time. As a result, the study area is now heavily regulated with lower flood flows and higher base flows, reducing dynamic processes and homogenizing the riparian and aquatic habitat. Opportunities The following were identified during the February 27, 2017 charrette as the major opportunities for this study, which were further refined throughout the feasibility study:

• Restore natural form and function to the South Platte River to a level attainable and feasible under a Section 1135 authority • Improve aquatic habitat for fish and other aquatic species • Restore floodplain wetlands and wetland fringe areas along the South Platte River

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• Improve the quality of existing riparian habitat in the project area • Reverse negative environmental effects of a flood risk management system that was built in the 1970s and 1980s which did not include the integration of sustainable environmental principles • Leverage current science and social values to restore a severely degraded urban stream corridor • Integrate recreation that reflects public interest and compliments restorations efforts into the project 2.2. PURPOSE: OBJECTIVES AND CONSTRAINTS Objectives In accordance with Engineer Regulation (ER) 1105-2-100 Appendix E, objectives are to be specific, flexible, measurable, realistic, attainable, and acceptable. For this study there were two sets of objectives, the Federal Objective, which is a requirement of every Corps Planning Study, and the project objectives, which are developed on a per project basis. These objectives are detailed below. Federal Objective. The federal objective for the Corps during ecosystem restoration planning is to restore structure, function and dynamic processes to degraded ecosystems and contribute to the National Ecosystem Restoration (NER) Account. Contributions to the NER Account, also referred to as NER outputs, are increases in the net quantity and/or quality of desired ecosystem resources. Measurement of NER outputs are based on changes in ecological resource quality as a function of improvement in habitat quality and/or quantity and expressed quantitatively in physical units or indexes; but not monetary units. Project Objectives. In addition to the federal objective, the non-federal sponsor and the Corps PDT developed the following list of project objectives: 1. Restore in-channel habitat complexity and connectivity in the South Platte River for native aquatic species through the planning period of analysis (50 years). Specifically increasing riffle habitat, increasing depth diversity and localized velocity changes, increasing the presence of course gravels and decreasing temperatures. 2. Restore riparian and wetland habitat quantity and quality in the South Platte River for migratory birds protected under the Migratory Bird Treaty Act and native species of plants and animals through the planning period of analysis. Specifically increasing the connectivity, width and patch side of riparian and wetland habitats, and quality and diversity of native vegetation. Constraints and Considerations A constraint for this study is that ecosystem restoration recommendations must not increase flood risk within the project area. The following considerations were identified during the February 27, 2017 charrette:

• The existing floodplain is sensitive to changes within the existing channel footprint, so revisions to the existing channel will need to be carefully analyzed to recognize and avoid impacts on the South Platte River floodplain. • The channel is completely urbanized, limiting the extents of the potential project area without resulting in socio-economic impacts. • High real estate values in the local area will make land acquisition difficult. • Large sanitary sewer lines parallel the South Platte River on one or both sides of the channel throughout the entire study area that cannot be relocated. • Utility and natural gas lines traverse the South Platte River under three drop structures

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• High cost associated with removing and replacing/relocating existing bridges and other structures. • Potential hazardous, toxic and radioactive waste (HTRW) contaminants throughout the project reach. • The project won’t be able to address the entire South Platte River within the City of Denver so improvements within the study area must be evaluated for impacts downstream of the project reach. 2.3. SIGNIFICANCE Identifying significance is a critical step in Corps ecosystem restoration planning. It helps establish federal interest in a restoration planning project and priority at national, regional, state, and local levels. Criteria are used to evaluate various project plans and communicate information to decision makers to support recommendations and justification for plan selection. Following a recommendation and approved decision document, significance criteria may also be analyzed by decision makers to inform budget priorities and allocation of funds among multiple approved projects. This section provides a summary of the institutional, public, and technical significance of the South Platte Valley Section 1135 project as described in the Economic and Environmental Principles and Guidelines for Water and Related Land Resources Implementation Studies and Resource Significance Protocol for Environmental Project Planning (IWR Report 97-R-4). It is important to note that these significance-based categories are not necessarily mutually exclusive and the significance of many Environmental Quality (EQ) resources and attributes may be recognized on more than one basis. Institutional Institutional significance is based on the importance of a resource or attribute acknowledged in the laws, adopted in plans and other policy states of public agencies or private groups. Sources of institutional recognition include laws, executive orders, rules, regulations, plans, directives, codes, ordinances and other policy statements made by local public entities and councils of government. Migratory and Shorebirds Restoring migratory bird habitat (shrubs/forested areas/wetlands) in close proximity to the South Platte River supports national efforts to comply with the Migratory Bird Treaty Act (MBTA; 16 USC 703-712). Currently there are 25 migratory “Birds of Conservation Concern,” all of which are defined within the project area. For this study, migratory bird habitat is equated to riparian forested and scrub-shrub wetland habitat. The U.S. Fish and Wildlife Service (USFWS) has stated that habitat restoration targeting aquatic, wetland, and riparian habitats would be consistent with goals of the U.S. Shorebird Conservation Plan, the North American Waterbird Conservation Plan, and the North American Waterfowl Management Plan. These plans are adopted by state and federal agencies and non-governmental organizations across the country to determine species, sites, and habitats that most urgently need conservation and/or restoration, making them institutionally significant for restoration plans within the study area. 2.3.1.1.1. The Central Flyway In studying the migratory routes of birds, specific pathways were delineated and are used to scientifically acknowledge their importance. The study area is located within the Central Flyway bird migration route. Over 400 species of birds across 50 families follow the Central Flyway (Johnsgard, 2012), utilizing wetlands, grasslands, and other habitat types in the study area throughout their lifecycles, including at least 14 birds on the USFWS’ Birds of Conservation Concern list. The USFWS (in partnership with other agencies) manages migratory birds based largely on routes the birds follow as they migrate between nesting and wintering areas. Based on those routes, four administrative Flyways (Atlantic, Mississippi, Central and Pacific) were established in North America to facilitate management of

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migratory birds and their habitats. The flyways have Councils consisting of representatives from each state, provincial, and territorial agency within that flyway. Councils are managed by technical committees consisting of biological staff from the member agencies. The technical committees evaluate population and habitat information and make recommendations to the Councils on matters of migratory bird conservation. The Central Flyway was formed in 1948 and consists of the states of Montana, Wyoming, Colorado, New Mexico, Texas, Oklahoma, Kansas, Nebraska, South Dakota, and North Dakota, and the Canadian provinces of Alberta, Saskatchewan and the Northwest Territories.

Figure 6. A sandbar willow (Salix exigua)/mesic graminoid shrubland community (photo derived from Carsey et al. 2003). This riparian forested community would be typical of habitat historic to the study area prior to upstream water impoundment and urbanization. Communities such as this provide diverse and necessary habitat for migrating birds

2.3.1.1.2. Migratory Birds Life History Requirements Migratory birds, one of the South Platte’s resources of national significance, key in on riverine corridors primarily because these corridors are more productive and provide food and cover resources. Without this valuable aquatic habitat, migratory birds would not have the needed resources to recover and continue their migration or successfully reproduce. The state of Colorado as a whole has experienced significant habitat losses including reductions of over 70 percent of riparian forests and over 50 percent of wetlands state-wide with even higher percentages in urban areas. Wetlands and riparian areas represent only about 2 percent of the total land area of Colorado, but 80 percent of wildlife species use these habitats. Riparian areas form essential habitat for over 50 percent of Colorado’s bird species. In arid climates like Colorado, where evaporation often exceeds precipitation, wetlands are an irreplaceable habitat for vast numbers of migrating birds that either breed or stop over in wetlands. Of the bird species using the area, 59 percent use the river year- round. The remaining 41 percent are neotropical species and other migrants that use the river as a migration corridor or stopover point in the otherwise mostly treeless terrain Endangered Species The federally-listed threatened Preble’s meadow jumping mouse (Zapus hudsonius preblei), Colorado butterfly plant (Gaura neomexicana coloradensis), and Ute ladies’-tresses orchid (Spiranthes diluvialis) were all three historically found along the South Platte River in what is now the Denver Metro Area

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(Figure 7). Due to the extreme impacts to the natural habitat that have occurred as a result of channelization of the river, development and urbanization of the floodplain, and the high amount of recreational use along the river within the city of Denver, the USFWS has designated block clearance areas for all proposed actions that could otherwise potentially impact the three listed species within the city of Denver. In other words, the areas along the South Platte River within the city of Denver have been so severely impacted, that the USFWS has determined that all three species have become locally extinct (extirpated) from the area. However, while the Preble’s meadow jumping mouse, Colorado butterfly plant, and Ute ladies’-tresses are no longer found in the proposed project area, and current habitat conditions on site are unlikely to support any of the three species, the project site is within their historic ranges. Proposed restoration efforts will likely improve habitat conditions that would be beneficial to all three species.

Figure 7. Left photo: Ute ladies’-tresses (photo credit: Delia Malone, derived from CNHP, Colorado rare plant guide); top right photo: Preble’s meadow jumping mouse (photo derived from the Colorado Observer); bottom right photo: Colorado butterfly plant (photo derived from USFWS, Endangered Species).

Wetland and Riparian Habitat Conservation and Protection Wetlands are a critically important feature of the riparian system along the South Platte River and are of federal interest and institutionally significant due to the Clean Water Act (CWA) and Executive Order (EO) 11990. Wetlands in highly urbanized watersheds, while impacted by development, still provide essential services. These services include flood control by absorbing excess runoff, erosion control through vegetation stabilization, water quality improvement by removing excess nutrient runoff, pollutants and contaminants from non-point sources (Smith and Kuhn, 2015). Management efforts for protecting and improving Denver’s urban wetlands should focus on protecting water quality and increasing opportunities for public education. Encouraging actions such as allowing shoreline vegetation to expand, reducing the use of herbicides and pesticides, reduced mowed immediately adjacent to wetlands and lakes, limiting development and impervious surfaces, and by utilizing environmentally

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friendly landscaping techniques would improve water quality and functionality of Denver’s wetland resources. Reconnecting rivers to their floodplains and facilitating structural diversity in wetlands adjacent to rivers would improve and restore a variety of wetland functions to existing wetlands (Smith and Kuhn, 2015). The project also area falls within one of seven pilot locations defined by the Urban Waters Federal Partnership (UWFP), which is a union of 13 federal agencies to improve coordination among federal agencies and collaborating with local community-led revitalization efforts for improving the Nation’s waters and promoting the economic, environmental and social benefits of the communities near them. The UWFP, established in June 2011, identified the South Platte River as an invaluable resource for drinking water, recreation and economic development. Below are a few investments made to date by the UWFP: . The U.S. Forest Service (USFS) Urban and Community Forestry Program has provided $114,000 through a competitive matching grant process to support green jobs and restoration. These projects include planting native tree species for storm water and flood control, removing invasive species and educating about watershed and water quality issues. . The USFS and Denver Urban Water completed 3,400 acres of fuel treatments and reforestation to date (according to the UWFP Activities Report: May, 2013). . The USFS provided funding to staff a two-year Urban Waters Ambassador to provide overall coordination for the pilot area. . The U.S. Environmental Protection Agency (EPA) awarded a $350,000 grant for green infrastructure, water quality and area-wide planning projects on the South Platte River. Regional and State 2.3.1.4.1. Importance of Wetland and Riparian Habitats The study area lies within the geographical range of the USFWS’s Mountain-Prairie Region which ranks riparian habitat, especially cottonwood-willow associations, as a critical wildlife resource (USFWS, 2001). The types of riparian habitat that would be restored under this Section 1135 would be these critical cottonwood-willow associations. As discussed under institutional significance, wetland restoration is also considered significant under regional and state importance. Restoring wetlands within the project area would contribute to an increase in availability of this diminished habitat type. Wetlands, especially around urban areas and along major rivers and streams, have been destroyed or profoundly altered from their pre-settlement condition. It has been estimated that in the state of Colorado, 10 million acres of wetlands have been lost since pre-settlement times (Dahl, 1990). Wetlands and riparian areas represent only about 2 percent of the total land area of Colorado, but 80 percent of wildlife species use these habitats. Updated wetland mapping results provided by the Colorado National Heritage Program (CNHP) in 2015 indicated that approximately 2.5 percent of the land area in Denver is classified as wetlands or waterbodies. The majority of acres mapped are the large, constructed water storage reservoirs, water conveyance canals and segments of the South Platte River and its contributing tributaries. These altered waterbodies provide surface water storage, sediment retention, groundwater recharge and limited aquatic habitat. Vegetated wetlands and small ponds represent only 0.7 percent of land area, but it is these habitats that provide the nutrient cycling, shoreline stabilization, biodiversity support, native plant community maintenance and terrestrial habitat function. In Denver, a combined total of 2,510 acres are classified as wetlands by the USFWS National Wetlands Inventory (NWI) (Smith & Kuhn, 2015). The types of wetland habitat that would be restored under this Section 1135 would be temporarily flooded,

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palustrine emergent wetlands. The South Platte River Valley has been designated as a Statewide Potential Conservation Area by the CNHP. A high proportion of Colorado wildlife species use wetland and riparian habitats, many of which are imperiled. Of the 295 species of birds, 123 mammals, 47 reptiles, and 18 amphibians that inhabit Colorado at some time during the year, 125 (26 percent) can be classified as “wetland-dependent species” (Ringelman 1996). Within this category of “wetland wildlife”, 98 species (78 percent) are migratory birds, 18 (14 percent) are amphibians, 6 (5 percent) are reptiles, 3 (1 percent) are Figure 8. Black rosy-finch (Leucosticte atrata). Colorado species of mammals. CNHP has categorized 34 concern, meaning, they are at risk due to declining population trends, threats to their habitat and have restricted distribution. Photo derived percent of these species (n=42; 29 from Montana Field Guide (2010). migratory birds, 11 amphibians, 1 reptile, and 1 mammal) as “rare and imperiled” (CNHP 1995). Many additional species use wetland and riparian habitats for some portion of their life cycle, but are not considered wetland- dependent. Relatively speaking, the conservation of wetlands and riparian areas has a greater positive impact on the diversity and vitality of Colorado’s wildlife populations than perhaps any other habitat conservation practice (CPW, 2015). Additionally, the project area falls within the geographic scope of the South Platte Wetland Focus Area Committee (SPWFAC) which is a working group of public and private partners organized to facilitate the development of wetland conservation projects. The purpose of SPWFAC is to conserve wetlands that provide ecological services and societal benefits. This organization is the local implementation arm of the Colorado Division of Wildlife (CDOW) Wetlands Program, the Intermountain West Joint Venture and the Playa Lakes Joint Venture. This focus group promotes the conservation of wetlands through protection, restoration/enhancement, creation, research/monitoring and education. Since the conception of this program in 1997, funding opportunities have increased dramatically for wetland work, examples include the following: . The CDOW Wetlands Program has dramatically increased funding opportunities. . Ducks Unlimited has identified the South Platte River as 1 of 3 priority areas in Colorado and provided a local staff of biologists, technicians and engineers. . The Intermountain West Joint Venture boundaries have been expanded to include the South Platte basin. . The Natural Resources Conservation Service (NRCS) has become active in wetland protection through the Wetland Reserve Program (which in 2014 was replaced with the Agricultural Conservation Easement Program). . Centennial Land Trust has been established as a private, non-profit organization to acquire and hold conservation easements on agricultural, wetland and other habitat and open space properties. . The South Platte Lower River Group (SPLRG); a consortium of water users and water providers concerned with best management practices for Colorado’s South Platte River water rights and the obligations Colorado has to the State of Nebraska and identified endangered species issues, has been active in developing partnerships and

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leveraging funds for several multiple-benefit projects on public and private lands. . The USFWS Partners for Fish and Wildlife has identified the South Platte drainage as a priority area. . Colorado Parks and Wildlife (CPW) encourages wetland and riparian conservation projects to benefit conservation priority species (as defined in the Colorado’s State Wildlife Action Plan). Denver County currently provides habitat for eight of the 26 priority wildlife species that are dependent upon wetland habitats (CPW, 2015). Local 2.3.1.5.1. Investment of Local Funds The River South Greenway Master Plan (2010) provides a conceptual vision for the South Platte River in Denver. The Greenway Foundation partnered with the Colorado Water Conservation Board, Urban Drainage and Flood Control District, Denver Public Works, Denver Parks and Recreation and Denver Water to provide a vision for environmental and recreation improvements along a 7-mile stretch of the South Platte River from the city of Denver boundary in Arapahoe County, downstream to 20th Street. Since 2011, these local entities have invested over $40 million in habitat restoration and enhancement projects along approximately 20 miles of the South Platte River in Denver County (Figure 9). Most of these restoration projects have taken place on public parks, utilized and enjoyed daily by residents and visitors. Restoration efforts conducted in these parks have included incorporating stormwater Figure 9. Local environmental and recreational restoration project along the outfall features to help filter runoff, South Platte River in downtown Denver replacing culverts with vegetated open channel, and removing invasive species and replanting with native vegetation. Trail enhancements, river access points, and other recreational features are typically incorporated into these restoration sites to better connect the community with Denver’s natural resources. An ecosystem restoration project across the 2-mile study area would serve to connect many of these patches of restored habitat into a significantly larger and continuous natural river corridor. 2.3.1.5.2. Chatfield Reservoir Environmental Pool The Chatfield Reservoir Reallocation Project came about as the result of a growing demand for water in Colorado’s Front Range and on northeast Colorado farms. It was determined that the Chatfield Reservoir can accommodate an additional 20,600 acre feet of water storage for water supply without compromising its flood control function. Of this 20,600 acre-feet, 2,100 acre-feet will be dedicated to the “environmental pool” that will directly benefit the reach of the South Platte River that this Section 1135 is addressing. The environmental pool will create 2,100 acre-feet of water storage in wet years to be released at strategic times of the year when river flows are low thus benefitting Denver’s South Platte River health through the city and the metropolitan area into northeast Colorado.

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Confluence Park Confluence Park is located in downtown Denver at the confluence of the Cherry Creek and South Platte River. An extremely popular spot for recreation, Confluence Park offers opportunities for fishing in the South Platte River, kayaking and tubing though rapids and chutes installed for recreation, biking and hike trails along the South Platte River and Cherry Creek, as well as swimming along the river’s shallow beaches. Public Letters received from the Audubon Society of Greater Denver support habitat restoration along the South Platte River in urban Denver. Comments received include the following: • “We are very interested in the restoration of the riparian area along the South Platte River between West Mississippi Ave. and Harvard Ave. and are concerned that it be done in a way to promote birds and other wildlife as well as recreational benefits for Denver residents…The normal hydrograph of the river, including spring floods, should be replicated as much as possible. This is necessary to restore the health of the riparian ecosystems along that stretch of the South Platte. Thought needs to be given to the replenishment of groundwater and to absorption of flooding that may periodically occur from natural precipitation events. Measures should be taken to ensure water quality that will support aquatic insect populations and the fish and other wildlife that depend on them. This also entails appropriate water quality, i.e. river flows, at appropriate times of the year…We strongly encourage the restoration of native trees, shrubs, forbs and grasses, to create a multi-layered vegetative cover..” • “The Corps should explore opportunities to expand the floodplain and restore natural meanders as this would create a healthier river. The Corps should evaluate opportunities to create wetlands within the study corridor. The study should also promote the maximum use of native riparian vegetation as well as work with the appropriate city agencies to establish natural "buffers" to further protect the river and riparian areas. The Corps and/or the City should explore opportunities to work with private land owners along this reach of the South Platte to implement similar measures on private lands. If there are particularly critical private lands along this reach, the Corps and/or City should explore working with appropriate land trusts (such as the Trust for Public Lands) to acquire these areas.”

Technical Significance based on technical recognition means that the importance of an EQ resource or attribute is based on scientific or technical knowledge or judgment of critical resource characteristics. Major sources of information that support technical recognition include published and unpublished literature as well as fieldwork. Scarcity, Status and Trends Scarcity is a measure of relative abundance. As noted above in Section 2.3.1.4.1, the study area lies within the geographical range of the USFWS Mountain-Prairie Region which ranks riparian habitat, especially cottonwood-willow associations, as a critical wildlife resource (USFWS, 2001). Furthermore, wetlands have been identified as quite scarce within the state of Colorado compared to historical averages. Specifically within the urbanized Metro of Denver, riparian and wetland habitat is especially rare. An ecosystem restoration project would increase the riparian, wetland and aquatic habitat quantity and quality and support technical significance of the area. Results of the 2015 CNHP wetland assessment of urban wetlands indicated that although Denver’s urban wetlands are highly altered, these sites are critical for providing wildlife and native plant habitat in an otherwise developed landscape. Other ecosystem services they provide include retaining stormwater and filtering pollutants.

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It has been noted that “natural riparian corridors are the most diverse, dynamic and complex biophysical habitats on the terrestrial portion of the earth” (Naiman et al., 1993). This is due to the interactions of the aquatic system with the adjacent terrestrial environment and the ecological processes that take place as a result. Urbanization typically leads to habitat fragmentation, associated development of residential and industrial areas in riparian corridors turn a ribbon of continuous habitat into a network of habitat patches which can become isolated from one another (Ellis, 2008). Not only does this lead to connectivity issues which may affect animal movements and migration routes and territory loss of breeding and feeding grounds, but it also increases the likelihood of non-native and generalist species out competing native diversity. Audubon Society Important Bird Areas The Audubon Society recognizes the South Platte River corridor where the project is located as a state priority important bird area (IBA) (National Audubon Society, 2017). IBAs are locations that have been identified and are monitored and protected by the Audubon Society. These sites are collaborated with 19 international partners to extend protection throughout the western hemisphere. Despite the narrow corridor and surrounding urbanized landscape, the area is considered valuable habitat and functions as cover, nesting and winter habitat for resident and migrating species. This stretch of the river can accommodate tens of thousands of ducks, geese, eagles, and other migrating birds at a time throughout the year. Landscape Considerations/Connectivity In the face of continued loss of habitat and habitat isolation, ecologists stress the need for providing connectivity, particularly in the form of wildlife movement corridors and stepping stones. Riparian corridors are of exceptional significance in a landscape. Despite discussion over the Figure 10. Section 1135 in Colfax, approximately 4 miles downstream of effectiveness of corridors in enhancing South Platte Valley Section 1135. Top photo is prior to construction. biodiversity, a growing empirical body Middle and bottom photos, post construction show widened channel, wetland benching and initial seeding. Connectivity between previously of research underlines the positive constructed projects provides for improved transportation corridors for benefits accruing from incorporating wildlife.

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higher quality linkages between habitat patches (Dramstad et al., 1996). In 2003, a Section 1135 project was completed on the Colfax reach of the South Platte River (Figure 10). Ecosystem restoration that took place included major excavations along the east bank, modifications to the west bank, three jetties, four hydraulic structures and a low-flow channel to improve the riparian and aquatic habitat of the area. To date, an on-going Corps’ General Investigations study approximately 2.5 miles downstream of the Section 1135 study area is determining ecosystem restoration opportunities along the South Platte River. Connectivity and compatibility between these ecosystem restoration features of these projects is extremely important. Biodiversity According to Miller et al. (1989), the top two causal factors leading to extinction of freshwater fishes during the 20th Century were habitat alterations and the effects of non-native species. Typically, stream habitat restoration and enhancement will have the greatest benefit in degraded systems that are habitat-limited. The habitat and stream functions have been severely altered and have led to a decreased biodiversity of fish species present within the study area. As described in Section 3.6.3, from 1982-1994, 29 species of fish were documented within and just beyond the project area. Between 2001 and 2004, only 20 species were recorded in the project area (CPW, 2008). Furthermore, the Functional Assessment of Colorado Wetlands (FACWet) and Functional Assessment of Colorado Streams (FACStream) were two hydrogeomorphic models used to assess the existing conditions of the study area. Both models evaluate biodiversity of the riparian and aquatic environment. Existing conditions of the vegetation along the study area indicate poor biodiversity scores (see Appendix A1: Sub- appendix I for more detailed information). An ecosystem restoration project would improve overall vegetative biodiversity of the area. 3. Current and Future Conditions 3.1. PLANNING HORIZON The base year, or the year that it is assumed construction of the project would be complete, for this study is 2022. The planning horizon assumes a 50-year period. The planning horizon attempts to capture project benefits, deferred installation costs, monitoring and adaptive management costs and operation and maintenance costs. The period of analysis for this study includes existing current conditions, future conditions with project and future conditions without a constructed project. For technical analysis of environmental benefits, conditions were assumed in four target years for both a future with project and a future without project In addition to existing baseline conditions, the base year (identified as Year 1 or 2022), 10 years post-base year (2032), 25 years post-base year (2047) and 50 years post-base year (2072) were analyzed. For formulation, an assumption was made that based on the fully urbanized nature of the watershed and the authorized purposes of the upstream flood control projects, hydrologic and hydraulic management of the South Platte River is anticipated to remain consistent with current conditions, with the exception of the additional flows allocated to the “environmental pool” from the Chatfield Reallocation (see Section 2.3.1.5.2). There will also be an opportunity for local agencies and stakeholders to purchase additional shares for environmental flows. This will provide an ecological future benefit during this planning horizon.

3.2. EXISTING CONDITIONS The existing conditions are an inventory of watershed conditions at the present time or very recent past. The development of the existing conditions allows the team to forecast the future without-project conditions, which will serve as the baseline for a fair measure and comparison of the value of proposed

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plans. The information used to develop and define the existing conditions comes from both baseline surveys of current conditions as well as the review of previous studies and projects within the study area. 3.3. PREVIOUS STUDIES The South Platte River within the Denver area has been extensively studied over the years. Some of the most pertinent past efforts to this study include the following:

• Denver County General Investigations Study, US Army Corps of Engineers (Ongoing) • Denver County Reach, South Platte River, Denver Colorado, US Army Corps of Engineers (2001) • Chatfield Reallocation (2014) • River Vision Implementation Plan, The Greenway Foundation (2010) • River South Greenway Master Plan, The Greenway Foundation (2010) • River North Greenway Master Plan, The Greenway Foundation (2009) • Water Conservation Plan, City of Denver Parks and Recreation (2003) • Denver County Project Feasibility Study, US Army Corps of Engineers (2003) • South Platte River Hydrologic Study, Urban Drainage (1983) • Water and Related Land Resource Management Study, Metropolitan Denver and South Platte River and Tributaries, Colorado, Wyoming and Nebraska, US Army Corps of Engineers (1980) 3.4. EXISTING PROJECTS The Corps constructed a series of three dams in the Denver Metropolitan Area during the 1950s, 1970s and 1980s. These three dams, Chatfield, Cherry Creek, and Bear Creek, are also known as the Tri-Lakes Projects. All three dams were constructed to reduce the flood risk in the Denver Area. However, a side effect of these projects was the degradation of the natural hydrology on the South Platte River downstream of the projects. This degradation was caused by the regulation of flows out of each of the projects, reducing the natural flows associated with seasonal high water events and by producing higher flows than would naturally occur during the low flow seasons. These effects are the primary reason this study is eligible for the Section 1135 Program. The project area is impacted by the outflows from Chatfield and Bear Creek as Cherry Creek intersects with the South Platte River downstream of the study area. Beyond the existing Corps Projects, Denver, and their many partners, have invested approximately $40M along the South Platte River over the last decade on projects to improve riparian and wetland habitats, in-channel aquatics, and recreation/educational opportunities along the river. Denver have produced two master plans, the River North Greenway Master Plan (2009) and the River South Greenway Master Plan (2009). The two master plans were the basis for the overall River Vision Implementation Plan (2010). The purpose of these plans was to collaborate with citizens, property owners, and stakeholders to introduce and develop opportunities for improving the river’s ecological, infrastructure and recreation systems. The master plans characterize existing conditions and offer recommendations on how to move forward and serve as an overarching framework to guide potential ecosystem restoration and other improvements. Some of the projects from the master plans have been completed using a variety of non-federal funds including: rehabilitation of Johnson Habitat Park and Pasquinel’s Landing Park, Weir Gulch, as well as constructing a series of in-stream riffles to replace a large drop structure at Overland Golf Course.

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3.5. PHYSICAL SETTING Climate The climate of the general Denver area is typically defined by warm to hot summers in most valleys, but cooler in the mountains. Winters are frequently cold in the mountains. In the mountains, precipitation occurs throughout the majority of the year and a deep snowpack accumulates. Snowmelt and precipitation from spring supply the surface waters of the South Platte River. Table 1 below depicts the 30-year average maximum and minimum temperature and precipitation in Denver.

Table 1. Average Maximum and Minimum Temperature and Precipitation for Denver, Colorado, from 1981 to 2010 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Avg. Max. 44.0 46.2 54.4 61.5 71.5 82.4 89.4 87.2 78.5 65.3 52.1 42.8 64.7 Temperature (°F)* Avg. Min. 17.4 18.9 26.4 33.3 42.7 52.3 58.9 57.9 48.3 36.6 24.5 17.1 36.3 Temperature (°F)* Avg. Total 0.41 0.37 0.92 1.71 2.12 1.98 2.16 1.69 0.96 1.02 0.61 0.35 14.3 Precipitation (inches)*

* Values are from the Denver International Airport weather station, approximately 20 miles northeast of the study area. Source: National Climatic Data Center, http://www.ncdc.noaa.gov/oa/ncdc.html Trends across the country indicate a variety of impacts associated with climate change, including higher average, minimum and maximum air and water temperatures; shifts in the amount of snowpack and timing of snowmelt; reduced ice cover extent; a longer frost-free season; and an accelerating rate of sea-level rise and acidification of ocean waters (Burkett & Davidson, 2013; Griffis & Howard 2013; Kunkel et al., 2013; as cited in Stein et al., 2014). According to the National Climate Assessment, the Southwest region, which includes the states of California, Arizona, Nevada, New Mexico, Utah and Colorado, is the hottest and driest region within the United States. It is estimated that this region will experience a significant population increase by 68 percent by 2050. Assessment of the Southwest region has shown markedly warmer temperatures since 1950 than any comparably long period in at least 600 years. The 2001 through 2010 decade was the warmest in the 110-year instrumental record. Temperatures are projected to continue to climb upwards (an estimated increase of 5.5°F to 9.5°F by 2070-2099) (Garfin et al., 2014). In addition to estimated increased temperatures, it is anticipated streamflow and snowpack amounts will decline, decreasing surface water supply. Increased drought will occur due to the lack of precipitation (Garfin et al., 2014). These trends show a clear directionality consistent with the expected implications of increasing greenhouse gases and have been documented in the atmosphere, oceans, soils and ice-covered areas spanning the planet (NRC, 2011). In 2015, the CNHP, for the Bureau of Land Management, assessed a statewide perspective on potential future influences of a changing climate on species and ecosystems. Results indicated the varying vulnerability of the 16 terrestrial ecosystem types and six freshwater ecosystem groups assessed. Terrestrial types included six forest or woodland types, four shrubland types, four herbaceous or grassland types and riparian and wetland areas. The South Platte River system would fall under the riparian and wetland group, and this group was classified as highly vulnerable with a specific subtype of riparian woodland and shrubland of lower elevation west slope areas classified as very highly vulnerable. The study area would also fall under the freshwater ecosystems (streams, river, lakes and reservoirs); this ecosystem type was evaluated based in regions (eastern plains, mountains and western valleys). Section 1135 June 2018 South Platte Valley 18

Overall vulnerability for all freshwater ecosystems was noticeably higher than the vulnerability of the terrestrial types (CNHP, 2015). Furthermore, the study conducted by CNHP assessed the vulnerability to climate change of 36 fauna species and 62 floral species that reside in the state of Colorado. Of those assessed species, 42 percent of the faunal species were ranked as highly to extremely vulnerable to climate change by mid-century and 95 percent of the floral species assessed were ranked as extremely vulnerable to climate change (CNHP, 2015). Geology The South Platte River flows in a valley cut into the landscape during Pleistocene, or recent, times. The valley floor is mostly reworked gravel overlain by a few feet of rich sandy silt. The valley floor varies from ½ to two miles wide in the Denver area, with an average width of approximately ¾ mile. Upstream from Sixth Avenue in Denver, there are a few outcrops of Wisconsin Stage gravel fills in the valley floor. One such location is at the Overland Park Municipal Golf Course. These gravels are chiefly granitic pebbles mostly less than one inch in diameter, well-bedded and well sorted. The Denver and underlying Araphoe Formations consist of nearly flat-lying shale and sandstone. These two formations are similar in lithology and are sometimes not differentiated. All samples of rocks in the Denver formation disintegrate in water after being allowed to dry in air. The alluvial deposits of the South Platte River are from five to 30 feet thick, with a maximum in excess of 50 feet. The Denver Formation outcrops in the river bed at a number of locations through the study reach. Soils Prime farmland, as defined by the NRCS, is land that has the best combination of physical and chemical characteristics for producing crops. The Farmland Protection Policy Act (FPPA) is intended to minimize impacts from federal programs that have unnecessary and irreversible conversion of farmland to nonagricultural uses. Due to the urbanized setting of the study area and a search on the WebSoil Survey online tool, no prime farmland exists within the study area. A letter was received from the Assistant Colorado State Soil Scientist (see Appendix A2), dated December 6, 2016, noting that the study area occurs within the boundaries of an urbanized area and is not subject to the FPPA. Water Quality Water quality in the South Platte River basin in Denver is managed by the Colorado Water Quality Control Commission’s (CWQCC) water quality monitoring program, which routinely monitors inflows and outflows, sediment loading and export, surface and groundwater quality, and the effectiveness of pollutant reduction facilities (PRFs) within the watershed. Some oversight is also provided by EPA. Under Section 304 (a)(1) of the Clean Water Act (CWA) of 1972, every state must adopt water quality standards to protect, maintain, and improve the quality of the nation’s surface waters. These standards, developed by the EPA, represent a desired level of protection for a waterbody. Water quality standards consist of the following:

• Beneficial uses for a waterbody are uses approved by state entities, with specific water quality standards assigned for each. • Surface water quality describes the existing quality of water in a waterbody and whether standards have been met for beneficial uses. • Clean Water Act 303(d) listings are designations of water segments that do not meet water quality standards.

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• Total maximum daily loads (TMDLs) are reports prepared for 303(d)-listed segments, detailing measures for restoring water quality for the listed parameter.

Classified beneficial uses in the South Platte River within the study area are designated as a Class 1 Aquatic Life Warm Water, Class E Recreation, Water Supply, and Agriculture. Colorado State Regulation No. 38 establishes classification and numeric standards assigned to stream segments. The State Regulation No. 38 defines Class 1 Warm Water Aquatic Life classification as capable of sustaining a wide variety of warm water biota, including some sensitive species, and biota where physical habitat, water flows or levels, and water quality conditions result in non-substantial impairment of the abundance and diversity of aquatic life. State Regulation No. 38 defines the Class 2 Warm Water Aquatic Life classification as not capable of sustaining a wide variety of warm water biota, including sensitive species, due to physical habitat, water flows or levels, or uncorrectable water quality conditions that result in substantial impairment of the abundance and diversity of species. The Class E Recreation is designated to protect primary body contact uses. The Class E Recreation classification designates surface waters as suitable for recreational activities in or on water where ingestion of small quantities of water is likely to occur. Under Class E, water in the South Platte River is classified as suitable or intended to become suitable for potable water supplies, irrigation, and a water source for livestock (CWQCC, 2016a). Impaired Waters Section 303(d) of the CWA requires states to identify waterbodies or stream segments where existing effluent limitations are not stringent enough to implement applicable water quality standards. Water- quality limited segments are those in which one or more classification or standard is not, or may not be fully achieved. The State is required to develop a TMDL assessment for every segment and parameter that is listed. The TMDL describes loading limits that will ensure attainment of the stream standard, with specific reference to a quantification of the amount of pollutants that a segment can assimilate without exceeding water quality standards. The TMDL document also apportions the allowable pollutant load among multiple pollutant sources. Within the study area, the South Platte River (Segment 14- Bowels Avenue to Burlington Ditch) is listed on the State’s 303(d) list for arsenic and Escherichia coli (E. coli). According to the Colorado Department of Public Health and Environment (CDPHE, 2016), TMDLs for E. coli and nitrate were approved by the EPA. Also within the study area, two artificial waterbodies on the east bank of the South Platte just north of Florida Avenue, Aqua Golf Lake and Overland Pond are on the 303(d) list for pH, acidity and caustic conditions. A TMDL is still needed for these waterbodies. Flood Risk Management Flood risk along the study area is primarily from the South Platte River. Other flood sources in the study area are Harvard Gulch, Sanderson Gulch and West Harvard Gulch. The primary flood threat results from heavy rainfall from intense thunderstorms. Snow melt flooding may occur if a heavy snow cover melts rapidly. Ice-affected flooding has not been a problem in the Denver area due to the relatively mild winter climate. Because the South Platte River channel has degraded below the surround terrain over time, the more frequent flood events such as the 2-, 5-, 10- and 25-year events are mostly contained within the high banks. The 100-year and greater flood events on the river would result in extensive inundation along the study area but elevated terrain exists adjacent to the river that may escape flooding.

The City and County of Denver have participated in the National Flood Insurance Program (NFIP) since April, 1986. The NFIP is administered by the Federal Emergency Management Agency (FEMA) and makes flood insurance available to all property owners in participating communities. In return, communities Section 1135 June 2018 South Platte Valley 20

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. The City of Denver has enacted local floodplain management regulations that meet the minimum standards of the NFIP and the State of Colorado. In the designated Special Flood Hazard Area (SFHA) zones (the 1-percent-annual-chance or 1-percent- annual-chance floodplain) floodplain development permits are required for all new development and the development must meet certain requirements, such as elevation of the lowest floor above the base (1-percent-annual-chance) flood. Areas in and adjacent to stream channels in some of the SFHA zones have been designated as regulatory floodways, where new development is severely restricted and must not cause adverse impacts to insurable structures by increasing the base flood elevations. Increases to base flood elevations may be allowed provided the development obtain a Conditional Letter of Map Revision (CLOMR) from FEMA prior to permit issuance. A detailed discussion of flood risk considerations for the project is presented in Appendix D. Air Quality The Clean Air Act (CAA) (42 U.S.C. § 7401 et seq.), enacted in 1970 tasked the EPA to establish National Ambient Air Quality Standards (NAAQS) to protect public health and welfare and to regulate emissions of hazardous pollutants. Air quality in the Denver Metro and the state of Colorado is monitored by the Colorado Department of Public Health and Environment (CDPHE). Sources of suspended particulate matter and air pollutants in the proposed project area include urban and industrial activities. From the 1970s to the early 1980s, Denver exceeded certain EPA air quality standards nearly 200 days annually. Since 1995, Denver has been in attainment for all pollutants except ozone which continues to be a persistent problem (CDPHE, 2018). Ambient monitoring at the time of writing indicates that the City of Denver is meeting established NAAQS and considered in attainment. AIRNow.gov is a website launched by EPA in the spring of 2005 and has national participation. This tool is used to relay real-time data to members of the public as well as predict conditions several hours into the future. PM2.5 (particulate matter) and ozone are both monitored through seven different stations throughout the city. CDPHE reports “moderate” to “good” air quality for both PM2.5 and ozone. Noise Sources of noise in the proposed project area result from the urban and industrial activities which all take place within close proximity. Due to the heavily urbanized setting of the study area, traffic, commercial businesses and industrial operations are likely the primary contributor of year-round noise pollution. Some land areas may be considered sensitive to noise. Noise sensitive receptors are land uses associated with indoor and or outdoor activities that may be subject to stress or interference from noise. This typically includes residential dwellings, transient lodging, hospitals, educational facilities and libraries. The majority of the study area is considered urban or commercial; however, there are residential areas in close proximity of Grant Frontier Park in Reach 3 of the study area which could be considered sensitive to noise. Hazardous, Toxic and Radioactive Wastes A HTRW Assessment was performed for this study to facilitate early identification and appropriate consideration of HTRW issues within the project area, in accordance with ER 1165-2-132, HTRW Guidance for Civil Works Projects. This HTRW Assessment was performed in two phases: the first phase was performed in the winter of 2016 and consisted of a records review, interviews with knowledgeable

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personnel, and a site visit, while the second phase was performed in the summer of 2017 and consisted of environmental sampling in specific locations within proposed project areas. Reports of both phases are available in Appendix I of this report. Phase I identified one recognized environmental condition (REC) along the South Platte River within the study area. According to a report of previous sampling performed for a city project, sediment from the South Platte River near Grant Frontier Park was found to contain polycyclic aromatic hydrocarbons (PAHs) at concentrations that exceed the EPA Regional Screening Levels (RSLs) for residential soil. Per ER 1165-2-132, “dredged material [qualifies] as HTRW only if [it is] within the boundaries of a site designated by the EPA or a state for a response action… under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), or if [it is] a part of a National Priority List (NPL) site under CERCLA.” Grant Frontier Park is not in a CERCLA site, so the PAHs in the sediment do not preclude USACE from performing work in this area. However, if sediments are dredged from the South Platte River near Grant Frontier Park, caution should be taken to minimize disturbance and mobilization of any contaminants in the sediments. The Phase I investigation also identified several data gaps within the study area that required further investigation. These data gaps consisted of historic fill areas along the South Platte River. The City of Denver has historically used fill (including materials such as construction debris, municipal waste, imported soil, refinery waste, etc.) to stabilize the banks of rivers in the metro area. Three of these historic fill areas overlap with proposed project areas on the Southern Platte Valley project. Phase II of the HTRW Assessment consisted of drilling into the historic fill areas along the South Platte River within the study area and sampling the buried materials to eliminate remaining data gaps. A small area between the South Platte River Regional Trail (hereafter referred to as the Regional Trail) and the South Platte River near Overland Golf Course was found to contain elevated concentrations of PAHs 5 feet below ground surface (bgs). Small amounts of construction debris (i.e., brick fragments, glass) were also observed near the surface in this area. Elevated concentrations of PAHs were also measured 4-6 feet bgs between the Regional Trail and the South Platte River just south of the intersection of South Santa Fe Drive and South Platte River Drive. Per ER 1165-2-132, the non-federal sponsor will be responsible for ensuring that any required response actions would be performed at 100 percent non- federal cost.

3.6. ECOLOGICAL RESOURCES Vegetation and Terrestrial Resources During a field investigation on September 7 through 9, 2016, data was collected on existing vegetative conditions (see Appendix A for more detail). Vegetative communities along the South Platte River were classified utilizing the U.S. National Vegetation Classification (USNVC) as described in NatureServe2013 (NatureServe, 2016) and Field Guide to Wetland and Riparian Plant Associations in Colorado (Carsey et al., 2003). Due to surrounding urbanization and invasive species, the vegetative community is highly disturbed and most closely resembles a Sandbar Willow/Mesic Graminoid Shrubland Community. This is a departure from the historic conditions of a vegetative structure composed of a Plains Cottonwood/Willow Woodland Community. Invasive/Exotic Species Under the Colorado Noxious Weed Act and Regulations, a prioritized list has been created which categorizes severity of infestation and subsequent level of eradication or control. List A Eradication species are weeds identified by the state as uncommon and are required to be completely eradicated, requiring elimination of the plant prior to a reproduction cycle. List B Eradication species are identified

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as having varied populations throughout the state, and zones may be established in areas where the weed is uncommon. List B Control species are those weeds identified as having varied populations throughout the state and in areas where the weed is more common, control and containment are required. List C Control species are weeds common throughout the state and property owners are encouraged to control. Of the noxious species identified throughout the study area, Siberian elm was the most prevalent, with some patches of Japanese brome (Bromus japonicus). These species are not on the prioritized list, however, they are both considered aggressive. Russian olive (Elaeagnus angustifolia), a List B classified species, was identified in the upstream portion (Reach 3) of the study area. Wetlands and Waters of the US As noted in Section 2.3.1.2, wetlands and riparian areas represent only about 2 percent of the total land area of Colorado, but 80 percent of wildlife species use these habitats. Updated wetland mapping results provided by the CNHP in 2015 indicated that approximately 2.5 percent of the land area in Denver is classified as wetlands or waterbodies. The majority of acres mapped are the large, constructed water storage reservoirs, water conveyance canals and segments of the South Platte River and its contributing tributaries. These altered waterbodies provide surface water storage, sediment retention, groundwater recharge and limited aquatic habitat. Vegetated wetlands and small ponds represent only 0.7 percent of land area, but it is these habitats that provide the nutrient cycling, shoreline stabilization, biodiversity support, native plant community maintenance and terrestrial habitat function. In Denver, a combined total of 2,510 acres are classified as wetlands by the USFWS NWI (Smith & Kuhn, 2015). According to NWI and confirmed Figure 11. NWI map of existing wetlands and water resources in the study area (Source: USFWS Wetlands Data Mapper). Note no NWI wetlands exist adjacent during the field investigation, no to the South Platte River within the study area. The PUBGx are treatment palustrine or emergent wetlands exist lagoons at Xcel. within area and no natural wetlands exist within the study area (Figure 11). The South Platte River is classified as Riverine, while Overland

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Pond Park and water treatment lagoons located within the Xcel Energy Powerplant campus classify as freshwater ponds. Aqua Golf is classified as a lake. During a site visit for data collection on September 7 through 9, 2016, and as discussed in Section 2.1.1 and Appendix A1, it was noted that channelization, bank armoring and a complete disconnect of the ecological floodplain have prohibited adequate hydrology to support hydrophytic vegetation and hydric soils which are necessary to support wetland habitats. Fisheries Fish in the South Platte River are naturally dispersed from high to low elevation and cold to warm temperature gradients, which is characteristic to the entire South Platte River Basin (Martin et al. 2013; Dennehy et al.1993). In the study area, the South Platte River is designated as a Class 1 and 2 Warm Water Aquatic Life stream, which is capable of sustaining a wide variety of warm water biota, including some sensitive species. Modifications of the South Platte River through channelization, controlled flows, and reduced flood plain have significantly altered the water quality and aquatic flora and fauna. In response to urbanization, sediment loads and pollution have increased in the river and its tributaries. As a result, the South Platte River fisheries have greatly diminished due to the lack of historical habitat conditions needed to meet the various life needs of these species. Several fish studies have been conducted within the South Platte River project area. CPW historically maintained several fish sampling sites within the project area and another just upstream of the project area. Some sampling records date back as early as 1912 but most date from 1984 and later. From 1982-1994, 29 species of fish were documented within and just beyond the project area. Between 2001 and 2004, 20 species were recorded in the project area (CPW 2008). The species are best described as Eastern Plains, warm-water transitional species and include a large number of non-native introductions, such as common carp. Common native species documented included the fathead minnow (Pimephales promelas), green sunfish (Lepomis cynellus), Johnny darter (Etheostoma nigrum), red shiner (Cyprinella lutrensis), sand shiner (Notropis stramineus) and white sucker (Catostomus commersoni) (CPW 2008). Fish that are very uncommon in the area (last observed date in parentheses) are brassy minnow (Hybognathus hankinsoni) (1988), brown trout (Salmo trutta) (1983), common shiner (Luxilus cornutus) (1983), northern redbelly dace (Chrosomus eos) (1914), mountain whitefish (Prosopium williamsoni) (1983), plains killifish (Fundulus zebrinus) (1994), plains topminnow (F. sciadicus) (2001), rainbow trout (Oncorhynchus mykiss) (1993) and river carpsucker (Carpiodes carpio) (1914) (CPW, 2008). CPW records indicated that fish species diversity has declined over time. According to CPW, the loss of native species and decreased species diversity is likely due to increases in water temperature, degradation of water quality, altered flow regimes, loss of spawning habitat and presence of migration barriers.

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In a more recent aquatic Table 2. Fish species observed in the South Platte project area from bioassessment study conducted by 2007-2012. Aquatics Associates, Inc. from 2007- Common Name Scientific Name Native Non-Native 2012, 25 fish species were Black crappie Promoxis nigromaculatus x identified within the urban segment Bluegill Lepomis macrochirus x of the South Platte River. Of the 25 Channel catfish Ictalurus punctatus x species identified, 18 species were Common carp Cyprinus carpio x located within the South Platte Creek chub Semotilus atromaculatus x River project area, of which 10 were Fathead minnow Pimephales promelas x native species. Error! Reference Green sunfish Lepomis cyanellus x source not found. indicates the fish Iowa darter Etheostoma exile x species observed during the study Johny darter Etheostoma nigrum x in the South Platte River project Largemouth bass Micropterus salmoides x area. Longnose dace Rhinichthys cataractae x Longnose sucker Catostomus catostomus x The most widespread native species Sand shiner Notropis stramineus x in the South Platte River project Smallmouth bass Micropterus dolomieu x area was white sucker, which was Spottail shiner Notropis hudsonius x abundant throughout the urban Walleye Stizostedion vitreum x segment of the river. Other White sucker Catostomus commersonii x abundant native species collected Yellow perch Perca flavascens x were the longnose dace, fathead minnow, and creek chub. Several non-native (introduced) species were also identified and included the common carp (Cyprinus carpio), smallmouth (Micropterus dolomieu) and largemouth bass (M. salmoides), walleye (Sander vitreus), and yellow perch (Perca flavascens). The presence of largemouth and smallmouth bass along with walleye and perch were largely due to CPW stocking activities and migration to the river from adjacent ponds. No state or federally-listed threatened and endangered fish species were found in the South Platte River project area; however, the Iowa darter (Etheostoma exile), CPW listed species of special concern, was collected in upper segments of river, just downstream of Chatfield Reservoir. Fish Passage Fish passage generally describes the ability of an individual species or a fish guilds’ ability to traverse a barrier to reach feeding, breeding or sheltering habitats during various life stages. One type of barrier commonly found in impounded and channelized waterways, such as the study area, are grade control structures, or referred to as drop structures. Oftentimes, grade control structures are necessary in modified waterways that have been straightened and armored as channelization increases water velocities and reduces drainage time. Grade control structures are used to stabilize a stream to reduce channel bed erosion or head-cutting that result from the increased water velocities moving through an area. Within the study area, seven concrete and rock grade control structures exist. In Reach 2, the City of Denver modified the existing grade control structure located near the Aqua Golf intake pumping house in 2015. The existing drop was extended over a length four additional upstream grade control structures across approximately 2,800 feet of stream length (Figure 12).

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Figure 12. Drop structures within the study area. The Aqua Golf Intake drop structure was modified in 2015 and grade elevation was reduced by placing four additional drop structures upstream of the existing structure. Overland and Xcel drop structures have not been modified.

Reach 1 has a grade control structure located near the Overland Pond Park, the height of this barrier is approximately 3 feet. An additional drop structure in the study area serving as an impediment to fish passage is the structure located near Xcel Energy with a barrier height of approximately 5 feet (Figure 13). Both existing drop structures have been notched for boat chutes. The Xcel drop structure was also constructed with a 1 vertical to 10 horizontal foot (1:10) ramp across a portion of the South Platte River. The Overland drop structure was not specifically designed to have any sort of ramp downstream of the structure, although sedimentation of larger boulders has led to the appearance of a ramp like structure.

Figure 13. Drop structures within the study area currently serving as impediments to fish passage. Left picture is the Overland drop structure in Reach 1 and the right picture is the Xcel drop structure in Reach 3. Section 1135 June 2018 South Platte Valley 26

Birds According to the Second Colorado Breeding Bird Atlas, from 1987 to 1995, 264 bird species had been confirmed in the state of Colorado. From 2007 to 2012, that number dropped to 263 (CBA, 2016). Historically, Colorado supported 428 bird species (Kingery, 1998). Bird distribution within the state has been altered as a result of the changing landscape and vegetation type and structure. According to Colorado Parks and Wildlife, Chatfield State Park, which is approximately 11 miles upstream of the study area, has confirmed 212 different species of birds within the area (CPW, 2013). Migratory Birds All federal agencies are subject to the provisions of the Migratory Bird Treaty Act (MBTA; 16 U.S.C. § 703-712, 709 is omitted) which regulates the take of any migratory bird species. If a Corps project is expected to impact any migratory bird species, coordination with the USFWS is typically initiated in order to minimize impacts to these species. The South Platte River within the study area falls within the Central Flyway Route which comprises more than half the landmass of the continental United States, before extending to Central and South America. Table 3 summarizes migratory birds of conservation concern identified in the USFWS’ Information for Planning and Conservation (IPaC) Trust Resources Report (Appendix A3). Growing concerns over Colorado’s migratory bird populations have initiated development and improvement of bird census programs (Meyer, 2008).

Table 3. Migratory birds of special conservation concern potentially existing within or near the South Platte River of the study area. COMMON NAME SCIENTIFIC NAME SEASON PRESENT American Bittern Botaurus lentiginosus Breeding Bald Eagle Haliaeetus leucocephalus Year-round Black Rosy-finch Leucosticte atrata Year-round Black Swift Cypseloides niger Breeding Brewer’s Sparrow Spizella breweri Breeding Burrowing Owl Athene cunicularia Breeding Cassin’s Finch Carpodacus cassinii Year-round Dickcissel Spiza americana Breeding Ferruginous Hawk Buteo regalis Year-round Flammulated Owl Otus flammeolus Breeding Golden Eagle Aquila chrysaetos Year-round Lark Bunting Calamospiza melanocorys Breeding Lewis’s Woodpecker Melanerpes lewis Breeding Loggerhead Shrike Lanius ludovicianus Year-round Long-billed Curlew Numenius americanus Breeding Mountain Plover Charadrius montanus Breeding Peregrine Falcon Falco peregrinus Breeding Prairie Falcon Falco mexicanus Year-round Sage Thrasher Oreoscoptes montanus Breeding Short-eared Owl Asio flammeus Wintering Swainson’s Hawk Buteo swainsoni Breeding Virginia’s Warbler Vermivora virginiae Breeding Western Grebe Aechmophorus occidentalis Breeding Williamson’s Sapsucker Sphyrapicus thyroideus Breeding Willow Flycatcher Empidonax traillii Breeding

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3.6.4.1.1. Bald Eagle The bald eagle (Haliaeetus luecocephalus) was delisted from federal protection as of July 9, 2007 but is still protected under The Bald and Golden Eagle Act and the Migratory Bird Treaty Act. The Bald and Golden Eagle Protection Act (16 U.S.C. 668-668c) enacted in 1940, prohibits the take of bald eagles or golden eagles, including their parts, nests, or eggs. The bald eagle is a North American species that historically occurred throughout the United States and Canada. Bald eagle distribution varies seasonally, ranging from Alaska and Canada to northern Mexico. Bald eagles generally nest near rivers, large lakes, reservoirs, and streams where an adequate food base is available. They often nest in mature or old- growth trees, dead trees, and on cliffs. In the winter, bald eagles will congregate near open water in tall trees for spotting prey and for shelter. Bald eagles prey on fish, waterfowl, carrion, and small mammals and birds. The State of Colorado, including the County of Denver, is part of the current bald eagle home range (USFWS, 2007a). In the winter, the bald eagle is a common visitor to reservoirs and lakes that surround the Denver Metro area. Bald eagles are also known to winter along the South Platte River basin in riparian woodlands but tend to avoid densely urbanized areas with limited cottonwood communities (Currier et al., 1985). Due to the lack of habitat and prey availability from altered river flows, bald eagles are not known to nest in the Denver Metro area and are only seen passing through. Other Wildlife Other wildlife resources expected within the study area are limited to generalist species that can tolerate disturbed habitats. It is anticipated that mammals such as Virginia opossum (Didelphis virginiana), raccoon (Procyon lotor), muskrat (Ondatra zibethicus), mink (Neovison vison), meadow vole (Microtus pennsylvanicus) and deer mouse (Peromyscus maniculatus) would be present in the area. Avian species noted during the site visit could also be classified as habitat generalists tolerant to disturbed areas; these species observed include red-winged blackbird (Agelaius phoeniceus), American robin (Turdus migratorius), Canada goose (Branta canadensis), and a variety of hybridized/domestic species of dabbling ducks. Western chorus frogs (Pseudacris triseriata), one of 23 herpetofuana species with potential to occur in Denver, were also noted during the site visit. Other herpetofauna species expected to be utilizing the study include American bullfrog (Rana catesbeiana), common garter snake (Thamnophis sirtalis), leopard frog (Rana pipens) and Woodhouse’s toad (Anaxyrus woodhousii). Threatened and Endangered Species Section 7 of the Endangered Species Act (ESA) (7 U.S.C. § 136, 16 U.S.C. § 1531 et seq.) states that all federal departments and agencies shall, in consultation with the assistance of the Secretary of the Interior, ensure that any actions authorized, funded or carried out by them do not jeopardize the continued existence of any threatened or endangered species. An official list of federally-listed threatened and endangered species in the County of Denver, Colorado was obtained through the USFWS IPaC online tool. A total of eight species were identified that may occur or could potentially be affected by activities within the study area. These species included three endangered species, the pallid sturgeon (Scaphirhynchus albus), interior least tern (Sternula antillarum) and whooping crane (Grus americana) and four threatened species, the Preble’s meadow jumping mouse, Mexican spotted owl (Strix occidentalis lucida), Ute ladies’-tresses and western prairie fringed orchid (Platanthera praeclara). A “block clearance” zone has been determined by the USFWS for the Preble’s meadow jumping mouse and the Ute ladies’-tresses for the area of the Denver Metropolitan where the study area exists. A block clearance zone is an area where the USFWS has determined that the species in question has been extirpated, or, is not likely to currently exist where it historically has been found. It is not likely that either of these species exists within the study area. Additionally, while it is not likely that the

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recommended plan would provide a mechanism for the return or occurrence of these two species, the improvements to the ecosystem within the project footprint are composed of those habitat types that historically occurred in the area and were utilized by Preble’s meadow jumping mouse. Due to the “block clearance” zone, the Corps did not included these two species in analysis of this integrated study. Mexican spotted owls favor secluded canyon bottoms and mixed coniferous forests, especially ponderosa pine (Pinus ponderosa) with an understory of smaller pines or shrubs, more typical of mountainous terrain. Typical forest composition of favored habitat includes white fir (Abies concolor), limber pine (Pinu flexillis), blue spruce (Picea pungens) and Gambel oak (Quercus gambellii) (USFWS, 1995). Because this species, like other spotted owls, is associated with dense stands of old-growth or mature forests and coniferous vegetation is not present within or near the project area, Mexican spotted owls are not known to be present. It is not anticipated that this threatened species would be found within the project area, before, during or after construction as this habitat type is not available, nor will the ecosystem restoration features under the Recommended Plan construct these habitat types. As such, the Corps did not include these two species in the analysis of this integrated study. Interior Least Tern and Piping Plover The interior least tern was federally listed endangered in 1985 (50 Federal Register 21784). The interior least tern is the smallest of terns found in North America. Widespread loss and alteration of its riverine nesting habitat has eliminated the least terns from many locations within its former breeding range. Least terns are highly dependent on the presence of dry, exposed sandbars and river flows that support a forage fish supply and isolate sandbars from the riverbanks. Typical riverine nesting sites include dry, flat, sparsely vegetated sand and gravel bars within a wide, unobstructed, water-filled river channel. Nests are initiated only after spring and early summer flows recede and dry areas on sandbars are exposed. The northern Great Plains population of the piping plover (Charadrius melodus) was listed as federally threatened in 1985 (50 Federal Register 50726). Habitat loss through degradation and woody plant encroachment as a result of decreased flows in the Platte River have affected this species. Piping plovers utilize open, sparsely vegetated sand or gravel beaches, and sand bars of major river systems for nesting. Plovers arrive on the breeding grounds during mid-March through mid-May and remain for three to four months per year. Whooping Crane The whooping crane was designated as federally endangered on March 11, 1967, prior to the enactment of the ESA. Their populations declined to an estimated 16 individuals in 1941 due to overhunting and habitat disturbance. Today, there is a small, self-sustaining wild population that nests in the Wood Buffalo National Park in Saskatchewan, Canada and overwinters on the Texas Gulf Coast at the Aransas National Wildlife Refuge. There are also few captive populations that have been in an experimental reintroduction program scattered across a handful of zoos and research parks (USFWS, 2001). Current population approximates 600 wild and captive individuals. The whooping crane is a tall wading bird, reaching up to 5 feet in height with a 7-foot wingspan, however, only weighing approximately 15 pounds. This omnivorous species feeds on invertebrates, fish, insects and herptofuana as well as grains and marsh plants. Whooping cranes are monogamous, upon finding a mate they will exclusively breed, but will re-mate following the death of a mate. Whooping cranes typically reach sexual maturity at age four and breed in Wood Buffalo National Park located in Alberta, Canada. A nest will be constructed out of bulrush and a clutch of one to three eggs will be laid in late April to early May. The eggs will incubate in about 30 days.

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Nest guarding and brood rearing are a shared duty between both parents. Migration to overwintering habitat begins in mid-September and most birds arrive by late-October to mid-November (USFWS, 2001). Pallid Sturgeon The pallid sturgeon was federally listed as endangered in 1990 (55 Federal Register 36641). They have experienced dramatic declines throughout its range due to river channelization, construction of impoundments, and altered water flows (USFWS 2015). The pallid sturgeon are bottom dwelling, slow growing fish that feed primarily on immature aquatic insects and small fish. These sturgeon are often found in large, turbid, free-flowing river habitat in the Missouri and Mississippi rivers. Pallid sturgeon have been present in the Platte River or near its mouth and in the Yellowstone River during above- normal spring flows. Western Prairie Fringed Orchid The western prairie fringed orchid is an herbaceous perennial that was listed as federally threatened on September 28, 1989. The range of the orchid extends west of the Mississippi River to the states of Iowa, Kansas, Minnesota, Nebraska, North Dakota, and in Manitoba, Canada. Data depicting known historical presence shows a 75 percent decline where these populations are now extirpated (USFWS, 1996). The western prairie fringed orchid occurs in mesic to wet tallgrass prairies and meadows but can be found in old fields and roadside ditches. Habitat loss, mostly through conversions to cropland and habitat degradation are the greatest threats to this orchid. Fire suppression, overgrazing, and competition with introduced alien plants have also threatened these species. 3.7. HYDROLOGICAL ANALYSIS Studies of the hydrology of the South Platte River by the Corps date back to the 1970’s. The earliest documented study of the entirety of the reach within Urban Drainage and Flood Control District’s (UDFCD) jurisdiction was conducted by Merrick in 1983. This subsequently led to a 1984 Phase A report (master plan) prepared by Wright Water Engineers, Inc. (WWE). The peak discharge profile in the Phase A report was determined from a modeling effort, based on the earlier model by the USACE. This included design storm assumptions (southeast and east storm centers) and yielded discharge profiles that have been in effect in the metropolitan Denver area for many years. Discharge Frequency Table 4 below shows the Discharge-Frequency values through the study area that were utilized for this project. In 2015, UDFCD undertook an update of the South Platte River Hydrology to take advantage of the additional 30 years of record in support of a CLOMR request. Upon the initiation of this feasibility study, the flows were still under review. The hydrology CLOMR was finalized and approved in June of 2016.

Table 4. Discharge-Frequency Values used for HEC-RAS Modeling River 50% 20% 10% 4% 2% ACE 1% ACE 0.5% 0.2% ACE* ACE ACE ACE (cfs) (cfs) ACE ACE (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) South 2,600 4,300 5,600 7,400 11,400 13,800 15,100 19,100 Platte

* ACE, or annual chance of exceedance, describes the probability of a flood even occurring in any given year Additional low flow analysis was performed in support of identifying flow needs for fish and water quality. The values were developed utilizing the Hydraulic Engineering Center’s Statistical Software

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Package (HEC-SSP) and the period of record of daily flow values for USGS 06711565 South Platte River at Englewood, Colorado (Table 5).

Table 5. Duration analysis for USGS 06711565 South Platte River at Englewood, Colorado

% of Time Exceeded Q (cfs) 99 20 95 33 90 41 80 54 50 114 25 278 15 428 10 630 5 1150 2 2130 1 2666.1 0.1 3698.1

3.8. HYDRAULIC ANALYSIS Hydraulic analysis under this study was performed utilizing the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) Version 5.0.3 (September 2016). The analysis performed under this study was done in collaboration with the UDFCD’s on-going effort to update the hydrologic and hydraulic modeling on the South Platte River. Specific to this study, the evaluation of the existing and future without project conditions, as well as the alternatives, was performed. Hydraulic Model The model used for the hydraulic analysis of the existing conditions was provided by the non-federal sponsor. This model utilizes HEC-RAS, and was updated in May 2016 by Olsson and Associates. Olsson, on behalf of UDFCD, combined data from various models developed since 1979 and formed them into one continuous geometry representing the best available data. The extent of the model covers from Chatfield Dam downstream to Baseline Road. Much of the model in the project study area has been updated with recent topographic data in connection with the improvements in Reach 2. The model is incomplete as it contains no cross-section data for about 13,000 feet downstream of the drop structure in Reach 1. The currently available UDFCD modeling was sufficient for the feasibility study. Future revisions to the hydraulic models would be used in the design and implementation phase. Channel Stability In general, banks within the study reach are largely stabilized and are able to withstand flows with minimal damage. The surface bed layer within the channel consists predominantly of sand and gravel. The South Platte River was observed to be in a degradational state, although the rate of degradation has slowed in recent history. This observation was made by reviewing sediment samples that were collected by UDFCD as part of a study of river improvements on the South Platte River downstream of 6th Avenue. Although these samples were collected approximately 5 miles downstream of this study area, the results are likely relevant due to similar hydrology and stream dimensions.

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A stability analysis was performed to evaluate the existing channel. In order to define a stable channel configuration for each alternative, the following three methods were applied: (1) hydraulic geometry relationships, (2) analogy or “reference reach” method, and (3) shear stress method. The hydraulic geometry and shear stress methods are quantitative methods used to evaluate channel stability while the analogy (reference reach) method was used in a primarily qualitative manner. 3.9. SOCIOECONOMIC SETTING The Southern Platte Valley socioeconomic analysis used a 0.25-mile buffer area around the project area and predominately used census block and census tract data. The size of the study area and 0.25-mile buffer is approximately 1.91 square miles. The area of the census blocks that entirely or partially contained in this buffer is approximately 3.48 square miles. The Southern Platte Valley study area is home to approximately 1,953 residents, less than 0.5 percent of the City’s total population. Given the industrial and commercial uses that are a large presence in the study area, the population density (at 561 persons per square mile) is below that of Denver as a whole (3,870 persons per square mile). Based on block group data, the home ownership rate (34.7 percent) is lower than citywide (46.4 percent). The percentage of the population which is of Hispanic or Latino ethnicity (49.9 percent) is higher than that of Denver as a whole (30.9 percent). The proportion of the non-Hispanic population in the study area which is white (81.2 percent) is marginally higher than that of Denver as a whole (76.1 percent). As shown in Table 6, the study area census tracts reflect a marginally lower than average median household income, as well as a higher than average proportion of families that are either unemployed or in poverty when compared to the City as a whole. The poverty rate in the study area is nearly twice that of Denver as well.

Table 6. Median Household Income, Unemployment Rate, and Poverty Rate within the Study Area Employment and Income Median Household Unemployment Poverty Rate (%) Income ($) Rate (%) * ** Study Area Tracts $49,314 6.6% 22.7% Denver $53,637 6.3% 12.8% * for population in labor force ** of all families

Educational attainment is detailed in Table 7 for the study area census tracts and the City of Denver. In the study area census tracts, more than two times the City’s average do not have a diploma (31.88 percent versus 13.89 percent). Study area residents are also much less likely to have a bachelor’s or graduate degree when compared to Denver as a whole (15.10 percent versus 27.33 percent and 7.21 percent versus 17.62 percent, respectively).

Table 7. Educational Attainment HS Some Graduate or No Graduate Associate’s Bachelor’s College, Professional Diploma or Degree Degree No Degree Degree Equivalent Study Area 31.88% 25.21% 16.05% 4.58% 15.10% 7.21% Tracts Denver 13.89% 17.66% 18.26% 5.24% 27.33% 17.62%

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Table 8 summarizes the employment by industry for those who live in the study area census tracts. As seen in Table 8, study area residents are more often employed in the “Construction,” “Retail trade,” and “Manufacturing” industries than the citywide rate, and are less often employed in the “Finance and insurance, and real estate and rental and leasing,” “Educational services, and health care and social assistance,” and “Information” industries.

Table 8. Employment by Industry Study Area Industry Denver Tracts Educational services, and health care and social assistance 20.3% 16.7% Professional, scientific, and management, and administrative and 17.4% 16.2% waste management services Arts, entertainment, and recreation, and accommodation and food 11.9% 13.0% services Retail trade 9.1% 12.0% Finance and insurance, and real estate and rental and leasing 8.3% 4.3% Construction 6.9% 14.9% Manufacturing 5.4% 7.0% Other services, except public administration 5.0% 5.3% Transportation and warehousing, and utilities 4.2% 3.8% Public administration 4.1% 2.7% Information 3.5% 1.7% Wholesale trade 2.8% 1.8% Agriculture, forestry, fishing and hunting, and mining 1.3% 0.7%

3.10. ECONOMIC SETTING Land uses within the study area include residential, commercial, industrial, transportation, and recreational / open space among others. Comprehensive plans, community and neighborhood plans, and zoning regulations guide and regulate land development and use. Denver has regulatory authority over land use in the immediate study area. The Denver Comprehensive Plan is the major planning document for the City and offers a higher-level framework than neighborhood plans to guide and influence decisions that affect the future of the City. It is used as a foundation for the more specific vision, recommendations, and strategies contained in neighborhood plans. Blueprint Denver, a supplement to Denver’s Comprehensive Plan 2000, focuses on land use and transportation. The following summarizes land use for the Southern Platte Valley study area defined as a ¼-mile buffer on either side of the river. To generate this summary, Geographic Information System (GIS) was used to select the areas in Denver County’s Blueprint Denver Concept Land Use database which intersects the study area. Land use in the South Platte study area is largely employment, industrial, golf course, and parks. Employment parcels, areas containing office, light manufacturing, and high tech uses such as information technology, are located in the southern portion of the study area. Heavy manufacturing, service, and warehouse businesses are lo cated in the northern industrial portion of the study area near Vanderbilt Park and Ruby Hill Park. Railroad tracks are located on the rights-of-way parcels with the primary users being Burlington Northern Santa Fe (BNSF) and Union Pacific. There is a small amount of residential development near the river within or adjacent to the Southern Platte study area, with remainder transit oriented development, bodies of water, and mixed use. Table 9 provides a summary of those land use categories. Figure 14 provides a map of land use in the study area. Acreages reported in the table correspond to only that acreage within the study area boundary, while the map shows how land use areas overlap the study area, in order to better visualize the land use along the edges of the

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study area. Acres in the table may not exactly match the area of the study area polygon, since the source dataset did not include all road rights-of-way.

Table 9. Land Use Distribution Land Use Acres %

Employment 12.4 24.3%

Industrial 10.5 20.6%

Golf Course 8.6 16.9%

Park 6.8 13.3%

Rights-of-Way 4.4 8.6%

Single Family Duplex 3.0 5.9%

Transit Oriented Development 2.3 4.5%

Water Body 1.4 2.7%

Mixed Use 1.0 2.0%

Single Family Residential 0.6 1.2%

Total 51 100%

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Figure 14. Land Use within the Study Area

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3.11. CULTURAL RESOURCES For the Class I portion of the Cultural Resource Investigation (Literature and Records Search), Colorado's On-line Cultural Resource Database (COMPASS) provided eligibility site status under the National Register of Historic Places (NRHP) criteria, and a description of each site. COMPASS also provided information about sites that are unevaluated, or for which the eligibility determination is not official; “Needs Data” is the label used for these sites. The proposed project is located in Township 4 South, Range 68 West, in Sections 21, 22, 27, and 28. The COMPASS search revealed two sites (5DV.658 and 5DV.2458) listed on the NRHP, 21 sites eligible for listing on the NRHP, and 26 unevaluated sites. Table 10 shows the breakdown of sites within the sections. Additional information on these sites can be found in the Cultural Resources Appendix. However, it should be noted that COMPASS did not show any recorded sites within the actual study area.

Table 10. Sites broken down by section. Listed on National Not Township Range Section Eligible Register Eligible Unevaluated Surveys

4S 68W 21 1 0 1 3 2 22 10 1 24 15 10

27 12 0 20 5 5

28 0 1 8 3 0

TOTAL 21 2 53 26 17

3.12. RECREATIONAL RESOURCES The Regional Trail, an 18-mile paved pathway adjacent to the river, passes through the study area with its southern terminus approximately 1.75 miles south of the project boundary. This trail is mainly used as a walking, running, and biking path and serves as a pedestrian connection route to downtown Denver as well as other trails, parks, and attractions in the area. Along the entirety of the South Platte in the study area are riverbank access points for anglers, providing many opportunities for fly fishing. There are several city parks located throughout the study area. At the north end of the study area, Overland Pond Park serves as a habitat sanctuary for migratory birds and native tree and fauna. It was redesigned as a learning park along the banks of the South Platte River and offers picnic areas and fishing docks. Just south is Overland Park Golf Course. Located across the South Platte on the west bank is Ruby Hill Park, a city park that offers three baseball fields during the warmer months and a ski and snowboard terrain park in the colder months with assistance of artificial snowmaking. First established in 2007, Ruby Hill attracted approximately 3,000 visitors with attendance growing to over 6,000 the next year. Pasquinel’s Landing Park is located directly south of the Overland Park Golf Course. The park has recently undergone beautification renovations to make the South Platte more aesthetically pleasing and accessible to pedestrians. Grant Frontier Park North (describes the renovations of Grant Frontier Park north of the pedestrian bridge), towards the south end of the study area, underwent similar reconstruction as Pasquinel’s Landing Park, improving riparian, recreation, and water quality features. These two renovation projects were part of the River Vision Implementation Plan, implemented by the City and County of Denver with collaboration with local agencies and non-profit organizations.

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3.13. FORECASTED FUTURE WITHOUT PROJECT CONDITIONS The forecasted future 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. Future Hydraulic and Hydrologic Conditions Hydrology and hydraulic properties of the project reach are unlikely to change in any significant manner in the without project condition. Hydrology is controlled by the presence of Chatfield Dam several miles upstream of the site. Local runoff is sourced from areas that are presently highly urbanized areas. The channel hydraulics are highly engineered and stable due to the presence of grade control, the straightened and uniform nature of the channel, and protection against lateral erosion in areas of concern. The USACE Engineering and Construction Bulletin No. 2016-25 (ECB, USACE 2016) requires a qualitative analysis of the impacts of climate change on the climate variables that may affect the hydrology of a project. This analysis does not affect the numerical results of a study but may indicate potential climatic trends. The ECB consists of both a first-order trend analysis on stream gauges in the area and a literature review of regional climate studies. The climate change analysis conducted under this study included a stream gauge trend analysis, a regional climate forecast model analysis, and a review of regional analysis studies. The Corps’ Climate Change Hydrology Assessment Tool was used to identify historic trends in instantaneous peak flows at USGS Gauge 06711565 as a proxy for understanding how flows in the watershed have changed over the period of record. Results of the literature review indicate an increase in extreme precipitation intensity, a decline in snowpack and streamflow, shift in the timing of runoff to earlier in the year, an increase in average monthly temperature for both summer and winter, and a decrease in snow water equivalent (SWE). The Corps’ Climate Change Hydrology Assessment Tool did not find statistically strong results for the South Platte River hydrologic unit code (HUC) and the stream gauge at the site. Analysis of historical trends as they relate to annual peak instantaneous streamflows indicate a slight decreasing trend in streamflow. Analysis of 93 climate-changed hydrology models of HUC 1019 South Platte indicate a mean result of little to no change in annual maximum monthly streamflows. Considering the full range of hydrologic models, there is a chance of significant increases in runoff volume at the site. Considering the mean of the projected annual maximum monthly streamflow projections from the 93 climate- changed hydrology models, the analysis shows a slight upward trend in the values projecting into the future. Overall, The Corps’ Watershed Vulnerability Assessment Tool does not indicate the project area to be at risk. While literature review and results indicate increases in extreme precipitation and annual peak flows, this qualitative analysis concludes that climate change impacts in the project area will not be significant over the life of the project. Future Ecosystem Conditions Without future restoration, planning, and remediation efforts, it is likely that the watershed condition of South Platte will continue to degrade. Future population growth will continue to place demands on watershed resources, and it seems likely that these demands will inevitably impair watershed health if no watershed-based planning or restoration efforts are employed. Increases in population and higher- intensity development will increase demand for water supply, likely precipitating the need for additional

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reservoir storage and new modifications to streamflow for irrigation supply. Each of these hydrologic modifications will continue to shift the watershed hydrology to a more altered state, further impairing watershed condition and having impacts on environmental resources utilized by fish and wildlife. For water quality, this increase in development suggests a subsequent increase in nonpoint source pollution throughout the watershed. Nonpoint source pollution, defined as water pollution that comes from many different sources in a watershed, is the leading remaining cause of water quality problems in the United States (EPA, 2005). Increases in the number of septic systems in the non-serviced area of the watershed will likely continue to load nutrients and E. coli to downstream waterbodies. Similarly, an increase in stormwater runoff from greater impervious cover and development-related construction activities will inevitably contribute to continued water quality degradation, unless BMPs and restoration activities that directly address these sources are implemented. In addition to continued pressure from population growth and urbanization, climate change will also likely impact the water resources of the area. Future projections suggest that, if current trends continue, global urban land cover will nearly triple by 2030 (Seto et al., 2012 as cited in Revi et al., 2014). In step with anticipated global trends, the Colorado State Demography Office in 2015 reported the City and County of Denver as supporting a population of 682,545 individuals. This population is expected to grow nearly 22% by Figure 15. Actual and forecasted future population of Denver 2050, to 833,221 individuals (CSDO, 2017, Figure County. Figure derived from U.S. Census, Colorado Department 15). of Local Affairs, as appeared in The Denver Post, 2017 As climate change continues, the frequency and severity of drought will increase, and wetlands and riparian corridors will become more vulnerable to loss. Rising temperatures will lead to an increased demand on water resources, particularly for large urban areas (Shafer et al., 2014) like the Denver Metro. A Future without Project (FWOP) analysis was conducted on the study area using FACWet and FACStream, to technically assess conditions of the existing wetland/riparian and aquatic habitat. Assumptions made for technical analysis include the continued degradation pressures of urbanization, and specifically real estate development in Reach 3. The Xcel Energy power plant has been decommissioned, so it is assumed within 50 years, that parcel will be purchased and actively developed. Within the 500 meters of the entire study area (the Habitat Connectivity Envelope described in FACWet), it assumed that existing habitat would continue to be encroached upon, creating neighboring habitat loss as well as increasing barriers to resident wildlife migration within the overall watershed. Continued urban development would increase impervious surfaces and non-point and point sources of pollution, while a decrease of wetlands within the watershed would remove the area’s natural ability to filtrate inorganic and organic compounds from entering the South Platte River. Invasive and non-native species will continue to out-compete native species within the remaining habitat. Vegetation structure and complexity will decrease, monocultures will continue to persist impacting the quality and functional value of the wetlands and riparian areas. The riparian corridor that once existed around the South Platte

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River has been severely depleted, and it is anticipated that continued pressure for development within the Metro would continue to stress the biotic community surrounding the river. Detailed analysis may be found in Appendix A1. Future Economic Conditions Data for the study area were obtained from the U.S. Census Bureau describing recent trends in study area population growth. The 2010 census block data estimated the population at 1,953. Since estimates are only available for 2010 at the block level and insufficient to detail trends, ACS census tract data and Census Bureau population data were used. According to the ACS, the estimated 2015 population for the study area census tracts was 30,998. Table 11 shows the study area census tract population from 2010 to 2015 and Table 12 shows the population between 2000 and 2015 for Denver and the state of Colorado to serve as regions of comparison.

Table 11. Study Area Tracts Population Average Annual Study Area Tracts Growth Rate 2010 26,208 - 2011 26,528 1.22% 2012 26,844 1.19% 2013 28,390 5.75% 2014 29,307 3.23% 2015 30,998 5.77% Source: U.S. American Community Survey

Table 12. Population 1970-2015 Average Average Annual Annual Denver Colorado Growth Rate Growth Rate (Denver) (Colorado) 1970 516,852 2,210,000 - - 1980 492,694 2,890,000 -0.47% -0.47% 1990 468,139 3,308,000 -0.50% -0.50% 2000 556,094 4,327,000 1.88% 1.88% 2001 564,411 4,426,000 1.50% 2.29% 2002 561,072 4,490,000 -0.59% 1.45% 2003 558,351 4,529,000 -0.48% 0.87% 2004 558,506 4,575,000 0.03% 1.02% 2005 561,323 4,632,000 0.50% 1.25% 2006 568,692 4,720,000 1.31% 1.90% 2007 578,789 4,804,000 1.78% 1.78% 2008 593,086 4,890,000 2.47% 1.79% 2009 610,345 4,972,000 2.91% 1.68% 2010 603,421 5,049,000 -1.13% 1.55% 2011 620,018 5,120,000 2.75% 1.41% 2012 634,542 5,192,000 2.34% 1.41% 2013 649,495 5,272,000 2.36% 1.54% 2014 663,963 5,342,000 2.23% 1.33% 2015 682,545 5,530,000 2.80% 3.52% Source: U.S. Census Bureau The average annual growth rate of the study area tracts from 2010 to 2015 was approximately 3.43% and the city of Denver experienced a similar average annual growth rate during that same time period, approximately 1.89%. In terms of percent population change from 2010 to 2015, the study tracts

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increased by 18.28%, the city of Denver increased by 13.11% and the state of Colorado increased approximately 9.53%. Future population growth is forecasted to show a continued increase in population, but at a slowing rate for the state of Colorado according to the Colorado State Demography Office as shown in Figure 16. The Colorado State Demography Office forecasted population growth by county as well, detailed in Table 13. The data report similar findings at the county level as at the state level, where average annual percent change is increasing from 2015 to 205 but at a decreasing rate.

Figure 16. Colorado Forecasted Population Growth Rates

Table 13. Population Forecast 2015 - 2050

Average Annual Average Annual Denver County Colorado Growth Rate Growth Rate (Denver County) (Colorado) 2015 680,658 5,448,055 - - 2020 733,765 5,907,198 1.5% 1.6% 2025 798,853 6,391,239 1.6% 1.6% 2030 861,706 6,892,192 1.6% 1.5% 2035 900,766 7,352,841 0.9% 1.3% 2040 925,098 7,773,481 0.5% 1.1% 2045 942,194 8,134,846 0.4% 0.9% 2050 952,955 8,461,295 0.2% 0.8%

4. Plan Formulation 4.1. SECTION 1135 POLICY Continuing Authorities Program (CAP) Section 1135 projects are relatively smaller scale environmental restoration projects, authorized up to 13.3 million. The solutions investigated allow for structural or operational modifications to existing Corps projects or areas directly impacted by existing Corps projects for restoration or enhancement of environmental values, especially fish and wildlife. To qualify for assistance under the Section 1135 authority, existing or previous Corps projects must have contributed

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to the ecosystem degradation. This project qualifies for the Section 1135 Program, as the upstream Chatfield and Bear Creek Projects have significantly altered the hydrology and stream flow throughout the entire South Platte River within the City of Denver. 4.2. STUDY PROCESS CAP Section 1135 projects are conducted in two phases: the feasibility phase which results in a Feasibility Report with an integrated Environmental Assessment; and the design and implementation phase which results in final design plans and specifications and construction of the project. Feasibility costs which exceed an initial $100,000 allocation of federal funding are cost-shared 50 percent Federal and 50 percent non-Federal, in accordance with a FCSA specific to the feasibility study. If the project is approved and advances to the design and implementation phase, all costs for that phase are cost-shared 75-percent Federal and 25-percent non-Federal in accordance with the terms of a Project Partnership Agreement (PPA) which would be prepared for the project at the start of that phase. The feasibility phase analysis follows policy guidance developed for implementing the Principles and Guidelines (P&G). The feasibility phase primarily consists of conducting a comprehensive analysis to quantify the existing environmental condition index within the study area; define a set of measureable objectives and identify any constraints for developing alternatives; formulate and evaluate alternatives to meet objectives and avoid constraints; compare the alternatives based on the metrics for the objectives, and identify a recommended plan. The results of the feasibility study are documented in this report and form the basis for a decision on project implementation. 4.3. CONSIDERATION OF PLANNING CRITERIA In the conduct of all Corps feasibility studies, alternative plans are formulated within the context of considering four fundamental planning 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 extent to which the alternative plans are acceptable in terms of applicable laws, regulations and public policies. 4.4. QUALITY MANAGEMENT To ensure quality and technical accuracy of the analyses and report, both District Quality Control (DQC) and Agency Technical Review (ATR) were conducted and certified prior to finalizing the report for public review. Legal certification was accomplished concurrent with the ATR process to ensure that the study meets and fulfills all legal requirements, and complies with all applicable federal, state, and local laws and regulations. This final report incorporates all comments received during the agency and public review process and any necessary revisions needed to address those comments, and the same quality management procedures were applied prior to submitting the report for approval.

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4.5. ALTERNATIVE FORMULATION On February 27th and 28th, 2017 the Corps and Denver facilitated an alternatives formulation workshop. Other agencies in attendance included the USFWS, CPW, and the Urban Drainage Flood Control District. Over the two-day span of the workshop an initial array of measures were developed, qualitatively assessed, and combined, culminating in the development of a list of alternatives to be evaluated under this study. The following sections provide more detail on this process, to include the measures considered and the alternatives developed. Initial Measures The initial array of measures listed below was the first thing developed during the alternatives workshop. The measures were developed on a reach-by-reach basis, similar to how they are shown below. Reach 1 – W. Mississippi Ave. to W. Florida Ave. • Modify the existing drop structure • Lay back the east bank to increase riparian/wetland habitat • In-stream structures such as vanes, riffles and boulder clusters • Lay back the west Bank and relocate the Regional Trail to increase riparian/wetland habitat • Remove golf course road and parks and recreation structure (portlet) to increase riparian/wetland habitat • Re-route the Southern Platte River channel through Overland Pond • Fill in part of Overland Pond to create additional land area for riparian habitat • Improve Overland Pond habitat with plantings, establish wetlands, etc.

Reach 2 – W. Florida Ave. to W. Evans Ave. • Modify the existing drop structure • Lay back the upstream west bank to increase riparian/wetland habitat • Lay back the upstream east bank and modify the existing Asbury Ave. outlet structure to create a wetland in the area that is currently the Southwest corner of the golf course • In-stream structures as vanes, riffles and boulder clusters. • Treat invasive species and re-plant native vegetation on the west bank • Re-vegetate the east bank • Create a low flow channel through the golf course

Reach 3 – W. Evans Ave. to W. Yale Ave. • Modify the existing drop structure • Modify bank to create wetland and riparian habitat along the south half of Grant Frontier Park (hereafter referred to as Grant Frontier Park South) • Modify bank to create wetland and riparian habitat along Grant Frontier Park on the west bank • Lay back banks and modify the existing pedestrian bridge to create riparian/wetland habitat • Lay back the east bank and modify the existing Harvard Gulch outlet structure to create wetland habitat • In-stream structures such as vanes, riffles and boulder clusters. • Acquire water rights to increase flows during low flow season(s)

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Measures Removed from Consideration After the initial array of measures was developed, each measure was qualitatively assessed to determine if the measure satisfied the objectives and the four planning criteria of complete, effective, efficient, and acceptable. From this qualitative assessment any measure that was found to not at least partially satisfy a study objective and each of the four planning criteria was eliminated from further consideration. One such measure that was eliminated was the Reach 1 measure of re-routing the South Platte River channel through Overland Pond. This measure was determined to not be efficient or acceptable, as there is known contamination in Overland Pond and the measure would requiring pumping to account for differences in water surface elevations. Modification of the drop structure in Reach 2 was eliminated from further consideration. Concerns were expressed in discussions with the non-federal sponsor regarding the technical feasibility of this measure. The drop structure in Reach 2 was previously modified in 2015 to the extent feasible without unacceptable impact to the water surface area. The West Florida Avenue Bridge is immediately downstream of this structure and further modification of the drop structure would likely require modification, or replacement, of the West Florida Avenue Bridge in order to mitigate impacts on future water surface elevations. Furthermore, the drop structure was part of a previous improvement project that lessened the height of the structure. However, due to the need to ensure that the intake infrastructure running underneath the structure would still receive flows from the South Platte River and distribute water to the Overland Golf Course and Overland Pond Park, further modification to the structure was deemed impractical during the previous effort.

Figure 17. Existing Drop Structure in Reach 2 near the Aqua Golf intake pumping house.

An additional measure preliminary discussed and ultimately removed from consideration was the modification of the Asbury Avenue outfall in Reach 2. This measure would have cutback the outfall structure and to supply flows to a wetland area and a constructed side channel. This alternative was eliminated from further consideration due to the required configurations of the Regional Trail. The

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Regional Trail is a heavily used commuter trail and has geometric design requirements to ensure the trail can effectively handle the commuter traffic volumes. The original concept for this alternative did not comply with these requirements, so the alternative was determined to be unacceptable. Some consideration was given to creating a bridge structure that would have mirrored the existing trail alignment, but the existing trail is within the golf course safety zones, so modifying the trail with a bridge was also not an acceptable measure. Initial Array of Site Alternatives The measures that were found to satisfy or partially satisfy the four planning criteria were combined into the initial array of site alternatives. The initial array of site alternatives were the final products developed during the alternatives workshop. Similar to the measures, the site alternatives listed below were developed on a reach-by-reach basis. Reach 1 – W. Mississippi Ave. to W. Florida Ave. Alt 1.1. In-stream features a. Alone with wetland benches b. With benches and replacing drop structure near Overland Pond Park (must maintain current drop elevation) Alt 1.2. Fill-in part of Aqua Golf Pond and create riparian habitat Alt 1.3. Relocate trail and create riparian and/or wetland habitat on east bank Alt 1.4. Modify drop structure near Overland Pond Park (must maintain current drop elevation)

Reach 2 – W. Florida Ave. to W. Evans Ave. Alt 2.1. Replant west bank, vegetate east bank Alt 2.2. Relocate Regional Trail, set-back bank, and create wetland and/or riparian habitat (west bank) Alt 2.3. Low flow channel through Golf Course

Reach 3 – W. Evans Ave. to W. Yale Ave. Alt 3.1. In-stream features with wetland benches Alt 3.2. Create wetland and riparian habitat within Grant Frontier Park South Alt 3.3. Harvard Gulch outfall wetland Alt 3.4. Grant Frontier west bank riparian/wetland habitat Alt 3.5. Low flow channel through Grant Frontier Park South Alt 3.6. Modify drop structure near Xcel Energy Alternatives Eliminated from Consideration Three alternatives were assessed by the PDT in varying levels of detail and technical discipline that were eliminated from consideration in the final array of alternatives. Reasons for elimination were a result of technical feasibility or acceptability based on City safety regulations.

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Alternative A: In-fill Northeast Corner of Aqua Golf Pond Alternative A in Reach 1 included two variations of infilling a portion of Aqua Golf Pond in Overland Lake, a man made recreational aquatic golf course, to create wetlands (Figure 18). These variations, Alternative A1 and A2, consisted of creating a larger wetland, approximately 1.28 acres or a smaller variation, 0.64 acres, respectively. These alternatives were included technically assessed using FACWet and CE/ICA; however, following further discussion with Denver Parks and Recreation, was removed from consideration. Concerns were raised regarding existing water rights for the Aqua Golf/Overland Golf Course facilities as well as the alternative’s potential impact to established safety hitting zones necessary for the safe operation of the Aqua Golf facility. Therefore, it was determined that this alternative no longer met the “acceptable” planning criteria, and it was removed from consideration.

Figure 18. Conceptual drawing of Alternative A: Aqua Golf in-fill in Reach 1 to create wetlands in Overland Lake. Top graphic depicts general cross-section while bottom graphic depicts conceptual plan view

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Alternative C: Restore Wetland/Riparian Habitat on East Bank of Reach 2 Alternative C proposed moving the Regional Trail into the western edge of the Overland Golf Course and re-grading the east bank of Reach 2 to restore a 1.67 acre wetland and riparian habitat complex between the Regional Trail and the South Platte River (Figure 19). This alternative was analyzed with FACWet and included in the initial CE/ICA assessment. However, after discussions with Denver Parks and Recreation this alternative was removed from further consideration due to concerns of this alternative’s potential impact to pedestrians of the relocated Regional Trail and the established safety hitting zones of the Overland Golf Course to protect pedestrians. It was determined this alternative was unacceptable.

Figure 19. Alternative C in Reach 2 near the Overland Golf Course

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Alternative D: Low-flow Channel through Overland Golf Course Alternative D proposed a low-flow channel hydrologically connected to the South Platte River that would meander on the western edge of the Overland Golf Course in Reach 2 (Figure 20). This alternative was technically analyzed with FACWet and FACStream and included in the initial CE/ICA analysis; however, was removed from further consideration. The non-federal sponsor has a multi-year contract with a third party to host concerts at the Overland Golf Course. The construction of this alternative would have caused issues for this existing contract, potentially leading to unnecessary financial burden on the non-federal sponsor. In addition, there were concerns with the playability of the golf course having the channel cross the fairway of one of the holes twice as well as the impact of additional maintenance efforts. Therefore, it was determined that this alternative no longer met the “acceptable” planning criteria and was removed from consideration.

Figure 20. Conceptual plan view of Alternative D in Reach 2 Final Array of Site Alternatives The naming convention of the alternatives was initially alphabetical ordering during formulation; however, as alternatives were modified, added or removed from consideration at various phases of the formulation process, the alphabetical ordering became disconnected. Alternative nomenclature was not changed for formulation consistency and previous technical analysis that had already utilized the designated nomenclature. Alternatives in this document are arranged by Reach in attempt to provide clarity to the reader. Table 14 provides a quick-reference list of the final alternatives that were considered as these alternatives were considered complete, effective, efficient and acceptable.

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Table 14. Final array of alternatives listed by Reach considered with FACWet and/or FACStream, Cost Estimates and CE/ICA. Note the alternatives with an asterisk (*) are part of the Recommended Plan.

Alternative Alternative Description Habitat Type Restore 1.15 acre riparian and wetland habitat complex on west bank by Riparian & B relocating Regional Trail and pedestrian bridge and re-grading bank Wetland Restore 1.30 acres of riparian habitat on west bank by removing invasive T* Riparian species and re-planting a desirable native cottonwood-willow community In-stream aquatic features such as dikes, cross vanes, j-hooks, riffles and K* Aquatic boulder clusters to increase the complextity and diversity of aquatic habitat

Reach 1 Modify the Overland drop structure by placing an auxillary weir immediately L Aquatic downstream of the existing grade control structure to reduce the barrier height Modify the Overland drop structure by placing an auxillary weir immediately P* downstream of the existing grade control structure to reduce the barrier height Aquatic and addition of a riffle ramp (1H:20V) O* Re-vegetate 3.92 acres of downstream portion of Reach 2 on east and west bank Riparian Restore 1.67 acres of riparian habitat on east bank by removing invasive species

Reach 2 S* Riparian and re-planting a desirable native cottonwood-willow community Restore 5.13 acres of riparian and wetland habitat in South Grant Frontier Park Riparian & E on east bank by relocate Regional Trail and re-grading bank Wetland Modify Harvard Gulch Outfall to redirect flows to an approximate 0.46 acre low- flow side channel that parrallels the South Platte River and relocate Regional Riparian, Wetland F Trail to re-grade bank to restore 4.97 acres of riparian and wetland habitat in and Aquatic South Grant Frontier Park on east bank. Restore 5.06 acres of riparian and wetland habitat in South Grant Frontier Park on east bank and create a 0.37 acre low-flow side channel on the north or Riparian, Wetland H downstream end of South Grant Frontier Park. Relocate Regional Trail to re- and Aquatic grade bank. Restore 5.08 acres of riparian and wetland habitat in South Grant Frontier Park on east bank and create a 0.35 acre low-flow side channel on the north or Riparian, Wetland I downstream end of South Grant Frontier Park. Relocate Regional Trail to re- and Aquatic grade bank. Restore 4.71 acres of riparian and wetland habitat in South Grant Frontier Park on east bank and create approximately 0.72 acres of aquatic habitat with two Riparian, Wetland J* low-flow channels (north and south) of South Grant Frontier Park. Relocate and Aquatic Regional Trail to re-grade bank

Reach 3 Restore 4.62 acres of riparian and wetland habitat in South Grant Frontier Park on east bank, modify Harvard Gulch to create a low-flow side channel that parrallels the South Platte River on the north or downstream end of South Grant Riparian, Wetland R Frontier Park and create an additional low-flow side channel on the upstream and Aquatic or south portion of South Grant Frontier Park, resulting in approximately 0.81 acres of aquatic habitat. Relocate Regional Trail to re-grade bank Restore 0.74 acres of wetland and riparian habitat by relocating Regional Trail to Riparian & G* re-grade west bank Wetland In-stream aquatic features such as dikes, cross vanes, j-hooks, riffles and M* Aquatic boulder clusters to increase the complextity and diversity of aquatic habitat Modify the Xcel drop structure by placing an auxillary weir immediately N Aquatic downstream of the existing grade control structure to reduce the barrier height Modify the Xcel drop structure by placing an auxillary weir immediately Q* downstream of the existing grade control structure to reduce the barrier height Aquatic and addition of a riffle ramp (1H:20V)

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Table 15 depicts alternatives that either cannot be combined with a certain other alternative as they are mutually exclusive and occur within the same footprint, or are dependent upon another alternative.

Table 15. Mutually exclusive and dependent alternatives, by reach

Reach Mutually Exclusive 1 B with T 1 L with P 2 C with S 3 F with E, H, I, J, or R 3 H with E, F, I, J, or R 3 I with E, F, H, J, or R 3 J with E, F, H, I, or R 3 N with Q 3 R with E, F, H, I, or J Reach Dependencies 3 G requires E, F, H, I, J, or R

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REACH 1 Reach 1 was primarily limited to alternatives that do not require grade work as the east bank is entirely underlain with the city sewer and cannot be removed. Half of the upstream portion of Reach 1 is not burdened by the sanitary system and thereby alternatives that included grading could be considered in this area. Figure 18 depicts a topographic view of Reach 1 in relation to the entire study area (Figure 21).

Figure 21. Reach 1 as relevant to the entire Section 1135 study area.

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Alternative B: Relocate Regional Trail and Restore Riparian/Wetland Habitat Alternative B includes relocating a portion of the existing Regional Trail and pedestrian bridge on the west bank of the South Platte River in Reach 1 (Figure 22). The Regional Trail would be maintained on the right bank following the removal and relocation of the pedestrian bridge. This would permit additional area for restoration of approximately 1.16 acres of riparian and wetland habitat. Restored wetland habitat would be designed to be inundated, at a minimum, two consecutive weeks out of the growing season. Restored wetland habitat types would be classified as palustrine emergent (PEM), seasonally and temporarily flooded, and palustrine scrub/shrub (PSS), seasonally and temporarily flooded. Riparian habitat would be restored with a transitional cottonwood-willow/mesic graminoid community, resonant of natural conditions that once existed prior to impoundment of the South Platte River and urbanization.

Figure 22. Location of habitat restoration and pedestrian bridge relocation of Alternative B in Reach 1.

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Alternative T: Restore Riparian Habitat on West Bank in Reach 1 Alternative T has the same project footprint as Alternative B for habitat restoration, therefore, it is considered mutually exclusive from T. The difference between these two alternatives is that Alternative T does not propose to relocated the pedestrian bridge. Additionally, no grading would occur with Alternative T. Habitat restoration would include restoring approximately 1.16 acres of riparian corridor habitat by removing invasive and undesirable species would be removed and replaced with a cottonwood-willow/mesic graminoid community, resonant of natural conditions that once existed prior to impoundment of the South Platte River and urbanization (Figure 23).

Figure 23. Location of riparian restoration of Alternative T in Reach 1

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Alternative K: In-stream Features to Restore Aquatic Habitat in Reach 1 Alternative K includes construction of hard point in-stream structures, such as rock vane dikes, cross vanes, riffles, boulder clusters and rootwad complexes. The existing channel in Reach 1 is generally uniformly wide, flat, and shallow and lacks the natural riverine processes for stable sediment dynamics and channel forming flows to maintain natural habitat diversity and ecological integrity, largely because of urbanization and large upstream water storage dams. As hard points, each feature will mimic the riverine geomorphic structure that would exist if natural flow and sediment dynamic processes were functioning in this reach of river. The construction of in-stream structures will increase depth diversity, velocity diversity and provide feeding and shelter habitat to benefit aquatic organisms. Rock vanes extend riverward from the bank terminating in the channel and direct flows from the bank back towards the center of the channel to maintain a thalweg. Scour pools generally from immediately downstream near the terminal end of vane structures that provide important pool habitat for fishes and other aquatic organisms. Often a gravel tailings substrate forms at the downstream of pools that can be utilized as spawning substrate for fishes, and additionally provides areas of primary production from attached algae and secondary production from the macroinvertebrate community. Vanes fitted with a “J-hook” at the terminal end of the structure can develop more robust scour pools, however may not perform thalweg maintenance for functional fish passage during periods of low flow as well as straight vanes. Cross vanes extend the channel from bank to bank and serve as grade control structures. Cross vanes usually direct flow towards the center of the structure and are capable of generating robust and quality pool habitats. The center or “low spot” of cross vanes can also be designed with boulders spaced to facilitate fish passage during periods of low flow. Pool habitats that form from engineered structures such as these can provide important thermal refuge for fishes during warm summer periods (Tate et al., 2007), and some cold/cool fishes modify their behavior to seek thermal refuge in constructed pool habitats during summer low flow periods (Elliott, 2000; Baird and Krueger 2003). This will allow for an eventual moderate improvement from existing conditions to restore habitat to more natural conditions to support a higher presence and diversity of native fish and macroinvertebrates (Dodrill et al., 2015). Figure 24 depict schematics of various rock vanes that could be placed within Reach 1 to improve the quality of the aquatic habitat.

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Figure 24. Schematic of potential in-stream features. Top left: rock vane; top right: J-hook; bottom: cross vane. Note the formation of scour pools created downstream of the structures and the depositional zones that accumulate sediment, creating a localized variety of depths and velocities beneficial to fish and other aquatic organisms (Images Craig Hill, after Rosgen, 2006, NRCS, 2007)

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Boulder clusters are simple, low risk, nature-based features that add visual appeal and provide concrete ecological benefit to aquatic life in degraded, uniform reaches of river. Boulder placement is a common method of fish habitat improvement which provides in-stream cover. Flow separation around the boulders lead to the formation of eddies (circular current of water). These eddies diffuse sunlight and create overhead cover for fish (Fischenich and Seal, 2000) and small pools may form on the downstream side of some boulder clusters. Velocities are increased surrounding the boulder cluster such that scour forms around the structure (Rosgen, 1996) and a localized flow velocity gradient develops in the “flow shadow” of the boulder cluster that can function as current-break resting habitat for migrating fishes. The scour, or developed pockets of deeper water, and the associated course substrate to add to the physical diversity of the habitat (Fischenich and Seal, 2000). By placing boulder clusters randomly throughout the entire reach, depth diversity, velocity diversity, habitat availability, and visual aesthetics would increase along the South Platter River within the project footprint (Figure 25).

Figure 25. Scour pattern around a boulder (derived from Fischenich and Seal, 2000)

Bank placed materials, such as root wads anchored in with boulder clusters would provide cover for fish, but also increase surface area for macroinvertebrates which provides an important food source for aquatic fauna. It is still assumed that the fisheries will be primarily compose of managed game fish and non-native species, however; a slight increase in native diversity would be expected within the localized project footprint. This alternative would qualitatively improve the existing aquatic habitat throughout all of Reach 1 (approximately 9.41 acres of aquatic habitat).

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Alternative L: Modify Overland Drop Structure with Auxiliary Weir Alternative L would modify the Overland drop structure in Reach 1 to reduce its impact as a barrier to fish passage and promote migration by functionally reducing the barrier height by 50 percent. It is currently estimated that this grade control structure has a single acute 3-foot drop that likely limits upstream fish movement during most of the year. This grade control structure sits atop a wastewater pipeline; therefore, the structure cannot be completely removed. To reduce the functional height of the drop, an auxiliary drop structure would be placed immediately downstream of the Overland drop structure, effectively making two 1.5-foot drop structures. Boulder clusters would be strategically installed along the footprint to provide additional habitat complexity in the scour pools created by these structures. Strategically placing boulders throughout the footprint immediately downstream of the existing Overland drop structure in the resting pool that Figure 26. Conceptual layout of modifications at Overland drop structure. would form between the existing Top graphic (plan view) the auxiliary weir would have boulder clusters structure and the new auxiliary weir strategically placed to allow fish to traverse the drop structure by step- and immediately downstream of the laddering from one boulder cluster to the next in the shelter shadows formed by the clusters. Bottom graphic (cross section) depicts the side auxiliary drop structure would provide profile of the existing structure and auxiliary weir (red) and resting pool resting areas for fish preparing to that would form between the structures traverse the final upstream drop. The crest of the drop structure could also be notched or fitted with boulders spaced to leave gaps to aid fish in traveling through and over the final upstream barrier. Because these boulder clusters would provide refuge in the form of “shadows” from upstream flows on the downstream faces of the boulder clusters, a network of boulder clusters could be designed to function much like a switchback road system (Figure 26). Although fish would swim longer total distance to traverse the entire barrier, they would be able to burst swim relatively short distances laterally from boulder cluster to boulder cluster, gaining elevation with each burst, expending less energy than burst swimming the entire longitudinal length of the ramp, and resting (and potentially opportunistically feeding) in the shadow of each boulder cluster to prepare for the next lateral burst to the next boulder cluster shadow. Fish would continue this “step-ladder” approach until they have successfully traversed the barrier.

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Alternative P: Modify Overland Drop Structure with Auxiliary Weir and Riffle Alternative P consists of modifying the drop structure at Overland Pond as discussed in Alternative L; however, an additional riffle structure would be constructed immediately downstream of the auxiliary drop structure. This riffle would have a 20:1 slope, elongating the gradient change of the riverbed over approximately 30 feet. Like Alternative L, a network of boulder clusters would be placed in the area between the existing Overland drop structure and auxiliary weir to aid aquatic life traversing the barrier (Figure 27). A network of boulder clusters would also be placed on the riffle structure ramp to similarly promote fish passage up and over the auxiliary weir. Further detailed refinement to modify the most upstream weir (i.e., the existing drop structure) could be designed to facilitate fish passage; possible refinements during design phase could include installing notches in the crest of the structure and/or armoring the crest with boulders fitted and spaced to leave gaps for fish to burst swim through and over the crest.

Consideration was given to constructing a riffle ramp from the existing drop structure, eliminating the need for the auxiliary structure. However, due to other utility infrastructure within the immediately downstream area (left bank) of the existing structure, and the additional cost associated with this larger riffle ramp structure, an alternative with a complete riffle ramp was not evaluated. However, it is believe that further investigation during the design and implementation (D&I) phase could demonstrate the constructability and economic viability of this alternative.

Figure 27. Conceptual modifications of the Overland drop structure. Top graphic (plan view) the auxiliary weir with additional riffle ramp would have boulder clusters strategically placed to allow fish to traverse the drop structure by step- laddering from one boulder cluster to the next. Bottom graphic (cross section) depicts the riffle ramp and resting pool with integrated boulder clusters

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REACH 2 Reach 2 alternatives were entirely limited to those that do not necessitate excavation as both the east and west bank are burdened by the city sanitary sewer lines. A small area on the east bank of the upstream portion of Reach 2, near Pasquinel’s Landing, is not underlain with the sewer system; however, the entire east bank is bordered by Overland Golf Course and the alternatives elevated for final consideration must adhere to hitting zone safety regulations. Figure 28 depicts Reach 2 in relation to the entire study area.

Figure 28. Reach 2 relevant to the entire Section 1135 study area

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Alternative O: Re-vegetate East and West Bank of Downstream Portion of Reach 2 Alternative O includes re-vegetating the east bank and clearing and re-vegetating a portion of the west bank in the downstream portion of Reach 2 (Figure 29). The right bank of this area was previously cleared and graded in 2014 and 2015 under the City and County of Denver project that modified the drop structure in this reach. Atypical, high flows following these plantings disrupted the area and the vegetation did not establish. The left bank was not cleared, graded and planted; therefore, there is opportunity to remove noxious species and replace the vegetation with higher floristic quality. This alternative restores approximately 3.92 acres of habitat over the 50-year project life as a result of vegetating bare areas with riparian vegetation.

Figure 29. Location of re-vegetation in the downstream portion of Reach 2 of Alternative O

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Alternative S: Restore Riparian Habitat of West Bank of Upstream Portion of Reach 2 Under Alternative S, approximately 1.67 acres of riparian habitat would be restored. Invasive and noxious species would be removed and replaced with a cottonwood-willow/mesic gramanoid community, resonant of the native vegetative community that would be found in this area prior to the upstream impoundment and urbanization. Figure 30 shows the footprint of Alternative S.

Figure 30. Location of riparian habitat restoration in Reach 2 of Alternative S

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REACH 3 Reach 3 had greater opportunity as compared to the other two reaches of the study area. No sewer system is present in the study area on the east bank; however it is on the west bank. Figure 31 depicts Reach 3 in relation to the entire study area. Alternatives at Grant Frontier Park South include concept variations and are discussed in Alternatives E, F, H, I, J and R with varying levels of environmental benefit and associated costs. All six of these alternatives are mutually exclusive and only one site plan would be selected. These six alternatives are all similar in that the Regional Trail on the east bank from South of the pedestrian bridge to West Harvard Avenue would be relocated away from the South Platte River to increase the terrestrial area for restoration alternatives. Under all six alternatives, restored wetland habitat would be designed to be inundated, at a minimum, two consecutive weeks out of the growing season. Restored wetland habitat types would be classified as PEM, seasonally and temporarily flooded, and PSS, seasonally and temporarily flooded. Riparian habitat would be restored with a transitional cottonwood-willow/mesic graminoid community, resonant of natural conditions that once existed prior to impoundment of the South Platte River and urbanization Additionally, all six alternatives include excavation of the east bank to restore wetland habitat. This excavation was determined to result in a change to the existing water surface elevation and regulatory floodplain which impacts the currently mapped NFIP floodplain that is administered and managed by FEMA and the UDFCD. Hydraulic analysis determined that the grading for the ecosystem restoration plan at Grant Frontier would result in both increases and decreases to flood profiles for various flood events including the base flood water surface profile at and upstream of the locations of the modifications. Appendix D provides detailed information of the changes to the regulatory floodplain as a result of the Grant Frontier Park South alternatives. As a result, all six alternatives at Grant Frontier Park South would require the pedestrian bridge immediately downstream of the site to be increased in span to increase the localized top-width of the river. The goal of the modification was to cause a no-rise to the regulatory and other flood profiles. The alteration of this bridge would include the expansion of the east span and placing the bridge abutments higher on the bank to accommodate the flood profile. The span will result in excavating back the bank approximately 30 feet immediately below this bridge which will increase the existing span of 90 feet to 120 feet. See Appendix F for further details on the modification of the pedestrian bridge downstream of Grant Frontier Park South.

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Figure 31. Reach 3 relevant to the entire Section 1135 study area

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Alternative E: Relocate Regional Trail through Grant Frontier Park South and Restore Riparian/Wetland Habitat on East Bank Under Alternative E, a total of 5.43 acres of wetland and riparian habitat would be restored. In Grant Frontier Park South, no sewer or utility lines occur on the east bank, thereby allowing the Regional Trail to be relocated to increase terrestrial area for restoration alternatives. . As a result of relocating the Regional Trail away from the river, approximately 1.58 acres of Grant Frontier Park South would be re- graded and restored into wetland habitat. Approximately 3.85 acres of riparian corridor habitat would be restored (Figure 32). The abutments of the pedestrian bridge immediately downstream of Grant Frontier Park South on the east bank would be moved farther upland on the bankline as the east span of the bridge is increased 30 feet to mitigate the change in water surface elevation (WSE) of the regulatory floodplain.

Figure 32. Alternative E at Grant Frontier Park in the downstream end of Reach 3. Left graphic depicts existing condition of Grant Frontier Park (“south” and “west bank”). The right graphic depicts the change to Grant Frontier Park South with restored wetland and riparian areas and a conceptual trail alignment of the Regional Trail. Conditions of Grant Frontier on the west bank retain the existing condition.

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Alternative F: Modify Harvard Gulch Outfall to Redirect Flow to Parallel Low- flow Channel and Restore Riparian/Wetland Habitat Alternative F includes the same concept discussed in Alternative E with the addition of modifying the outlet structure of Harvard Gulch to redirect flows and create an aquatic channel that flows through the restored wetland and habitat area. Under Alternative F, a total of 5.43 acres of aquatic, wetland and riparian habitat would be restored. Approximately 1.33 acres of Grant Frontier Park South would be re- graded and restored into PEM and PSS designated wetland habitat. Approximately 3.83 acres of riparian corridor habitat would be restored. The side channel from the modification of the Harvard Gulch outfall, approximately 0.46 acres, would provide increased surface flows to the restored habitat and generate localized depth diversity and slower velocities as compared to the main channel of the South Platte River. Aquatic habitat features such as woody debris and boulder clusters would be added within the side channel to increase feeding and shelter habitat for aquatic organisms. The abutments of the pedestrian bridge immediately downstream of Grant Frontier Park South on the east bank would be moved farther upland on the bankline as the east span of the bridge is increased 30 feet to mitigate the change in WSE of the regulatory floodplain (Figure 33).

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Alternative H: Relocate Regional Trail, North Low-flow Channel and Restore Riparian/Wetland Habitat Alternative H also would relocate the Regional Trail at Grant Frontier Park South in order to create additional terrestrial area for restoration. Under Alternative H, a total of 5.43 acres of aquatic, wetland and riparian habitat would be restored. Approximately 1.21 acres of Grant Frontier Park South would be re-graded and restored into PEM and PSS designated wetland habitat. Approximately 3.85 acres of riparian corridor habitat would be restored. The “north” side channel, approximately 0.37 acres, would meander through the restored habitat and generate localized depth diversity and slower velocities as compared to the main channel of the South Platte River. Aquatic habitat features such as woody debris and boulder clusters would be added within the side channel to increase feeding and shelter habitat for aquatic organisms (Figure 34). The abutments of the pedestrian bridge immediately downstream of Grant Frontier Park South on the east bank would be moved farther upland on the bankline as the east span of the bridge is increased 30 feet to mitigate the change in WSE of the regulatory floodplain.

Figure 34. Alternative H at Grant Frontier Park in the downstream end of Reach 3. Left graphic depicts existing condition of Grant Frontier Park (“south” and “west bank”). The right graphic depicts the change to Grant Frontier Park South with restored wetland and riparian areas, an additional channel created (“north channel”) and a conceptual trail alignment of the Regional Trail. Conditions of Grant Frontier on the west bank retain the existing condition.

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Alternative I: Relocate Regional Trail, South Low-flow Channel and Restore Riparian/Wetland Habitat Under Alternative I, a total of 5.43 acres of aquatic, wetland and riparian habitat would be restored. Approximately 1.23 acres of Grant Frontier Park South would be re-graded and restored into PEM and PSS designated wetland habitat. Approximately 3.85 acres of riparian corridor habitat would be restored. The “south” side channel, approximately 0.35 acres, would meander through the restored habitat and generate localized depth diversity and slower velocities as compared to the main channel of the South Platte River. Aquatic habitat features such as woody debris and boulder clusters would be added within the side channel to increase feeding and shelter habitat for aquatic organisms (Figure 35). The abutments of the pedestrian bridge immediately downstream of Grant Frontier Park South on the east bank would be moved farther upland on the bankline as the east span of the bridge is increased 30 feet to mitigate the change in WSE of the regulatory floodplain.

Figure 35. Alternative I at Grant Frontier Park in the downstream end of Reach 3. Left graphic depicts existing condition of Grant Frontier Park (“south” and “west bank”). The right graphic depicts the change to Grant Frontier Park South with restored wetland and riparian areas, an additional channel created (“south channel”) and a conceptual trail alignment of the Regional Trail. Conditions of Grant Frontier on the west bank retain the existing condition

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Alternative J: Relocate Regional Trail, North and South Low-flow Channel and Restore Riparian/Wetland Habitat Under Alternative J, a total of 5.43 acres of aquatic, wetland and riparian habitat would be restored. Approximately 0.86 acres of Grant Frontier Park South would be re-graded and restored into PEM and PSS designated wetland habitat. Approximately 3.85 acres of riparian corridor habitat would be restored. The “south” and “north” side channel, approximately 0.72 acres of aquatic habitat total, would meander through the restored habitat and generate localized depth diversity and slower velocities as compared to the main channel of the South Platte River. Aquatic habitat features such as woody debris and boulder clusters would be added within the side channel to increase feeding and shelter habitat for aquatic organisms (Figure 36). The abutments of the pedestrian bridge immediately downstream of Grant Frontier Park South on the east bank would be moved farther upland on the bankline as the east span of the bridge is increased 30 feet to mitigate the change in WSE of the regulatory floodplain.

Figure 36. Alternative J at Grant Frontier Park in the downstream end of Reach 3. Left graphic depicts existing condition of Grant Frontier Park (“south” and “west bank”). The right graphic depicts the change to Grant Frontier Park South with restored wetland and riparian areas, an additional channel created (“south channel” and “north channel”) and a conceptual trail alignment of the Regional Trail. Conditions of Grant Frontier on the west bank retain the existing condition.

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Alternative R: Modify Harvard Gulch to Re-direct Flow to Parallel Channel, Create South Low-flow Channel and Restore Riparian/Wetland Habitat Under Alternative R, a total of 5.43 acres of aquatic, wetland and riparian habitat would be restored. Approximately 0.96 acres of Grant Frontier Park South would be re-graded and restored into PEM and PSS designated wetland habitat. Approximately 3.66 acres of riparian corridor habitat would be restored. The “south” side channel and a side channel created from the modification of the Harvard Gulch outfall structure, approximately 0.81 acres of aquatic habitat total, would meander through the restored habitat and generate localized depth diversity and slower velocities as compared to the main channel of the South Platte River. Aquatic habitat features such as woody debris and boulder clusters would be added within the side channel to increase feeding and shelter habitat for aquatic organisms The abutments of the pedestrian bridge immediately downstream of Grant Frontier Park South on the east bank would be moved farther upland on the bankline as the east span of the bridge is increased 30 feet to mitigate the change in WSE of the regulatory floodplain.

Figure 37. Alternative R at Grant Frontier Park in the downstream end of Reach 3. Left graphic depicts existing condition of Grant Frontier Park (“south” and “west bank”). The right graphic depicts the change to Grant Frontier Park South with restored wetland and riparian areas, an additional channel created (“south channel” and Harvard Gulch channel) and a conceptual trail alignment of the Regional Trail. Conditions of Grant Frontier on the west bank retain the existing condition

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Alternative G: Relocate Regional Trail on West Bank of Reach 3 and Restore Riparian/Wetland Habitat Unlike the east bank of Grant Frontier Park, the west bank of Grant Frontier Park has existing sewer lines paralleling the river. As such, the Regional Trail would be relocated on top of the sewer line to create a smaller terrestrial area for restoration alternatives. Under Alternative G, approximately 0.28 acres of Grant Frontier Park on the west bank would be re-graded and restored into PEM and PSS designated wetland habitat. Approximately 0.68 acres of riparian corridor habitat would be restored. This alternative is dependent upon an alternative selected at Grant Frontier Park South (Alternatives E, F, H, I, J or R) (Figure 38).

Figure 38. Alternative G on the west bank of Grant Frontier Park in Reach 3. The existing riparian habitat on Grant Frontier Park South is depicted in this graphic; however, an alternative at Grant Frontier Park South (E, F, H, I, J or R) must be selected in order for Alternative G to also be selected.

Alternative M: In-stream Features to Restore Aquatic Habitat in Reach 3 Alternative M, like Alternative K in Reach 1 (Section 4.5.4.3) includes construction of in-stream hard point structures, such as rock vane dikes, cross vanes, riffles, boulder clusters and rootwad complexes to increase depth diversity, velocity diversity and provide feeding and shelter habitat to benefit various

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aquatic organisms in Reach 3. This alternative would improve the quality of the existing habitat throughout all of Reach 3 (approximately 12.23 acres of aquatic habitat). Alternative N: Modify Xcel Drop Structure with Auxiliary Weir Alternative N would modify the Xcel Energy drop structure in Reach 3 to reduce its impact as a barrier to fish passage and promote migration by functionally reducing the barrier height by 50 percent. It is currently estimated that this grade control structure has a single acute 5-foot drop that likely limits upstream fish movement during most of the year. This grade control structure sits on a utility line; therefore, the structure cannot be completely removed. To reduce the functional drop, an auxiliary drop structure would be placed immediately downstream of the Xcel Energy drop structure to reduce the incremental drop of each structure, effectively making two 2.5-foot drop structures.. As discussed in Alternative L for Reach 1 (Section 4.5.4.4), a network of boulder clusters would be installed immediately downstream of the existing Xcel drop structure in the resting pool that would form between the existing structure and the new auxiliary weir and immediately downstream of the auxiliary drop structure. These boulder clusters would function as a switchback road system and the crest of the drop structure could also be Figure 39. Conceptual layout of modifications at Excel drop structure. Top graphic notched or fitted with (plan view) the auxiliary weir would have boulder clusters strategically placed to boulders spaced to leave allow fish to traverse the drop structure by step-laddering from one boulder cluster gaps to aid fish in traveling to the next in the shelter shadows formed by the clusters. Bottom graphic (cross section) depicts the side profile of the existing structure and auxiliary weir (red) and through and over the final resting pool that would form between the structures upstream barrier.

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Alternative Q: Modify Xcel Drop Structure with Auxiliary Weir and Riffle Alternative Q consists of modifying the drop structure at Xcel Energy as described for Alternative N ; however, a riffle structure would be constructed downstream of the existing structure instead of an auxiliary drop structure. This riffle would have a 20:1 slope, elongating the gradient change of the riverbed over approximately 100 feet. Like Alternatives L and P in Reach 1 and Alternative N in Reach 3, boulder clusters would be placed in the area between the existing drop structure and auxiliary weir to aid aquatic life traversing the barrier. A network of boulder clusters would also be placed on the riffle structure ramp to similarly promote fish passage up and over the auxiliary weir. Further detailed refinement to modify the most upstream weir (i.e., the existing drop structure) could be designed to facilitate fish passage; possible refinements during design phase could include installing notches in the crest of the structure and/or armoring the crest with boulders fitted and spaced to leave gaps for fish to burst swim through and over the crest (Figure 40).

Figure 40. Conceptual layout of modifications at Xcel drop structure. Top graphic (plan view) the auxiliary weir with additional riffle ramp would have boulder clusters strategically placed to allow fish to traverse the drop structure by step-laddering from one boulder cluster to the next. Bottom graphic (cross section) depicts the riffle ramp and resting pool with integrated boulder clusters.

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Similar to the Overland drop structure, consideration was given to constructing a riffle ramp from the existing Xcel drop structure, eliminating the need for the auxiliary structure. However, due to the West Harvard Gulch confluence with the South Platte River being the immediately downstream area of the existing structure, and the additional cost associated with this larger riffle ramp structure, an alternative with a complete riffle ramp was not evaluated. However, it is believe that further investigation during the D&I phase could demonstrate the constructability and economic viability of this alternative. 4.6. ALTERNATIVE EVALUATION Alternatives were evaluated based on their environmental output and economic cost using IWR Planning Suite Software (Version 2.0.6.0, Corps certified, September 22, 2010), FACWet and FACStream, and costing information. FACWet and FACStream Environmental Evaluation Each of the remaining 17 alternatives were evaluated using the FACWet and FACStream models which are discussed in depth in Appendix A1. An assessment of the existing condition of the study area was conducted based on the departure from a reference standard condition. These models are used to compare the baseline condition to a future without project (FWOP) and a future with project (FWP) condition over a 50-year planning horizon period. Based on the alternative being 1) solely aquatic (e.g. Alternatives K, L, M, N); 2) solely riparian/wetland (e.g. Alternatives E, O, S); or 3) a combination of aquatic and riparian/wetland (e.g. Alternatives J, H, I, R), then alternatives would be assessed with 1) FACStream only; 2) FACWet only or; 3) both FACStream and FACWet. As discussed in Appendix A1, an array of variables and supporting sub-variables produce a Functional Capacity Index (FCI) which is a weighted index score for seven separate key functions assessed in FACWet and four separate key functions assessed in FACStream. For each model, the seven functions or the four functions are then further weighted and averaged together to produce a final composite FCI score. These index scores are based on a 0.0 to 1.0 scale, with 1.0 being pristine. The composite index scores are then translated into habitat units (HUs). HUs are quantifiable units calculated by multiplying the index score (model output) by the total habitat area (in acres). Total existing habitat acreages were calculated for each of the three reaches, and separated as aquatic habitat or riparian/wetland habitat. Each measure was assessed based on its ability to increase existing habitat; quantitatively (acres) and/or qualitatively (index score). Dependent upon the measure, habitat improvement for aquatic habitat only, riparian/wetland only, or both aquatic and riparian/wetland habitat were assessed utilizing the appropriate model. For example, measure K, which proposes to construct in-stream features, was assumed an aquatic-based measure only and FACStream only was utilized as no improvement to wetland/riparian habitat is occurring under this measure. While the riparian/wetland model, FACWet, was not used to determine effects of this aquatic-based measure, FWOP riparian/wetland conditions (riparian/wetland FWOP HUs) were added to the restored FWP aquatic condition (aquatic FWP HUs as a result of measure K) to still provide a community HU which comprises both habitat types, despite a measure only impacting one habitat type. This depicts the net lift in HUs each measure individually provides to the total reach. Conversely, a measure that was assumed to have both aquatic and riparian/wetland impacts used both models. For example, measure H proposes to grade Grant Frontier Park South to restore wetland benches and improve riparian habitat but it also proposes to construct one low-flow side channel. As such, this measure was able to be assessed under both models as both habitat types are impacted. FWP condition HUs for both aquatic and riparian/wetland were added together to produce the community HU (Table 16).

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Table 16. Community habitat units* for existing condition, 50-year FWOP and 50-year FWP for each individual alternative and its associated increase of HU** over the 50-year project life and percent increase.

Reach 1 Community HU (Aquatic + Riparian) Net Gain 50-Year Increase in HUs over 50-year Percentage Increase of HUs Alternative FACWet FACStream Existing 50-Year FWP FWOP Project Life (FWP - FWOP) over 50-year Project Life B  3.96 0.99 33% K  3.77 0.80 27% L  4.25 2.97 3.64 0.67 23% T  3.95 0.82 28% P  3.79 0.98 33% Reach 2 Community HU (Aquatic + Riparian) Net Gain O  4.67 3.04 187% 2.93 1.63 S  3.10 1.47 90% Reach 3 Community HU (Aquatic + Riparian) Net Gain E  7.83 3.00 62% F   9.75 4.92 102% G   6.01 1.18 24% H   9.77 4.94 102% I   9.77 4.94 102% 6.77 4.83 J   9.81 4.98 103% M  5.85 1.02 21% N  5.82 0.99 20% Q  6.07 1.24 26% R 9.79 4.96 103%   *Note existing habitat is for the entire river reach evaluated. Aquatic habitat and terrestrial habitat were separated for modeling purposes but computed together to produce a “community habitat unit” which reflects the addition of aquatic and terrestrial habitat. **Note habitat units presented in this table are raw data (area multiplied by FCI) and prior to annualization with CE/ICA

HUs for both FWP and FWOP were calculated for target years 0 (baseline condition), 1 (first year after project construction completed), 10, 25 and 50. For each measure and FWOP and FWP target year, HUs were entered into the NER Outputs calculator in the IWR-Planning Suite (Version 2.0.6.0), decision support software. Economic Evaluation The IWR Planning Suite calculator determined the gross average annual HUs (AAHUs) over the 50-year period using linear interpolation from the inputs of the HUs from FACWet and FACStream. The net AAHUs for each alternative consists of a positive number, and the net AAHUs for the no action alternative equal zero. A cost-effectiveness incremental cost analysis (CE/ICA) was completed to compare the alternatives under consideration for the project site. The purpose of the analysis is to evaluate the effectiveness and efficiency of the site alternatives at producing environmental outputs, so the costs of the alternatives and the expected environmental outputs are inputs for CE/ICA, in the form

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of average annual costs and average annual habitat units, respectively. CE/ICA results in the identification of cost-effective plan alternatives. A cost-effective plan alternative is defined as one where no other plan alternative can achieve the same level of output at a lower cost, or a greater level of output at the same or less cost. A sub-set of cost-effective plan alternatives are identified as ‘best buy plans. Best buy plans are cost-effective plan alternatives that provide the greatest increase in environmental output for the least increase in cost per habitat unit. This analysis eliminates inefficient plan alternatives by comparing an alternative’s total average annual environmental output in AAHUs and its total average annual cost. Plans are cost effective if no other plan produces an equal or greater number of environmental outputs at a lower cost. Cost Evaluation In addition to analyzing each of the alternatives via the FACWet and FACStream models, conceptual- level quantities and cost estimates were developed for each of the alternatives. This allowed the PDT to determine how much the entire array of alternatives would cost to implement, and compare this value to the CAP Section 1135 per project cost limit of just over $13.3 million. It was determined that the entire array of 17 alternatives could not be implemented under the program cost limit, but many of the alternatives were also mutually exclusive, such as the numerous alternatives for the Grant Frontier Park South project area, so all alternatives were carried forward for the alternatives comparison step. Additional HTRW Investigation Due to uncertainty associated with the fill materials used to develop the existing South Platte River channel, a Phase II HTRW Environmental Site Assessment (ESA) was performed. The purpose of the Phase II ESA was to determine if contaminants were present within the potential sites of interest identified during the Phase I ESA. It is the Corps policy to not mitigate existing contamination within a potential project area, any such clean-up effort, and the associated cost, would be the responsibility of the non-Federal sponsor. Furthermore, the general rule-of-thumb is to avoid contaminated project sites if at all possible. Therefore, the information collected during the Phase II assessment was used to screen out or modify any alternative within the final array that would require construction activities within a contaminated site. Results from the Phase II ESA can be found in Appendix I, but the high level summary of what was found during the Phase II ESA was that most of the project footprint does fall within historical fill sites, but there were no sites determined to be characteristically hazardous. However, the Phase II ESA showed that the soils within Grant Frontier Park appeared to be the natural material and not fill like the rest of the potential project sites. The significance of this is that there is a local requirement for material excavated within the Denver City Limits to be hauled to, and disposed of at, the Denver Arapahoe Disposal Site (DADS) Landfill. However, the Denver Department of Public Health and Environment (DDPHE) has recognized the need for clean fill material throughout the local area due to on-going development efforts. Therefore, DDPHE developed guidance for the reuse of excavated soils that are found to be suitable for reuse. To ensure compliance with this DDPHE guidance additional testing beyond the Phase II ESA effort was performed within the Grant Frontier Park area and it was found that the in-place material is reusable. This had a substantial impact on the Grant Frontier Park South Alternatives (E, F, H, I, J, and R), reducing the cost of each of the alternatives by over $2 million. Additional Flood Risk and Floodplain Management Analysis Environmental restoration projects, while beneficial and desirable, cannot result in increases in the flood risk to the community. The primary drivers of flood risk are the water surface profiles for the flood events of various frequencies. Increasing the elevation of the flood profiles compared to pre-project conditions usually results in increased risk while decreases in the profile elevations usually results in Section 1135 June 2018 South Platte Valley 74

reduced risk. Slight increases in flood profiles may not result in a significant increase in the flood risk if these increases do not result in measurable increases in damages to property or life safety risk. In order to address this change of the flood profile from the construction of any of the Grant Frontier Park South alternatives, it was determined that the pedestrian bridge immediately downstream of Grant Frontier could be modified to expand the top-width of the river and mitigate this impact. The goal of the modification was to cause a no-rise to the regulatory and other flood profiles. The alteration of this bridge would include the expansion of the east span and placing the bridge abutments higher on the bank to accommodate the flood profile. The span will result in excavating back the bank approximately 30 feet immediately below this bridge which will increase the existing span of 90 feet to 120 feet. See Appendix F for further details on the modification of the pedestrian bridge at Grant Frontier Park. 4.7. ALTERNATIVE COMPARISON As stated in Section 4.6, Corps IWR Planning Suite version 2.0.6 was used to compare the final array of alternatives. Specifically the alternatives were compared utilizing the CE/ICA feature of the planning suite. The plan alternative with the lowest incremental costs per unit of output of all plans will be considered the first best buy plan. After the first best buy plan is identified, all larger cost-effective plan alternatives are compared to the first best buy plan in terms of increases in (increments of) cost and increases in (increments of) output. The plan alternative with the lowest incremental cost per unit of output (for all cost-effective plans larger than the first best buy plan) is the second best buy plan. This process of comparison continues until all best buy plan alternatives are identified. The cost effectiveness analysis ensures that the least cost plan was identified for each possible level of environmental output and aids in the decision- making and selection justification process.

Figure 41. CE/ICA Best Buy Plans (white-boxed numbers). Note that best buy plan 1 is the No The CE/ICA model Action Alternative. The output along the x-axis describes the AAHUs achieved under each best determined that buy plan while the y-axis describes the incremental cost there were 8,424 different combinations of the alternatives, with just over 100 of these combinations being found to be cost effective. Out of these 101 cost effective combinations, 11 “best buy” plans were developed by the model. Error! Reference source not found. shows the CE/ICA graphical output for the 11 best buy plans. Table 17 further details the best buy plans, to include showing the incremental cost and AAHUs

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associated with each sequential plan, which alternatives are included in each plan, and the overall total cost of each best buy plan.

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Table 17. CE/ICA Output for Best Buy Plans

AA Cost Estimated Average Incremental Output per Total Project Plan Alternative Plans Annual Cost/ Output (AAHU) Output Cost (AA) Cost (AAHU) (Cumulative)

1 No Action NA NA NA NA NA $238,932

2 S $8,850 1.13 $7,830 7,832 $1,705,218 3 S O $63,160 3.77 $16,750 $20,573 $2,150,804 4 S O N $79,670 4.51 17,660 $22,304 $2,498,454 5 S O N T $92,550 5.08 $18,220 $22,591 $2,663,009 6 S O N T M 98,640 5.33 $18,510 $24,380 $3,170,564 7 S O - T M Q $117,440 6.10 $19,250 $24,416 $3,694,341 8 S O - T M Q G H $136,840 6.77 $20,210 $29,957 $9,885,663 9 S O - T M Q G H P $366,170 12.29 $29,790 $41,546 $10,590,689 10 S O - T M Q G - P J K $392,290 12.91 $30,390 $42,121 $11,384,540 11 S O - T M Q G - P J K R $451,390 12.92 $34,940 $5,910,000

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Best Buy Plans Considered for Selection All best buy plans produced by the CE/ICA model are eligible for selection as the project plan under Corps’ policy. Although CE/ICA does not provide a discrete decision criterion, it does provide for the explicit comparison of the relevant changes in cost and environmental outputs upon which such decisions may be made. It is by considering the information assembled by the cost analyses in combination with other “subjective” information pertaining to resource significance, and where appropriate, descriptions of other “unintended” effects that tradeoffs can be made across different alternatives and a preferred alternative can be selected (USACE, 1995). With this in mind, the study team preliminarily identified the following three plans for consideration as the final project plan: Plan 3, Plan 9 and Plan 10. Plan 3 proposed restoration of 5.59 acres of riparian corridor habitat in Reach 2; however, it did not provide wetland or riparian habitat restoration throughout the remaining two reaches of the study area. As discussed in Section 2.3.1.1.5, wetlands are critically important features along a riparian system that filtrate pollutants from surface runoff, provide specialized habitat to endemic fauna and flora and stopover habitat for migrating birds as well as general feeding, breeding and sheltering habitat for a variety of birds and wildlife at some phase in their lifecycles. Section 2.3.3.3 notes that natural riparian corridors are the most diverse, dynamic and complex biophysical habitats (Naiman et al., 1993) which results from the interactions of the aquatic system with the adjacent terrestrial environment and the ecological processes. By only restoring one habitat type in one reach of the study area, project objectives are not fully realized. Plan 3 does not fulfill either project objective (Section 2.2.1) as it does not propose to restore in-channel habitat complexity and connectivity in the South Platte River nor does it restore wetland habitat quantity or quality. While Plan 3 is a cost effective best buy plan, it was eliminated from selection as it does not fully addressing the Project Objectives nor does it provide aquatic and riparian corridor connectivity throughout the study area. The two remaining plans, Plan 9 and Plan 10, are shown in Figure 42 and Figure 43, respectively. The figures are broken into two parts to separate the alternatives that restore riparian habitat and those that restore aquatic habitat.

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Figure 42. Riparian (left) and Aquatic (right) Alternatives included in Plan 9

Figure 43. Riparian (left) and Aquatic (right) Alternatives included in Plan 10

The difference between Plan 9 and Plan 10 is that Plan 10 replaces Alternative H with Alternative J at Grant Frontier Park South and includes Alternative K. Alternative J has slightly higher AAHUs associated with it due to the inclusion of a second low flow channel in the southern portion of the alternative footprint. Alternative K, detailed in Section 4.5.4.3, provides in-stream features, such as vanes and dikes, throughout Reach 1 of the study area. By selecting Plan 10 over Plan 9, restoration of aquatic

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habitat and connectivity is achieved throughout the entire study area. Plan 10 is the first best buy plan that proposes to restore all three identified habitat types (wetland, riparian and aquatic) and spans all three reaches providing both aquatic and terrestrial landscape connectivity of the study area. By restoring this circuitry to all habitat types throughout the study area, benefits accrue from incorporating higher quality linkages between habitat patches and reestablishing the sensitive interconnectedness of the localized ecosystem. Plan 11 was eliminated from consideration as the Recommended Plan as the incremental costs were exponentially greater, nearly fourteen times the cost per output than Plan 10, and only provides a slight additional incremental output of 0.01. 4.8. ANCILLARY RECREATION PLAN FORMULATION Under the Section 1135 authority, the primary objective is ecosystem restoration. Within the context of the Section 1135 authority there is also an opportunity to address recreation features that provide further benefits to the community in relation to the project. Recreation components are added following selection of the preferred restoration plan. Recreation plan formulation was conducted on the South Platte River throughout each reach. Recreation benefits were estimated using Unit Day Value (UDV) calculations with the full analysis detailed in Appendix K. The goal of the recreation alternative plan is to provide recreational access to the NER project area, both where recreational features do and do not already exist, that supports public education and enjoyment of the environment while maintaining the restored habitat. Related objectives include expanding upon the opportunities and experiences already provided by the existing Southern Platte Valley parks and recreation facilities, while expanding the nature-base recreation opportunity on designated trails within the restored area and educating the public about the significance of the restored habitat areas. The recreation alternative plan was developed through a collaborative process between the Corps and the City and County of Denver. Given that one of the goals of the recreation alternative is to provide ancillary recreation benefits through access to the restored area in a manner that minimizes impact to the restored habitat, multiple wide- ranging recreation alternatives were not evaluated. Rather, a more focused approach was taken by looking for opportunities to complement existing city trails and recreation features. Alternatives considered that take Figure 44. Conceptual schematic of Harvard Gulch outfall modification and boardwalk in Grant Frontier Park South. into account this constraint include educational signage throughout the project area, a modified outfall structure that provides a viewing platform over the restored environment, and a boardwalk that provides a recreation users the opportunity to better view ecosystem restoration alternatives without negatively affecting them.

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5. SELECTED PLAN Based on a review of best buy plan results and a comparison of incremental costs and benefits, Plan 10 was identified as the tentatively selected plan (TSP). The incremental cost per HU by best buy plan increases gradually, on a rather uniform basis indicating that while the improvement of habitat quality is important adding additional area to the restoration plan is most effective. Plan 9 incremental cost/AAHU is $30,620 where Plan 11 incremental cost/AAHU is $42,980 (a 40.3% increase) Under the TSP, improvements to riparian habitat in Reach 1 would occur under Alternative T. Alternative T would restore 1.16 acres of riparian habitat on the east bank of Reach 1. Improvements to the aquatic environment would occur under Alternative K which would construct a series of in-stream features such as dikes, cross vanes and boulder clusters to increase depth diversity, velocity diversity and feeding and shelter habitat to benefit various guilds of aquatic organisms. Alternative P would improve fish passage by reducing the barrier height which currently serves as an impediment to faunal movement. . Improvements to riparian habitat in Reach 2 would occur under Alternatives O and S which both restore 5.59 acres total of riparian habitat by removing existing vegetation and re-vegetating the area with native trees, shrubs and herbaceous species. Improvements to the wetland/riparian habitat in Reach 3 would occur as a result of restoring a wetland and riparian habitat complex at Grant Frontier Park South by pulling the Regional Trail away from its existing location and grading the banks down. Approximately 0.86 acres of Grant Frontier Park South and 0.28 acres on the west bank of Grant Frontier Park would be re-graded to restore palustrine emergent /scrub shrub wetland habitat. Wetlands would be designed to be inundated two consecutive weeks out of the growing season. The remaining 3.85 acres of Grant Frontier Park South and 0.68 acres at Grant Frontier Park on the west bank would be restored riparian habitat planted with a transitional cottonwood-willow/mesic graminoid community. Improvements to the aquatic environment in Reach 3 are similar to those benefits discussed in Reach 1. Under Alternative M a series of in-stream features such as dikes, cross vanes and boulder clusters would be constructed to increase depth diversity, velocity diversity and feeding and shelter habitat to benefit various guilds of aquatic organisms. Alternative Q would improve fish passage by reducing the barrier height which currently serves as an impediment to faunal movement (Table 18).

Table 18. Recommended Plan contributions to the NER Account

Habitat Type (acre) Net Gain (50-year Project Life) Reach Alternative Increase in Percent Riparian Wetland Aquatic Habitat Units Increase T 1.16 ⁻ ⁻ 0.82 28% 1 K ⁻ ⁻ 9.41 0.8 27% P Improve Fish Passage 0.98 33% O 3.92 ⁻ ⁻ 3.04 187% 2 S 1.67 ⁻ ⁻ 1.47 90% J 3.85 0.86 0.72 4.98 103% G 0.68 0.28 ⁻ 1.18 24% 3 M ⁻ ⁻ 12.23 1.02 21% Q Improve Fish Passage 1.24 26% Totals 11.28 1.14 22.4 ⁻ ⁻ As a result of the FWP-TSP condition, total ecological lift of the project site improved by nearly 69 percent of FWP-Year 50 compared to today’s existing conditions and improved by nearly 150 percent of FWOP-Year 50 compared to FWP-Year 50. A total of 12.42 acres of wetland and riparian habitat would be restored along the South Platte River and 8,196 feet of stream length (22.4 acres) of low quality aquatic habitat would be improved through the construction of in-stream features such as dikes, cross

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vanes, riffles and boulder clusters. Additionally, the length of this total river reach within the study area would be improved for fish passage as a result of the drop structure modifications. Total cumulative ecosystem restoration project cost is currently estimated at $9,221,750 at FY18 price levels. 5.1. ANCILLARY RECREATION PLAN The proposed recreation alternative aims to provide reasonable access to the restoration areas, while limiting potential impacts to the restored areas. The overall recreation plan includes modifying the aesthetic of Harvard Gulch outfall to provide a viewing platform over the restored habitat areas of Grant Frontier Park South, a boardwalk from the relocated Regional Trail to the restored habitat areas of Grant Frontier Park South to provide controlled access to these sites and educational signage placed outside of restored areas in all three reaches. Using the UDV dollar values per visit and visitation estimates generated and detailed in Appendix K, recreation values for the without and with recreation project conditions were calculated. Taking the difference between the FWP and the FWOP conditions, net recreation benefits were estimated. It is assumed that benefits would accrue consistently in all years of the period of analysis. The following table summarizes expected recreation benefits in terms of present value and an amortized annual value. Amortization over the period of analysis uses the FY2018 Federal discount rate of 2.750% over a 50-year period of analysis (USACE, Economic Guidance Memorandum, 18-01, Federal Discount Rate for Fiscal Year 2018). The analysis estimates a present value benefit of $866,295 and expected annual benefit of $32,088.

Table 19. Summary of Recreation Value Calculations

Expected Unit Day Average Annual Net Present Alternative General $ / Day Annual Points Visitors Value Benefits Existing 24 $5.62 188,900 $1,061,618 $39,323.31 With Project 38 $7.29 264,460 $1,927,913 $71,411.67 Net Benefit 14 $1.67 75,560 $866,295 $32,088.36

Recreation alternative costs were estimated based upon specific features included in the recreation plan. Trail cost estimates are based upon a per linear foot cost estimate and the estimated length of the trail proposed for the restoration area, while interpretive signs are estimated based upon the size and type of signage proposed, as well as the number of signs proposed for the restoration area. Costs are presented in FY2018 price levels. The total estimated investment cost for the proposed recreation features is $830,475. A more detailed cost estimate is provided in the Cost Engineering Appendix.

Table 20. Recreation Facilities Cost Estimate (FY2018)

Cost Line Item Cost Construction Cost $534,000 *E&D, S&A, and Contingency $274,250 Estimated Total: $808,250 IDC (1 yr., 2.750%): $22,225 Investment Cost: $830,475 Annualized Investment Cost: $30,760 *E&D – engineering and design; S&A – supervision and administration

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Based on the results of the recreation analysis detailed in Appendix K, net recreation benefits would be approximately $32,088 expected annual value over the 50-year period of analysis. In this analysis, benefits exceed the cost, which is anticipated to be $30,760. The benefit cost ratio is therefore estimated to be 1.043. The benefits are expected to exceed the costs for the proposed recreation features and therefore the recreation features are economically justified.

Table 21. Benefit-to-Cost Ratio

Alternative Net Annual Benefits ($) Annual Costs ($) BCR No Action $0 $0 0.00 With Project Condition $32,088 $30,760 1.043

5.1. TOTAL PROJECT COST The total project costs for the selected environmental restoration plan and the ancillary recreation plan are shown in Table 22. These numbers are estimated at the fully funded cost of the project through completion.

Table 22. Total Project Cost

Cost Line Item Cost Construction Cost with Contingency $8,097,000 *E&D and S&A $1,400,000 LEERDs $1,025,000 Fully Funded Project Cost: $10,522,000** Annualized Investment Cost: $390,000 *E&D – engineering and design; S&A – supervision and administration; LEERDs – Lands, Easements, Relocations, Rights-of-Way, and Disposal Areas

**Includes Recreation Costs Detailed below. 5.2. COST SHARE The non-federal sponsor is responsible for a minimum of 25 percent of total project costs to a maximum of 50 percent of total project costs during the design and implementation phase. In accordance with the terms of the PPA, the non-federal sponsor must pay a minimum of five percent of total project costs in cash; provide all lands, easements, relocations, rights-of-way and disposal areas (LERRDs) required for the project; participate in the Project Coordination Team; perform necessary non-federal audits; and perform investigations necessary to identify the existence and extent of any hazardous substances on lands required for the project. The value of the LERRD (including the value of any project lands already owned by the sponsor) and the value of in-kind participation in the other activities described are added to the five percent cash as part of the 25 percent non-federal cost share. If the total value of the LERRD, the five percent cash, and the other activities is less than 25 percent of total project costs, the non- federal sponsor must contribute additional cash so that its total share is equal to 25 percent of total project costs. Once construction is complete, the project will be turned over to the non-federal sponsor for all operation and maintenance after the monitoring and adaptive management phase of the project is completed (O&M). 5.3. DESIGN AND IMPLEMENTATION Section 1135 projects are divided into two phases; the feasibility phase and the design and implementation (D&I) phase. The D&I phase includes all activities to take the selected plan through to

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construction. This phase begins once the Northwestern Division Commander approves this integrated feasibility report and recommends proceeding into the design and implementation phase. The first action of the design and implementation phase is the negotiation and execution of a PPA which is the cost-sharing agreement that outlines the responsibilities of both the Corps of Engineers and the non- federal sponsor required to implement the project. Along with the PPA, a new Project Management Plan (PMP) will be developed that outlines the scope and schedule for completing design and construction activities. The design processes would include collection of field data (surveys and soil borings) as necessary to finalize the design, and preparation of final design plans and specifications. The design process will also include hydraulic analyses to incorporate modifications to the Grant Frontier Park pedestrian bridge to mitigate the adverse hydraulic impacts of the original design as noted in Section 4.6.2. Project implementation would include preparation of a project real estate footprint outlining all necessary LERRD elements for the sponsor to obtain. Following this would be the advertising and award of the construction contract, construction management and supervision during the construction period. The final steps in project implementation would include preparation of the Operation & Maintenance Manual for the project sponsor to use in operating and maintaining the project, and final financial and cost-sharing balancing, close-out, and project transfer to the non-federal sponsor. Based on available funding, a preliminary schedule for the design and implementation of this project can be found in Table 23.

Table 23. Preliminary Design & Implementation Schedule Milestone Schedule

Public Review of Feasibility Report June 2018

Feasibility Report Approval September 2018

Sign Project Partnership Agreement with Sponsor December 2018

Initiate Plans and Specifications January 2019

Design Complete December 2019

Sponsor Complete LERRD Acquisitions July 2020

Construction Contract Award September 2020

Complete Project December 2021

5.4. RISK AND UNCERTAINTY A risk and uncertainty analysis was performed which is an analysis that integrates the uncertainty from the hydrology, hydraulics, environmental, cost engineering, economics and other aspects of the project into the plan formulation process. Feasibility study team members select their best estimates for hydrologic, hydraulic, environmental and economic parameters used in the analysis and determine their related uncertainty. Each discipline integrates risk and uncertainty differently into their respective calculated outputs. Economic Analysis The analysis for FWP and FWOP conditions for the feasibility study was performed using the IWR Planning Suite Version 2.0.6.1. The basic assumption underlying use of a risk analysis program is that the field data in ecosystem restoration studies are based on imperfect knowledge and those key

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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. Natural variability, specifically in the computation of environmental outputs, results from inherent variability in the physical world and may affect the accuracy of the calculated habitat units for each measure. This type of uncertainty cannot be reduced or altered by obtaining more information, although collection of more information may improve the estimation of the natural variability that exists. All cost engineering and environmental data are entered into the IWR Planning Suite program in terms of median or most likely values. The risk and uncertainty incorporated into these inputs for each discipline are detailed below. Environmental Analysis In this analysis, environmental outputs are forecasted for a 50-year period of analysis and annualized before being entered into IWR Planning Suite. As noted, both FACWet and FACStream are hydrogeomorphic models that were used to assess existing, FWP and FWOP conditions. Both models attempt to reduce the inherent complexity of ecosystems by making the basic assumption that natural systems function optimally for their type until they are perturbed by human impact. This underlying assumption is the basis for scoring degrees of impairment of all variable and sub-variables, or “how far the site condition has departed from a reference standard condition.” To characterize ecosystem function, these models utilize the Environmental Protection Agency’s 1-2-3 Assessment Level tiered framework. Level 1, a reconnaissance effort, relies entirely on desktop-based research, “windshield surveys,” and documentation of environmental stressors extrapolated from existing available data on landscape-scale inventories. Level 2 is a routine effort which builds from Level 1 and includes field documentation of site stressors, ecological indicators and direct observations. Level 3, an intensive effort, builds from Level 2 and includes additional site visits, qualitative monitoring and reference-based parameters. When scoring each variable, these are weighted with a confidence rating, since often times best professional judgment is being applied in scoring impairment factors. This further attempts to reduce risk and uncertainty associated with habitat scoring assumptions by making the quality of the assessment transparent. Hazardous, Toxic and Radioactive Waste There are low levels of risk and uncertainty in regards to HTRW for this project. The data collected during drilling and sampling performed for the Phase II ESA were used by Corps Environmental Professionals to determine the environmental conditions of project areas. Due to the extensiveness of drilling, USACE personnel were able to characterize the contents of historic fill areas along the South Platte River with a high degree of certainty. Sample results from the Phase II ESA showed that there are no known Corps concerns in project areas where intrusive soil-disturbing activities are planned, resulting in a low risk to the project. Hydraulic and Hydrologic Analysis The hydraulic and hydrologic (H&H) with and without project conditions rely on forecasts of future conditions and assumptions. Sources of uncertainty for H&H analysis include unknown impact of streamflow and rainfall events on the performance of the Recommended Plan. Extended drought following construction of the project could impact the performance of planting measures specific to desired habitat type. Extreme events could cause geotechnical failures or exceed the design capacity of structures. Additional uncertainty includes assumptions used for parameters in H&H modeling; specifically uncertainty in the modeling and calculation of stage are the error in the selection of Manning's “n”, or the roughness coefficient utilized for the modeling of bridges and other flow obstructions, as well as calibration to observed high water marks, modeling of channel cross sections, expansion/contraction factors for changes in channel width, and starting water surface profiles. The

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state of the art of hydraulic analysis is not yet able to handle all of the natural sources of variability. Uncertainty surrounding channel stability include assumptions of sedimentation processes which could lead to excess scour or deposition within the proposed side channels at Grant Frontier Park South. Excess scour around proposed in-channel aquatic features could increase the frequency of maintenance assumed in this study. Structural Analysis Uncertainty surrounding the pedestrian bridge modifications at Grant Frontier Park were assessed for the feasibility phase of this Section 1135. Detailed plans and specification of the existing bridge were not available, and the assumption was made that the bridge manufacturer spliced the bridge at the bridge pier (or the mid-point of the existing structure). If the bridge manufacturer did not splice the bridge at this location, or the existing middle pier does not have enough capacity to support an additional 30 foot span, the entire bridge may need to be replaced. Additional and detailed analysis will occur during D&I on the modifications to the pedestrian bridge at Grant Frontier Park. Geotechnical Analysis The grading plans provided in Appendix E were developed from light detection and ranging (LIDAR) data that was collected in 2014 and provided to the Corps by the City and County of Denver. This LIDAR data pre-dates the work completed by the City at Grant Frontier Park North in 2017. Neither as-built plans nor terrain models for that project were available to the Corps. The proposed plans for Alternatives E, F, H, I, J, and R (all located in Grant Frontier Park South) would require the east bridge abutment to be moved eastward up the bank approximately 30 feet. The required bank regrading will potentially have a minor impact on the newly constructed area of Grant Frontier Park. The grading plan will need to be revised in the D&I phase once new surveys of the park are completed. Earthwork quantities could vary slightly from the feasibility-level design to account for the new terrain. It is anticipated that the change in excavated material would be a relatively small percentage of the total volume. Furthermore, detailed plans of the existing right bank bridge abutment were not available during the feasibility phase of this study. As this is a pedestrian bridge only and is not expected to carry large loads, the geotechnical design of both the existing and proposed abutment should be relatively simple. The soils on site are anticipated to be sufficient to support the new bridge span. Some areas in Grant Frontier Park South will require excavation up to 15 feet below the current ground surface. Borings performed for the HTRW analysis only extended through the existing fill or about 5 fot 10 feet below ground surface. Other borings along the river performed for other projects indicate that it is possible to encounter hard claystone or siltstone bedrock at depths ranging from 5 to 20 feet below ground surface. These hard clays will likely be difficult to break down and process for use as site grading fill. Since this project will almost exclusively feature excavation with very few fill areas, this does not result in much risk to the project. Flood Risk Analysis The ability of the proposed project to avoid adverse flood risk impacts is a relative and not absolute evaluation based on the comparison of water surface profiles for existing (without project) and proposed (with-project) conditions. Uncertainty in the water surface profiles is a combination of the uncertainty in the hydrologic analyses that provided the flows for each profile and uncertainty in the hydraulic computations. It was considered that the uncertainty in the water surface profiles would be consistent for existing and proposed conditions. Given that, the differences in elevation between the water surface profiles of a given flood frequency would be less affected by uncertainty than the absolute elevation of the profiles.

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Cost Engineering Appropriate contingencies were applied in the development of project costs to address the relevant uncertainties that may or may not occur in the construction phase. Contingencies were based on the perceived risk and uncertainty of forecasting construction and implementation costs. A higher associated risk, or product of the probability and significance of impact related to a potential cost change, is directly related to a higher contingency associated with the cost contingency. The risk elements included in this analysis include project management and scope growth, acquisition strategy, construction elements, specialty construction or fabrication, technical design and quantities, cost estimate assumptions, and external project risks. All construction features with any sort of risk or uncertainty surrounding its cost estimate were detailed in the relevant risk element category. After determining the likely severity of impact and probability of the impact to the cost estimate, a risk level is assigned to each construction feature. The risk levels of each individual feature are aggregated and determine the overall risk present in the cost estimation process which in turn determine the appropriate construction cost contingency.

5.5. SUMMARY OF PLAN EFFECTS ACROSS FOUR P&G ACCOUNTS Corps Civil Works decision documents evaluate, display and compare alternative plans effects across all four Planning and Guidance (P&G) accounts. The four accounts are National Economic Development (NED), Regional Economic Development (RED), Environmental Quality (EQ) and Other Social Effects (OSE). National Economic Development The NED account considers increase in the net value of the national output of goods and services, expressed in monetary units. They are the direct net monetary benefits that accrue in the planning area and the rest of the nation. Recommended ecosystem restoration alternatives and associated alternative plans do not need to exhibit net NED benefits, but are evaluated based on non-monetary outputs compatible with P&G selection criteria (discussed in Section 4.4). Although it is likely that action alternatives would produce incidental NED benefits, for this study, the main focus is increasing national value by contributing to the nation’s ecosystems through restored habitat. In addition, the net benefits associated with the proposed recreation alternative were evaluated and could be considered part of the national economic benefits associated with ecosystem restoration. As described in Appendix K, annual recreation benefits associated with the proposed recreation plan are $32,088. The average annual cost is $30,255, leading to a net annual benefit of $1,833 and a recreation benefit-to-cost ratio (BCR) of 1.04:1. Regional Economic Development The RED account considerations are factors that affect the Denver regional economy while not necessarily affecting the NED. For the purposes of this study, RED impacts have not been quantified; however, it is expected that the proposed ecosystem restoration and recreation plans would have a positive impact on the regional economy due to both the direct construction costs and the positive on- going effect the restored area would have on improved quality recreation opportunities. In addition, habitat restoration on the South Platte River will add aesthetic and intrinsic value to the urban area, increasing the desirability and livability of the nearby community. Environmental Quality The EQ account evaluation conducted included defining resources, inventorying and forecasting resource conditions and assessing and evaluating effects on those resources. No significant adverse effects would occur to significant EQ resources. Significant beneficial effects would occur to

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wetland/riparian habitat and aquatic habitat as a result of increasing the quantity and quality of these habitat types, increasing habitat connectivity within the project site and benefiting international migratory birds and native flora and fauna. Other Social Effects The recommended plan would be a substantial financial commitment for the non-federal sponsor. The proposed recreational features would complement local Master Plans and existing recreation features and would enhance community recreation experiences. 6. Environmental Compliance and Social Effects Corps Civil Works studies and projects should be in compliance with all applicable federal environmental statutes and regulations and applicable state laws and regulations where the federal government has clearly waived sovereign immunity. NEPA requires federal agencies, including the Corps, to comply with a process that includes the inventory and assessment of the environmental resources within the study area. NEPA also requires the evaluation and comparison of alternatives to determine impacts to ecological, cultural and aesthetic resources identified and investigated. Involvement by resource agencies and the general public during the study process is also required. The Corps’ NEPA guidance may be found in ER-200-2-2, and was integrated with the Corps’ six-step planning process (as described in Section 1.3). This section addresses the ecosystem restoration components of the No Action Alternative, which also serves as the FWOP condition and the Recommended Plan and assesses potential impacts to existing resources. There would be little difference between the environmental impacts of the components of the Recommended Plan, and those alternatives that were screened out, as they generally propose the same type of activities, such as excavating, spreading topsoil, clearing and grubbing invasive species, planting vegetation, and restoring terrestrial and aquatic connectivity. 6.1. ENVIRONMENTAL CONSEQUENCES The Recommended Plan would include clearing and grubbing invasive species and re-planting native species on approximately 6.75 acres within Reaches 1 and 2 (Alternatives T, S and O), and restoring approximately 1.14 acres of palustrine emergent/ scrub shrub wetlands 4.53 acres of riparian corridor habitat in Reach 3 (Alternatives G and J), constructing two side channels which increases aquatic habitat by 0.86 acres in Reach 3 (Alternative J), constructing in-stream features ) to promote depth diversity, velocity diversity and feeding and shelter habitat for aquatic organisms in Reaches 1 and 3 (Alternatives K and M) and modifying two drop structures in Reaches 1 and 3 to promote fish passage (Alternatives P and Q) by constructing an auxiliary weir and riffle ramps immediately downstream of these drop structures. On the east bank of the river, the piers of the pedestrian bridge at Grant Frontier will be relocated higher on the existing bank to ensure that the existing water surface elevation will not rise as a result of restoring the wetland benches and side channels from Alternative J. Additionally, a boardwalk will be installed at Grant Frontier Park South from the newly relocated trail down to the wetland area in an effort to control human traffic in the area and reduce the amount of potential plant mortality from human disturbance. In the analysis below, all work being done to complete these restoration alternatives will be collectively referred to as “ecosystem restoration.” These alternatives are broken out by individual resource groups similar to the arrangement in Section 3, or grouped where logical.

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Physical Geography/Topography and Soils Recommended Plan The selected plan would result in permanent construction-related impacts to soils as a result of the proposed project. Approximately 40,000 cubic yards (cy) of material would be removed from Grant Frontier Park on both banks in Reach 3 as a result of grading and shaping the bank to construct wetlands. Typical earth-moving equipment would be used to dig, grade, trench and shape the soils during construction activities. Following construction activities, disturbed areas would be seeded with a native seed mixture, planted with wetland seedling transplants and planted with bareroot trees and willow poles. Because significant amounts of these soil types occur throughout the project area and because the soil in the proposed project area has been disturbed in the past for urban use, impacts to soils would be considered minor and not significant. Impacts would be considered beneficial in nature as vegetation plantings and sloping banks will decrease soil erosion. Minimal, temporary soil disturbance activities are proposed in Reach 2 and Reach 1 as a result of selective clearing and grubbing of noxious species and planting of native vegetation. No major grading or shaping is proposed in these two reaches, therefore the proposed action would have negligible impacts to soil and area topography as a result of ecosystem restoration in Reach 1 and Reach 2. No Action The No Action Alternative would have negligible impacts to soils or area topography. While no construction would take place and disturb the localized area, the banks would likely continue to slough during higher frequency events. This could cause increased soil erosion and localized scouring. If ecosystem restoration does not occur in Grant Frontier Park, it is possible the area surfaces could be developed with hardened structures and impervious surfaces which could contribute to complete loss of native soils in the area. Water Quality Recommended Plan Riparian vegetation slows water runoff, traps sediment, and intercepts pesticides, pathogens, and heavy metals from entering waterways. Floristic quality of the study area would improve as a result of removing invasive species and re-vegetating areas with desirable, native species as well as restoring wetlands which are currently a rare and scarce habitat type. Associated permanent benefits to water quality associated with these actions include filtering pollutants, nutrients and surface runoff, trapping sediment and stabilizing soils. Temporary and minor impacts to water quality may occur during construction activities as excavation will be necessary to grade and slope banks to restore wetlands in Reach 3, and as a result of selective removal of invasive species in Reaches 1 and 2. This work would be completed under Section 404 Nationwide Permit 27 which permits ecosystem restoration activities associated with the restoration, enhancement and establishment of wetlands and aquatic habitat. The state of Colorado certifies this action under its 401 water quality certification for all work completed under Nationwide permits. 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.

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BMPs would minimize any incidental fallback of material into the river during construction and would minimize the introduction of fuel, petroleum products, or other deleterious material from entering into the waterway. Such practices and measures could include, but are not limited to: the use of erosion control fences; storing equipment, solid waste and petroleum products above the ordinary high water mark and away from areas prone to runoff and requiring that all equipment is clean and free of leaks. To prevent fill from reaching water sources by wind or runoff, fill would be covered, stabilized or mulched and silt fences used as required. With an expectation that BMPs would be required as a part of the National Pollutant Discharge and Elimination System (NPDES) permit and implemented during construction activities, no significant impacts to water quality are anticipated. No Action Under the No Action Alternative, water quality in the study area would continue to degrade. Continued urban development would increase impervious surfaces and non-point and point sources of pollution, while a decrease of wetlands within the watershed would remove the area’s natural ability to filtrate inorganic and organic compounds from entering the South Platte River. Flood Risk Management Recommended Alternative The Section 1135 Feasibility Study selected alternative will be located in and adjacent to the Special Flood Hazard Area and partly in the regulatory floodway. Coordination of project features and local, state and federal floodplain management criteria or policy must occur before project construction begins. Depending on how the selected alternative might affect flood water surface profiles and floodplain boundaries, a CLOMR may need to be obtained as part of the project. No Action Alternative Under the No Action Alternative, no change to regulatory floodway would occur. The regulatory floodplain would continue to be administered through FEMA and the City and County of Denver. Air Quality Recommended Alternative There would be no long-term impacts to air quality as a result of this project. Short-term impacts would include an increase in fossil fuel pollutants by construction equipment during construction activities and an increase in particulate matter in the form of dust. Impacts are considered to be short-term and negligible. No Action Because no construction would occur under the No Action Alternative, no impacts to air quality would occur. Noise Recommended Plan The preferred alternative would result in minor short-term, construction-related noise impacts. These impacts would result from the operation of heavy machinery during project construction. These noise levels would be in addition to those produced in this urban setting. Construction activities would be conducted during normal business hours. Following construction, the area would resume normal ambient level noise conditions the same as existing conditions.

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No Action Because no construction would occur under the No Action Alternative, no impacts to the existing noise environment would occur. Hazardous, Toxic and Radioactive Waste Recommended Plan As a Phase I and Phase II HTRW Assessment were conducted during the feasibility study, it is not anticipated that any disturbance of HTRW-classified materials would occur. Excavation is primarily occurring at Grant Frontier Park along both banks as a result of Alternatives G and J. Minor excavation and soil disturbance would also occur as a result of clearing and grubbing invasive vegetation and replanting native vegetation. As noted previously, in accordance with ER-1165-2-132, the non-federal sponsor is solely responsible for the handling, disposal and remediation of HTRW materials or areas, should they be discovered during construction. No Action Under the No Action Alternative, no impacts would occur as no construction would take place. The riverbank within the project footprint would continue to be composed of the historic fill where it currently exists and Grant Frontier Park would continue to be composed of native materials were determined in the Phase II Assessment. Vegetation and Terrestrial Resources Recommended Plan The purpose of ecosystem restoration is to improve the riparian habitat within the study area through the primary means of removing noxious invasive species and replanting desirable native species which would increase the floristic quality of vegetation within the existing terrestrial habitat. Furthermore, wetlands would be restored in Reach 3, restoring the area to a more natural condition with floodplain habitat types in the local area that are deemed scarce and rare. Under Alternative G and J, approximately 1.14 acres on both the east and the west bank of Grant Frontier would be graded down to restore these wetlands, which would require some clearing and grubbing of the riparian vegetation present. Within these areas, some native species, such as cottonwood, Scotch pine (Pinus sylvestris), blue spruce (Picea pungens), green ash (Faxinus pennsylvanica) and honey locust (Gleditsia triacanthos) would be removed in order to excavate the riverbank down. These removals will be minimized to the greatest extent practicable. During D&I, specific trees will be identified for removal requirements. Where removing native species is unavoidable for bank grading activities in Grant Frontier Park South, the trees will be surveyed by the Denver City Forestry Department for health and condition and appropriate mitigation or replacement of trees will be conducted in accordance with requirements by the City of Denver Temporary and minor impacts to the riparian corridor would occur during construction. Invasive species would be selectively removed, thinning the available amount of vegetation while the new, native plantings establish. Overall, impacts to vegetation and terrestrial resources would be permanent and beneficial. No Action The habitat in the riparian corridor that once existed around the South Platte River has been severely depleted, and it is anticipated that under the No Action alternative, continued pressure for development within the city would continue to stress the biotic community surrounding the river. The overall biotic condition of study area is also assumed to degrade from existing conditions over the 50-year planning

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horizon. Invasive and non-native species will continue to out-compete native species within the remaining habitat. Vegetation structure and complexity will decrease, and monocultures will continue to persist, impacting the quality and functional value of the wetlands and riparian areas. Wetlands and Waters of the United States Recommended Plan Permanent and beneficial impacts would occur to wetlands and Waters of the United States as a result of the Recommended Plan. As noted above, approximately 1.14 acres of palustrine emergent and scrub- shrub wetlands would be restored within the project area where no wetlands currently exist. As discussed in the Institutional and Technical Significance of Section 2.3.1 and 2.3.3, wetlands of this habitat type are rare and scarce, not only within the study area, but also within the arid region of the Front Range Mountains. Restoration of wetlands and improvements of the aquatic environment of the South Platte River also supports multiple federal, regional and statewide plans, objectives, partnership and committees (e.g. Colorado Statewide Plan, South Platte Wetland Focus Area Committee, Urban Waters Federal Partnership, U.S Shorebird Conservation Plan). Ecosystem restoration of wetland and aquatic environments can provide critical floodplain and river corridor connections, habitat for state- listed and endangered species and provide habitat for international migratory birds. No Action The No Action Alternative would have negligible, adverse impacts to wetlands and Waters of the United States. No wetlands would be restored and the study area would continue to ecologically degrade without ecosystem restoration. Furthermore, the No Action Alternative would not support the significant resources deemed federally, regionally or locally important. Fish and Wildlife Recommended Plan The project area has been highly disturbed with industrial activities and commercial and residential areas. Permanent, beneficial effects to fish and wildlife would result from riparian/wetland and aquatic habitat restoration and improvements. Replacing invasive species with native species and planting more trees, shrubs and emergent vegetation will provide the habitat terrestrial wildlife needs to forage, breed and rear their young. Improving fish passage by decreasing the drop structures and increasing habitat complexity and depth diversity will provide feeding, sheltering and breeding habitat for aquatic life. The Recommended Plan would result in minor, temporary, construction-related adverse impacts to fish and wildlife resources. The impacts to fishery resources would be related to site runoff and increased turbidity, which could make feeding, breeding and sheltering difficult for species not accustomed to these conditions. As noted in Section 6.1.2.1, BMPs would minimize any incidental fallback of material into the river during construction and would minimize the introduction of fuel, petroleum products, or other deleterious material from entering into the waterway. The impacts to wildlife resources would be related to noise and visual disturbance during the construction activity. All construction would take place outside of nesting season of migratory birds in order to minimize impacts to nesting birds. No significant, negative impacts would occur to fish and wildlife as a result of the Recommended Plan. No Action Under the No Action Alternative, no ecosystem restoration would occur. At Grant Frontier Park, it is possible the area surfaces could be developed with hardened structures and impervious surfaces which would have negative impacts to terrestrial wildlife. Invasive species would continue to out-compete native species and monocultures will persist, impacting the quantity and quality of existing habitat used by terrestrial wildlife. No improvements to the aquatic habitat would occur and the river within the Section 1135 June 2018 South Platte Valley 92

study area would continue to only support those generalist aquatic species that are more tolerant to degraded conditions, low dissolved oxygen and minimal depth diversity or limited velocity changes. Migratory Birds Recommended Plan Under the recommended alternative, impacts to migratory songbirds and raptors are anticipated to be minor and short-term as a result of construction. Although the provisions of the MBTA are applicable year-round, most migratory neo-tropical bird nesting activity in the proposed project location occurs from April 1st to July 15th, most raptor nesting in this region occurs from February 1st to July 15th. The best time to avoid all nesting birds is between September 15th and January 31st. Under the MBTA, construction activities in rivers, wetlands, streams, riparian forests, woodlands and grassland habitats that would potentially result in the taking of migratory birds, eggs, young, and/or active nests should be avoided completely outside of the primary nesting season. Clearing and grubbing would be scheduled to occur outside of the primary nesting periods. Should any clearing and grubbing occur within the nesting season, a qualified biologist would conduct a field survey not more than 10 days prior to any proposed clearing and grubbing activities to determine the presence or absence of any nesting migratory birds. If any nesting species be found in the project area, the USFWS would be contacted immediately for further guidance and assistance. Proposed construction activities involved with this project could have the potential to result in temporarily disturbing migratory birds in the form of displacement and determent of utilization of the area during construction. However, in order to minimize impacts to migratory species, all clearing and grubbing activities would occur outside of the migratory bird nesting season. Following construction, beneficial permanent effects to migratory birds would occur. This ecosystem restoration project would restore migratory bird habitat (shrubs/forested areas/wetlands) in close proximity to the South Platte River which supports national efforts to comply with the MBTA. Replacing wetland habitats, which have been federally identified as rare and scare habitat types within the region the study area falls within, will provide stopover habitat to many migrating birds. One study in South Dakota demonstrated the importance of riparian corridor stopover habitat to migrating birds by studying the increased cortisol levels (stress response) and decreased body conditions (fat reserves) of migrating species that have to travel further between stopover habitats (Liu and Swanson, 2014). The Recommended Plan would increase the availability of stopover habitat for migrating species, thus providing the potential to reduce stress responses and starvation in migrating birds that travel through this area. No Action Under the No Action Alternative, no ecosystem restoration would take place. The invasive species in the study area that provide little to no habitat to migrating birds would continue to persist and out-compete native species. No wetlands, a necessary habitat for most migrating birds, would be restored. The No Action Alternative would have long-term and negative impacts to migrating birds. Threatened and Endangered Species (Biological Assessment) As noted in Section 3.6.6, eight threatened and endangered species have potential to be found within the study area, three of which were not analyzed as they would not likely occur (two species have a block clearance zone, and the Mexican spotted owl is found in old-growth forests). The following sections will evaluate potential impacts to these species and provide an effect determination. For all species, under the No Action Alternative, no adverse impacts or beneficial effects, would occur to the listed species.

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Interior Least Tern and Piping Plover As noted in Section 3.6.1.2, least terns and piping plovers require dry, exposed sandbars and river flows that support a forage fish supply and isolate sandbars from the riverbanks. Typical riverine nesting sites include dry, flat, sparsely vegetated sand and gravel bars within a wide, unobstructed, water-filled river channel. These conditions are not currently present within the study area, nor would this habitat type be available with the implementation of the Recommended Plan. There is potential for both bird species to generally pass through the area during its migration period, however; it is anticipated that the interior least tern and piping plover would not be further impacted by construction activities due to the general urbanization and anthropomorphic activities already existing within the project area. The Corps concludes that the proposed project would have a “may effect, not likely to adversely affect” determination on the interior least tern and piping plover based on the premise that the project area is not located within or readily near suitable nesting habitat for this species; however, there is potential for them to generally pass through the area during construction activities. If the interior least tern or piping plover do pass through during construction, the impact would be temporary and negligible as the birds would likely be deterred by surrounding urbanization and anthropomorphic activities already occurring. Temporary construction activities would only further deter the birds from utilizing the immediate project area. Whooping Crane Whooping crane migration periods occur between March and May and September to November and would likely only be found in this area as it is passing through. Migrating birds will feed in croplands and roost in shallow, freshwater wetlands or during migration in the study area due to the lack of freshwater wetlands. It is not likely that the migrating birds would stopover within the study area during construction. After construction, approximately 1.14 acres of freshwater, palustrine and scrub shrub wetlands will be available for whooping crane to utilize during migration. This would provide a beneficial effect to this endangered species. As such, the Corps determines the Recommended Plan “may affect, but not likely to adversely affect” the whooping crane. Pallid Sturgeon As noted in Section 3.6.1.5, pallid sturgeon are often found in large, turbid, free-flowing river habitat in the Missouri and Mississippi rivers. Pallid sturgeon have been present in the Platte River or near its mouth and in the Yellowstone River during above-normal spring flows. It is not anticipated that pallid sturgeon would be present within the study area before, during or after construction. The South Platte River within the study area does not support the biological requisites or habitat types that support the pallid sturgeon. As such, the Corps concludes a “no effect” determination for the pallid sturgeon under the Recommended Plan. Western Prairie Fringe Orchid The disturbance caused by associated factors with urbanization has likely sequestered this species’ ability to thrive within the study area. It is not expected that the western prairie fringed orchid would be found within the project area before, during or after construction. Confirmed through desktop analysis and site visits, no high quality prairie or wet meadows exist within the project area. Furthermore, high quality prairie and/or wet meadows will not be restored as part of the Recommended Plan and the existing and continued urbanization of the area would likely preclude the ability of the species from being supported in the study area. Therefore the Corps concludes that the Recommended Plan would have “no effect” on the western prairie fringed orchid based on the lack of suitable habitat within the project area.

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Cultural Resources Recommended Plan As noted in Section 3.11, a cultural resources survey was conducted for this Section 1135 Feasibility Study. The records search conducted (see Appendix J) did not show any recorded sites within the study area, though two sites are listed on the NHRP, 34 sites are eligible for listing and 26 sites are unevaluated. However, these sites fall outside of the project area. If an inadvertent discovery of cultural resources occurs during project ground disturbing activities, all work within 100 feet of the discovery area will stop and the contractor will notify the Corps archeologist and Colorado SHPO. An archeologist, approved by the Corps, will evaluate the new discovery for eligibility and project effect. The Corps, with the archeologist’s recommendations and in consultation with the SHPO, will notify the contractor when work can proceed. No impacts are anticipated to cultural resources under the Recommended Plan. No Action No ground disturbing activities would occur under the No Action Alternative. The No Action Alternative would have no effect on cultural resources. Socioeconomics Recommended Plan The proposed project would provide $1,833 annual net benefits from recreation. The recreational features developed as part of the Corps recreation alternative are oriented towards improving the outfall structure of the Harvard Weir Gulch and providing trail access to the restored areas, compatible with ecosystem restoration objectives. Trails within the NER areas would be designed to minimize human disturbance to plant and animal communities. The Regional Trail, in Alternative G where it is pulled away from the river, will be restored to the City of Denver’s requirements. In the restored habitat areas, crushed fines or a packed earthen trail would be utilized to minimize the trails’ impact to the area and to integrate with the aesthetics. Environmental restoration of the project provides positive benefits to socioeconomic conditions and overall community well-being. Positive and long-term impacts to the socioeconomic area would occur as a result of the Recommended Plan. No Action Under the No Action Alternative, the net increase in recreational benefits would not be realized, nor would the positive community health benefit occur from environmental restoration. The study area would continue to experience the level of visitation commensurate with existing conditions and the Regional Trail would continue to be utilized heavily by recreationists and pedestrians passing through. 6.2. CUMULATIVE IMPACTS The combined incremental effects of human activity are referred to as cumulative impacts (40CFR 1508.7). While these incremental effects may be insignificant on their own, accumulated over time and from various sources, they can result in serious degradation to the environment. The cumulative impact analysis must consider past, present and reasonably foreseeable actions in the study area. The analysis also must include consideration of actions outside of the Corps, to include other state and federal agencies. As required by NEPA, the Corps has prepared the following assessment of cumulative impacts related to the alternatives being considered in this integrated EA. Historically, the City of Denver was initially settled on the banks of the South Platte River as a gold mining boomtown in 1858. Gold was panned in Cherry Creek and the South Platte River, though gold deposits were not overly abundant to support the prospectors and the resource was quickly exhausted. Gold reserves were discovered in greater abundance west of the settlements, and the City of Denver

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provided for materials and goods to supply these new mines. In 1862 the Pacific Railway Act was passed, though the Union Pacific Railroad chose to go north through Cheyenne, Wyoming. The Colorado Territorial Governor, along with other local business leaders and investors formed a railroad company that would link Denver to the transcontinental Union Pacific Railroad in Cheyenne. Silver was discovered in the mid-1860s which caused a boom in Denver. The city’s economy grew and by 1890, it became the 26th largest city, rooted in railroads, wholesale trade, manufacturing, food processing, agriculture and ranching. Through the last two centuries, Denver has experienced exponential growth and urban sprawl. Today Denver ranks as the 21st largest city and it is anticipated the city will continue to grow. Of the reasonably foreseeable projects and associated impacts that would be expected to occur, further urbanization of the area would probably have the greatest impact on the previously mentioned resources. The South Platte River has been channelized within the urbanized areas of Denver, and water from the river is artificially managed from the upstream Tri-Lakes Project. These modifications, coupled with the land use, water demands and diversions, wastewater treatment, flood control, recreation and pollution, have significantly and severely impacted the environmental resources of not just the South Platte River within the study area, but within the entire watershed. It is reasonably expected that these conditions will persist and continue to worsen. In addition to continued pressure from population growth and urbanization, climate change will also likely impact the water resources of the area. Future projections suggest that, if current trends continue, global urban land cover will nearly triple by 2030 (Seto et al., 2012 as cited in Revi et al., 2014). Colorado State Demography Office in 2015 reported the City and County of Denver as supporting a population of 682,545 individuals. This population is expected to grow nearly 22% by 2050, to 833,221 individuals (CSDO, 2017). As global climate change continues, the frequency and severity of drought will increase, and wetlands and riparian corridors will become more vulnerable to loss. Rising temperatures will lead to an increased demand on water resources, particularly for large urban areas (Shafer et al., 2014) like the Denver Metro. Overall, the Recommended Plan would increase the quantity and quality of environmental resources within the project footprint. Minor and localized improvements in water quality may occur as a result of the restored wetlands as the assumption that the restored wetlands would assist in filtration and uptake of excessive nutrients. Vegetative communities would steadily improve throughout the life of the project as native plantings would establish. Improvements to the aquatic habitat would locally increase fish passage, and in-stream features such as boulder clusters and woody debris structures would provide increased feeding, breeding and sheltering habitat for aquatic organisms. The shallower portions of the side channels would also support emergent, submergent and floating macrophytes within the localized area. The adverse effects associated the restoration of the ecosystem restoration features are short-term and minor. These minor adverse effects would be greatly offset by providing the area with rare and scare habitat types that were historically present and increasing the quantity and quality of the environmental resources available, as well as providing potentially minor offsets to the impact of likely, future activities. The Recommended Plan will also provide the citizens of Denver with increased intrinsic and aesthetic value as a result of improvements to the South Platte River within this heavily urbanized community.

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6.3. ENVIRONMENTAL COMPLIANCE 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 U.S.C. § 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. Informal ESA consultation is ongoing with the USFWS. A Biological Assessment (BA) has been prepared and integrated in this document. See Section 6.1.11 for effect determinations. Through evaluation of effects, it was determined that the proposed project would have “no effect” on the pallid sturgeon and western prairie fringed-orchid. A “may affect, not likely to adversely affect” determination was for the interior least tern, piping plover and whooping crane. The assessment is used to determine if formal consultation with the federal agency and the USFWS would be required. Formal consultation would not likely be required for the proposed project, as adverse impacts to listed species or their habitats are not anticipated. See Section 6.1.11. 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 state fish and wildlife agencies regarding impacts on fish and wildlife resources and measures to mitigate these impacts. Full consideration is to be given to USFWS recommendations. Coordination has been ongoing with the USFWS and CPW and correspondence may be found in Appendix A2. On November 8, 2016, the Omaha District sent the USFWS Region 6, Colorado Ecological Services Field Office an initial scoping letter regarding the feasibility study for the Section 1135 Ecosystem Restoration Project on the South Platte River in the City and County of Denver. The Corps requested the USFWS to provide a list of threatened, endangered and/or candidate species that may be affected by the proposed habitat project as well as any information on possible beneficial or adverse effects of the proposed project on those species. Within the same letter, the Corps also requested information in regards to fish and wildlife and sensitive resources within the project area for the study as required under the FWCA. Further correspondence from the Ecological Services Office indicated a lack of resources to contribute to the feasibility study, so the USFWS Colorado Fish and Wildlife Conservation Office was sourced by the Ecological Services Office to provide technical assistance and support. An initial Agency Team Meeting and Alternative Formulation Workshop occurred on February 27 and 28, 2017 where the USFWS, the Corps, the non-federal Sponsor (the City and County of Denver) and CPW discussed potential opportunities and alternatives for ecosystem restoration within the study area. Following this workshop, on March 7, 2017, the Corps transmitted the draft Existing Conditions and raw data analyzed using the proposed hydrogeomorphic assessment models, FACWet and FACStream to the USFWS and the CPW for initial comment. On April 7, 2017, a final Scope of Work (SOW) between the Corps and USFWS was approved by both agencies. Through coordination, a SOW outlining necessary tasks and deliverables, responsible of both agencies, was discussed. On July 14, 2017, the USFWS provided a Planning Aid Letter (PAL) responding to the information transmitted to USFWS on March 7, 2017. In this letter, the USFWS agreed that the FACWet and

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FACStream assessment models were appropriate to address the existing conditions and the benefits of the ecosystem restoration and that they had been properly applied. Assumptions made on scoring the variables were also deemed appropriate and the stressors of the study area where adequately identified within the models. The USFWS also indicated that wetlands are critically important features of the riparian system along the South Platte River and are of federal interest and institutionally significant due to the Clean Water Act and Executive Order 11990. Within Colorado, wetland and riparian areas represent only about two percent of the land area; however, 80 percent of wildlife species use these habitats. Urbanization of the Denver metropolitan area has dramatically impacted the South Platte River which has been channelized and encroached upon by development. As a result, the quality and quantity of aquatic, riparian and wetland habitat has been significantly reduced. An additional Agency Team Meeting was held on November 1, 2017 to present the alternatives formulated and analyzed utilizing FACWet and FACStream and the preliminarily preferred plan. USFWS, CPW, Trout Unlimited, the non-federal Sponsor attended. Informal correspondence was sent to USFWS, CPW, Colorado Division of Water Resources, Department of Environmental Quality and Colorado Water Conservation Board as well as Comanche Nation, Northern Cheyenne and Kiowa Tribes on March 26 and 27, 2018 to send an interim update following the Corps’ Omaha District Major Decision Milestone (MDM) briefing to the Northwestern Division (NWD) Office. On February 5, 2018, the District PDT briefed NWD the preliminarily preferred plan that was presented to the agencies and public in November 2017. An additional Agency Team Meeting will be held on June 18, 2018. Colorado SHPO, tribes, USFWS, EPA, CPW, the Nature Conservancy, Trout Unlimited, the Colorado Division of Water Resources and Colorado DDPHE have been invited. Clean Water Act Federal limits on the amounts of specific pollutants that could be discharged to surface water in order to restore and maintain the chemical, physical and biological integrity of the water are governed by the CWA (33 U.S.C. § 1251 et seq., as amended), 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 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 in Waters of the United States are also mandated by the CWA, under Section 404. The Corps authorizes this permit under the Regulatory Program. This project would be authorized under a Nationwide Permit 27 which permits ecosystem restoration activities associated with the restoration, enhancement and establishment of wetlands and aquatic habitat. The state of Colorado certifies this action under its 401 water quality certification for all work completed under Nationwide permits. Migratory Bird Treaty Act Under the MBTA, 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 primary nesting season, April 1st through July 15th in Colorado, to minimize the take of migratory birds. A migratory bird survey would be conducted prior to the commencement of construction activities by a qualified biologist.

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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 NRCS takes steps to ensure that prime farmlands lost to development are documented and provided to Congress in a yearly report. No Prime Farmland exists within the project area and was noted as such in a letter from NRCS. See Appendix A2 for correspondence. National Environmental Policy Act Federal agencies use NEPA (42 U.S.C. § 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 EA to serve as documentation necessary to incorporate the NEPA process into the feasibility planning process. If no significant impacts are determined that would warrant the preparation of an Environmental Impact Statement (EIS), a Finding of No Significant Impact (FONSI) would be prepared and NEPA compliance would be fulfilled. Cultural Resources In accordance with the National Historic Preservation Act (NHPA) and its implementing regulations, the State Historic Preservation Officer (SHPO), Tribes and other interested parties have been consulted to determine if there are any concerns regarding any proposed actions. During scoping, letters were sent to Cheyenne River Sioux Tribe, Cheyenne-Arapaho Tribes, Comanche Nation of Oklahoma, Eastern Shoshone Tribe, Kiowa Tribe, Lower Brule Sioux Tribe, Northern Arapaho Tribe, Northern Cheyenne Tribe, Oglala Sioux Tribe, Rosebud Sioux Tribe, Sisseton-Wahpeton Oyete, Standing Rock Sioux Tribe and Ute Mountain Tribe to provide information on the Feasibility Study the Corps and the non-federal sponsor were conducting on November 8, 2016. This letter also sought input, comments or suggestions the Tribes may have for the Corps to take into consideration during scoping and plan formulation. The Corps received comments from the Kiowa Tribe which stated that the study area would likely have minimum potential affect to any known Kiowa sites of cultural significance, though, to notify the Tribe should any inadvertent discovery occur. The Northern Cheyenne Tribe also responded with a request to have a cultural specialist from the Northern Cheyenne Tribe assist with any survey work that would be conducted. Comanche Nation stated that “No Properties” were found during a files search (See Appendix A2 for Correspondence). The remaining Tribes did not comment on the scoping letter. The Colorado SHPO was also sent a letter during the scoping phase on December 30, 2016. A response was received on January 25, 2017, where the SHPO recommended that the Corps consider conducting a geoarchaeological sensitivity model to assess and identify soils and sediments likely to contain cultural artifacts as well as develop a programmatic agreement. An informational letter was sent to the SHPO, Northern Cheyenne Tribe, Northern Arapaho Tribe, and the Ute Mountain Tribe on December 19, 2017. The Colorado SHPO responded to the Corps on January 25, 2018, again requesting a geoarchaeological sensitivity model and development of a programmatic agreement for the phased development of this project. On February 6, 2018, the Northern Cheyenne Tribe responded requesting to assist with a survey. The remaining Tribes did not comment on the Corps informational letter. On January 29, 2018, the Corps sent a determination letter to the Colorado SHPO and Northern Cheyenne Tribe. This letter involved a “no historic properties affected” determination for the proposed project. The Northern Cheyenne Tribe as of April 10, 2018 has not responded to the determination

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letter. The Colorado SHPO responded on March 15, 2018 “not objecting” to the Corps’ Area of Potential Effect. The Colorado SHPO requested a cultural resources survey and subsurface testing. On April 5, 2018, a Corps archeologist conducted a cultural resources inventory (CRI) of the area of potential effect. On April 30, 2018, the Corps sent a letter to the Colorado SHPO with the survey results which concluded no historic properties observed. The Colorado SHPO has been invited to the Agency Team Meeting, being held on June 18, 2018 and coordination is on-going. Executive Order 11988 Floodplain Management EO 11988 seeks “to avoid to the extent possible the long and short term adverse impacts associated with the occupancy and modification of floodplains and to avoid direct or indirect support of floodplain development wherever there is a practicable alternative”. The EO further states, “Each agency shall provide leadership and shall take action to reduce the risk of flood loss, to minimize the impact of floods on human safety, health and welfare, and to restore and preserve the natural and beneficial values served by floodplains in carrying out its responsibilities”. The EO requires each federal agency to evaluate the potential effects of any actions it may take in a floodplain. . Flood risk may be increased directly by building facilities in the floodplain that could be damaged by floods and/or by developing projects causing changes in the characteristics of flooding, such as increases in flood stages, which could result in increased flood damage. Flood risk may also be increased indirectly by actions that promote increased development in floodplains. The Feasibility Study recommended plan will be located in a designated floodplain and must comply with the executive order. The process for Corps compliance with EO11988 is given in ER 1165-2-26, Implementation of Executive Order 11988 on Floodplain Management. The ER 1165-2-26 evaluation for this project is described in Appendix D, Flood Risk and Floodplain Management. The restored aquatic habitat is functionally dependent on being adjacent to the South Platte River and the creation of habitat is recognized a beneficial use of floodplains. The recommended plan would not include structures that could be damaged by flooding and also would not result in increased development in the floodplain. As discussed in Section 4.7.2, hydraulic analyses determined that alternatives which included bank excavation at Grant Frontier Park would result in increases and decreases to the South Platte River base (1-percent annual chance) flood of the NFIP as well as other water surface profiles. The increased flood risk for large, infrequent flood events is of concern because of the extensive development along the left bank of the South Platte River adjacent to the location where the project would result in increased flood stages. An important criteria in formulating Corps environmental restoration projects is that flood risk not be increased. The aquatic habitat restoration benefits from this project would not offset potential adverse impacts from the increases in flood risk. The hydraulic analyses for this study determined that the adverse impacts to flood stages resulted from the contraction and expansion of flows through the Grant Frontier Park trail bridge. That situation resulted from the proposed and existing excavations along the riverbank upstream and downstream of the bridge structure. Additional analyses have determined that modifications to the project design decreasing the flow constriction at the bridge can reduce the increase in flood stages from existing conditions. The project modifications would lengthen the bridge on the right (east) bank to allow excavation of a wider, less constricted channel. The recommended plan has been modified to incorporate the modifications, which will be fully developed in the design phase. As discussed in Appendix D, coordination with the responsible local and regional officials responsible for floodplain management has developed a plan through which the proposed project would be permitted

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under the effective floodplain regulations. A CLOMR from FEMA would be required if the final project design results in increases to the water surface profile of the 1-percent annual chance flood. The modified recommended plan would provide significant environmental benefits, with localize increases in flood profiles. The incorporation of the bridge realignment and additional excavation will significantly reduce or eliminate the hydraulic impacts. With the incorporation of this mitigation, the project would meet the criteria of EO 11988. 6.4. PUBLIC INVOLVEMENT Public involvement is an important component of any civil works study. The PDT integrates input from the public into the six-step planning process. Typically a minimum of two public meetings are held but more may be held as needed to obtain input from the public. The first is a public meeting typically referred to as a scoping meeting, which is held early on in the study to gather input on the ecosystem problems, restoration opportunities, study objectives, and to brainstorm potential restoration alternatives. Scoping meetings are also required by the NEPA regulations (40 CFR Parts 1500-1508). As part of the scoping process the Corps also conducts an agency scoping meeting, which is intended to receive comments from relevant local, state, and federal resource agencies on the project. The second public meeting typically occurs during the evaluation of plans. This second meeting, held later in the study, was conducted to gather input on the final array of alternatives being evaluated and the likely recommended plan. An additional public meeting will be held in June/July 2018 to inform the public of this draft document’s availability for public comment. Public Meetings February 2017 Public Involvement Meeting: An open-house style public meeting was held the evening of February 28, 2017 at the Fleming Mansion, 1510 Grant Street in Denver, Colorado with approximately 30 people in attendance. Four formal comments were submitted to the Corps team via comment forms and several handwritten comments were recorded on project maps displayed at the public meeting. Comments focused on post construction monitoring and vegetation management of invasive species; planting native vegetation to support pollinator species; improvement of water quality, recreation, habitat and biodiversity in the area; and improving recreation features (see Appendix L). November 2017 Public Involvement Meeting: An open-house style public meeting was held the evening of November 1, 2017 at the Harvard Gulch Recreation Center, 550 E. Iliff Avenue in Denver, Colorado with approximately 12 people in attendance. Three formal comments were submitted to the USACE team via comment forms and focused on river access, recreation features and planting appropriate vegetation to support avian diversity (see Appendix L). June 2018 Public Involvement Meeting: An open-house style public meeting is being planned for June 18, 2018, at the Decker Branch Library, 1501 S Logan St, Denver, CO 80210 from 5:30—7:30 pm. The public involvement meeting will update members of the general public the Recommended Plan and the anticipated project schedule moving forward. Agency Coordination November 8, 2016: Initial scoping agency coordination letters were provided to the EPA, USFWS, CDNR- Division of Water Resources and Colorado Water Conservation Board, CPW, NRCS, National Park Service and U.S. Forest Service. Scoping letters were also sent to 14 Tribes. In a response letter dated December 28, 2016 the Colorado Division of Water Resources noted that dependent upon the study’s findings and proposed alternatives, the project may impact Colorado’s water rights system and be subject to administration of the CDWR. The Corps was advised to contact Section 1135 June 2018 South Platte Valley 101

the CDWR regarding any component that may expose groundwater, create a permanent pool, create new wetlands, require active irrigation or change the stream in a way that that may impact operation of the water rights system. NRCS sent a letter, dated December 6, 2016, stating that for the purposes of the Farmland Protection Policy Act (FPPA), the study area occurs within the boundaries of an urbanized area and is therefore not subject to the FPPA. NRCS encouraged the Corps to utilize accepted erosion control practices during construction activities. Comanche Nation responded on January 6, 2017, stating that no properties of historic archeological definition were found in a records search. Kiowa Tribe notified the Corps on November 25, 2016 that the proposed project location likely had minimal potential to adversely affect any known archaeological, historical or sacred sites. The Colorado SHPO sent a later, dated January 25, 2017 stating that a limited archaeological inventory has been completed within the study area and the potential for buried archaeological sites within the stratified terrace and bank deposits is good, and recommends the Corps consider developing a geo-archaeological sensitivity model to identify soils and sediments likely to contain intact cultural deposits. February 27-28, 2017: A Plan Formulation and concurrent Agency Team Meeting occurred on-site prior to the February 27, 2017 Public Involvement Meeting. The sponsor, members of the Corps, CPW and USFWS formulated potential feasible alternatives for further investigation based on the three reaches of the study area. The team also identified the project objectives and constraints to formulate alternatives around. November 1, 2017: An Agency Team Meeting was held to provide an interim update on the planning process and preliminary tentatively selected plan. In addition to the Corps and the non-federal sponsor, representatives from USFWS, Denver Trout Unlimited and CPW attended and the Kiowa Tribe joined via teleconference. A brief project description and history was given, along with initial CE/ICA results and components of the best buy plan 10 were discussed. Support for the project was received from attendees. At that time, Alternative A variants were still being assessed. Following the Agency Team Meeting and further discussion with the non-federal sponsor and Denver Parks and Recreation, Alternative A and its variants were screened out. As a result of this meeting, the PDT re-assessed the alternative analysis with CE/ICA. March 26, 2018: An update, via e-mail, was sent to USFWS, CPW, Denver Department of Health, Colorado Division of Water Resources, Colorado Water Conservation Board, Kiowa Tribe, Northern Cheyenne Tribe and Comanche Nation. This e-mail detailed the recommended plan briefed to NWD during the MDM on February 5, 2018 and provided a preliminary timeline for the draft report availability. May 9, 2018: An invite, via email, was sent to USFWS, CPW, EPA, Colorado Division of Water Resources, DDPHE, Trout Unlimited and The Nature Conservancy, to inform these agencies of an upcoming Agency Team Meeting scheduled for June 18, 2018. Invite letters were sent to Cheyenne River Sioux, Cheyenne- Arapaho, Comanche Nation, Eastern Shoshone, Kiowa, Lower Brule Sioux, Northern Arapaho, Northern Cheyenne, Northern Ute, Oglala, Pawnee Nation, Rosebud, Sisseton-Wahpeton Oyete, Standing Rock Sioux and Ute Mountain Tribes to also attend. A webinar and teleconference line were provided as most of these Tribes do not live in close proximity to the study area.

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7. MONITORING AND ADAPTIVE MANAGEMENT After initial construction activities are complete, monitoring and adaptive management are necessary to address uncertainties and ensure project success. Success criteria were defined based on specific hypothesis, which were formed based on the goals of the project. Monitoring activities were identified to determine whether the project has met these success criteria and adaptive management actions were designed to redirect the restoration effort in the event the restored areas do not perform as predicted. The goal of monitoring is to assess project performance and to determine if the goals of the project are being attained. Monitoring methodology, measures for ecological successes, and other information are available in greater detail in Appendix A5. Success criteria of the restored riparian and wetland habitats include greater than 80 percent survivability, native species presence greater than 60 percent, a floristic quality index greater than 6 and invasive species presence not to exceed greater than 15 percent coverage. For wetland restored habitats, percent native hydrophyte coverage and presence must be greater than 50 percent and the sites must have a prevalence index less than 3. Success criteria for restored aquatic habitat includes water temperature differentials between established water temperatures on gradient transects traversing the river at restored sites, pool habitat presences measured and small woody debris and leaf litter/detritus presence. Monitoring occurs following construction and will occur annually for up to five years. Monitoring and adaptive management will also be conducted on constructed in-stream features to ensure they are functioning as designed. Monitoring is estimated to cost $5,720 per year for the five-year monitoring period. This is part of the total project cost shared between the Corps and the sponsor. Implementation responsibilities for the monitoring plan will be identified in the Project Partnership Agreement.

It is a Corps requirement that ecosystem restoration projects include monitoring, for assessing performance and determining whether adaptive management is needed to attain project benefits. The purpose of adaptive management is to make changes to the project after construction in order to better achieve the project objectives. The adaptive management plan assumes potential minor project adjustments, in accordance with the moderate scale of the project. The nature and cost of potential adjustment measures assumes activities such as replanting failed vegetation, replacing failed stone/boulder/rock riprap, removing accumulated sediment from side channels and altering the inlet/outlet structures approximately. These costs will be further defined in the Design and Implementation phase. Omaha District in consultation with the sponsor, federal and state agencies and NWD will determine any adaptive management that may be needed. Adaptive management would need concurrence from the sponsor and would be cost shared with the sponsor. Monitoring and adaptive management are not the same as inspections or operation and maintenance for which the sponsor would be responsible even during the monitoring period. 8. OPERATION AND MAINTENANCE Upon physical completion of the project, the District Commander will notify the non-federal sponsor in writing that construction of the project is complete, and will provide the non-federal sponsor with an O&M Manual. Upon receipt of the notice of completion of construction of the project, the non-federal sponsor will operate and maintain the project in accordance with the O&M Manual.

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9. RECOMMENDATIONS I recommend implementation of the recommended plan described in this integrated Feasibility Report and Environmental Assessment for the South Platte Valley Section 1135 Ecosystem Restoration Project. The recommended plan consists of five riparian restoration alternatives and four in-stream restoration alternatives. Specific components of restoration recommended for implementation include in-stream habitat structures to benefit the aquatic environment, modification to two drop structure to allow for improved fish passage within the project area, and riparian habitat restoration adjacent to the South Platte River. The ecosystem restoration plan calls for placement of rock habitat structure in the creeks, excavation, grading, plantings, and seeding, at a total project cost of $9,221,750 at FY18 price levels, including real estate interests. Stream restoration benefits include restoration of 8,196 feet of stream length (approximately 22.4 acres estimated using aerial imagery dated 2015) of low quality aquatic habitat of the South Platte River through the construction of in-stream features such as dikes, cross vanes, riffles and boulder clusters. The recommended plan also opens up a migratory pathway connection for fish by improving the gradient of two existing drop structures. Riparian restoration benefits include approximately 11.28 acres of riparian habitat and 1.14 acres of palustrine emergent/scrub shrub wetlands across the entire project area in downtown Denver. The recommended plan provides 12.91 net total average annual habitat units. The average annual cost per unit of habitat is $34,940. This plan is recommended with full support from the non-federal sponsor. It also carries wide ranging support from local and state agencies and the public. Recreation features planned for this project include 1,200 feet of elevated boardwalk at Grant Frontier Park South, which in addition to providing controlled access to the river, will help regulate foot traffic and reduce damage to the restored habitat areas. Other recreation features include interpretive educational signs, and the setback and aesthetic modification of the existing Harvard Gulch outfall where a viewing platform would be constructed, overlooking the restored areas of Grant Frontier Park South. These recreational features provide connectivity to existing recreational facilities in the community. Considering only the costs of recreation features, they will provide recreation benefits to the community with a benefit to cost ratio of approximately 1.04 to 1 and less than 10 percent of the overall project cost, estimated at $830,475 for recreation. The estimated cost-shared total project cost is $10,522,000. Of the total project cost, $1,025,000 is for land, easement, rights-of-way, relocation, and disposal costs, for which credit will be given to the sponsor. Of the total cost, the federal portion is approximately $7,891,000 and the non-federal portion is approximately $2,630,000. Of the total non-federal portion, approximately $1,630,000 will be provided in cash and $1,000,000 will be provided in land, easement, rights-of-way, relocation, and disposal costs. Estimated average annual cost for operations and maintenance is $95,515 for ecosystem restoration. I have given consideration to all significant aspects in the overall public interest. 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 City and County of Denver, has stated that prior to implementation it will, through signing of the Project Partnership Agreement, agree to perform the required items of cooperation including provision of all needed real estate interests, provision of cash as needed beyond real estate values to constitute its share of total costs, and post- construction operation and maintenance of the project.

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I recommend that the plan proposed herein for aquatic and riparian ecosystem purposes and related recreation purposes be approved and implemented through the Section 1135 program. 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.

______John W. Henderson, P.E. Colonel, Corps of Engineers Omaha District Engineer

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10. LITERATURE CITED Aquatics Associates, Inc. 2013. Results of the Aquatic Monitoring Program in the South Platte River For SPCURE, 2007-2012. Baird, OE. and CC Krueger. 2003. Behavioral thermoregulation of brook and rainbow trout: comparison of summer habitat use in an Adirondack River, New York. Transactions of the American Fisheries Society 132: 1194-1206. CBA (Colorado Bird Atlas). 2016. The Second Colorado Breeding Bird Atlas. http://www.cobreedingbirdatlasii.org/species-summary-data.html. Accessed February 3, 2017. Colorado Department of Public Health and Environment (CDHPE). 2018. Detailed Air Quality Summary. https://www.colorado.gov/airquality/air_quality.aspx. Accessed January 10, 2018. Colorado Natural Heritage Program (CNHP). 2015. Climate Change Vulnerability Assessment for Colorado Bureau of Land Management. K. Decker, L. Grunau, J. Handwerk and J. Siemers, editors. CNHP, Colorado State University, Fort Collins, Colorado. Colorado Parks and Wildlife. 2008. Aquatic Data Analysis. Accessed on November 16, 2016. http://cpw.state.co.us/learn/Pages/ResearchAquaticPublications.aspx CPW. 2013. Birds of Chatfield State Park and Waterton Canyon. Complied by H. Kingery, F and J. Justice, J. Kellner and J. Steffen. http://cpw.state.co.us/placestogo/parks/Chatfield/Pages/Nature.aspx. Accessed February 3, 2017. CPW. 2015. Colorado State Wildlife Action Plan. http://cpw.state.co.us/aboutus/Pages/WetlandsPrioritySpecies.aspx. Accessed May 8, 2017. Colorado Water Quality Control Commission (CWQCC). 2016a. Regulation No. 38 Classifications and Numeric Standards for South Platte River Basin. Colorado Water Quality Control Commission (CWQCC). 2016b. Regulation No. 93 – Colorado’s Section 303(d) List of Impaired Waters and Monitoring and Evaluation List. 5 CCR 1002-93. CSDO (Colorado State Demography Office). 2017. Populations Totals for Colorado Counties. https://demography.dola.colorado.gov/population/population-totals-counties/#population- totals-for-colorado-counties. Accessed September 5, 2017. Currier, P.J., G.R. Lingle, and J.G. VanDerwalker. 1985. Migratory Bird Habitat on the Platte and North Platte Rivers in Nebraska. Platte River Whooping Crane Critical Habitat Maintenance Trust. The High Pressure Press. Marquette, Nebraska. Dahl, T.E. 1990. Wetland Losses in the United States: 1780’s to 1980’s. U.S. Department of Interior, U.S. Fish and Wildlife Service, Washington D.C. Dennehy, K.F., D.W. Litke, C.M. Tate, and J.S. Heiny. 1993. South Platte River Basin – Colorado, Nebraska, and Wyoming. Water Resources Bulletin, American Water Resources Association. Vol. 29, No. 4. Denver Post. July 28, 207. Colorado’s Population Could Increase According to Forecast Numbers. https://www.denverpost.com/2017/07/28/colorado-population-forecast/. Accessed May 10, 2018.

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Dramstad, W.E., J.D. Olson and R.T.T. Forman. 1996. Landscape Ecology Principles in Landscape Architecture and Land-use Planning. Island Press. Harvard University. 80 pgs. Dodrill, MJ, CB Yackulic, B Gerig, WE Pine III, J Korman, and C Finch. 2015. Do management actions to restore rare habitat benefit native fish conservation? Distribution of juvenile native fish among shoreline habitats of the Colorado River. River Research and Applications 31: 1203-2117. Elliott, JM. Pools as refugia for brown trout during two summer droughts: trout responses to thermal and oxygen stress. Journal of Fish Biology 56: 938-948 Ellis, J.H. 2008. Scientific Recommendations on the Size of Stream Vegetated Buffers Needed to Protect Wildlife and Wildlife Habitat: Part III, The Need for Stream Vegetated Buffers, What Does Science Say? Report to Montana Department of Environmental Quality. EPA/DEQ Wetland Development Grant, Montana Audubon, Helena, Montana. Fischenich, C.J. 2003. Effects of Riprap on Riverine and Riparian Ecosystems. U.S. Army Corps of Engineers- Engineer Research and Development Center. ERDC/EL TR-03-4. Fischenich, C.J. and R. Seal. 2000. Boulder Clusters. U.S. Army Corps of Engineers- Engineer Research and Development Center. ERDC-TN-EMRRP-SR-11. Garfin, G., G. Franco, H. Blanco, A. Comrie, P. Gonzales, T. Piechota, R. Smyth and R. Waskom. 2014. Chapter 20: Southwest. Climate Change Impacts in the United States: The Third National Climate Assessment, J.M. Melillo, Terese Richmond, and G.W. Yohe. U.S. Global Change Research Program, 462-486. http://nca2014.globalchange.gov/report/regions/southwest. Accessed January 23, 2017. Johnson B., M. Beardsley, J. Doran. 2016 Functional Assessment of Colorado Streams. http://www.ecometricscolorado.com/functional-assessment.html. Accessed May 8, 2017. Khosronejad, A., C. Hill, S. Kang and F. Sotiropoulos. 2013. Computational and Experimental Investigation of Scour Past Laboratory Models of Stream Restoration Rock Structures. Elsevier. 54:191-207. Kingery, H. 1998. (Editor) Colorado Breeding Bird Atlas, Colorado Bird Atlas Partnership and Colorado Division of Wildlife. Denver, Colorado. Liu, M. and D.L. Swanson. Stress Physiology of Migrant Birds During Stopover in Natural and Anthropogenic Woodland Habitats of the Northern Prairie Region. 2014. Conservation Physiology, Volume 2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4806743/. Accessed January 12, 2018. Martin, L.M., C.M. Tate and J.D. Woodling. 2013. Fish Communities of the South Platte River Basin. National Water Quality Assessment Program South Platte River Basin Study. USGS. https://co.water.usgs.gov/nawqa/splt/meetings/MARTIN1.html. Accessed January 11, 2017. Meyer, K. 2008. Assessment of the Rocky Mountain National Park Breeding Bird Monitoring Program. Department of Forest, Rangeland and Watershed Stewardship. Colorado State University, Fort Collins, Colorado. http://dspace.library.colostate.edu/webclient/DeliveryManager/digitool_items/csu01_storage/ 2008/12/12/file_1/25059. Accessed January 24, 2017.

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Naiman, R.J., H. De`Camps, and M. Pollock. 1993. The Role of Riparian Corridors in Maintaining Regional Biodiversity. Ecological Applications. 3(2):209-212. National Research Council (NRC). 2011. America’s Climate Choices. National Academies Press. Washington D.C. Ravi, A., D.E. Satterthwaite, F. Arago-Durand, J. Corfee-Morlot, R.B.R. Kiunsi, M. Pelling, D.C. Roberts and W. Solecki. 2014. Climate Change 2014: Impacts, Adaptation and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Chapter 8: Urban Areas. http://www.ipcc.ch/pdf/assessment-report/ar5/wg2/WGIIAR5-Chap8_FINAL.pdf. Accessed May 19, 2017. Segelquist, C.A., M.L. Scott, G.T. Auble. 1993. Establishment of Populus deltoides Under Simulated Alluvial Groundwater. The American Midland Naturalist. 130(2): 274-285. Shafer, M., D. Ojima, J.M. Antle, D. Kluck, R.A. McPherson, S. Petersen, B. Scanlon and K. Sherman. 2014. Chapter 19: Great Plains. Climate Change Impacts in the United StatesL The Third National Climate Assessment. U.S. Global Change Research Program, 441-461. Smith, P. and B. Kuhn. 2015. Survey and Assessment of Critical Urban Wetlands: City and County of Denver. Colorado Natural Heritage Program, Colorado State University, Fort Collins, Colorado. Stein, B.A., P. Glick, N. Edelson and A. Staudt (eds). 2014. Climate-Smart Conservation: Putting Adaption Principles into Practice. National Wildlife Federation, Washington D.C. Tate, KW., DL Lancaster, and DF Lile. 2007. Assessment of thermal stratification within stream pools as a mechanism to provide refugia for native trout in hot, arid rangelands. Environmental Monitoring and Assessment 124: 289-300 Tomaz, S.M. and E.R. da Cunha. 2010. The Role of Macrophytes in Habitat Structuring in Aquatic Ecosystems: Methods of Measurement, Causes and Consequences on Animal Assemblages’ Composition and Diversity. Biological Limnology. 22(2). U.S. Census Bureau. 2017. QuickFacts: Colorado. http://www.census.gov/quickfacts. Accessed January 20, 2017. Urban Waters Federal Partnership in Action. 2012. https://www.epa.gov/sites/production/files/2014- 06/documents/uw-federal-partnership-report_v7al.pdf. Accessed March 14, 2017. USFWS. 2001. Whooping Crane Fact Sheet. https://www.fws.gov/northflorida/whoopingcrane/whoopingcrane-fact-2001.htm. Accessed January 24, 2017. U.S. Fish and Wildlife Service (USFWS). 2003. Draft Recovery Plan Preble’s Meadow Jumping Mouse (Zapus hudsonius preblei). U.S. Department of Interior, Fish and Wildlife Service Mountain- Prairie Region. USFWS. 2005. Recovery Plan for the Mexican Spotted Owl. U.S. Fish and Wildlife Service. Albuquerque, New Mexico. http://www.fws.gov/southwest/es/arizona/Documents/RecoveryPlans/MexicanSpottedOwl.pdf . Accessed January 24, 2017.

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USFWS. 2007a. National Bald Eagle Management Guidelines. May 2007. USFWS. 2007b. Preble’s Meadow Jumping Mouse Block-Clearance for the Denver Metropolitan Area – Revised 2007. Submitted by Urban Drainage and Flood Control District, Denver, Colorado. Approved by USFWS 2007. USFWS. 2012. Final Recovery Plan for the Mexican Spotted Owl (Strix occidentalis lucida), First Revision. U.S. Fish and Wildlife Service. Albuquerque, New Mexico. https://www.fws.gov/southwest/es/arizona/Documents/SpeciesDocs/MSO/2012MSO_Recover y_Plan_First_Revision_Final.pdf. Accessed January 24, 2017. USFWS. 2015. Mountain-Prairie Region Regional Priorities. October. USGS (U.S. Geological Survey). 1995. Review of Sediment Data in the South Platte River Basin, Colorado, 1980-92. Urban Drainage and Flood Control District, South Platte River Hydrologic Study, Chatfield Dam to Sand Creek, Prepared by Merrick and Company, Denver, Colorado, May 1983 USACE (U.S. Army Corps of Engineers). 1995. Evaluation of Environmental Investments Procedures Manual. Interim: Cost Effectiveness and Incremental Cost Analysis. IWR #95-R-1. By Robinson, R., W. Hansen, K. Orth and in collaboration with S. Franco.

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