Prepared for:

Anne Arundel County Department of Public Works

UPPER MILL CREEK STREAM RESTORATION DESIGN DEVELOPMENT REPORT

SEPTEMBER 2018 Contract No. B552203

Prepared by:

Consultants & Designers, Inc. “Integrating Engineering and Environment” 7455 New Ridge Road, Suite T Phone: (410) 694-9401 Hanover, Maryland 21076 Fax: (410) 694-9405 Website: www.baylandinc.com Upper Mill Creek Stream Restoration Design Development Report

TABLE OF CONTENTS

1. INTRODUCTION ...... 6 Overview ...... 6 Background ...... 9 Programmatic Goals ...... 9 2. WATERSHED ASSESSMENT ...... 10 Watershed ...... 10 Physiography ...... 10 Soils ...... 12 Climate ...... 12 Land Use and Land Cover ...... 14 Existing & Ultimate Land Use ...... 14 Historical Land Use ...... 17 Land Use Influences on Channel Processes ...... 17 Influence of Beaver Activity ...... 18 Presence of Mills and Dams ...... 19 Jurisdictional Wetlands and Streams ...... 19 Historic Wetlands ...... 20 Historic Wetland Analysis – Method 1 ...... 20 Historic Wetland Analysis – Method 2 ...... 24 Plant Community Descriptions ...... 24 Rare, Threatened and Endangered Species ...... 25 Cultural Resources ...... 25 3. REACH DESCRIPTION ...... 26 Upper Mill Creek Upstream Conditions ...... 26 Upper Mill Creek Project Reaches ...... 28 Upper Mill Creek Reach 1 (UM-1) ...... 28 Upper Mill Creek Reach 2 (UM-2) ...... 29 Upper Mill Creek Reach 3 (UM-3) ...... 30 Upper Mill Creek Reach 4 (UM-4) ...... 31 Upper Mill Creek Reach 5 (UM-5) ...... 32 Upper Mill Creek Reach 6 (UM-6) ...... 33 Upper Mill Creek Reach 7 (UM-7) ...... 34

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Upper Mill Creek Reach 8 (UM-8) ...... 34 Upper Mill Creek Reach 9 (UM-9) ...... 35 Upper Mill Creek Reach 10 (UM-10) ...... 36 Upper Mill Creek Reach 11 (UM-11) ...... 39 4. CONSTRAINTS ANALYSIS ...... 40 Environmental Screening Results ...... 40 Utilities and Infrastructure ...... 43 Property Ownership and Easements/Site Access ...... 43 FEMA Floodplain/Hydrologic Trespass ...... 43 Forest Conservation Priority Areas...... 44 RTE and In-Stream Work Restrictions ...... 44 5. HABITAT AND BIOLOGICAL ASSESSMENT ...... 45 Methodology ...... 45 Results ...... 45 6. HYDROLOGIC ANALYSIS ...... 47 Methodology ...... 47 Development of Hydrologic Inputs...... 47 Hydrologic Analysis ...... 51 Calibration ...... 51 7. ADDITIONAL HYDROLOGIC ANALYSIS – UM-10 ...... 54 Methodology (UM-10) ...... 54 Development of Hydrologic Inputs (UM-10) ...... 54 Hydrologic Analysis (UM-10) ...... 56 8. DESIGN DISCHARGE ...... 57 Methods ...... 57 Results ...... 58 9. GEOMORPHOLOGY ...... 59 Longitudinal Profile ...... 59 Cross Sections ...... 59 Bed Material Characterization ...... 59 At-a-Station Hydraulics ...... 60 Stream Classification ...... 62 Sediment Supply and Transport ...... 64 Stream Evolution Model (SEM) ...... 64

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Bank Erosion and Lateral Stability ...... 66 BANCS Assessment...... 66 Estimated Erosion Rates ...... 67 Measured Erosion Rates ...... 68 10. HYDRAULIC ANALYSIS ...... 69 Hydraulic Analysis Methodology ...... 69 Hydraulic Analysis Results ...... 70 2-Dimensional Modeling ...... 93 11. FUNCTION BASED ASSESSMENT (UM-1 through UM-9) ...... 94 Introduction ...... 94 Reach Scale Function Based Assessment ...... 95 Design Objectives ...... 95 Proposed Design Approach ...... 96 Proposed Design ...... 97 General Design Approach ...... 97 In-Stream and Floodplain Stabilization Structures ...... 98 Channel Design Criteria ...... 99 Stone Sizing Computations ...... 102 Functional Uplift ...... 103 Proposed Condition...... 103 12. PROPOSED DESIGN – UM-10 ...... 105 General Design Approach ...... 105 Water Quality Computations ...... 106 Facility Hydraulics ...... 107 13. POLLUTANT REMOVAL ...... 109 14. PERMITTING ...... 111 15. COST ANALYSIS ...... 112 16. CONCLUSION ...... 113 17. REFERENCES ...... 114

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LIST OF FIGURES Figure 1 – Vicinity Map ...... 8 Figure 2 – Watershed Map ...... 11 Figure 3 – Existing Land Use ...... 15 Figure 4 – Ultimate Land Use ...... 16 Figure 5a – Concept Wetland Restoration Opportunities ...... 22 Figure 5b – Concept Wetland Restoration Opportunities ...... 23 Figure 6 – Reaches ...... 27 Figure 7 – Due Diligence Sites ...... 42 Figure 8 – Upper Mill Creek Sub-Drainage Areas ...... 48 Figure 9 – Soils Map ...... 50 Figure 10 – UM-10 Sub-Drainage Areas ...... 55 Figure 11 – Stream Evolution Model ...... 65 Figure 12 – Typical Step-Pool Storm Conveyance Profile ...... 105

LIST OF TABLES Table 1 – USDA-NRCS Soils within Study Area ...... 12 Table 2 – USDA-NRCS Official Soil Series Descriptions ...... 12 Table 3 – Average Daily and Annual Values for Temperature and Precipitation ...... 13 Table 4 – Land Use ...... 14 Table 5 – Upper Mill Creek Wetland Delineation Summary ...... 20 Table 6 – Vegetative Community Summary ...... 25 Table 7 – Typical Databases with Sites Identified in the Maryland Area ...... 40 Table 8 – Habitat and Biological Assessment Monitoring Results ...... 46 Table 9 – HSG Coverage ...... 49 Table 10 – Hydrologic Inputs ...... 49 Table 11 – WinTR-20 Peak Discharges ...... 51 Table 12 – Peak Discharge Results, Study Point 1 ...... 52 Table 13 – Peak Discharge Results, Study Point 2 ...... 52 Table 14 – Peak Discharge Results, Study Point 3 ...... 52 Table 15 – Hydrologic Inputs (UM-10)...... 54 Table 16 – Hydrologic Summary: WinTR-20 Peak Discharges to SP-1 and SP-2 ...... 56 Table 17 – Hydrologic Summary: WinTR-20 Peak Discharges to Pond 824 ...... 56 Table 18 – Upper Mill Creek Design Discharge Estimates ...... 58 Table 19 – At-a-Station Hydraulics ...... 61 Table 20 – Bankfull Channel Dimensions at Classification Riffles ...... 63 Table 21 – Stream Evolution Model Stage ...... 65 Table 22 – BEHI/NBS Ratings and Total Erosion Per Year ...... 67 Table 23 – Existing and Proposed River Stationing Descriptions ...... 69 Table 24 – Peak Discharge Flow Change Locations ...... 70 Table 25 – Main Stem Existing and Proposed Floodplain Access ...... 72 Table 26 – East Tributary Existing and Proposed Floodplain Access ...... 75 Table 27 – Main Stem 2-Year Storm Event Existing and Proposed Shear Stresses and Velocities ...... 78

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Table 28 – Main Stem 10-Year Storm Event Existing and Proposed Shear Stresses and Velocities ...... 82 Table 29 – East Tributary 2-Year Storm Event Existing and Proposed Shear Stresses and Velocities ...... 86 Table 30 – East Tributary 10-Year Storm Event Existing and Proposed Shear Stresses and Velocities ...... 89 Table 31 – Assessment Parameters by Pyramid Level ...... 94 Table 32 – Pre-Restoration Condition Rating ...... 95 Table 33 – Design Objectives ...... 96 Table 34 – Design Criteria ...... 101 Table 35 – Proposed Condition ...... 104 Table 36 – WQv Summary ...... 107 Table 37 – Hydraulic Summary: Existing Pond 824 ...... 107 Table 38 – Hydraulic Summary: Proposed RSC System ...... 107 Table 39 – Interim Pollutant Load Removal Efficiencies ...... 110 Table 40 – Pollutant Removal and Impervious Area Treated (UM-10) ...... 110

APPENDICES Appendix A – Historic Aerial Photographs Appendix B – Wetland Delineation Attachment A: Wetland Delineation Plans Attachment B: Wetland Datasheets Attachment C: Site Photographs Appendix C – Forest Stand Delineation & Trilogy Letters Attachment A: Forest Stand Delineation Plan Attachment B: DNR, USFWS, and MHT Project Review Responses Attachment C: Forest Stand Delineation Datasheets Appendix D – Site Photographs Appendix E – Easement Exhibit Appendix F – Existing Condition Hydrologic Computations Appendix G – Existing Condition Hydrologic Computations – UM-10 Appendix H – Geomorphic Mapping Appendix I – Geomorphic Data Appendix J – At a Station Computations Appendix K – BEHI/NBS Computations Appendix L – Hydraulic Analysis Appendix M – Function Based Assessment Attachment A: MBSS & EPA Habitat Assessment Data Sheets Appendix N – Design Development Plans Appendix O – WQv and Design Computations – UM-10 Appendix P – Facility Hydraulics – UM-10 Appendix Q – Pollutant Removal Efficiency Appendix R – Cost Estimate Appendix S – Stream Restoration & BMP Tracking Forms

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1. INTRODUCTION

Overview

The Anne Arundel County Department of Public Works (DPW) has contracted BayLand Consultants & Designers, Inc. (BayLand) to provide engineering analysis and design services for the Upper Mill Creek Stream Restoration Project (hereafter referred to as the Project). The Project is intended to provide stream stabilization in actively eroding channels, riparian wetland establishment, and reconnection with riparian wetlands wherever feasible to maximize water quality credit for Anne Arundel County’s municipal separate storm sewer systems (MS4) permit.

The Study Area is located in the Mill Creek sub-watershed within the greater Magothy River watershed. The Study Area was developed based on retrofit sites identified as potential sediment sources to the tidal waters of Mill Creek as part of a comprehensive assessment of the entire Mill Creek watershed. The findings were summarized in the Mill Creek Waterway Headwaters Restoration Retrofit Assessment (BayLand, 2008). The Study Area is generally located between College Parkway and Governor Ritchie Highway (Maryland Route 2), and includes the stream channels, adjacent floodplain and floodplain terrace areas (Figure 1).

The Study Area includes the Upper Mill Creek Main Stem that originates at a culvert under East Joyce Lane just east of Governor Ritchie Highway (Maryland Route 2) and proceeds downstream approximately 4,144 linear feet to a relatively stable reach located just west of Kings College Drive. It also includes an unnamed tributary (hereafter referred to as the East Tributary) that originates at a storm drain outfall (outfall T16O001) north of Sheridan Road and continues downstream approximately 3,185 linear feet to the confluence with the Upper Mill Creek Main Stem. An intermittent channel that originates at outfall S15O012, west of the Upper Mill Creek Main Stem, is also included in the Study Area. The channel flows through an on-line stormwater management (SWM) pond, Pond 824, to the confluence with the Upper Mill Creek Main Stem. Additional information regarding the Study Area and project reaches can be found in Section 3 and Figure 6. Overall, the Study Area is approximately 21.7 acres.

Preliminary data collection for the Project involved review of past watershed studies, land use, property information, utilities, topography, geology, and soils. A historical analysis of the watershed was also performed using historic aerial topographic maps, and hydrologic calculations were performed to describe the current discharge regime. A Natural Resources Inventory (NRI) was conducted in April and May of 2016. As part of the NRI assessment, a wetland delineation and forest stand delineation assessment were completed. All trees with a diameter at breast height (DBH) 30 inches or greater within the Project stream valley were identified and located, and rated for condition as “good,” “fair” or “poor.” A limited desktop environmental due diligence review was also completed in January 2016.

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Geomorphic assessments were conducted from February to April 2016. The assessments included representative longitudinal profile and cross section surveys, and substrate analyses for each reach. Bank erosion assessments and geomorphic mapping were also completed for each linear foot of stream. Measurements were evaluated to characterize current conditions and provide validation of the estimates of the extent, magnitude and rate of instability throughout the project reaches.

Results of all data analysis efforts are presented in this report and were used to develop design parameters and support the development of design alternatives for each reach. A Function-Based Framework for Stream Assessment and Restoration Projects (Harman et al., 2012) was utilized throughout the entire Project process to ensure that the most appropriate design approach would ultimately be selected.

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Study Area 2011 AA County Mill Creek Watershed Sources: Esri, HERE, DeLorme, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), swisstopo, MapmyIndia, © OpenStreetMap contributors, and the GIS User Community UPPER MILL CREEK STREAM Consultants & Designers, Inc. RESTORATION PROJECT FIGURE 1 - VICINITY MAP “Integrating Engineering and Environment”and Engineering “Integrating ANNE ARUNDEL COUNTY 1 in=2,000 feet 7455 New Ridge Road, Suite T Phone: (410) 694-9401 Hanover, Maryland 21076 Fax: (410) 694-9405 2,000 1,000 0 2,000 Feet Website: www.baylandinc.com Upper Mill Creek Stream Restoration Design Development Report

Background

The cumulative effects of development are pervasive within the Upper Mill Creek sub- watershed. Urban development coupled with a lack of sufficient SWM infrastructure and channel alteration has resulted in degraded habitat, channel incision, bank erosion and irregular planform geometry among other signs of instability. Therefore, Upper Mill Creek has been targeted for restoration to improve hydrologic, hydraulic, geomorphic, water quality and biological functionality.

The Project is also intended to support the requirements of the National Pollutant Discharge Elimination System (NPDES) MS4 permit issued to the County by the Maryland Department of the Environment (MDE) and to assist the County in meeting pollutant load reductions associated with the Chesapeake Bay Total Maximum Daily Load (TMDL).

Programmatic Goals

The programmatic goals for the Project are to:

• Provide stream valley restoration, including the establishment or reconnection with riparian wetlands and optimizing floodplain reconnection volume. • Provide design features that promote denitrification during baseflow. • Provide significant reduction in annual mass of sediment and attached nutrients originating from on-site channel degradation (i.e., “Prevented Sediment”) and upstream loss being delivered to downstream receiving waters. • Enhance stream and riparian ecological functions. • Provide an integrated stabilization approach to all storm drain outfalls. • Document water quality (and/or other) credit towards Anne Arundel County’s NPDES MS4 permit watershed restoration requirement and assist in meeting Anne Arundel County’s wasteload allocation towards the Chesapeake Bay TMDL.

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2. WATERSHED ASSESSMENT

Watershed

The Upper Mill Creek sub-watershed is approximately 0.8 square miles (539 acres) and is located within the Magothy River watershed (02-13-10-01) (Figure 2). The Magothy River watershed encompasses approximately 35.6 square miles and is a mix of urban residential, commercial and forested land uses (Anne Arundel County, 2017).

The Magothy River watershed was first identified on the 1996 303(d) List submitted to United States Environmental Protection Agency (EPA) by MDE as impaired by nutrients, sediments and fecal coliform (MDE, 1996). Biological impacts in non-tidal portions was added to the list in 2002 (MDE, 2002) and biological impacts in tidal portions was added to the list in 2004 (MDE, 2004). On the 2004 303(d) List, the fecal coliform impairment was clarified with the identification of four specific restricted shellfish harvesting areas within the basin. Listings of impaired by polychlorinated biphenyls (PCBs) in fish tissue was added in 2006 (MDE, 2006), and fecal coliform in the Deep Creek Tributary was added in 2012 (MDE, 2012).

As a result of the 303(d) listings, several TMDLs have been established and approved for the Magothy River watershed. On February 20, 2006, a fecal coliform TMDL was approved by the EPA (EPA, 2006) and on December 29, 2010, the Chesapeake Bay TMDL was approved by the EPA (EPA, 2010). Additionally, since the Magothy River watershed area is included in the Magothy River Mesohaline Chesapeake Bay tidal segment, it is part of an overall TMDL for polychlorinated biphenyls that was established and approved in March 2015 (EPA, 2015).

The Project is intended to address waste load allocations (WLAs) to meet TMDLs for the Chesapeake Bay as mandated by the EPA under section 402(p) of the Clean Water Act. The Chesapeake Bay TMDL sets watershed limits for nitrogen, phosphorus and sediment. The pollutant removal efficiencies for total nitrogen (TN), total phosphorus (TP) and total suspended sediment (TSS) associated with the Project will be based on the criteria in the guidance document Final Recommendations of the Expert Panel to Define Removal Rates for Individual Stream Restoration Projects (Schueler, T., Stack, B., 2014).

Physiography

The Project is located in the Atlantic Coastal Plain physiographic province within the Crownsville Upland District (511400) (Maryland Geological Survey, 2008). This landform is an undulating upland with an appearance similar to the Glen Burnie Rolling Upland District, but somewhat more dissected. Lithologies are mainly argillaceous, micaceous, glauconitic fine-grained sands and silts. Geologic structure is essentially flat-lying to gently southeast-dipping sedimentary beds. Drainage patterns are dendritic (Maryland Geological Survey, 2008).

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Upper Mill Creek Watershed

2016 Watersheds

Patapsco Tidal Bodkin Creek Magothy River

Severn River Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, South River USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community UPPER MILL CREEK STREAM RESTORATION PROJECT Consultants & Designers, Inc. FIGURE 2 - WATERSHED MAP “Integrating Engineering and Environment”and Engineering “Integrating ANNE ARUNDEL COUNTY 7455 New Ridge Road, Suite T Phone: (410) 694-9401 1 inch = 10,000 feet Hanover, Maryland 21076 Fax: (410) 694-9405 10,000 5,000 0 10,000 Feet Website: www.baylandinc.com Upper Mill Creek Stream Restoration Design Development Report

Soils

Soils within the Study Area were determined using the United States Department of Agriculture Natural Resources Conservation Service (USDA-NRCS) Web Soil Survey. The soils are listed in Table 1. A detailed soils map is included in Appendix B, Figure 6.

Table 1 – USDA-NRCS Soils within Study Area Map Acres in Percent Hydrologic Unit Map Unit Name Study of Study Soil Type Symbol Area Area Widewater and Issue soils, 0 to 2 percent slopes, WBA C/D 13.9 69.0% frequently flooded Collington, Wist, and Westphalia soils, 15 to 25 CSE A 2.4 12.1% percent slopes Collington and Annapolis soils, 10 to 15 percent CRD B 1.6 7.8% slopes CoC Collington-Wist complex, 5 to 10 percent slopes B 1.2 5.8% SME Sassafras and Croom soils, 15 to 25 percent slopes C 0.8 4.1% AsC Annapolis fine sandy loam, 5 to 10 percent slopes C 0.2 0.8% CoB Collington-Wist complex, 2 to 5 percent slopes B 0.1 0.4%

USDA-NRCS Official Soils Series Descriptions (OSDs), available online, were utilized to obtain additional information regarding each soil series. A summary of pertinent information associated with each soil series is provided in Table 2, including: depth class, agricultural drainage class and parent material.

Table 2 – USDA-NRCS Official Soil Series Descriptions Soil Series Agricultural Description Depth Parent Material Drainage Class Name Annapolis Very Deep Well Drained Loamy Glauconitic Fluviomarine Deposits Galuconite Bearing Eolian and/or Fluviomarine Collington Very Deep Well Drained Deposits Croom Very Deep Well Drained Gravelly Fluvial Deposits Somewhat Poorly Issue Very Deep Loamy and Sandy Alluvium Drained Sassafras Very Deep Well Drained Loamy Fluviomarine Sediments Westphalia Very Deep Well Drained Loamy Fluviomarine Deposits Widewater Very Deep Poorly Drained Loamy Alluvium Wist Very Deep Well Drained Glauconite Bearing Fluviomarine Deposits

Climate

Anne Arundel County’s climate is largely influenced by its location in the warm temperate zone of the Eastern United States. The County typically experiences generally mild winters and hot, humid summers. This region is dominated for most of

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the year by a broad band of eastward-moving air that encircles the globe throughout the latitudes 30 to 60 degrees north. The general flow is characterized by waves of air currents responsible for the movement of rain-bearing atmospheric depressions. In summer, weather is dominated by air masses that originate over the Gulf of Mexico, drifting in from a southerly direction. These warm, moist air masses bring the hot, humid, hazy conditions with afternoon thunderstorms, typical of summer. These thunderstorms produce intense, short duration rain events that are highly localized and often widely scattered. Occasionally during summer, easterly winds bring cooler air from the Atlantic Ocean. Although winters are dominated by cold, dry air from Central Canada, several depressions moving northeast along the coast pass over the region in any winter. Moisture from such depressions is commonly widespread, prolonged and fairly gentle, giving soaking rain that fills reservoirs and recharges groundwater supplies. Drought may occur in any month or any season, but serious drought is most likely to occur in summer.

As shown in Table 3, the mean annual temperature is 55.0 degrees F with an average summer temperature of 75.4 degrees F and an average winter temperature of 35.7 degrees F. Mean monthly high and low temperatures range from 24.0 degrees F to 41.2 degrees F for January and 88.2 degrees F to 67.1 degrees F in July (National Weather Service Forecast Office, 2016).

Precipitation is uniformly distributed during the year. In winter the precipitation is generally in the form of light snows and showers and in other seasons it comes as light prolonged rains or quick hard showers. Most of the rainfall during the growing season comes from summer thunderstorms but may vary widely from place to place and from season to season. Winter rainfall results mostly from low pressure storms moving through the area and is less variable than summer rainfall. Mean annual precipitation is 41.9 inches, with mean monthly precipitation varying from a low of 2.9 inches in February to a high of 4.1 inches in July. Some snow falls every winter, with average amounts ranging from 0.1 to 8.0 inches. Mean annual snowfall is 20.1 inches (National Weather Service Forecast Office, 2016).

Table 3 – Average Daily and Annual Values for Temperature and Precipitation at the Baltimore-Washington International Airport in Hanover, Maryland* Average Daily and Annual Values Parameter Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Average Temperature 32.9 35.8 43.6 53.7 62.9 72.4 77.0 75.1 67.8 56.1 46.5 36.7 55.0 (F°) Precipitation 3.1 2.9 3.9 3.2 4.0 3.5 4.1 3.6 4.0 3.3 3.3 3.4 41.9 (Inches) Snowfall 6.8 8.0 1.9 0.1 0 0 0 0 0 0 0.4 3.0 20.1 (Inches) *Source: National Weather Service Forecast Office, 2016

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Land Use and Land Cover

Existing & Ultimate Land Use

The total Project watershed is approximately 0.8 square miles (538.7 acres). It is moderately urbanized, with 22.5 percent impervious area. According to Anne Arundel County Existing Land Use data, the majority of development in the watershed is low density residential (AACO, 2014). Ultimate land use was derived from Anne Arundel County Zoning data (AACO, 2016). The Existing Land Use and Ultimate Land Use data is depicted in Table 4 and Figures 3 and 4.

Table 4 – Land Use Parameter Acres Percentage of Drainage Area Drainage Area 538.7 N/A Impervious Area 121.4 22.5 Existing Land Use Woods 141.5 26.2 Residential-1/4 acre 108.6 20.2 Residential-1 acre 76.0 14.1 Residential-1/2 acre 80.8 15.0 Residential-2 acre 42.3 7.8 Urban District-Commercial/ Business 26.7 5.0 Transportation 23.9 4.4 Open Space 28.7 5.3 Residential-1/8 acre 4.9 0.9 Pasture/Hay 4.0 0.7 Urban District-Industrial 1.2 0.2 Ultimate Land Use R5 Residential 369.5 68.6 R1 Residential 140.9 26.2 Urban District-Commercial/Business 14.2 2.6 LDR-Low Density Residential 14.0 2.6

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Anne Arundel

Upper Mill Creek ³ Anne Arundel Watershed

Upper Mill Creek Drainage Area Study Area 2011 AA County Streams Modified by Bayland 2014 AA County Existing Land Use Transportation Commercial Industrial Residential 2-acre Residential 1-acre Residential 1/2-acre Residential 1/4-acre Residential 1/8-acre Pasture/Hay Woods-Mixed Open Space

UPPER MILL CREEK STREAM Consultants & Designers, Inc. FIGURE 3 - EXISTING LAND USE RESTORATION PROJECT “Integrating Engineering and Environment”and Engineering “Integrating ANNE ARUNDEL COUNTY 7455 New Ridge Road, Suite T Phone: (410) 694-9401 Hanover, Maryland 21076 Fax: (410) 694-9405 1 inch = 1,000 feet 1,000 500 0 1,000 Feet Website: www.baylandinc.com Anne Arundel

Upper Mill Creek Anne Arundel ³ Watershed

Upper Mill Creek Drainage Area

Study Area 2011 Anne Arundel County Streams Modified by Bayland AA County Zoning 2016 C2 Commercial - Office

C3 Commercial - General R1 (Residential-1 ac) R5 (Residential-1/4 ac) LDR (Low Density Residential)

UPPER MILL CREEK STREAM Consultants & Designers, Inc. FIGURE 4 - ULTIMATE LAND USE RESTORATION PROJECT “Integrating Engineering and Environment”and Engineering “Integrating ANNE ARUNDEL COUNTY 7455 New Ridge Road, Suite T Phone: (410) 694-9401 Hanover, Maryland 21076 Fax: (410) 694-9405 1 inch = 1,000 feet 1,000 500 0 1,000 Feet Website: www.baylandinc.com Upper Mill Creek Stream Restoration Design Development Report

Historical Land Use

Land use changes in a watershed can have large impacts on watershed hydrology and channel morphology in stream networks (Bierman, 2005; Miller et al., 1993; Costa, 1975; Knox, 1977; Wolman and Schick, 1967). In order to develop a broader understanding of former land use influences on the past and ongoing evolution of the Upper Mill Creek channel morphology, a brief investigation of land use history in the vicinity of the Project was conducted.

Historic information indicates that the area was first settled in 1649 and throughout the 18th and the 19th century, the surrounding area remained largely rural with a few tobacco and diversified crop plantations. The implementation of utility and road infrastructure at the end of the 19th century and the beginning of the 20th century has had a large impact on the area. At the end of the 19th century, the Baltimore and Annapolis Short Line Railroad was constructed and subsequently, increased accessibility to the area led to rapid development. Development accelerated in the area in the late 1930s when the State completed Governor Ritchie Highway (Maryland Route 2) connecting Baltimore and Annapolis.

Various historic topographic maps and aerial photographs corroborate the rapid population growth. A Maryland Forestry Service map from 1913 indicates that Upper Mill Creek had a predominately forested riparian buffer, inhabited by a mix of 2nd class Culled Hardwoods and Scrub Pine Saplings (Baltimore Maryland Geological Survey, 1913). Historic aerial photography from 1938 depicts the area as primarily forested with several small open areas. Construction of Governor Ritchie Highway (Maryland Route 2) is also depicted on the 1938 aerial photograph. Historic aerial photographs for the years of 1957 and 1969 show an increase in residential development from the late 1930s and Arnold Elementary School was constructed in the mid-1960s (MD Department of Assessments & Taxation, 2016). The aerial photographs are provided in Appendix A.

Topographic maps obtained from the United States Geological Survey (USGS) online map locator, show a large increase in development around the area from 1944 to 1956, including the construction of roads for commercial complexes and residential developments. Aerial photographs from 1969 to 1981 depict ongoing residential development and since 1981 there has been a substantial increase in residential development, predominately northeast of Upper Mill Creek (Environmental Data Resources, Inc., 2016).

Land Use Influences on Channel Processes

Agricultural expansion in Anne Arundel County during the 18th century led to deforestation. The absence of soil conservation and management practices led to rapid degradation of agricultural fields due to intensive tobacco farming (Anne Arundel County, 2016). This resulted in significant sedimentation of local stream channels and

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floodplains. The later shift to less intensive ‘truck farming’ coupled with the eventual implementation of soil conservation techniques led to reduced agricultural deposition.

When the core of the U.S. agricultural market shifted to the mid-west after 1930 many eastern agricultural areas were reforested and sediment and water runoff from the remaining crop fields was greatly reduced by the implementation of soil conservation techniques. However, aerial photographs from 1957 depict a few agricultural fields adjacent to Upper Mill Creek still present.

Large-scale development first appears in the historic aerial photographs in 1969 with the construction of commercial and residential development throughout the watershed. The Anne Arundel Community College opened in 1961 followed by the opening of the Arnold Elementary school in 1967. The construction of these building also influenced the development of more residential areas which was first seen in the 1981 aerial mapping of the watershed.

The majority of the development in the watershed occurred prior to the implementation of Maryland’s Stormwater Management Regulations in 1983. Increasing impervious surface in a watershed has been shown to reduce infiltration and evapotranspiration, and increase runoff into stream networks (MDE, 2000). Upper Mill Creek has a flashy flow regime due to development occurring prior to modern stormwater regulations.

Various SWM ponds discharge into the Study Area including Pond #824. Pond #824 was constructed as an on-line detention facility designed to provide quantity control. However, the facility was installed prior to 2002 SWM requirements and therefore does not meet current requirements for water quality treatment (WQv) or channel protection volume (Cpv). Additional information regarding Pond #824 is included in discussion of the intermittent reach that flows through the pond, UM-10.

Influence of Beaver Activity

Beaver dams are capable of impounding water and retaining sediment to substantially alter the physical, chemical and biological characteristics of the surrounding river ecosystem. The potential benefits include higher water tables, reconnected and expanded floodplains, more hyporheic exchange, expanded wetlands, improved water quality and greater habitat complexity (Pollock, et al., 2015). However, beaver impoundments often convert to ‘beaver meadows’ over time as the ponds fill in with sediment and may fail gradually from decay after abandonment, or catastrophically from blowouts during flooding (Butler and Malanson, 2005). Consequently, beaver dams have the potential to be a source of fine sediment for downstream reaches.

There is no evidence of past beaver activity on aerial photography and no narrative accounts of beaver activity were found for the Study Area. Therefore, the potential for beaver to influence channel geomorphology will be considered in the restoration design.

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Presence of Mills and Dams

Recent scientific work by Walter and Merritts (2008) has shown that many floodplains along Mid-Atlantic streams flow through fill terraces that can be attributed to sediment accumulation. While these fill terraces are often located behind colonial-era mill dams, they may also be the result sediment deposition caused by other factors (Donovan et al, 2016). Shifts in upstream land use generating excess sediment and runoff from forest clearing and agricultural activity on upland slopes were transported through stream networks during storm events. Sediment loads were then deposited on the valley bottom as flood waters retreated or, in the case of a mill dam, were deposited behind the dam. When the mill dams are eventually abandoned, breached, or removed, the stream channel incises to its former base level and remobilizes the pond sediment (Walter and Merritts, 2008). In the absence of a mill dam, increased intensity of stormflows that have accompanied modern urbanization have the potential to cut through this sediment. In either case, the result is a stream channel with near-vertical banks and a high sediment load from excessive bank erosion (Walter and Merritts, 2008).

A review of the 1860 Martinet Map of Anne Arundel County and aerial photography dating back to 1938 revealed no evidence of the presence of mills or mill dams adjacent to or up-gradient of the Study Area. Copies of historic aerial photographs are enclosed in Appendix A. No evidence of a buried organic layer was observed during field studies. However, much of the valley upland valley bottom does contain 3 to 4 feet of bright alluvial soils.

Jurisdictional Wetlands and Streams

A wetland delineation was conducted in March and April 2016, pursuant to the 1987 Corp of Engineers Wetland Delineation Manual (Environmental Laboratory, 1987) and the Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Atlantic and Gulf Coastal Plain Region, Version 2.0 (USACE, 2010).

All wetlands delineated within the Study Area are palustrine and with the exception of a few emergent areas, all wetlands are forested wetlands. On-site wetlands are primarily seep areas that emerge at the base of the surrounding valley side-slopes. Vertical channel incision and aggradation has largely isolated wetlands from the channel except for narrow overflow depressions. The total wetland area delineated for the Study Area is summarized in Table 5 and a complete discussion regarding wetland conditions is included in the Upper Mill Creek Wetland Delineation Report (Appendix B).

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Table 5 – Upper Mill Creek Wetland Delineation Summary Wetland Area (ft2) 313,950 Wetland Area (AC) 7.21 Perennial Stream Length (LF) 7,656 Perennial Stream Area (ft2) 38,510 Intermittent Stream Length (LF) 1,565 Intermittent Stream Area (ft2) 6,408

Jurisdictional stream limits generally include channels that contain intermittent to perennial flow. From a regulatory perspective, the U.S. Army Corps of Engineers (USACE) regulates the lateral extent of stream channels to the ‘Ordinary High Water Mark’ (33 CFR 328.3(e)). In this region, the ‘Ordinary High Water Mark’ typically approximates bankfull conditions. Jurisdictional stream limits for the Project are based on a combination detailed geomorphic assessment data as discussed below, topographic survey information and assessment completed during wetland investigations.

Historic Wetlands

Estimating the historic extent of wetlands has value in determining restoration potential, but wetland limits are not static. Natural factors such as major storm events can influence wetland dynamics. However, a major driver of wetland loss is direct anthropogenic wetland impact as well as anthropogenic modifications in the upstream watershed that indirectly alter wetlands through sedimentation within stream valleys. Significant valley alteration from large scale deforestation that occurred in the Eastern United States during the 18th and 19th Centuries has been well-documented (Elliott et al. 2013, Voli et al. 2009). These influences have made it difficult to determine the historic extent of wetlands. Therefore, two methods were utilized to estimate the historic limits of wetlands within the Study Area and quantify wetland restoration potential. The first method involves utilizing hydric soils mapping in combination with other map sources and field data to determine the extent of historic wetlands. The second method is derived from the theory that the entire stream valley bottom was once wetlands and involves utilizing hydraulic modeling to predict the impacts of the proposed restoration on the floodplain.

Historic Wetland Analysis – Method 1

The NRCS-USDA Web Soil Survey (2016) is a valuable tool for identifying soil properties and broadly defining suitability for land use planning. Hydric soil limits found in soil survey mapping can be utilized as a proxy for historic wetland limits (Tiner & Bergquist, 2003; Tiner, 2005). Employed in combination with other data sources including topographic information, aerial photography and field investigations, hydric soils mapping can be refined to identify opportunities for wetland restoration.

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Figures 5a and 5b show delineated wetland limits overlaid onto soils mapping and Anne Arundel County Geographic Information System (GIS) topography (AACO, 2011). Soils are classified according to NRCS-USDA estimated hydric ranges. Analysis of this mapping in combination with field investigation yielded several areas that offer prospective opportunities for wetland restoration. Of these areas, two categories were defined based on field conditions.

The first category includes areas that would benefit from increased hydrology via an increase in the stream bed elevation. Increasing stream bed elevation would raise nearby groundwater levels and reconnect the existing channel with its floodplain. The dark green hatch areas on Figure 5a and 5b show approximately 1.6 acres of floodplain/ terrace that is mapped as hydric and are primarily located between existing wetlands and stream channels. The areas contain marginal redoximorphic features that do not meet hydric criteria. Some areas also contain mixed soil matrices near the surface with marginal redoximorphic features at greater depths. Typical soils within these areas are dark brown to olive dark brown with strong brown redoximorphic concentrations at about 4 to14 inches. The stream channel appears to have a localized effect on groundwater as evidenced by the well-defined separation between wetlands and stream channel. Surface soils in these areas also typically exhibit bright coloration in the upper 12 inches of the profile. While this is likely the result of historic fluvial deposition, these areas lack near-surface evidence of historic wetland conditions. Additional floodplain wetland areas are expected to develop over time; however, it will be dependent upon several factors, including soil permeability and post-restoration frequency of out of bank flows and bed elevation.

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PgB

CoC

CoB SME UxD DxD ³ CoC WBA DxC DxB

CRD

DxC

CoB SnB SME

CRD CSE

CoC

CoC CSE Upper Mill Creek Main Stem

CpD

WBA CoB CSE

CRD CRD

CSE

East Tributary

CoC Matchline

See Figure 5B CoC MxB CoB

CoC

AsC

CRD

CRD LegendCoB Study Area 2011 AA County 2' Topography Delineated Wetland Boundaries Soils Delineated Perennial Streams

Delineated Intermittent Streams USDA Hydric Soils CoC WetlandCSE Restoration/Creation 1-32% Increase Hydrology 33-65% Fill Removal CSE 66-99% Source: Anne Arundel County Soils, Anne WetlandCRD Creation CRD Arundel County 2014 Aerial Imagery CSE Figure 5a 0 125 250 500 Feet Upper Mill Creek 1 " = 250 ' Concept Wetland Restoration Opportunities PgB AsE ³ UxD AuD SME SME DwD SnD

SnB DxD

CSE

CRD

DwB CoC CpD AuB

CSE

CSE

East Tributary

SaB

CRD

Matchline

See Figure 5a UxD

CSE WBA

CoB CoC

CoC MxB CRD

CSE

CoC

CRD

Legend Study Area 2011 AA County 2' Topography Delineated Wetland Boundaries Soils Delineated Perennial Streams CoC

Delineated Intermittent Streams CRD USDA Hydric Soils CSE Wetland Restoration/Creation 1-32% CoB Increase Hydrology 33-65% Fill Removal CoC 66-99% Source: Anne Arundel County Soils, Anne Wetland Creation Arundel County 2014 Aerial Imagery CRD Figure 5b 0 125 250 500 Feet Upper Mill Creek 1 " = 250 ' Concept Wetland Restoration Opportunities Upper Mill Creek Stream Restoration Design Development Report

The other category consists of two small areas that may have been directly filled during a previous anthropogenic activity. These areas are represented by a brown hatch area that totals 0.1 acre. Soils within these areas have bright coloration near the surface with redoximorphic features present at depths greater than 10 inches with strong hydric soils on both sides of the fill areas.

The total approximate wetland restoration area based on the first method is 1.7 acres. Three additional areas were also identified that could be a potential wetland creation area (purple hatch areas on Figure 5a and 5b). These areas were not mapped as hydric but have similar soil characteristics and landscape position as the other potential wetland restoration areas. These areas are directly adjacent to existing wetlands that are also outside of the hydric soils boundary. With the addition of hydrology resulting from channel elevation and floodplain reconnection, these areas offer and additional 0.1 acre of wetland creation potential.

Historic Wetland Analysis – Method 2

The second method was developed from studies that indicate that pre-colonial stream valleys in the mid-Atlantic region consisted of broad wetland complexes with a shallow anastomosed stream network (Walter and Merritts 2008, Voli et al. 2009). Under this scenario, the entire valley bottom may have been a wetland. Since the proposed design involves raising the stream bed and consequently, groundwater levels in the immediate vicinity of the channel, it is anticipated that additional wetland area may be created through near-surface saturation of soils adjacent to the restored channel (USDA-NRCS, 2008). USACE Hydrologic Engineering Center’s River Analysis System (HEC-RAS) 2- dimensional modeling software was employed to establish base flow water surface elevations along the restored channels. USACE standards for wetland hydrology determination minimally require soil saturation within 12 inches of the soil surface for 14 consecutive days (USACE, 2005). The post-restoration valley area vertically within the 12 inches of the base flow water surface was measured excluding stream channels and existing wetland area. Based on this methodology, wetland restoration area is estimated at 6.5 acres. Additional information regarding the 2-dimensional modeling is included in Section 10.3.

Plant Community Descriptions

A Forest Stand Delineation (FSD) was completed to characterize all vegetative communities within the Study Area in accordance with methodology from the State Forest Conservation Technical Manual, Third Edition, 1997. Five communities were identified, three of which are forested. The vegetative areas are summarized below in Table 6 and the complete FSD is included in Appendix C.

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Upper Mill Creek Stream Restoration Design Development Report

Table 6 – Vegetative Community Summary Mixed Mesic Flatwoods (F1) 14.97 AC Mixed Mesic Flatwoods with Invasives (F2) 3.30 AC Mesic Upland/Heath Forest (F3) 1.26 AC Field 0.66 AC Phragmites 0.04 AC

Rare, Threatened and Endangered Species

The protection of Rare, Threatened and Endangered Species (RTEs) in Maryland is managed by the U.S. Fish and Wildlife Service (USFWS) and Maryland Department of Natural Resources (DNR). The DNR list of protected species is generally more comprehensive and includes both state and federally-protected species. The current DNR list of RTEs for Anne Arundel County (DNR Plants and Wildlife website, 2016) identifies 38 state listed and no federally listed animal species, as well as 99 state listed and 3 federally listed plant species. Inquiries were submitted to both USFWS and DNR for a review of RTE records for the Study Area.

USFWS maintains the Information for Planning and Conservation (IPAC) website for federal RTE queries. An IPAC inquiry was submitted in February 2016 and did not return any known RTE records or critical habitats expected to be impacted by the Project. A copy of the review response letter dated February 18, 2016 is enclosed in Appendix B.

Additionally, a written inquiry was submitted to the DNR Wildlife and Heritage Service requesting information on records of the RTE’s. However, similar to the USFWS inquiry, DNR has no records of RTEs in the vicinity of the Study Area. A copy of the DNR review response, dated February 4, 2016, is enclosed in Appendix B.

Cultural Resources

The Maryland Historical Trust (MHT) serves as the state level agency responsible for the preservation of historic and cultural resources. Federal and state permit reviews require consultation with MHT to ensure that proposed projects will have no adverse effect on historic sites and/or cultural resources. Anticipating the need for federal and state authorizations to complete the Project, a project review request was submitted to MHT in January 2016. In preparation of the inquiry form, a review of the Maryland Inventory of Historic Properties, National Register of Historic Properties and MHT Preservation Easements GIS data layers was completed. Data layers are maintained by the Maryland Environmental Resource and Land Information Network (MD MERLIN website, 2016). This preliminary review did not identify any specific conflicts with the Project. However, three Maryland historic sites were identified within the vicinity of the Study Area and were provided to MHT to aid the review. The MHT review response received in February 2016 determined that the Project will have no adverse effect on historic properties or cultural resources.

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Upper Mill Creek Stream Restoration Design Development Report

3. REACH DESCRIPTION

On January 7, 2016, an initial site walk and visual assessment was conducted in order to identify specific areas of concern and determine project reaches thought to be representative of the entire Project. It was established during the site walk that there are no reaches within the vicinity of the Project that are stable or have desirable characteristics that could be utilized as a reference reach during design. The individual project reach breaks were based primarily on Rosgen Stream Classification, although significant changes in hydrology and riparian vegetation were also considered. Nine distinctive perennial project reaches were identified for assessment and design efforts (UM-1 to UM-9). The East Tributary was divided into reaches UM 1 to UM 3 and the Upper Mill Creek Main Stem was divided into reaches UM-4 to UM-9. Additionally, two intermittent reaches were identified as in need of stabilization (UM-10 and UM-11). The various project reaches are shown in Figure 6. Brief descriptions with photographs of each project reach are provided below and additional photographs are provided in Appendix D.

Upper Mill Creek Upstream Conditions

As part of the visual assessment, a desktop and field investigation into conditions upstream of the project reaches was conducted.

The Upper Mill Creek Main Stem originates south of East Joyce Lane at an existing outfall along Governor Ritchie Highway (Maryland Route 2) that consists of a 36 inch corrugated metal pipe (CMP) with a concrete headwall (Figure 6). Approximately 285 linear feet downstream, an additional outfall, consisting of an 18 inch corrugated metal pipe (CMP), discharges into the channel on the left. The outfall locations are depicted on Figure 6.

Both outfalls are owned by the Maryland State Highway Administration (MD SHA) and are at risk of failure due to undercutting. Uncontrolled flow from the outfalls has resulted in an incised and unstable channel downstream with rates of high bank erosion. The banks are near-vertical and raw, ranging from approximately 4 to 5 feet high. Approximately 550 linear feet downstream of the 18 inch corrugated metal pipe (CMP) outfall, the channel regains partial floodplain connectivity and appears more stable as a result. Further downstream, at the crossing under East Joyce Lane, the channel has good floodplain connectivity. Evidence of sediment deposition in the channel and across the floodplain suggests that the culvert under East Joyce Lane is providing grade control and a backwater condition may exist, causing aggradation in this area. Therefore, since upstream sediment is being deposited upstream of East Joyce Lane, the eroding reaches do not significantly contribute sediment to the project reaches.

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%% % %% % % % %% % % % %%% % %% % Upper Mill Creek Design Development Report

It should be noted that the unstable outfalls and associated channels are scheduled for future repair/stabilization by others. Design plans for proposed development in the area (Arnold Overlook Final Plans, dated November 2015) indicate that a pipe will be installed to connect the 36 inch and 18 inch corrugated metal pipes (CMPs,) and the 18 inch corrugated metal pipe (CMP) outfall will be stabilized. This will mitigate erosive discharge from the outfalls and significantly reduce channel instabilities downstream.

Upper Mill Creek Project Reaches

Upper Mill Creek Reach 1 (UM-1)

UM-1 is an incised, single-thread channel (Rosgen Stream Classification G4c, for more information see Section 9.5) that originates at the upstream end of the East Tributary at Outfall T16O001 and extends downstream approximately 1,640 linear feet to the confluence with a tributary on the east (Figure 6). The upstream end of UM-1 is characterized by an intermittent channel that has bank erosion and numerous mid- channel gravel bars. It proceeds downstream for approximately 210 linear feet where it transitions into a perennial channel characterized by excessive bank erosion, large debris jams and multiple head cuts (Photos 1 to 3). The reach receives additional drainage an outfall on the east (Outfall T16O030), as well as a recently constructed regenerative stormwater conveyance system from the Hawthorne’s Grant at Broadneck Development on the west. Also, as part of the ongoing residential development, two sewer line crossings were recently installed at the upstream end of the reach.

Bank heights along UM-1 vary greatly, ranging anywhere from 4 to15 feet high. The higher banks are susceptible to erosion and rotational failure, and the potential for continued bank erosion, loss of trees and channel migration is high. The banks are dominated by a silty loam and compared to the rest of the Upper Mill Creek stream network, the bed material is relatively course.

Photo 1 – Reach representative photo Photo 2 – Head cut on left bank

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Photo 3 – Debris jams and downed tree

Upper Mill Creek Reach 2 (UM-2)

UM-2 is an incised, perennial, single-thread channel (Rosgen Stream Classification F5, for more information see Section 9.5) that originates at the downstream end of UM-1 and extends downstream for 830 linear feet, just upstream of the confluence with the Outfall Channel T15O019 / Pond 839 (Photo 4). UM-2 is significantly wider than UM-1, likely a result of increased drainage from an outfall channel at its upstream end (Photo 5). UM-2 is characterized by excessive bank erosion, debris jams and head cuts (Photo 6). The bed material is primarily composed of fine substrate. Bank heights consistently range from 3.5 to 7 feet high and are composed of clay, silt and sand.

Photo 4 – Outfall channel from T15O019/Pond #839 Photo 5 – Reach representative photo

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Photo 6 – Head cut on right bank

Upper Mill Creek Reach 3 (UM-3)

UM-3 is an incised, perennial, single-thread channel (Rosgen Stream Classification G5c, for more information see Section 9.5) that originates at the downstream end of UM-2 and extends 500 linear feet to the confluence with the Upper Mill Creek Main Stem (Photo 7). It is characterized by excessive bank erosion, debris jams and downed trees (Photo 8). The bed material is primarily composed of fine substrate. Bank heights consistently range from 4 to 6 feet high and are composed of clay, silt and sand. The reach also has irregular meander geometry with multiple tight and tortuous meander bends (Photo 9).

Photo 7 – End of reach at confluence with UM-5 Photo 8 – Reach representative photo

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Photo 9 – Tortuous meander bend

Upper Mill Creek Reach 4 (UM-4)

UM-4 is an incised, perennial, single-thread channel (Rosgen Stream Classification F5, for more information see Section 9.5) that originates at the downstream end of UM-3 and extends downstream for 460 linear feet. It is characterized by debris jams, downed trees and a high sediment supply (Photos 10 and 11). Approximately 85 linear feet downstream there is a tortuous meander bend with exposed soil strata (Photo 12). There is a large head cut that has developed from overflow from an outfall off of Kings College Drive on the right bank (Photo 13). Bank heights along the reach range from 3 to 5 feet.

Photo 10 – Reach representative photo Photo 11 – Large debris Jam

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Photo 12 – Tortuous meander bend Photo 13 – Head cut on right bank

Upper Mill Creek Reach 5 (UM-5)

Upper Mill Creek Reach 5 (UM-5) is located at the downstream end of the Study Area. It is a moderately incised, perennial single-thread channel (Rosgen Stream Classification G5c, for more information see Section 9.5) that originates downstream of UM-4 and extends downstream for 535 linear feet (Photo 14). It is characterized by debris jams and irregular lateral bars composed primarily of fine depositional materials (Photo 15). Bank heights range from 3.5 to 5 feet. Approximately 260 linear feet downstream, drainage from an outfall off Kings College Drive Place discharges into the stream on the right (Photo 16).

Photo 14 – Reach representative photo Photo 15 – Lateral bar

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Photo 16 – Looking upstream at outfall channel from T15O006 off of Kings College Drive

Upper Mill Creek Reach 6 (UM-6)

UM-6 originates immediately downstream of East Joyce Lane and continues downstream for approximately 440 linear feet. It is an incised, perennial, single-thread channel (Rosgen Stream Classification G4c, for more information see Section 9.5) characterized by excessive bank erosion, despite thick riparian vegetation along the left and right banks (Photo 17). Downstream, two intermittent channels enter the reach from the west (Photo 18). Bank heights along the reach vary greatly, ranging anywhere from 2 to 10 feet. The banks are dominated by silt and compared to the rest of the Upper Mill Creek stream network, the bed material is relatively course.

Photo 17 – Reach representative photo Photo 18 – Confluence with tributary

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Upper Mill Creek Reach 7 (UM-7)

UM-7 is an incised, perennial, single-thread channel (Rosgen Stream Classification G5c, for more information see Section 9.5) that originates downstream of UM-6, approximately 440 linear feet downstream of East Joyce Lane (Photo 19). It extends downstream for 1,160 linear feet to the confluence with Outfall Channel S15O012 (Photo 20). Similar to UM-6, UM-7 is characterized by excessive bank erosion. UM-7 lacks bed form diversity and there are multiple irregular lateral bars along the left and right banks (Photo 21). At the end of the reach the tributary from Outfall S15O012 enters UM-7 from the left bank (Photo 22). Bank heights along UM-7 range from 4.5 to 7.5 feet.

Photo 19 – Reach representative photo Photo 20 – Confluence with outfall channel S15O012

Photo 21 – Lateral bars Photo 22 – Confluence with tributary

Upper Mill Creek Reach 8 (UM-8)

UM-8 is an incised, perennial, single-thread channel (Rosgen Stream Classification G5c, for more information see Section 9.5) that originates downstream of UM-7 at the confluence with an outfall channel and continues downstream for 690 linear feet (Photo

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23). Drainage from Outfall T15O017 enters UM-8 from the west approximately 560 feet downstream (Photo 24). The overall condition of the reach is characterized by bank erosion and multiple debris jams. Bank heights along the reach range from 4 to 20 feet high.

Photo 23 – Reach representative photo Photo 24 – T15O017 outfall channel

Upper Mill Creek Reach 9 (UM-9)

UM-9 is an incised, perennial, single-thread channel (Rosgen Stream Classification G5c, for more information see Section 9.5) that originates at the downstream end of UM-8 (Photo 25) and extends downstream for 615 linear feet to the confluence with UM-3. Banks are primarily composed of silt, clay and sand, and range from 3.5 to 5 feet high. The overall condition of the reach is characterized by excessive bank erosion and multiple debris jams (Photo 26). Approximately 310 feet downstream, outfall T15O018 discharges into the stream on the left (Photo 27). The reach does not have well-defined bed forms such as pools/riffles and the bed material is predominately composed of fine depositional substrate.

Photo 25 – Facing downstream at start of reach, Photo 26 – Debris jam representative photo

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Photo 27 – Outfall T15O018 channel

Upper Mill Creek Reach 10 (UM-10)

UM-10 is an intermittent channel that originates at Outfall S15O012 and continues downstream approximately 795 linear feet until the confluence with the Upper Mill Creek Main Stem. Outfall S15O012 consists of a 30-inch corrugated metal pipe (CMP) with a metal end section that conveys flow from a closed storm drain system under Finneans Run Road (Photo 28).

UM-10 is confined by a narrow, steep valley for the first 200 linear feet (Photo 29), after which the valley begins to widen. At the confluence with the Upper Mill Creek Main Stem, there is a 4-foot high knickpoint which, if left in place, will eventually propagate upstream (Photo 30). Approximately 188 linear feet downstream, the reach receives drainage from an outfall channel to the southwest (outfall S15O014).

Although not originally identified by AA County as an outfall in need of retrofit, outfall S15O014 was identified during field assessment. It is located off of the Elmridge Road cul-de-sac and discharges into an outfall channel which eventually flows into the outfall channel associated with S15O012. The S15O014 outfall channel has a very steep gradient (approximately 19 percent) and there is a large vertical drop at the tie in with the existing channel. Currently the outfall is not visible and appears to be buried by debris. However, according to Anne Arundel County GIS data, it consists of an 18-inch BCCMP storm drain.

There is also an on-line SWM pond (Pond 824) (Photo 32) located within UM-10, approximately 388 linear feet downstream of Outfall S15O012. Examination of the construction drawings, Morgans Purchase Subdivision #85-258, indicate that Pond 824 was originally designed as a detention facility in 1986. The riser structure consists of a corroded 54-inch CMP with a 78-inch anti-vortex device and a 12-inch low flow orifice (Photos 32 & 33). The barrel pipe consists of a 36-inch BCCMP that outfalls to an existing intermittent channel (Photo 34). The channel flows for approximately 100-feet before going subterranean through a forested wetland area. It resurfaces downstream and eventually discharges into the Upper Mill Creek Main Stem. It appears that the 12-

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inch low flow orifice may be clogged since the water surface elevation during a recent field investigation was well above the low flow opening. There is also a chain link fence surrounding the facility that appears to be failing in multiple places (Photo 35).

Photo 28 – Outfall S15O012 Photo 29 – Narrow valley associated with channel downstream of S15O012.

Photo 30 – Knick point at confluence of the channel Photo 31 – Pond 824 downstream of S15O012 and Upper Mill Creek Main Stem.

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Photo 32 – Riser at Pond 824 Photo 33 – Riser at Pond 824

Photo 34 – Outfall from Pond 824 Photo 35 – Failing chain link fence at Pond 824

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Upper Mill Creek Reach 11 (UM-11)

UM-11 discharges into the Upper Mill Creek Main Stem from the west, approximately 130 linear feet downstream of East Joyce Lane. It is an incised, intermittent channel and is approximately 240 feet long with bank heights ranging from 3 to 4 feet (Photo 36).

Photo 36 – UM-11

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4. CONSTRAINTS ANALYSIS

Environmental Screening Results

A limited environmental due diligence review was completed for the Study Area. The review included a desktop evaluation of readily available government database records and mapping sources to determine the likelihood for potential environmental conditions resulting from the presence and/or release of regulated substances. Examples of regulated substances include petroleum-based products, lead-based paints, products containing volatile organic compounds and asbestos.

The Study Area boundary was submitted to Environmental Data Resources Incorporated (EDR) for an American Society of Testing and Material (ASTM E-1528-13) compliant radius search. EDR maintains an extensive records database that includes numerous government records. A typical non-exhaustive list of records included in this review are summarized in Table 7. This review also included a review of Sanborn Fire Insurance Maps and historic aerial photography.

Table 7 – Typical Databases with Sites Identified in the Maryland Area Federal/State List Acronym Database Description NPL National Priority List (Superfund) Comprehensive Environmental Response, CERCLIS Compensation & Liability Information System Federal RCRA Resource Conservation and Recovery Act ERNS Emergency Response Notification System BROWNFIELDS Local Brownfields site SHWS Notice of Potential Hazardous Waste Sites SWF/LF Permitted Solid Waste Disposal Facilities OCPCASES MDE Oil Control Program Cases MDE Leaking Underground Tank Recovery sites prior to HIST LUST 1999 State UST Registered Underground Storage Tanks AST Permitted Aboveground Storage Tanks Sites with caps, liners, etc. implemented to eliminate ENG substances from impacting the environment or human CONTROLS health MD Lead Maryland Lead Testing database

The Study Area was defined with a spatially-referenced polygon of the stream valleys. Upon submittal, several offset radii are generated for records search criteria. Records with the applicable search criteria are then mapped relative to the Study Area and summarized in report form. The report includes both the mapping and text summaries of each site, its distance from the subject area, and information regarding the specific database or incident. Particular attention was given to the Study Area and the property immediately adjacent to it.

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Five database citations were identified in proximity to the Study Area (Figure 7). One property is the residence located at 226 Waycross Way in which an Oil Control Program Case (OCPCASE) was initiated and closed in 1992. No release or clean-up activity was reported and no ongoing monitoring requirement was identified. This case is not expected to have an impact on the Project. The residence located at 39 Sheridan Road is identified on EDR’s High Risk Historical Records Historic database as a Historic Automotive site. Such properties may have been utilized as filling stations or utilized potentially hazardous materials during operation. No other database citations were identified for 39 Sheridan Road. The property was forested prior to the 1960s when the existing residence was constructed. An outbuilding located in the back of the property may have been utilized for automotive repair/restoration, but no evidence of site utilization such as a gas station was observed. Some debris was noted in the forested area behind the property, but no evidence of contamination was observed during field work. This property is not expected to adversely impact the Project.

Two sites are on MDE’s State Master List of potentially hazardous waste sites. The A.S. Pearmon Site (MD-452) located at 1283 Hardy Drive and Green Valley Road Site (MD - 178) located at the end of Green Valley Road are directly adjacent to each other.

These properties were utilized as unpermitted dump sites during the 1970s and 1980s. The properties which are directly adjacent to the Study Area were reportedly utilized to dispose of industrial solvents and paints and other waste and debris. Waste materials were apparently dumped over the embankment toward the stream valley. Some material was removed and limited soil testing revealed elevated levels of organic compounds in the early 1990s. Later testing in 2001 revealed little contamination present. The A.S. Pearmon Site is currently developed as a single-family residential property and the Green Valley Road Site is under construction as a townhouse development. During site investigations, some debris including metal and tires were observed on the slope and within the stream channel in this vicinity; however, no evidence of hazardous materials were observed. Observation of conditions during any restoration work in this area should be conducted, but these sites are not expected to have an impact on the success of the Project. The fifth citation is located on 1286 Hardy Road. Records indicate that no violations occurred and state that the property is adjacent to the A.S. Pearmon property. As a result, 1286 Hardy Road is not expected to have any adverse impact on the Project.

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¥

226 Waycross Way A.S. Pearmon (MD-452) Site

1286 Hardy Road Green Valley Road (MD-178) Site

39 Sheridan Road

Legend Study Area Sources: Esri, HERE, DeLorme, USGS, Intermap, increment P Corp., 2011 AA County Streams Modified by Bayland NRCAN, Esri Japan, METI, Esri China (Hong Kong), Esri (Thailand), MapmyIndia, © OpenStreetMap contributors, and the GIS User Community

Feet Figure 7 0 300 600 1,200 1,800 Consultants & Designers, Inc. “Integrating Engineering and Environment”and Engineering “Integrating Environmental Due 7455 New Ridge Road, Suite T Phone: (410) 694-9401 1 inch = 600 feet Hanover, Maryland 21076 Fax: (410) 694-9405 Diligence Sites Website: www.baylandinc.com P:\5_12201_Upper Mill CreekP:\5_12201_Upper SchematicMill Design\GIS\JPA VicinityMill Maps\Upper Creek Map.mxd Upper Mill Creek Design Development Report

Utilities and Infrastructure

According to Anne Arundel County engineering records and Anne Arundel County Sewer Main GIS data (AACO, 2016), there is an existing sewer line that runs along the east side of UM-1, crosses an outfall channel, and runs parallel along the east side of UM-2, UM-3, UM-4 and UM-5. In instances where the sewer line encroaches upon the floodplain, the extent of grading is restricted.

A review of plans associated with ongoing development at Hawthorne’s Grant revealed that there are two recently installed sewer lines that cross UM-1. The first is a 10 inch ductile iron pipe (DIP) sewer extension from Admiral Drive that crosses the reach approximately 305 linear feet downstream. The second is an 8 inch polyvinyl chloride (PVC) sewer from the Hawthorne’s Grant development that crosses UM-1 approximately 400 linear feet downstream.

Property Ownership and Easements/Site Access

Although the anticipated Limits of Disturbance (LOD) are largely located on property owned by Anne Arundel County, both temporary and permanent easements will need to be acquired from multiple private property owners. The properties were identified using the best available plat and deed records. Preliminary easement exhibits are included in Appendix E. The easements depict proposed permanent floodplain easements determined from the 100-year floodplain boundary delineated by BayLand, as well as permanent access easements and temporary construction easements.

Proposed access to the Main Stem may be obtained from East Joyce Lane and proposed access to the East Tributary may be obtained off of Treyburn Way, through a public utility easement. Access to UM-10 may be obtained through an existing 20-foot wide stormwater management pond access easement off of Finnean’s Run and also through an existing utility easement off of Elmridge Road.

Although temporary and permanent impacts to wetlands, forests and Waters of the U.S. will be unavoidable, the Project is designed to minimize impacts to the maximum extent practicable (MEP).

FEMA Floodplain/Hydrologic Trespass

The limits of the Study Area are not mapped within a flood hazard area according to the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) panels 24003C0167F and 24003C0186F, effective February 18, 2015 (FEMA, 2015). However, an existing and proposed HEC-RAS model were developed to determine the exact limits of the 100-year floodplain boundary. Additional information regarding the model is provided in Section 10.

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Forest Conservation Priority Areas

The Maryland State Forest Conservation Manual (DNR, 1997) identifies priority retention areas as forests that contain sensitive features or species that provide significant ecological or historical value. Specific priority retentions areas are forests that contain:

• 100-year nontidal floodplains • Intermittent and perennial stream channels • Stream buffers • Wetlands • Slopes greater than 15% • Forests connecting greenway corridors • Rare, threatened or endangered species (RTE) • Historic or cultural resources • Specimen trees (trees having a diameter at breast height of 30 inches or greater)

The stream restoration Study Area is composed of the stream valley which varies from 40 to 200 feet in width. Minimum Anne Arundel County stream buffers are 100 feet. As a result, the entire restoration Study Area is a forest conservation priority area. The Study Area also contains specimen trees and wetland areas throughout the valley. Steep slope areas do exist but are generally restricted to the edge of the valley and are not expected to be disturbed. No FEMA 100-year floodplain exists within the Study Area and no RTE or historic/cultural resources were identified by DNR or MHT. Any tree clearing resulting from the proposed restoration is anticipated to be replanted for the benefit of environmental resources and ecological uplift. As a result, there will be a net improvement of the subject riparian corridor as well as connectivity with adjacent forested areas.

RTE and In-Stream Work Restrictions

As discussed in Section 2.9, RTE review results did not identify any known occurrences or habitat in the vicinity of the Study Area. As a result, in-stream work restrictions can be expected to be limited to the annual stream closure period discussed below.

The MDE classifies all streams into one of eight stream “uses.” Stream use designations are defined based on known and expected aquatic life habitat requirements as wells as public water withdrawal sources. Each classification has an annual closure period when in-stream activity is prohibited to minimize potential impact on aquatic life movements and spawning.

As promulgated in the COMAR 26.08.02.08 all reaches within the Study Area are designated as “Use I” waters (MDE website 2016). “Use I” designated streams are described as Water Contact Recreation and Protection of Nontidal Warmwater Aquatic Life. The closure period for “Use I” designated waters is March 1 through June 15, inclusive of any year.

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5. HABITAT AND BIOLOGICAL ASSESSMENT

Methodology

Baseline biological and habitat assessments were completed at four sites along Mill Creek between 2010 and 2016 as part of the Anne Arundel Countywide Biological Monitoring Program (CBMP). Three of the targeted monitoring sites, MC-02, MC-03 and MC-04, are located within the Study Area (Figure 6).

Biological monitoring was conducted in accordance with Maryland Department of Biological Stream Survey (MBSS) protocols for spring and summer sampling. A Benthic Index of Biological Integrity (BIBI) score was developed from sampling data to qualitatively classify the benthic macroinvertebrate community. Physical habitat was evaluated using the USEPA Rapid Bio Assessment Protocol (RBP) for low-gradient streams and the Maryland DNR Physical Habitat Index (PHI). A more detailed description of methodology and results can be found in the monitoring report, Biological Monitoring Report for Targeted Sites in the Dividing Creek, Mill Creek, and Reference Reach Watersheds (Baughman et al., 2016).

Results

The average BIBI scores over the monitoring period are shown below in Table 8 and range between a “poor” and “fair” benthic macroinvertebrate community. The lowest scoring metrics included the number of ephemeroptera taxa, percent ephemeroptera and percent intolerant urban. The results are indicative of poor water quality since ephemeroptera are sensitive to water quality conditions and decrease in number and percent as water quality decreases. Additionally, percent intolerant urban decreases as water quality decreases.

The RBP scores were determined from a variety of parameters including epifaunal substrate/available, pool substrate characterization, pool variability, sediment deposition, channel flow status, channel alteration, channel sinuosity, bank stability, vegetative protection and riparian zone width. The average RBP scores over the monitoring period are shown below in Table 8 and range from “non-supporting” to “partially supporting”. Overall, the riparian zone width was high at all sites although bank stability and sediment ratings were very low.

The PHI score is based on instream habitat, epifaunal substrate, velocity/depth diversity, pool/glide/eddy quality, riffle/run quality, bank stability, embeddedness, shading, riparian buffer zone width, remoteness, aesthetic rating (trash) and number of woody debris and root wads. The average PHI scores over the monitoring period are shown below in Table 8 and range from “degraded” to “partially degraded”. Generally, the PHI score was very low due to low bank stability ratings.

The data generated by the assessments supports the need for a restoration project which could result in stable habitat for the establishment macroinvertebrates and a

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significant improvement in BIBI, RBP and PHI scores. Also, the assessments establish a baseline for future comparison with post-construction data.

Table 8 – Habitat and Biological Assessment Monitoring Results Parameter MC-02 MC-03 MC-04 BIBI 2.9 2.9 2.6 RBP 111.5 120.3 111.2 PHI 67.3 75.1 75.4

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6. HYDROLOGIC ANALYSIS

Methodology

In order to assess the existing morphological state of a stream, it is essential to determine the current discharge regime. Estimates of volume of various frequency flood discharges, as well as the horizontal and vertical extent of flood prone areas are an essential part of restoring stream stability. For the Project, estimates of hydrology were based largely upon hydrologic modeling.

The estimation of the hydrologic parameters required for analysis of rainfall simulations was based upon National Resource Conservation Services’ (NRCS) methodologies. There are three primary hydrologic parameters required to describe the runoff characteristics; drainage area size (DA), runoff curve number (RCN) and time of concentration (Tc). The methodology used to develop these parameters was based upon NRCS’s Urban Hydrology for Small Watersheds, Technical Release No. 55, 2nd Edition. The estimation of stormwater runoff resulting from a simulated rainfall event was based upon NRCS’s Project Formulation - Hydrology, Technical Release No. 20.

Various hydrologic models were developed to adequately characterize existing hydrologic conditions within the Study Area. A primary hydrologic model was developed to characterize the perennial project reaches (UM-1 to UM-9). The Study Area was divided into three sub-drainage areas using three study points (SP-1 to SP-3) (Figure 8). The study points correspond with hydrologically significant areas, such as junctions and outlets, and were selected to sufficiently characterize the hydrologic regime.

A secondary hydrologic model was developed for project reach UM-10 since the restoration will involve decommissioning an existing pond embankment. The second model is described in Section 7.0.

Development of Hydrologic Inputs

GISHydro 2000 software was initially utilized to delineate each sub-drainage area, however, since GISHydro 2000 is based on 30-meter resolution digital elevation models, the sub-drainage areas were manually verified using Anne Arundel County 2011 topography (1:2400) and edited as appropriate.

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SP-3 ^_ ³ C

SP-1 ^_^_ SP-2

A B

2011 AA County Streams Modified by BayLand

UPPER MILL CREEK STREAM Consultants & Designers, Inc. “Integrating Engineering and Environment”and Engineering “Integrating FIGURE 8 - SUB-BASINS RESTORATION PROJECT 7455 New Ridge Road, Suite T Phone: (410) 694-9401 ANNE ARUNDEL COUNTY Hanover, Maryland 21076 Fax: (410) 694-9405 Website: www.baylandinc.com 1 inch = 1,000 feet 1,000 500 0 1,000 Feet Upper Mill Creek Design Development Report

An RCN was developed for each sub-drainage area. The RCN reflects the runoff potential for each drainage area and is developed from cover (i.e. land use) and soil type. Existing land use data was compiled from published data including 2014 GIS layers from Anne Arundel County’s GIS Office. The land use matrix was broken into the basic components of Open Space, Impervious Surface and Woods. Soils data was obtained from the USDA-NRCS Web Soil Survey which classifies soils according to the four hydrologic soil groups (HSG) that range from type “A” (high infiltration rates, low runoff) to type “D” (low infiltration rates, high runoff).

The soils within each sub-drainage area depicted in Figure 8 are listed in Table 9 and the soil types are shown in Figure 9.

Table 9 – HSG Coverage Sub- A A B B C C D D Drainage (Acres) (%) (Acres) (%) (Acres) (%) (Acres) (%) Area A 56.8 20.2 162.1 57.6 40.1 14.3 22.5 8.0 B 109.1 47.9 99.4 43.6 5.6 2.5 13.7 6.0 C 10.7 36.4 6.8 23.1 9.3 31.7 2.6 8.8

Additionally, a Tc was developed for each sub-drainage area. The Tc is the time needed for water to flow from the hydrologically most remote point in a watershed to the watershed outlet. It is a function of topography, geology and land use within the watershed.

The hydrologic inputs for each sub-drainage area is shown below in Table 10. Supporting computations for the development of the RCN and Tc can be found in Appendix F.

Table 10 – Hydrologic Inputs Sub- Area Study Area Drainage (Square RCN Tc (Hours) Point (Acres) Area Miles) A SP-1 281.4 0.44 66 0.78 B SP-2 227.9 0.36 64 0.73 C SP-3 (Outlet) 29.4 0.05 65 0.29

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Anne Arundel

AnneUpper Arundel Mill Creek ³ Watershed

Upper Mill Creek Drainage Area Study Area 2011 AA County Streams Modified by Bayland 2016 NRCS SSURGO Hydrologic Soil Group A B C D UPPER MILL CREEK STREAM Consultants & Designers, Inc. FIGURE 9 - SOILS MAP RESTORATION PROJECT “Integrating Engineering and Environment”and Engineering “Integrating ANNE ARUNDEL COUNTY 7455 New Ridge Road, Suite T Phone: (410) 694-9401 1 inch = 1,000 feet Hanover, Maryland 21076 Fax: (410) 694-9405 1,000 500 0 1,000 Feet Website: www.baylandinc.com Upper Mill Creek Design Development Report

Hydrologic Analysis

WinTR-20 modeling was used to determine direct runoff to all of the study points. Stream reaches were used to route sub-drainage area hydrographs to the watershed outlet. A schematic of the WinTR-20 model is included in Appendix F.

The NOAA Atlas 14 24-hour rainfall distribution was run for the 1-, 2-, 5-, 10-, 25-, 50- and 100-year storm events for each sub-drainage area. An antecedent runoff condition (ARC) of 2 was used to represent average surface moisture prior to the rainfall event. A summary of the WinTR-20 results is provided as Table 11.

Table 11 – WinTR-20 Peak Discharges Study 1-YR 2-YR 5-YR 10-YR 25-YR 50-YR 100-YR Point (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) 1 27.6 54.4 109.0 160.2 241.2 309.9 386.2 2 17.9 37.9 80.5 121.7 186.4 244.6 307.0 3 46.2 94.5 196.0 292.1 446.0 579.6 724.5

Calibration

The Maryland Hydrology Panel report (2010) recommends that if the Tc is less than 6 hours, then the 6-hour or 12-hour storm should be used for the 1-, 2-, 5- and 10-year storm events. Since the total Tc for the Project is less than 6 hours, the 12-hour storm was run for the 1-, 2-, 5- and 10-year events, and the 24-hour storm was run for the 25-, 50- and 100-year events. The resulting peak discharges to each study point are provided in Tables 12 through 14.

Standard hydrologic practice dictates that all deterministic models, including WinTR-20, be calibrated where sufficient actual, and measured rainfall and runoff data are locally available. When data is not available, regional regression equations derived from USGS stream flow data may be used as a basis to calibrate the model (MD Hydrology Panel report, 2010).

A search of USGS stream gages within the Study Area did not reveal any active stream gages. Therefore, the Western Coastal Plain Fixed Regional Regression (FRR) equation peak discharges were compared to the WinTR-20 peak discharges. The results are shown in Tables 12 through 14, below. According to the 2010 MD Hydrology Panel Report, the calibration window is defined by the regression estimate (expected value) and the upper bound of plus one standard error of prediction.

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Table 12 – Peak Discharge Results, Study Point 1 Storm Regression WinTR-20 Standard Lower Upper Recurrence Peak Peak Error Limit Limit Interval Discharge Discharge (%) (cfs) (cfs) (yrs) (cfs) (cfs) 1 N/A N/A N/A N/A 18.5 1.25 33.4 39.0 20.9 47.7 N/A 1.5 44.8 36.4 29.3 62.8 N/A 2 56.7 33.2 38.9 77.5 38.9 5 98.4 38.2 62.0 138.8 80.9 10 139.7 42.7 81.6 203.3 122.6 25 218.0 48.1 115.3 329.0 241.2 50 294.3 54.0 137.9 461.8 309.9 100 393.6 61.2 155.6 646.4 386.2

Table 13 – Peak Discharge Results, Study Point 2 Storm Regression WinTR-20 Standard Lower Upper Recurrence Peak Peak Error Limit Limit Interval Discharge Discharge (%) (cfs) (cfs) (yrs) (cfs) (cfs) 1 N/A N/A N/A N/A 11.4 1.25 20.0 39.0 12.5 28.5 N/A 1.5 26.6 36.4 17.3 37.2 N/A 2 32.3 33.2 22.1 44.1 26.2 5 49.6 38.2 31.3 69.9 58.3 10 67.1 42.7 39.2 97.5 90.9 25 100.5 48.1 53.1 151.5 186.4 50 132.3 54.0 61.9 207.3 244.6 100 172.7 61.2 68.2 283.2 307.0

Table 14 – Peak Discharge Results, Study Point 3 Storm Regression WinTR-20 Standard Lower Upper Recurrence Peak Peak Error Limit Limit Interval Discharge Discharge (%) (cfs) (cfs) (yrs) (cfs) (cfs) 1 N/A N/A N/A N/A 31.6 1.25 51.3 39.0 29.9 68.1 N/A 1.5 68.1 36.4 41.4 88.7 N/A 2 84.8 33.2 54.2 108.1 66.8 5 139.2 38.2 83.1 185.7 144.0 10 192.9 42.7 107.0 266.4 220.9 25 293.4 48.1 147.5 420.9 446.2 50 389.8 54.0 173.7 581.5 579.6 100 513.2 61.2 192.9 801.6 724.5

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The Western Coastal Plain FRR equations were developed from 24 rural and urban USGS gage stations with drainage areas ranging from 0.41 to 349.6 square miles, imperviousness ranging from 0.0 to 36.8 percent, and the sum of C and D soils ranging from 13.0 to 74.7 percent (MD Hydrology Panel, 2010). The Project drainage area has characteristics consistent with the above ranges. The total drainage area is 0.8 square miles, the total imperviousness is 19.9 percent, and the total sum of type C and D soils is 17.4 percent. Since the peak discharges predicted by WinTR-20 using the 12-hour storm event for the 1-, 2- 5- and 10-year storms and the 24-hour storm event for the 50- and 100- year storms fall within the acceptable ranges for the overall drainage area, it was determined that further calibration of the model was not needed.

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7. ADDITIONAL HYDROLOGIC ANALYSIS – UM-10

Methodology (UM-10)

A separate model was developed characterize hydrologic conditions at reach UM-10. The drainage area was divided into two sub-drainage areas using two study points (SP- 1 and SP-2). SP-1 is located just upstream of the confluence with Outfall S15O014 and SP-2 is located downstream of Pond 824.

As described in Section 6.1, the estimation of the hydrologic parameters was based upon NRCS’s Urban Hydrology for Small Watersheds, Technical Release No. 55, 2nd Edition and the estimation of stormwater runoff resulting from a simulated rainfall event was based upon NRCS’s Project Formulation - Hydrology, Technical Release No. 20.

Development of Hydrologic Inputs (UM-10)

The same data sources described in Section 6.2 were used to develop the inputs required for the UM-10 hydrologic model. The drainage area and Tc path were delineated using Anne Arundel County 2011 topography (1:2400) and land use data was developed from the most current GIS data published by Anne Arundel County’s GIS Office. Ultimate land use data was developed from Anne Arundel County 2016 zoning data. Soils data was obtained from the USDA-NRCS Web Soil Survey. The drainage area and soils associated with the drainage area is depicted in Appendix G along with supporting computations for the development of the RCN and Tc.

The drainage area to SP-1 was determined to be 14.8 acres with approximately 1.9 acres (14 percent) of impervious area. The drainage area to SP-2 was determined to be 22.6 acres with approximately 4.5 acres (19.9 percent) of impervious area. The drainage area acreage, RCN and Tc are shown in Table 15 and a drainage area map with the study points is provided as Figure 10.

Table 15 – Hydrologic Inputs (UM-10) Area Existing Ultimate Area Tc Study Point (Square Land Use Land Use (Acres) (Hours) Miles) RCN RCN SP-1 14.8 0.023 55 71 0.24 SP-2 22.6 0.035 60 71 0.30

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³

SP-1

^_

SP-2

^_

2011 AA County Streams Modified by BayLand

UPPER MILL CREEK STREAM Consultants & Designers, Inc. “Integrating Engineering and Environment”and Engineering “Integrating POND 824 SUB-BASINS RESTORATION PROJECT 7455 New Ridge Road, Suite T Phone: (410) 694-9401 ANNE ARUNDEL COUNTY Hanover, Maryland 21076 Fax: (410) 694-9405 Website: www.baylandinc.com 1 inch = 200 feet 200 100 0 200 Feet Upper Mill Creek Design Development Report

Hydrologic Analysis (UM-10)

WinTR-20 modeling was used to determine direct runoff to both study points for existing and ultimate land use conditions. The models were developed without the inclusion of the stormwater management facility, Pond 824, in order to provide a conservative estimate for use in design. The NOAA Atlas 14 24-hour rainfall distribution, which was also utilized to characterize channel hydrology, was run for the 1-, 2-, 10- and 100-year storm events for each drainage area. An antecedent runoff condition (ARC) of 2 was used to represent average surface moisture prior to the rainfall event. A summary of the WinTR-20 results is provided as Table 16.

Table 16 – Hydrologic Summary: WinTR-20 Peak Discharges to SP-1 and SP-2 Study Land Use 1-YR 2-YR 10-YR 100-YR Point Condition (cfs) (cfs) (cfs) (cfs) Existing 0.3 1.3 8.0 26.1 SP-1 Ultimate 5.5 9.4 21.8 43.4 Existing 1.5 4.0 16.1 43.1 SP-2 Ultimate 7.2 12.4 29.4 59.4

An additional WinTR-20 model was developed in order to accurately compare the change in water quantity management from existing to proposed conditions. The WinTR-20 model included the stage-discharge-storage curve associated with Pond 824 and assumed ultimate land use conditions with a NRCS Type II 24-hour rainfall distribution. A summary of the peak discharge results is provided in Table 17 and additional supporting computations are provided in Appendix G.

Table 17 – Hydrologic Summary: WinTR-20 Peak Discharges to Pond 824 Study Land Use 1-YR 2-YR 10-YR 100-YR Point Condition (cfs) (cfs) (cfs) (cfs) To Pond Ultimate 13.5 22.9 58.6 105.9 824

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8. DESIGN DISCHARGE

Methods

Design or channel forming (Qcf) discharge is a critical aspect of channel design. For alluvial channels, Qcf is normally determined from the following four methods: effective discharge (Qeff), bankfull discharge (Qbf), discharge of a certain recurrence interval, typically the 1- to 2-year event (Qri), and regional curves relating bankfull discharge to drainage area (Qrc). Each of the four methods was considered and those that were applicable to the project reaches were utilized to estimate Qcf. For the Project, estimates of Qcf from multiple methods were compared and cross checked against each other to reduce uncertainty in the final Qcf estimate.

Qeff determination requires a flow duration curve with at least 10 years of data at 15- minute intervals on small, flashy streams (Biedenharn et al., 2000). However, there are no USGS stream gage stations within the vicinity of the Project, therefore this method was not utilized.

Qbf is typically determined utilizing field indicators identified during the geomorphic assessment. However, due to the degraded nature of the project reaches, bankfull indicators were sparse. UM-5 was the only project reach to exhibit a bankfull indicator.

Recurrence interval discharges (Qri) for the 1- and 2-year storm events were calculated using the WinTR-20 hydrologic model.

There are several published regional curves relating bankfull discharge to drainage area (Qrc). Curves with drainage area characteristics similar to that of the Project watershed, such as physiographic region and amount of imperviousness, were compared to predict bankfull discharge and recurrence interval discharges for each reach. The USFWS Western Coastal Plain regional curves (McCandless, 2003) were developed using 14 study reaches throughout the Coastal Plain hydro-physiographic province with drainage basin areas ranging from 0.3 to 113.0 square miles and the imperviousness of the watersheds draining to the study reaches ranging from 0 to 17.5 percent. Although the Project drainage areas are slightly more impervious (19 percent), the USFWS regional curve was still compared to the bankfull discharge determined from UM-5.

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Results

There is ample literature suggesting that the recurrence interval of bankfull discharge in the Coastal Plain is less than one year (Sweet and Geratz, 2003; Smoot et al., 2015). Given that discharges with sub-annual recurrence intervals cannot be modeled using TR-20, the USFWS Western Coastal Plain Regional Curve provides the best estimate of bankfull discharge in the absence of any reliable field bankfull indicators. Therefore, Qrc from the USFWS Western Coastal Plain Regional Curve was used as Qcf for all project reaches with the exception of UM-5 which had a reliable bankfull indicator. Design discharge estimates are summarized in Table 18.

Table 18 – Upper Mill Creek Design Discharge Estimates Qrc USFWS Western Coastal Qri 1-year/2-year Reach Qbf Plain Regional Curve (cfs) (cfs) UM-1 N/A 11.4 / 26.2 14.7 UM-2 N/A 11.4 / 26.2 14.7 UM-3 N/A 11.4 / 26.2 14.7 UM-4 N/A 26.5 / 58.8 27.6 UM-5 28.5 26.5 / 58.8 27.6 UM-6 N/A 13.5 / 31.0 17.2 UM-7 N/A 13.5 / 31.0 17.2 UM-8 N/A 13.5 / 31.0 17.2 UM-9 N/A 13.5 / 31.0 17.2

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9. GEOMORPHOLOGY

A preliminary geomorphic assessment and survey was conducted from January to April 2016 in order to document the existing conditions and provide baseline data for the restoration design. The field data collection activities were based on the Rosgen methodologies described in Applied Fluvial Morphology (Rosgen, 1996) and on the data collection methods described in Stream Channel Reference Sites: An Illustrated Guide to Field Technique (Harrelson et al., 1994). An overall site map was sketched at the time of the field investigation to document the stream’s geomorphic features, as well as locations of utility crossings. These field sketches are included in Appendix H.

Longitudinal Profile

A longitudinal profile was surveyed to characterize the slope and morphology of the stream channel through project reaches UM-1 through UM-9. The longitudinal profile survey recorded bed elevations, water depths, bed features (riffle, run, pool, glide) along the thalweg, bankfull elevations and the top of bank in each reach. Field data were recorded manually and entered into the Reference Reach spreadsheet STREAM module 4.2L (Mecklenburg, 2006). Individual pool length, depth and pool to pool spacing were determined from longitudinal profile data, as well as individual riffle lengths and slopes. Individual reach longitudinal profiles, including cross section locations, are presented in Appendix I.

Cross Sections

A minimum of one representative riffle was measured in project reaches UM-1 through UM-9 in order to determine the channel dimensions and hydraulic characteristics of the stream channel and for use in Rosgen stream type classification (hereafter referred to as the classification riffle). Data analysis included estimation of bankfull cross-sectional area, width, depths, hydraulic radius and wetted perimeter. The cross section survey data for each reach is provided in Appendix I.

Bed Material Characterization

Bed material (substrate) characterization is an important parameter in stream restoration design since the composition of the stream bed influences the character of the bed forms, sediment transport, macroinvertebrate habitat and fish habitat (Harrelson et al., 1994). For the Project, the channel substrate analysis included collecting modified Wolman pebble counts in each project reach following protocols described by Rosgen (1996). Two pebble counts were collected in each project reach to characterize the stream substrate. One pebble count was collected within the wetted width of the classification riffle to estimate roughness for velocity and discharge calculations. The frequency of particles in each size class was also used to determine the grain size distribution for incipient motion calculations. The second pebble count was collected throughout the project reach as a representative sample of the entire bed substrate for use in Rosgen stream classification. Bed material data collected was used in the

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analysis of hydraulic variables, stream classification, incipient motion and design discharge calculations. Results from reach pebble counts are provided in Appendix I.

At-a-Station Hydraulics

Data collected from riffle cross sections, pebble counts and profiles were used to develop an evaluation of hydraulic variables at classification riffles in the project reaches. Hydraulic variables were evaluated for the bankfull and top of bank water stages, and if different, compared to the 1- and 2-year peak discharges calculated using the TR-20 model.

Hydraulic variables used to determine bankfull and top of bank discharges for the project reaches are presented in Table 19. Appendix J contains the complete At-a- Station hydraulic analyses for each project reach.

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Table 19 – At-a-Station Hydraulics -1 -1 -2 -3 -4 -5 -6 -7 -8 -9

UM UM UM UM UM UM UM UM UM

Drainage Area (mi2) 0.217 0.278 0.357 0.812 0.842 0.290 0.353 0.432 0.440 Bankfull Discharge (cfs) 14.7 14.7 14.7 27.6 28.5 17.2 17.2 17.2 17.2 Slope (%) 0.58* 0.58* 0.50* 0.29* 0.27 0.82 0.60 0.39* 0.38* Cross Sectional Area (ft2) 4.8 6.3 5.2 11.2 8.1 6.0 4.9 5.7 6.0 Wetted Perimeter (ft) 6.5 11.7 9.1 12.8 9.3 9.7 9.1 10.2 9.8 Hydraulic Radius (ft) 0.7 0.5 0.6 0.9 0.9 0.6 0.5 0.6 0.6 Width (ft) 5.0 11.2 8.3 11.7 8.0 9.2 8.7 9.8 9.3 Mean Depth (ft) 1.0 0.6 0.6 1.0 1.0 0.6 0.6 0.6 0.6 Width/Depth Ratio 5.1 20.2 13.2 12.2 8.0 14.3 15.4 16.9 14.4 Maximum Depth (ft) 1.5 1.0 0.8 1.2 1.3 0.9 0.7 1.0 0.8 Velocity (ft/s) 3.1 2.3 2.9 2.5 3.5 2.9 3.5 3.0 2.9 Shear Velocity (ft/s) 0.37 0.32 0.30 0.29 0.27 0.40 0.32 0.26 0.27 Shear Stress (lbs/ft2) 0.27 0.19 0.18 0.16 0.15 0.32 0.20 0.14 0.14 Froude Number 0.63 0.56 0.67 0.46 0.67 0.65 0.84 0.71 0.65 Threshold Grain Size (mm) 13 10 9 8 7 15 10 7 7 Roughness 0.030 0.032 0.025 0.030 0.020 0.034 0.022 0.021 0.023 Top of Bank Discharge (cfs) 50.0 269.8 154.9 109.6 158.5 119.8 186.8 124.9 132.7 Top of Bank Area (ft2) 11.6 44.1 25.5 27.7 27.3 21.2 27.2 21.7 23.4 *Local slope utilized

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All of the project reaches have top of bank (TOB) discharges much higher than the bankfull discharge estimates. Using interpolated values from WinTR-20, it was estimated that the TOB discharge for UM-1 corresponds to a 9-year storm event, UM-2 corresponds to a 117-year storm event, UM-3 to a 33-year storm event, UM-4 to a 4- year storm event, UM-5 to a 7-year storm event, UM-6 to an 8-year storm event, UM-7 to a 16.5 year-storm event, UM-8 to a 9-year storm event and UM-9 to a 10-year storm event. This indicates that all of the project reaches are highly incised.

Stream Classification

The cross section data at the classification riffle was used in conjunction with pattern and profile data, and pebble count data, to determine the Rosgen stream type (Rosgen, 1996) and to calculate the velocity, discharge and average boundary shear stress.

Table 20 lists the bankfull dimensions and the Rosgen stream classifications for the classification riffle cross sections in each reach.

Valleys in Coastal Plain areas are typically classified as the Unconfined Alluvial: River Deltas (U-AL-RD) valley type, with stable stream types relating to C, DA and E, and landscape slopes less than 2 percent.

At Upper Mill Creek, UM-2, UM-4, UM-7 and UM-8 are Rosgen F5 stream types. F5 streams are sand dominated, incised, meandering channels, deeply incised in gentle terrain. Sediment supply in F5 stream types is moderate to high, depending on stream bank erodibility conditions (Rosgen, 1998).

UM-1 and UM-6 are Rosgen G4 stream types, and UM-3, UM-5 and UM-9 are Rosgen G5 stream types. The G4 stream type is a deeply incised channel that is typically very unstable due to the very high sediment supply available from both upslope and channel derived sources. The G5 stream type is an entrenched, moderately steep, step/pool channel deeply incised in sandy materials. Both G4 and G5 stream types are very sensitive to disturbance and tend to make significant adverse channel adjustments to changes in flow regime and sediment supply from the watershed (Rosgen, 1998).

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Table 20 – Bankfull Channel Dimensions at Classification Riffles

Bankfull Channel -1 -2 -3 -4 -5 -6 -7 -8 -9

Dimension Parameter UM UM UM UM UM UM UM UM UM

Drainage Area (mi2) 0.217 0.278 0.357 0.812 0.842 0.290 0.353 0.432 0.440 Cross Sectional Area 2 4.8 6.3 5.2 11.2 8.1 6.0 4.9 5.7 6.0 (Abkf) (ft ) Bank Height Ratio 2.5 3.7 5.1 3.1 2.9 5.8 5.7 4.8 4.0 Bankfull Width (Wbkf) 5.0 11.2 8.3 11.7 8.0 9.2 8.7 9.8 9.3 (ft) Mean Depth (dbkf) (ft) 1.0 0.6 0.6 1.0 1.0 0.6 0.6 0.6 0.6 Width to Depth Ratio 5.1 20.2 13.2 12.2 8.0 14.3 15.4 16.9 14.4 (Wbkf/dbkf) Width of Flood-prone 6.7 14.7 9.6 13.8 12.0 10.7 8.8 10.9 10.7 Area (Wfpa) (ft) Entrenchment Ratio 1.3 1.3 1.2 1.2 1.5 1.2 1.0 1.1 1.2 (ER) Median Material Size 1.30 0.25 0.34 2.7 0.23 8.20 0.19 0.22 0.23 (D50) (mm) Water Surface Slope 0.0058* 0.0058* 0.0050* 0.0029* 0.0027 0.0082 0.0060 0.0039* 0.0038* (S) (ft/ft) Channel Sinuosity (K) 1.08 1.48 1.04 1.92 1.48 2.80 1.50 1.35 1.76 Rosgen Stream G4c F5 G5c F5 G5c G4c F5c F5c G5c Classification Valley Type U-AL-RD U-AL-RD U-AL-RD U-AL-RD U-AL-RD U-AL-RD U-AL-RD U-AL-RD U-AL-RD

Valley Slope (Sv) (ft/ft) 0.016 0.009 0.005 0.005 0.004 0.023 0.009 0.005 0.006 *Local slope utilized for hydraulic calculations is shown in Table 20, overall slope was used to calculate channel sinuosity

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Sediment Supply and Transport

Bedload sediments typically come from eroding channel banks in the Coastal Plain physiographic region (Gellis et al., 2006). However, an investigation was conducted to identify any additional potential sediment supply sources to the project reaches. As mentioned previously, there is a short outfall channel upstream of the East Tributary that is eroding but will be stabilized as part of the overall Project. Additionally, there are two outfalls on the Upper Mill Creek Main Stem, located upstream of East Joyce Lane and downstream of Governor Ritchie Highway (Maryland Route 2), with uncontrolled discharge that has contributed to degraded channel conditions immediately downstream. However, the channel regains floodplain connectivity upstream of the culvert under East Joyce Lane and the channel is actively aggrading. Therefore, it is unlikely that any significant bedload supply is passing through the culvert under East Joyce Lane. The main source of sediment to the project reaches appears to consist of localized bank erosion from the project reaches themselves.

Stream Evolution Model (SEM)

Channel Evolution Models (CEMs) have traditionally been used in stream restoration in order to conceptualize how single-thread alluvial channels may respond to disturbances. The responses occur through a series of morphological adjustments, which can be generalized into an evolutionary sequence common to streams in different physiographic settings. In 1984, Schumm et al. identified a five-stage CEM to demonstrate the process of channel succession in disturbed systems. The process involves the change from a stable channel and floodplain (Stage I) to an incised channel (Stage II), which then widens (Stage III), and undergoes aggradation and planform adjustment (Stage IV), until it forms a stable channel and floodplain at a new elevation (Stage V). Simon and Hupp (1986) developed a six-stage adaptation of the model, which included a construction stage between the pre-modified and degradation stages of the Schumm et al. (1984) model. The CEMs have been modified since, notably by Thorne (1999) who proposed that an additional stage, Stage VI/VII be added to existing CEMs to account for late-stage incised channel evolution from straight or braided to meandering. Cluer and Thorne (2014) recently further revised CEMs by proposing a Stream Evolution Model (SEM), in order to promote consideration of the links between stream evolution and ecosystem services. The SEM differs from traditional CEMs by recognizing that streams may naturally be multi-threaded prior to disturbance, and representing stream evolution as a cyclical, rather than linear phenomenon. The SEM includes a precursor stage to better represent pre-disturbance conditions as well as two successor stages to cover late-stage evolutionary changes. The Cluer and Thorne (2014) SEM model is shown in Figure 11.

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Figure 11 – Stream Evolution Model

The Cluer and Thorne (2014) SEM stage was determined for each project reach in order to inform and support proposed design concepts, as well as provide insight into the physical and vegetative attributes and the habitat and ecosystem benefits associated with each SEM stage. The SEM stage for each project reach is shown in Table 21.

Table 21 – Stream Evolution Model Stage Reach Stage UM-1 4- Degradation and Widening UM-2 4- Degradation and Widening UM-3 4- Degradation and Widening UM-4 5- Aggradation and Widening UM-5 5- Aggradation and Widening UM-6 5- Aggradation and Widening UM-7 4- Degradation and Widening UM-8 5- Aggradation and Widening UM-9 4- Degradation and Widening

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UM-1, UM-2, UM-3, UM-7 and UM-9 are all considered to be in the degradation and widening stage. They are incised with unstable, retreating banks and no floodplain connectivity. In this stage, an extreme range of flood peaks is contained within the channel, and groundwater recharge and hyporheic connectivity are dysfunctional. Hydraulic diversity remains low due to channel scour and there is no capacity to store sediment and wood. Sediment inputs increase from bank retreat and mass failures eliminate stable banks. The aquatic plant community is dysfunctional due to ongoing bed degradation and riparian plants are destroyed by rapid widening. There is little in- channel habitat and bed degradation creates low levels of biodiversity. Additionally, water clarity, nutrient cycling and temperature control are all dysfunctional and the ecosystem is highly sensitive to disturbance.

UM-4, UM-5, UM-6 and UM-8 are in the aggradation and widening stage as evidenced by aggradation increasing bed elevation and banks stabilizing and berming. In this stage, the majority of flood peaks are still contained within the channel and groundwater recharge remains dysfunctional, although some hyporheic connectivity has been recovered. Aggradation renews depth/velocity variability improving hydraulic diversity and generating some bedforms and bars, although wood and sediment can still not be effectivity stored. The development of bars encourages the development of aquatic plants, although floodplain vegetation is still physically and hydrologically isolated. The channel is still impoverished with respect to rich and diverse habitat although the creation of in-channel features increases channel resilience and marginally improves nutrient cycling. However, water clarity and temperature control remain dysfunctional.

Overall, the SEM stages of the project reaches are far away in the evolutionary cycle from complete recovery, corroborating the need for the restoration Project.

Bank Erosion and Lateral Stability

BANCS Assessment

The Bank Assessment for Non-point source Consequences of Sediment (BANCS) model developed by Rosgen (1996, 2001) was utilized to evaluate stream bank erosion hazard potential for the project reaches. The BANCS model encompasses two quantitative tools: Bank Height Erosion Index (BEHI) and Near Bank Stress (NBS) (Rosgen, 2001). These tools involve evaluating the bank slope, rooting depth, floodplain accessibility and flow distribution along the stream edge to determine a bank erosion risk rating.

BEHI measures parameters including the bank height, bankfull height, root depth, root density, bank angle and surface protection to obtain a bank erosion hazard index that corresponds to ratings ranging from very low to extreme.

In each project reach, the left and right banks were examined and described using a BEHI rating. Using these banks as a reference, BEHI risk ratings were determined for all of the actively eroding banks in each reach. The length and height of each eroding

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bank were also measured and recorded. The results of the BEHI assessment are provided in Appendix K.

NBS is the result of turbulent flow occurring at the channel boundary and contributes to bank stability and erosion rates. The NBS can be evaluated with a variety of assessment methodologies, ranging from visual estimates to detailed velocity profile measurement techniques. For this Project, NBS was evaluated using method 2 (the ratio of radius of curvature to bankfull width) and method 5 (the ratio of the near-bank maximum bankfull depth and the mean bankfull depth). The corresponding rating was determined from these ratios, ranging from very low to extreme.

Estimated Erosion Rates

In the absence of appropriate regional empirical relations, annual bank erosion rates were predicted using relationships between BEHI and NBS from North Carolina. Bank erosion rates were then combined with the measured bank heights and lengths to estimate sediment loss per year from the stream banks. The sediment loss amounts for each bank were summed to calculate the total predicted amount of erosion occurring in the reach per year and converted to tons per year (Table 22) using measured bulk density values. Four bulk density sample locations were selected to represent each of the main Unified Soil Classification System (USCS) soils identified within the Study Area. Bulk density samples were collected in situ using a density drive sampler, then transported to BayLand for bulk density and moisture content analysis.

Table 22 – BEHI/NBS Ratings and Total Erosion Per Year Total Sediment Load Total Erosion Per Unit Stream Reach (tons/year) Length (tons/year/foot) UM-1 323.9 0.103 UM-2 100.7 0.059 UM-3 92.3 0.128 UM-4 5.5 0.007 UM-5 2.0 0.002 UM-6 83.0 0.158 UM-7 413.7 0.191 UM-8 19.8 0.015 UM-9 2.4 0.002 UM-10 41.53 0.030 UM-11 5.2 0.018

BEHI values within the project reaches are generally high and the NBS values range from very low to moderate (Appendix K). The high bank erosion rates indicate that there is a high sediment flux within the channel system which contributes to an unstable substrate and unsuitable habitat for macroinvertebrates.

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Measured Erosion Rates

Monitoring of cross sections established during the geomorphic assessment will continue through the semi-final design phase to determine the representative bank migration rate over a longer time frame. Additionally, toe pins were monumented at cross sections that are representative of the dominate BEHI/NBS condition. The measured bank erosion rates will be used to evaluate the lateral stability of the channel.

It should be noted that three cross sections within the Study Area were previously monumented and surveyed by the County annually from 2010 to 2013 as detailed in Biological Monitoring Report for Targeted Sites in the Dividing Creek, Mill Creek, and Reference Reach Watersheds (Baughman et al., 2016). The cross sections are located at reaches UM-2, UM-4 and UM-9. The monitoring data suggests that the channel shape at UM-2 was generally consistent. However, at UM-4, there was approximately 1 foot of aggradation and at UM-9, there was about 6 inches to 1 foot of lateral erosion along the left bank from 2010 to 2011 and aggradation in the channel bed. The measured rates of all monumented cross sections will be compared to estimated rates during future stages of design.

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10. HYDRAULIC ANALYSIS

Hydraulic Analysis Methodology

HEC-RAS version 5.0.5 River Analysis System, developed by the USACE, was used to establish the water surface, velocity and channel shear stresses for existing and proposed conditions. Table 23 describes the hydraulic cross sections for the Project and additional information is included in Appendix L.

Critical depth was used as an upstream boundary condition and normal depth was used as the downstream boundary condition for the 1 through 100-year recurrence interval storm events. The State National Flood Insurance Program (NFIP) identified the Study Area as Zone X, meaning there was no 100-year water surface elevation boundary condition provided.

Table 23 – Existing and Proposed River Stationing Descriptions Stations Along HEC-RAS Proposed River Stations Description Alignment Existing Proposed East Tributary 50+73.50 to 31+40.0 to 31+40.0 to Existing: Upstream end of unstable reach 53+22.0 28+77.0 28+77.0 Proposed: Cobble-Sandstone Step System Existing: Mid to downstream end of 53+67.0 to 27+98.7 to 27+98.7 to unstable reach 81+55.0 00+10.7 00+10.7 Proposed: Restored channel with log grade controls and log-cobble riffles Main Stem 00+80.0 to 43+08.0 to 43+08.0 to Existing: Upstream end of unstable reach 01+55.0 42+33.0 42+33.0 Proposed: Cobble-Sandstone Step System Existing: Mid to downstream end of 01+73.5 to 42+14.5 to 42+14.5 to unstable reach 41+39.9 00+52.1 00+52.1 Proposed: Restored channel with log grade controls and log-cobble riffles

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Table 24 identifies the developed study point peak discharges with the associated cross section hydraulic models flow change locations.

Table 24 – Peak Discharge Flow Change Locations Channel 1-YR 2-YR 10-YR 100-YR Condition (cfs) (cfs) (cfs) (cfs) Existing & Proposed Main 18.5 38.9 122.6 286.2 Stem Upstream of Confluence Existing & Proposed East 11.4 26.2 90.9 307.0 Tributary Existing & Proposed Main 31.6 66.8 220.9 724.5 Stem Downstream of Confluence

For the existing conditions model, a Manning’s “n” value of 0.035 was used for the channel and 0.10 was used for the floodplain. For the proposed conditions model, a manning’s “n” value of 0.05 was used for the cobble-sandstone steps, 0.04 was used for the log-cobble riffles and log grade controls, 0.035 was used for pools and 0.10 was used for the floodplain.

Hydraulic Analysis Results

A comparison between existing and proposed hydraulic conditions for the 2- , 10-, and 100-year storm events is provided in Tables 25 to 30.

The results are consistent with the goals of the Project, which include: increasing floodplain connectivity to reduce erosive velocities within the channel, stabilizing channel reaches experiencing accelerated lateral and vertical bed and bank erosion and creating a stable channel with planform and dimensional geometries consistent with the hydrological and sedimentological regimes of the watershed.

The proposed design provides increased floodplain connectivity, allowing for less intense, more frequent storms to access the floodplain. As a direct result, water surface elevations (WSE) increased from existing to proposed conditions. The increase in floodplain connectivity will significantly increase the 100-year floodplain boundary and will impact multiple private properties. Properties that will be impacted are depicted on the proposed easement exhibits (Appendix E). The proposed permanent easement boundaries are based on the proposed 100-year floodplain boundary.

Fluctuations of velocity and shear stress were observed along different reaches of the channel. These fluctuations are attributed to the proposed geomorphological features of the stream bed, along with stream meander geometry changes from the existing to the proposed conditions and do not reflect any adverse changes to the proposed reach.

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The Valley Restoration Design Checklist (Starr, R. et al., 2015), recommends a maximum shear stress in the channel and across floodplain of 2 pounds per square foot. Overall, the design discharge analysis resulted in low shear stress values. However, there are a few instances where shear stress values in the channel and the floodplain are high, primarily due to large increases in floodplain flow depth from existing conditions. In these areas where the design cannot yield shear stress values less than 2 pounds per square foot, valley grade-control structures are proposed in the channel and across the floodplain. Additionally, high velocities and shears will be mitigated by constructed riffle grade control features with aptly sized cobble bed stability mix.

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Table 25 – Main Stem Existing and Proposed Floodplain Access Existing River Proposed River Existing Floodplain Proposed Floodplain Proposed Alignment Station Station Station Access Access 43+18.0 43+18.0 PHANTOM > 100-year storm event < 1-year storm event 43+08.0 43+08.0 0+80.0 > 100-year storm event 2-year storm event 43+00.0 43+00.0 0+88.0 100-year storm event < 1-year storm event 42+75.0 42+75.0 1+13.0 100-year storm event 2-year storm event 42+67.0 42+67.0 1+21.0 100-year storm event 2-year storm event 42+38.0 42+38.0 1+50.0 25-year storm event < 1-year storm event 42+33.0 42+33.0 1+55.0 25-year storm event < 1-year storm event 42+14.5 42+14.5 1+73.5 100-year storm event < 1-year storm event 41+54.0 41+54.0 2+34.0 > 100-year storm event < 1-year storm event 41+13.0 41+13.0 2+75.0 > 100-year storm event < 1-year storm event 40+55.3 38+59.0 3+33.0 25-year storm event < 1-year storm event 40+01.7 38+13.5 3+78.6 100-year storm event < 1-year storm event 39+67.3 37+86.6 4+05.5 50-year storm event < 1-year storm event 38+96.2 36+63.8 5+28.2 100-year storm event 1-year storm event 38+53.0 36+28.8 5+63.3 100-year storm event < 1-year storm event 38+35.5 36+12.7 5+79.3 100-year storm event < 1-year storm event 38+27.4 36+02.0 5+90.0 25-year storm event < 1-year storm event 38+04.8 35+87.9 6+04.1 50-year storm event < 1-year storm event 37+92.8 35+60.5 6+31.5 50-year storm event < 1-year storm event 37+78.9 35+47.1 6+44.9 100-year storm event < 1-year storm event 37+44.0 35+27.0 6+65.0 50-year storm event < 1-year storm event 37+37.4 35+20.5 6+71.6 50-year storm event < 1-year storm event 37+02.9 34+89.4 7+02.7 > 100-year storm event < 1-year storm event 36+55.0 34+45.2 7+46.8 > 100-year storm event < 1-year storm event 36+15.5 34+07.9 7+84.1 > 100-year storm event < 1-year storm event 35+12.0 32+87.0 9+05.0 100-year storm event < 1-year storm event 34+50.4 32+50.0 9+42.0 > 100-year storm event < 1-year storm event 33+92.4 32+02.0 9+90.0 50-year storm event < 1-year storm event 33+69.8 31+66.7 10+25.4 50-year storm event < 1-year storm event 33+09.2 31+13.0 10+79.1 50-year storm event < 1-year storm event

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Table 25 – Main Stem Existing and Proposed Floodplain Access Existing River Proposed River Existing Floodplain Proposed Floodplain Proposed Alignment Station Station Station Access Access 32+85.1 30+89.4 11+02.7 100-year storm event < 1-year storm event 32+62.9 30+65.9 11+26.1 > 100-year storm event < 1-year storm event 31+98.1 29+82.0 12+10.0 50-year storm event < 1-year storm event 31+48.6 29+44.0 12+48.0 50-year storm event < 1-year storm event 31+33.5 29+22.0 12+70.0 100-year storm event < 1-year storm event 31+19.7 29+04.0 12+88.0 100-year storm event < 1-year storm event 30+54.1 28+16.1 13+76.0 100-year storm event < 1-year storm event 30+12.4 27+66.7 14+25.4 100-year storm event < 1-year storm event 29+65.8 27+20.6 14+71.4 100-year storm event < 1-year storm event 29+46.1 27+05.9 14+86.1 50-year storm event < 1-year storm event 29+32.7 26+87.0 15+05.0 50-year storm event < 1-year storm event 28+99.2 26+57.0 15+35.0 100-year storm event < 1-year storm event 28+44.0 26+06.9 15+85.1 > 100-year storm event < 1-year storm event 28+14.5 25+77.0 16+15.0 > 100-year storm event < 1-year storm event 27+97.5 25+60.0 16+32.0 > 100-year storm event < 1-year storm event 27+51.7 25+34.0 16+58.0 > 100-year storm event < 1-year storm event 26+29.4 23+90.0 18+02.0 100-year storm event < 1-year storm event 26+12.5 23+77.0 18+15.0 > 100-year storm event < 1-year storm event 25+78.4 23+41.7 18+50.3 > 100-year storm event < 1-year storm event 25+29.6 23+07.0 18+85.1 > 100-year storm event < 1-year storm event 24+68.2 22+28.1 19+63.9 > 100-year storm event < 1-year storm event 24+44.5 21+80.1 20+11.9 100-year storm event < 1-year storm event 23+68.3 21+36.2 20+55.8 100-year storm event < 1-year storm event 23+46.8 21+17.1 20+75.0 > 100-year storm event < 1-year storm event 22+87.2 20+31.9 21+60.2 > 100-year storm event < 1-year storm event 22+66.4 20+11.1 21+81.0 100-year storm event < 1-year storm event 22+58.2 20+03.0 21+89.0 > 100-year storm event < 1-year storm event 22+22.8 19+77.7 22+14.4 100-year storm event < 1-year storm event 21+95.4 19+31.4 22+60.6 25-year storm event < 1-year storm event 21+69.7 18+97.8 22+94.2 50-year storm event < 1-year storm event

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Table 25 – Main Stem Existing and Proposed Floodplain Access Existing River Proposed River Existing Floodplain Proposed Floodplain Proposed Alignment Station Station Station Access Access 21+22.1 18+55.1 23+36.9 > 100-year storm event < 1-year storm event 20+68.2 18+11.9 23+80.1 100-year storm event < 1-year storm event 20+43.8 17+69.4 24+22.6 100-year storm event < 1-year storm event 19+78.0 17+14.0 24+78.0 100-year storm event < 1-year storm event 19+66.3 16+77.0 25+15.0 > 100-year storm event < 1-year storm event 19+33.7 16+61.3 25+30.7 50-year storm event < 1-year storm event 18+61.0 15+64.0 26+28.0 100-year storm event < 1-year storm event 17+99.9 15+21.0 26+71.1 100-year storm event < 1-year storm event 17+73.4 14+70.0 27+22.0 50-year storm event < 1-year storm event 17+31.0 14+42.0 27+50.0 100-year storm event < 1-year storm event 17+15.1 14+24.0 27+68.0 > 100-year storm event < 1-year storm event 16+63.8 13+52.0 28+40.0 25-year storm event < 1-year storm event 16+07.2 13+12.0 28+80.0 25-year storm event < 1-year storm event 15+68.9 12+62.0 29+30.0 25-year storm event < 1-year storm event 15+18.3 12+12.0 29+80.0 25-year storm event < 1-year storm event 14+78.1 11+68.0 30+24.0 25-year storm event < 1-year storm event 13+95.0 10+87.0 31+05.0 25-year storm event < 1-year storm event 12+63.7 10+07.0 31+85.0 25-year storm event < 1-year storm event 12+31.4 9+77.0 32+15.0 25-year storm event < 1-year storm event 11+97.5 9+34.0 32+58.0 25-year storm event < 1-year storm event 11+48.6 8+92.0 33+00.0 25-year storm event < 1-year storm event 11+27.1 8+72.0 33+20.0 25-year storm event < 1-year storm event 10+80.9 8+27.0 33+65.0 10-year storm event < 1-year storm event 10+55.4 8+02.0 33+90.0 25-year storm event < 1-year storm event 10+10.8 7+57.0 34+35.0 10-year storm event < 1-year storm event 9+63.7 7+10.0 34+82.0 10-year storm event < 1-year storm event 8+89.0 6+37.0 35+55.0 25-year storm event < 1-year storm event 8+20.7 5+70.0 36+22.0 25-year storm event < 1-year storm event 7+78.1 5+27.0 36+65.0 25-year storm event < 1-year storm event 7+41.4 4+90.0 37+02.0 25-year storm event < 1-year storm event

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Table 25 – Main Stem Existing and Proposed Floodplain Access Existing River Proposed River Existing Floodplain Proposed Floodplain Proposed Alignment Station Station Station Access Access 6+98.8 4+47.0 37+45.0 25-year storm event < 1-year storm event 6+68.9 4+19.9 37+72.2 25-year storm event < 1-year storm event 6+50.5 4+02.0 37+90.0 10-year storm event < 1-year storm event 5+89.8 3+42.0 38+50.0 25-year storm event < 1-year storm event 4+82.8 2+57.0 39+35.0 10-year storm event < 1-year storm event 4+20.3 1+97.0 39+95.0 10-year storm event < 1-year storm event 3+68.2 1+52.0 40+40.0 5-year storm event < 1-year storm event 3+46.4 1+32.0 40+60.0 5-year storm event < 1-year storm event 2+81.4 0+92.0 41+00.0 5-year storm event < 1-year storm event 2+31.7 0+52.1 41+39.9 5-year storm event < 1-year storm event 2+31.0 0+52 PHANTOM 5-year storm event < 1-year storm event

Table 26 – East Tributary Existing and Proposed Floodplain Access Existing River Proposed River Existing Floodplain Proposed Floodplain Proposed Alignment Station Station Station Access Access 31+41.0 31+41.0 PHANTOM 100-year storm event 2-year storm event 31+40.0 31+40.0 50+73.5 100-year storm event 2-year storm event 31+28.0 31+28.0 50+83.5 100-year storm event 2-year storm event 31+03.0 31+03.0 51+07.0 100-year storm event 2-year storm event 30+91.0 30+91.0 51+19.0 25-year storm event < 1-year storm event 30+44.0 30+44.0 51+60.0 100-year storm event 1-year storm event 30+32.0 30+32.0 51+72.0 100-year storm event < 1-year storm event 30+01.0 30+01.0 52+00.0 50-year storm event 1-year storm event 29+89.0 29+89.0 52+12.0 25-year storm event < 1-year storm event 29+62.0 29+62.0 52+39.0 > 100-year storm event 1-year storm event 29+50.0 29+50.0 52+51.0 > 100-year storm event 1-year storm event 29+31.0 29+31.0 52+69.0 > 100-year storm event 2-year storm event 29+19.0 29+19.0 52+81.0 > 100-year storm event < 1-year storm event 28+89.0 28+89.0 53+10.0 100-year storm event 2-year storm event 28+77.0 28+77.0 53+22.0 > 100-year storm event < 1-year storm event

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Table 26 – East Tributary Existing and Proposed Floodplain Access Existing River Proposed River Existing Floodplain Proposed Floodplain Proposed Alignment Station Station Station Access Access 28+29.3 27+98.7 53+67.0 100-year storm event < 1-year storm event 27+91.5 27+60.7 54+05.0 100-year storm event < 1-year storm event 27+63.9 27+33.7 54+32.0 100-year storm event < 1-year storm event 27+26.6 26+95.7 54+70.0 > 100-year storm event < 1-year storm event 26+43.3 26+37.7 55+28.0 50-year storm event < 1-year storm event 26+30.0 26+24.7 55+41.0 25-year storm event < 1-year storm event 25+89.0 25+90.7 55+75.0 25-year storm event < 1-year storm event 25+77.4 25+79.7 55+86.0 50-year storm event < 1-year storm event 25+67.2 25+57.7 56+08.0 50-year storm event < 1-year storm event 25+05.4 25+20.7 56+45.0 100-year storm event < 1-year storm event 24+96.6 24+89.7 56+76.0 100-year storm event < 1-year storm event 24+63.1 24+64.7 57+01.0 > 100-year storm event < 1-year storm event 24+24.4 24+29.7 57+36.0 > 100-year storm event < 1-year storm event 23+79.2 23+90.7 57+75.0 50-year storm event < 1-year storm event 23+62.9 23+74.7 57+91.0 > 100-year storm event < 1-year storm event 23+27.3 23+44.7 58+21.0 100-year storm event < 1-year storm event 22+99.1 23+25.2 58+40.5 50-year storm event < 1-year storm event 22+87.5 22+99.7 58+66.0 50-year storm event < 1-year storm event 22+64.9 22+81.7 58+84.0 50-year storm event < 1-year storm event 22+30.7 22+47.7 59+18.0 100-year storm event < 1-year storm event 21+98.6 22+15.7 59+50.0 25-year storm event < 1-year storm event 21+72.5 21+89.7 59+76.0 50-year storm event < 1-year storm event 21+58.9 21+76.1 59+89.6 25-year storm event < 1-year storm event 21+45.5 21+62.7 60+03.0 50-year storm event < 1-year storm event 21+08.0 21+32.7 60+33.0 > 100-year storm event < 1-year storm event 20+96.0 21+22.7 60+43.0 100-year storm event < 1-year storm event 20+65.0 20+86.7 60+79.0 50-year storm event < 1-year storm event 20+54.8 20+77.8 60+87.9 50-year storm event < 1-year storm event 20+25.3 20+48.7 61+17.0 100-year storm event < 1-year storm event 19+97.8 20+23.7 61+42.0 > 100-year storm event < 1-year storm event

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Table 26 – East Tributary Existing and Proposed Floodplain Access Existing River Proposed River Existing Floodplain Proposed Floodplain Proposed Alignment Station Station Station Access Access 19+67.5 19+96.7 61+69.0 > 100-year storm event < 1-year storm event 19+34.8 19+66.2 61+99.5 > 100-year storm event < 1-year storm event 18+93.2 19+30.7 62+35.0 > 100-year storm event < 1-year storm event 18+52.8 18+78.7 62+87.0 100-year storm event < 1-year storm event 17+89.0 18+07.7 63+58.0 > 100-year storm event 1-year storm event 16+98.3 17+31.7 64+34.0 > 100-year storm event 2-year storm event 15+89.1 16+30.6 65+35.0 > 100-year storm event 2-year storm event 15+81.3 16+07.4 65+58.3 50-year storm event < 1-year storm event 15+34.3 15+68.7 65+97.0 100-year storm event < 1-year storm event 14+71.4 14+96.7 66+69.0 100-year storm event < 1-year storm event 14+11.6 14+32.7 67+33.0 > 100-year storm event < 1-year storm event 13+75.3 13+95.7 67+70.0 > 100-year storm event < 1-year storm event 13+40.9 13+36.7 68+02.0 > 100-year storm event < 1-year storm event 12+48.3 12+45.7 69+20.0 > 100-year storm event < 1-year storm event 12+23.0 12+19.7 69+46.0 100-year storm event < 1-year storm event 11+91.9 11+89.7 69+76.0 100-year storm event < 1-year storm event 11+60.5 11+59.7 70+06.0 > 100-year storm event < 1-year storm event 11+09.4 11+18.7 70+47.0 > 100-year storm event < 1-year storm event 10+69.5 10+70.7 70+95.0 100-year storm event < 1-year storm event 10+39.5 10+32.7 71+33.0 > 100-year storm event < 1-year storm event 10+00.4 9+97.7 71+68.0 > 100-year storm event < 1-year storm event 9+87.9 9+70.7 71+95.0 > 100-year storm event < 1-year storm event 9+39.5 9+30.7 72+35.0 > 100-year storm event < 1-year storm event 9+15.6 8+95.7 72+70.0 100-year storm event < 1-year storm event 8+36.5 8+29.7 73+36.0 100-year storm event < 1-year storm event 7+95.5 7+50.7 74+15.0 50-year storm event < 1-year storm event 7+19.1 6+89.7 74+76.0 100-year storm event < 1-year storm event 6+58.9 6+35.7 75+30.0 50-year storm event < 1-year storm event 6+11.1 5+78.7 75+87.0 > 100-year storm event < 1-year storm event 5+51.3 5+21.7 76+44.0 > 100-year storm event < 1-year storm event

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Upper Mill Creek Design Development Report

Table 26 – East Tributary Existing and Proposed Floodplain Access Existing River Proposed River Existing Floodplain Proposed Floodplain Proposed Alignment Station Station Station Access Access 5+24.6 4+80.7 76+85.0 100-year storm event < 1-year storm event 5+06.0 4+69.7 76+96.0 100-year storm event < 1-year storm event 4+96.9 4+58.7 77+07.0 50-year storm event < 1-year storm event 4+66.2 4+22.7 77+43.0 100-year storm event < 1-year storm event 3+69.1 3+39.7 78+26.0 25-year storm event < 1-year storm event 3+27.0 2+97.7 78+68.0 50-year storm event < 1-year storm event 3+01.4 2+68.7 78+97.0 50-year storm event < 1-year storm event 2+61.3 2+30.7 79+35.0 25-year storm event < 1-year storm event 2+36.6 1+98.7 79+67.0 25-year storm event < 1-year storm event 1+82.3 1+59.7 80+06.0 25-year storm event < 1-year storm event 1+43.0 1+21.7 80+44.0 25-year storm event < 1-year storm event 0+91.6 0+79.7 80+86.0 25-year storm event < 1-year storm event 0+31.2 0+10.7 81+55.0 25-year storm event < 1-year storm event

Table 27 – Main Stem 2-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 43+18.0 43+18.0 PHANTOM 0.20 0.36 80.0 2.33 2.29 -1.7 43+08.0 43+08.0 0+80.0 0.23 1.26 447.8 2.49 4.05 62.7 43+00.0 43+00.0 0+88.0 0.13 0.38 192.3 1.87 2.31 23.5 42+75.0 42+75.0 1+13.0 0.23 1.21 426.1 2.66 3.85 44.7 42+67.0 42+67.0 1+21.0 0.21 0.68 223.8 2.59 3.08 18.9 42+38.0 42+38.0 1+50.0 0.27 0.28 3.7 2.83 2.02 -28.6 42+33.0 42+33.0 1+55.0 0.20 0.19 -5.0 2.45 1.73 -29.4 42+14.5 42+14.5 1+73.5 0.31 0.31 0.0 3.04 2.2 -27.6 41+54.0 41+54.0 2+34.0 0.61 0.40 -34.4 4.23 2.49 -41.1 41+13.0 41+13.0 2+75.0 0.98 1.05 7.1 5.06 3.97 -21.5 40+55.3 38+59.0 3+33.0 0.49 0.29 -40.8 3.87 2.81 -27.4

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Upper Mill Creek Design Development Report

Table 27 – Main Stem 2-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 40+01.7 38+13.5 3+78.6 0.08 0.14 75.0 2.52 1.72 -31.7 39+67.3 37+86.6 4+05.5 0.06 0.49 716.7 2.11 3.57 69.2 38+96.2 36+63.8 5+28.2 0.38 0.38 0.0 5.06 2.52 -50.2 38+53.0 36+28.8 5+63.3 0.42 0.56 33.3 5.32 3.38 -36.5 38+35.5 36+12.7 5+79.3 0.09 0.73 711.1 2.57 4.05 57.6 38+27.4 36+02.0 5+90.0 0.14 0.13 -7.1 3.21 2.07 -35.5 38+04.8 35+87.9 6+04.1 0.03 0.19 533.3 1.45 2.32 60.0 37+92.8 35+60.5 6+31.5 0.47 1.33 183.0 5.71 5.3 -7.2 37+78.9 35+47.1 6+44.9 0.02 0.27 1250.0 1.34 2.53 88.8 37+44.0 35+27.0 6+65.0 0.03 0.06 100.0 1.46 1.41 -3.4 37+37.4 35+20.5 6+71.6 0.07 0.12 71.4 2.33 1.9 -18.5 37+02.9 34+89.4 7+02.7 0.24 1.11 362.5 4.17 5.7 36.7 36+55.0 34+45.2 7+46.8 0.11 0.28 154.5 2.84 2.9 2.1 36+15.5 34+07.9 7+84.1 0.36 1.08 200.0 4.97 5.5 10.7 35+12.0 32+87.0 9+05.0 0.25 0.11 -56.0 4.28 1.69 -60.5 34+50.4 32+50.0 9+42.0 0.31 0.23 -25.8 4.76 2.41 -49.4 33+92.4 32+02.0 9+90.0 0.11 0.30 172.7 2.97 2.69 -9.4 33+69.8 31+66.7 10+25.4 0.27 0.22 -18.5 4.41 2.39 -45.8 33+09.2 31+13.0 10+79.1 0.18 0.10 -44.4 3.77 1.3 -65.5 32+85.1 30+89.4 11+02.7 0.28 0.19 -32.1 4.52 2.02 -55.3 32+62.9 30+65.9 11+26.1 0.53 0.18 -66.0 5.89 2 -66.0 31+98.1 29+82.0 12+10.0 0.34 0.18 -47.1 4.75 2.06 -56.6 31+48.6 29+44.0 12+48.0 0.09 0.26 188.9 2.63 2.29 -12.9 31+33.5 29+22.0 12+70.0 0.43 0.23 -46.5 5.44 2.58 -52.6 31+19.7 29+04.0 12+88.0 0.09 0.20 122.2 2.55 2.19 -14.1 30+54.1 28+16.1 13+76.0 0.35 0.36 2.9 4.69 2.93 -37.5 30+12.4 27+66.7 14+25.4 0.13 0.03 -76.9 2.97 0.97 -67.3 29+65.8 27+20.6 14+71.4 0.05 0.93 1760.0 2.05 4.27 108.3

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Upper Mill Creek Design Development Report

Table 27 – Main Stem 2-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 29+46.1 27+05.9 14+86.1 0.11 0.29 163.6 2.91 2.47 -15.1 29+32.7 26+87.0 15+05.0 0.09 0.13 44.4 2.64 1.87 -29.2 28+99.2 26+57.0 15+35.0 0.46 0.07 -84.8 5.67 1.44 -74.6 28+44.0 26+06.9 15+85.1 0.48 0.18 -62.5 5.67 2.3 -59.4 28+14.5 25+77.0 16+15.0 0.65 0.98 50.8 6.37 4.45 -30.1 27+97.5 25+60.0 16+32.0 0.43 0.95 120.9 5.37 4.53 -15.6 27+51.7 25+34.0 16+58.0 0.84 0.32 -61.9 6.77 2.88 -57.5 26+29.4 23+90.0 18+02.0 0.31 0.48 54.8 4.67 2.98 -36.2 26+12.5 23+77.0 18+15.0 0.36 0.24 -33.3 5.1 2.22 -56.5 25+78.4 23+41.7 18+50.3 0.21 0.58 176.2 4.09 3.68 -10.0 25+29.6 23+07.0 18+85.1 0.18 0.42 133.3 3.81 3.19 -16.3 24+68.2 22+28.1 19+63.9 0.30 1.21 303.3 4.74 5.36 13.1 24+44.5 21+80.1 20+11.9 0.12 0.12 0.0 3.16 1.69 -46.5 23+68.3 21+36.2 20+55.8 0.10 0.14 40.0 2.94 1.61 -45.2 23+46.8 21+17.1 20+75.0 0.11 0.13 18.2 3.02 1.67 -44.7 22+87.2 20+31.9 21+60.2 0.35 0.26 -25.7 5.12 2.47 -51.8 22+66.4 20+11.1 21+81.0 0.09 0.64 611.1 2.66 3.88 45.9 22+58.2 20+03.0 21+89.0 0.15 0.30 100.0 3.42 3.15 -7.9 22+22.8 19+77.7 22+14.4 0.06 0.57 850.0 2.36 4.12 74.6 21+95.4 19+31.4 22+60.6 0.04 0.20 400.0 1.78 2.51 41.0 21+69.7 18+97.8 22+94.2 0.12 0.07 -41.7 3.09 1.36 -56.0 21+22.1 18+55.1 23+36.9 0.50 0.17 -66.0 5.86 2.35 -59.9 20+68.2 18+11.9 23+80.1 0.08 0.26 225.0 2.46 2.88 17.1 20+43.8 17+69.4 24+22.6 0.33 1.13 242.4 4.79 5.59 16.7 19+78.0 17+14.0 24+78.0 0.08 0.56 600.0 2.32 3.67 58.2 19+66.3 16+77.0 25+15.0 0.38 0.18 -52.6 4.72 1.8 -61.9 19+33.7 16+61.3 25+30.7 0.02 0.19 850.0 1.09 2.05 88.1 18+61.0 15+64.0 26+28.0 0.20 0.26 30.0 3.63 2.52 -30.6

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Upper Mill Creek Design Development Report

Table 27 – Main Stem 2-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 17+99.9 15+21.0 26+71.1 0.07 0.20 185.7 2.28 1.88 -17.5 17+73.4 14+70.0 27+22.0 0.11 0.16 45.5 2.71 1.86 -31.4 17+31.0 14+42.0 27+50.0 0.27 0.17 -37.0 4.08 2.41 -40.9 17+15.1 14+24.0 27+68.0 0.26 1.10 323.1 4.07 5.58 37.1 16+63.8 13+52.0 28+40.0 0.19 0.03 -84.2 3.45 0.89 -74.2 16+07.2 13+12.0 28+80.0 0.15 0.06 -60.0 3.14 1.32 -58.0 15+68.9 12+62.0 29+30.0 0.11 0.23 109.1 2.64 2.48 -6.1 15+18.3 12+12.0 29+80.0 0.10 0.41 310.0 2.53 2.86 13.0 14+78.1 11+68.0 30+24.0 0.44 0.18 -59.1 5.25 2.16 -58.9 13+95.0 10+87.0 31+05.0 0.23 0.33 43.5 3.17 2.8 -11.7 12+63.7 10+07.0 31+85.0 0.09 0.31 244.4 1.95 2.67 36.9 12+31.4 9+77.0 32+15.0 0.16 0.15 -6.3 2.71 1.99 -26.6 11+97.5 9+34.0 32+58.0 0.36 0.11 -69.4 3.78 1.94 -48.7 11+48.6 8+92.0 33+00.0 0.13 0.60 361.5 2.45 4.49 83.3 11+27.1 8+72.0 33+20.0 0.27 0.63 133.3 3.43 4.29 25.1 10+80.9 8+27.0 33+65.0 0.06 0.16 166.7 1.67 1.97 18.0 10+55.4 8+02.0 33+90.0 0.14 0.25 78.6 2.55 2.53 -0.8 10+10.8 7+57.0 34+35.0 0.28 0.25 -10.7 3.46 2.84 -17.9 9+63.7 7+10.0 34+82.0 0.63 0.84 33.3 4.92 5.1 3.7 8+89.0 6+37.0 35+55.0 0.37 0.28 -24.3 3.95 2.92 -26.1 8+20.7 5+70.0 36+22.0 0.24 0.17 -29.2 3.26 2.38 -27.0 7+78.1 5+27.0 36+65.0 0.22 0.32 45.5 3.14 2.84 -9.6 7+41.4 4+90.0 37+02.0 0.35 0.29 -17.1 3.83 3.06 -20.1 6+98.8 4+47.0 37+45.0 0.14 0.24 71.4 3.69 2.86 -22.5 6+68.9 4+19.9 37+72.2 0.15 0.36 140.0 3.77 3.59 -4.8 6+50.5 4+02.0 37+90.0 0.06 0.55 816.7 2.42 4.19 73.1 5+89.8 3+42.0 38+50.0 0.15 0.26 73.3 3.84 2.56 -33.3 4+82.8 2+57.0 39+35.0 0.18 0.30 66.7 4.14 3 -27.5

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Upper Mill Creek Design Development Report

Table 27 – Main Stem 2-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 4+20.3 1+97.0 39+95.0 0.06 0.60 900.0 2.57 4.23 64.6 3+68.2 1+52.0 40+40.0 0.02 0.53 2550.0 1.6 3.49 118.1 3+46.4 1+32.0 40+60.0 0.11 0.37 236.4 3.35 3.08 -8.1 2+81.4 0+92.0 41+00.0 0.04 0.42 950.0 2.06 3.7 79.6 2+31.7 0+52.1 41+39.9 0.15 0.20 33.3 3.73 2.28 -38.9 2+31.0 0+52 PHANTOM 0.15 0.21 40.0 3.82 2.36 -38.2

Table 28 – Main Stem 10-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 43+18.0 43+18.0 PHANTOM 0.39 0.80 105.1 2.30 3.61 57.0 43+08.0 43+08.0 0+80.0 0.48 2.01 318.8 2.32 5.51 137.5 43+00.0 43+00.0 0+88.0 0.43 0.67 55.8 2.23 3.29 47.5 42+75.0 42+75.0 1+13.0 0.31 2.30 641.9 3.75 5.72 52.5 42+67.0 42+67.0 1+21.0 0.64 0.87 35.9 4.17 3.87 -7.2 42+38.0 42+38.0 1+50.0 0.82 0.54 -34.1 3.87 3.09 -20.2 42+33.0 42+33.0 1+55.0 1.58 0.45 -71.5 3.34 2.87 -14.1 42+14.5 42+14.5 1+73.5 1.29 0.77 -40.3 4.71 3.70 -21.4 41+54.0 41+54.0 2+34.0 0.17 0.85 400.0 5.07 3.85 -24.1 41+13.0 41+13.0 2+75.0 0.13 1.35 938.5 7.11 4.79 -32.6 40+55.3 38+59.0 3+33.0 0.39 0.61 56.4 6.67 4.37 -34.5 40+01.7 38+13.5 3+78.6 0.40 0.31 -22.5 3.89 2.77 -28.8 39+67.3 37+86.6 4+05.5 0.10 0.79 690.0 3.45 4.82 39.7 38+96.2 36+63.8 5+28.2 0.22 0.59 168.2 5.73 3.53 -38.4 38+53.0 36+28.8 5+63.3 0.04 0.96 2300.0 5.75 4.74 -17.6 38+35.5 36+12.7 5+79.3 0.69 0.68 -1.4 3.03 4.13 36.3

82 BayLand Consultants & Designers, Inc.

Upper Mill Creek Design Development Report

Table 28 – Main Stem 10-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 38+27.4 36+02.0 5+90.0 0.04 0.48 1100.0 4.42 4.09 -7.5 38+04.8 35+87.9 6+04.1 0.06 0.87 1350.0 1.99 5.16 159.3 37+92.8 35+60.5 6+31.5 0.14 1.65 1078.6 7.52 6.24 -17.0 37+78.9 35+47.1 6+44.9 0.42 0.61 45.2 1.97 3.99 102.5 37+44.0 35+27.0 6+65.0 0.23 0.25 8.7 2.32 2.98 28.4 37+37.4 35+20.5 6+71.6 0.55 0.43 -21.8 3.52 3.75 6.5 37+02.9 34+89.4 7+02.7 0.43 0.64 48.8 6.00 4.64 -22.7 36+55.0 34+45.2 7+46.8 0.48 0.65 35.4 4.54 4.62 1.8 36+15.5 34+07.9 7+84.1 0.24 1.20 400.0 6.76 6.23 -7.8 35+12.0 32+87.0 9+05.0 0.38 0.25 -34.2 6.11 2.72 -55.5 34+50.4 32+50.0 9+42.0 0.46 0.38 -17.4 6.44 3.38 -47.5 33+92.4 32+02.0 9+90.0 0.91 0.41 -54.9 4.63 3.48 -24.8 33+69.8 31+66.7 10+25.4 0.99 0.36 -63.6 5.75 3.35 -41.7 33+09.2 31+13.0 10+79.1 0.36 0.36 0.0 6.31 2.69 -57.4 32+85.1 30+89.4 11+02.7 0.14 0.39 178.6 8.57 3.28 -61.7 32+62.9 30+65.9 11+26.1 0.66 0.33 -50.0 8.77 3.08 -64.9 31+98.1 29+82.0 12+10.0 1.80 0.27 -85.0 5.54 2.86 -48.4 31+48.6 29+44.0 12+48.0 0.53 0.40 -24.5 3.56 3.10 -12.9 31+33.5 29+22.0 12+70.0 0.11 0.53 381.8 7.38 4.17 -43.5 31+19.7 29+04.0 12+88.0 0.08 0.40 400.0 11.04 3.44 -68.8 30+54.1 28+16.1 13+76.0 0.13 0.41 215.4 6.44 3.48 -46.0 30+12.4 27+66.7 14+25.4 0.11 0.10 -9.1 3.23 1.79 -44.6 29+65.8 27+20.6 14+71.4 0.71 0.36 -49.3 2.70 2.93 8.5 29+46.1 27+05.9 14+86.1 0.87 0.40 -54.0 3.46 3.15 -9.0 29+32.7 26+87.0 15+05.0 0.35 0.28 -20.0 3.25 2.97 -8.6 28+99.2 26+57.0 15+35.0 0.65 0.20 -69.2 7.68 2.62 -65.9 28+44.0 26+06.9 15+85.1 1.44 0.43 -70.1 8.29 3.78 -54.4 28+14.5 25+77.0 16+15.0 0.24 1.20 400.0 5.48 5.31 -3.1

83 BayLand Consultants & Designers, Inc.

Upper Mill Creek Design Development Report

Table 28 – Main Stem 10-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 27+97.5 25+60.0 16+32.0 0.54 1.28 137.0 7.25 5.62 -22.5 27+51.7 25+34.0 16+58.0 0.39 0.70 79.5 9.95 4.61 -53.7 26+29.4 23+90.0 18+02.0 0.37 0.62 67.6 4.69 3.69 -21.3 26+12.5 23+77.0 18+15.0 0.44 0.39 -11.4 6.89 3.05 -55.7 25+78.4 23+41.7 18+50.3 0.19 0.76 300.0 6.04 4.64 -23.2 25+29.6 23+07.0 18+85.1 0.25 0.64 156.0 5.83 4.29 -26.4 24+68.2 22+28.1 19+63.9 0.30 0.50 66.7 6.37 3.84 -39.7 24+44.5 21+80.1 20+11.9 0.49 0.17 -65.3 4.35 2.22 -49.0 23+68.3 21+36.2 20+55.8 0.18 0.17 -5.6 4.94 1.99 -59.7 23+46.8 21+17.1 20+75.0 0.27 0.20 -25.9 5.33 2.22 -58.3 22+87.2 20+31.9 21+60.2 0.15 1.26 740.0 6.61 5.58 -15.6 22+66.4 20+11.1 21+81.0 0.09 0.71 688.9 4.16 4.41 6.0 22+58.2 20+03.0 21+89.0 0.28 0.56 100.0 5.02 4.55 -9.4 22+22.8 19+77.7 22+14.4 0.73 0.59 -19.2 3.90 4.55 16.7 21+95.4 19+31.4 22+60.6 0.13 0.33 153.8 3.06 3.42 11.8 21+69.7 18+97.8 22+94.2 0.49 0.23 -53.1 5.09 2.61 -48.7 21+22.1 18+55.1 23+36.9 0.16 0.52 225.0 7.79 4.36 -44.0 20+68.2 18+11.9 23+80.1 0.63 1.76 179.4 3.44 7.58 120.3 20+43.8 17+69.4 24+22.6 0.03 0.72 2300.0 6.48 4.65 -28.2 19+78.0 17+14.0 24+78.0 0.30 0.51 70.0 3.65 3.91 7.1 19+66.3 16+77.0 25+15.0 0.15 0.35 133.3 6.74 2.79 -58.6 19+33.7 16+61.3 25+30.7 0.16 0.38 137.5 1.62 3.10 91.4 18+61.0 15+64.0 26+28.0 0.29 0.39 34.5 4.68 3.43 -26.7 17+99.9 15+21.0 26+71.1 0.36 0.32 -11.1 3.48 2.69 -22.7 17+73.4 14+70.0 27+22.0 0.20 0.32 60.0 3.55 2.82 -20.6 17+31.0 14+42.0 27+50.0 0.14 0.27 92.9 4.68 3.16 -32.5 17+15.1 14+24.0 27+68.0 0.12 0.33 175.0 5.31 3.39 -36.2 16+63.8 13+52.0 28+40.0 0.11 0.11 0.0 3.98 1.84 -53.8

84 BayLand Consultants & Designers, Inc.

Upper Mill Creek Design Development Report

Table 28 – Main Stem 10-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 16+07.2 13+12.0 28+80.0 0.30 0.17 -43.3 3.36 2.34 -30.4 15+68.9 12+62.0 29+30.0 0.41 0.33 -19.5 3.07 3.20 4.2 15+18.3 12+12.0 29+80.0 0.13 0.16 23.1 3.00 1.98 -34.0 14+78.1 11+68.0 30+24.0 0.34 0.18 -47.1 4.91 2.41 -50.9 13+95.0 10+87.0 31+05.0 0.39 0.50 28.2 4.63 3.73 -19.4 12+63.7 10+07.0 31+85.0 0.27 0.53 96.3 2.66 3.81 43.2 12+31.4 9+77.0 32+15.0 0.56 0.46 -17.9 4.26 3.66 -14.1 11+97.5 9+34.0 32+58.0 0.12 0.36 200.0 4.42 3.69 -16.5 11+48.6 8+92.0 33+00.0 0.35 0.56 60.0 3.64 4.62 26.9 11+27.1 8+72.0 33+20.0 0.56 0.66 17.9 5.40 4.83 -10.6 10+80.9 8+27.0 33+65.0 0.86 0.38 -55.8 2.57 3.22 25.3 10+55.4 8+02.0 33+90.0 0.59 0.48 -18.6 4.31 3.74 -13.2 10+10.8 7+57.0 34+35.0 0.47 0.49 4.3 5.27 4.26 -19.2 9+63.7 7+10.0 34+82.0 0.41 0.67 63.4 6.46 4.98 -22.9 8+89.0 6+37.0 35+55.0 0.50 0.40 -20.0 5.46 3.82 -30.0 8+20.7 5+70.0 36+22.0 0.27 0.36 33.3 4.95 3.70 -25.3 7+78.1 5+27.0 36+65.0 0.21 0.56 166.7 4.61 4.03 -12.6 7+41.4 4+90.0 37+02.0 0.13 0.53 307.7 5.05 4.48 -11.3 6+98.8 4+47.0 37+45.0 0.28 0.38 35.7 5.58 3.86 -30.8 6+68.9 4+19.9 37+72.2 0.41 0.83 102.4 4.77 5.67 18.9 6+50.5 4+02.0 37+90.0 0.19 0.66 247.4 3.95 4.95 25.3 5+89.8 3+42.0 38+50.0 0.07 0.41 485.7 5.56 3.43 -38.3 4+82.8 2+57.0 39+35.0 0.28 0.47 67.9 6.68 4.09 -38.8 4+20.3 1+97.0 39+95.0 0.11 1.06 863.6 4.78 6.08 27.2 3+68.2 1+52.0 40+40.0 0.24 0.71 195.8 3.02 4.41 46.0 3+46.4 1+32.0 40+60.0 0.27 0.57 111.1 5.67 4.09 -27.9 2+81.4 0+92.0 41+00.0 0.11 0.55 400.0 3.75 4.59 22.4 2+31.7 0+52.1 41+39.9 0.24 0.31 29.2 5.26 3.04 -42.2

85 BayLand Consultants & Designers, Inc.

Upper Mill Creek Design Development Report

Table 28 – Main Stem 10-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 2+31.0 0+52 PHANTOM 0.27 0.32 18.5 5.62 3.09 -45.0

Table 29 – East Tributary 2-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 31+41.0 31+41.0 PHANTOM 0.16 0.34 112.5 2.40 2.13 -11.3 31+40.0 31+40.0 50+73.5 0.20 1.13 465.0 2.61 3.70 41.8 31+28.0 31+28.0 50+83.5 0.53 0.24 -54.7 4.05 1.83 -54.8 31+03.0 31+03.0 51+07.0 0.73 1.14 56.2 4.77 3.74 -21.6 30+91.0 30+91.0 51+19.0 0.05 0.15 200.0 1.46 1.48 1.4 30+44.0 30+44.0 51+60.0 0.24 0.60 150.0 2.99 2.85 -4.7 30+32.0 30+32.0 51+72.0 0.24 0.33 37.5 3.01 2.18 -27.6 30+01.0 30+01.0 52+00.0 0.20 0.47 135.0 2.71 2.54 -6.3 29+89.0 29+89.0 52+12.0 0.03 0.23 666.7 1.22 1.83 50.0 29+62.0 29+62.0 52+39.0 0.54 0.73 35.2 4.41 3.10 -29.7 29+50.0 29+50.0 52+51.0 0.49 0.35 -28.6 4.22 2.23 -47.2 29+31.0 29+31.0 52+69.0 0.29 1.40 382.8 3.25 4.15 27.7 29+19.0 29+19.0 52+81.0 0.35 0.30 -14.3 3.54 2.09 -41.0 28+89.0 28+89.0 53+10.0 0.27 1.03 281.5 3.18 3.56 11.9 28+77.0 28+77.0 53+22.0 0.66 0.23 -65.2 4.73 1.81 -61.7 28+29.3 27+98.7 53+67.0 0.31 0.53 71.0 3.41 2.74 -19.6 27+91.5 27+60.7 54+05.0 0.76 0.34 -55.3 5.17 2.23 -56.9 27+63.9 27+33.7 54+32.0 1.00 0.71 -29.0 5.83 4.49 -23.0 27+26.6 26+95.7 54+70.0 0.13 0.42 223.1 2.27 3.28 44.5 26+43.3 26+37.7 55+28.0 0.43 0.96 123.3 3.97 4.39 10.6 26+30.0 26+24.7 55+41.0 0.32 0.26 -18.8 3.44 2.84 -17.4

86 BayLand Consultants & Designers, Inc.

Upper Mill Creek Design Development Report

Table 29 – East Tributary 2-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 25+89.0 25+90.7 55+75.0 0.07 0.11 57.1 1.78 1.59 -10.7 25+77.4 25+79.7 55+86.0 0.91 0.09 -90.1 5.63 1.75 -68.9 25+67.2 25+57.7 56+08.0 0.03 0.51 1600.0 1.09 3.80 248.6 25+05.4 25+20.7 56+45.0 0.22 0.72 227.3 2.87 4.31 50.2 24+96.6 24+89.7 56+76.0 0.27 0.42 55.6 3.12 3.31 6.1 24+63.1 24+64.7 57+01.0 0.68 0.29 -57.4 4.81 2.85 -40.7 24+24.4 24+29.7 57+36.0 1.56 0.52 -66.7 7.05 3.39 -51.9 23+79.2 23+90.7 57+75.0 0.12 0.35 191.7 2.23 3.15 41.3 23+62.9 23+74.7 57+91.0 0.28 0.65 132.1 3.29 4.31 31.0 23+27.3 23+44.7 58+21.0 0.72 0.89 23.6 5.03 4.92 -2.2 22+99.1 23+25.2 58+40.5 2.40 1.14 -52.5 8.61 5.39 -37.4 22+87.5 22+99.7 58+66.0 0.12 0.46 283.3 2.19 3.15 43.8 22+64.9 22+81.7 58+84.0 0.17 0.65 282.4 2.65 4.25 60.4 22+30.7 22+47.7 59+18.0 0.92 0.65 -29.3 5.75 4.13 -28.2 21+98.6 22+15.7 59+50.0 0.27 0.59 118.5 3.27 3.95 20.8 21+72.5 21+89.7 59+76.0 0.17 1.06 523.5 2.68 4.62 72.4 21+58.9 21+76.1 59+89.6 0.24 0.25 4.2 3.07 2.79 -9.1 21+45.5 21+62.7 60+03.0 0.85 0.67 -21.2 5.52 4.22 -23.6 21+08.0 21+32.7 60+33.0 1.51 0.94 -37.7 6.96 4.34 -37.6 20+96.0 21+22.7 60+43.0 0.08 0.45 462.5 1.88 3.60 91.5 20+65.0 20+86.7 60+79.0 0.14 1.14 714.3 2.26 4.62 104.4 20+54.8 20+77.8 60+87.9 0.12 0.32 166.7 2.20 3.12 41.8 20+25.3 20+48.7 61+17.0 0.43 0.25 -41.9 4.04 2.53 -37.4 19+97.8 20+23.7 61+42.0 0.78 0.20 -74.4 5.20 2.31 -55.6 19+67.5 19+96.7 61+69.0 0.14 0.53 278.6 2.38 3.35 40.8 19+34.8 19+66.2 61+99.5 0.30 0.64 113.3 3.34 4.23 26.6 18+93.2 19+30.7 62+35.0 0.57 0.46 -19.3 4.49 3.58 -20.3 18+52.8 18+78.7 62+87.0 0.06 0.38 533.3 1.48 3.12 110.8

87 BayLand Consultants & Designers, Inc.

Upper Mill Creek Design Development Report

Table 29 – East Tributary 2-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 17+89.0 18+07.7 63+58.0 0.68 0.22 -67.6 4.82 2.02 -58.1 16+98.3 17+31.7 64+34.0 0.15 0.09 -40.0 2.41 1.41 -41.5 15+89.1 16+30.6 65+35.0 0.24 0.89 270.8 2.99 4.16 39.1 15+81.3 16+07.4 65+58.3 0.09 0.04 -55.6 1.76 1.18 -33.0 15+34.3 15+68.7 65+97.0 0.34 0.18 -47.1 3.29 2.31 -29.8 14+71.4 14+96.7 66+69.0 0.34 0.25 -26.5 3.16 2.78 -12.0 14+11.6 14+32.7 67+33.0 0.24 0.28 16.7 2.81 2.89 2.8 13+75.3 13+95.7 67+70.0 0.33 0.24 -27.3 3.08 2.57 -16.6 13+40.9 13+36.7 68+02.0 0.20 0.85 325.0 2.46 4.06 65.0 12+48.3 12+45.7 69+20.0 0.27 0.06 -77.8 2.86 1.18 -58.7 12+23.0 12+19.7 69+46.0 0.13 0.80 515.4 1.99 4.42 122.1 11+91.9 11+89.7 69+76.0 0.26 0.15 -42.3 2.91 1.84 -36.8 11+60.5 11+59.7 70+06.0 0.18 0.15 -16.7 2.45 1.61 -34.3 11+09.4 11+18.7 70+47.0 0.68 0.12 -82.4 4.41 1.68 -61.9 10+69.5 10+70.7 70+95.0 0.03 1.17 3800.0 1.11 4.76 328.8 10+39.5 10+32.7 71+33.0 0.36 0.10 -72.2 3.32 1.44 -56.6 10+00.4 9+97.7 71+68.0 0.23 0.07 -69.6 2.66 1.29 -51.5 9+87.9 9+70.7 71+95.0 0.23 0.12 -47.8 2.71 1.65 -39.1 9+39.5 9+30.7 72+35.0 0.60 0.23 -61.7 4.07 2.31 -43.2 9+15.6 8+95.7 72+70.0 0.05 0.13 160.0 1.32 1.50 13.6 8+36.5 8+29.7 73+36.0 0.16 0.29 81.3 2.28 2.61 14.5 7+95.5 7+50.7 74+15.0 0.26 0.12 -53.8 2.89 1.70 -41.2 7+19.1 6+89.7 74+76.0 0.79 0.22 -72.2 4.95 1.91 -61.4 6+58.9 6+35.7 75+30.0 0.14 0.11 -21.4 2.14 1.63 -23.8 6+11.1 5+78.7 75+87.0 0.78 0.14 -82.1 4.84 1.85 -61.8 5+51.3 5+21.7 76+44.0 0.14 0.12 -14.3 2.18 1.74 -20.2 5+24.6 4+80.7 76+85.0 0.30 0.40 33.3 2.98 2.80 -6.0 5+06.0 4+69.7 76+96.0 0.46 0.08 -82.6 3.77 1.62 -57.0

88 BayLand Consultants & Designers, Inc.

Upper Mill Creek Design Development Report

Table 29 – East Tributary 2-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 4+96.9 4+58.7 77+07.0 0.16 0.07 -56.3 2.32 1.31 -43.5 4+66.2 4+22.7 77+43.0 0.15 0.19 26.7 2.84 2.37 -16.5 3+69.1 3+39.7 78+26.0 0.10 0.71 610.0 2.35 3.73 58.7 3+27.0 2+97.7 78+68.0 0.07 0.01 -85.7 2.00 0.39 -80.5 3+01.4 2+68.7 78+97.0 0.11 0.02 -81.8 2.53 0.72 -71.5 2+61.3 2+30.7 79+35.0 0.05 0.12 140.0 1.67 1.63 -2.4 2+36.6 1+98.7 79+67.0 0.48 0.10 -79.2 4.89 1.34 -72.6 1+82.3 1+59.7 80+06.0 0.04 0.12 200.0 1.64 1.79 9.1 1+43.0 1+21.7 80+44.0 0.10 0.10 0.0 2.43 1.64 -32.5 0+91.6 0+79.7 80+86.0 0.11 0.79 618.2 2.51 4.29 70.9 0+31.2 0+10.7 81+55.0 0.03 0.06 100.0 1.44 1.15 -20.1

Table 30 – East Tributary 10-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 31+41.0 31+41.0 PHANTOM 0.36 0.80 122.2 3.92 3.56 -9.2 31+40.0 31+40.0 50+73.5 0.40 2.04 410.0 4.11 5.44 32.4 31+28.0 31+28.0 50+83.5 0.55 0.63 14.5 4.72 3.19 -32.4 31+03.0 31+03.0 51+07.0 0.32 1.38 331.3 3.69 4.57 23.8 30+91.0 30+91.0 51+19.0 0.08 0.28 250.0 1.96 2.21 12.8 30+44.0 30+44.0 51+60.0 0.38 1.23 223.7 4.16 4.49 7.9 30+32.0 30+32.0 51+72.0 0.38 0.89 134.2 4.15 3.90 -6.0 30+01.0 30+01.0 52+00.0 0.22 0.87 295.5 3.18 3.78 18.9 29+89.0 29+89.0 52+12.0 0.09 0.55 511.1 2.07 3.07 48.3 29+62.0 29+62.0 52+39.0 0.87 1.01 16.1 6.06 4.00 -34.0 29+50.0 29+50.0 52+51.0 1.09 0.60 -45.0 6.72 3.15 -53.1

89 BayLand Consultants & Designers, Inc.

Upper Mill Creek Design Development Report

Table 30 – East Tributary 10-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 29+31.0 29+31.0 52+69.0 0.52 1.88 261.5 4.77 5.38 12.8 29+19.0 29+19.0 52+81.0 0.59 0.65 10.2 5.05 3.31 -34.5 28+89.0 28+89.0 53+10.0 0.50 1.86 272.0 4.72 5.23 10.8 28+77.0 28+77.0 53+22.0 0.99 0.34 -65.7 6.41 2.41 -62.4 28+29.3 27+98.7 53+67.0 0.36 1.16 222.2 3.93 4.41 12.2 27+91.5 27+60.7 54+05.0 1.06 0.63 -40.6 6.62 3.27 -50.6 27+63.9 27+33.7 54+32.0 1.37 1.35 -1.5 7.55 6.68 -11.5 27+26.6 26+95.7 54+70.0 0.26 0.82 215.4 3.54 4.98 40.7 26+43.3 26+37.7 55+28.0 0.38 1.76 363.2 4.16 6.40 53.8 26+30.0 26+24.7 55+41.0 0.32 0.46 43.8 3.82 4.03 5.5 25+89.0 25+90.7 55+75.0 0.18 0.22 22.2 2.96 2.40 -18.9 25+77.4 25+79.7 55+86.0 1.23 0.22 -82.1 7.10 2.85 -59.9 25+67.2 25+57.7 56+08.0 0.09 1.26 1300.0 2.20 6.40 190.9 25+05.4 25+20.7 56+45.0 0.43 0.89 107.0 4.34 5.23 20.5 24+96.6 24+89.7 56+76.0 0.64 0.43 -32.8 5.19 3.75 -27.7 24+63.1 24+64.7 57+01.0 0.88 0.37 -58.0 5.84 3.51 -39.9 24+24.4 24+29.7 57+36.0 1.98 0.56 -71.7 8.91 3.88 -56.5 23+79.2 23+90.7 57+75.0 0.33 0.54 63.6 3.96 4.35 9.8 23+62.9 23+74.7 57+91.0 0.58 1.13 94.8 5.07 6.26 23.5 23+27.3 23+44.7 58+21.0 1.05 1.84 75.2 6.63 7.72 16.4 22+99.1 23+25.2 58+40.5 0.46 1.30 182.6 4.57 6.42 40.5 22+87.5 22+99.7 58+66.0 0.17 0.64 276.5 2.90 4.10 41.4 22+64.9 22+81.7 58+84.0 0.38 1.56 310.5 4.26 7.12 67.1 22+30.7 22+47.7 59+18.0 1.37 0.91 -33.6 7.64 5.34 -30.1 21+98.6 22+15.7 59+50.0 0.48 0.93 93.8 4.71 5.48 16.3 21+72.5 21+89.7 59+76.0 0.36 1.97 447.2 4.15 6.84 64.8 21+58.9 21+76.1 59+89.6 0.39 0.79 102.6 4.32 5.24 21.3 21+45.5 21+62.7 60+03.0 1.40 1.44 2.9 7.76 6.68 -13.9

90 BayLand Consultants & Designers, Inc.

Upper Mill Creek Design Development Report

Table 30 – East Tributary 10-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 21+08.0 21+32.7 60+33.0 2.74 1.12 -59.1 10.38 5.11 -50.8 20+96.0 21+22.7 60+43.0 0.19 1.04 447.4 2.94 5.84 98.6 20+65.0 20+86.7 60+79.0 0.12 1.09 808.3 2.41 5.11 112.0 20+54.8 20+77.8 60+87.9 0.19 1.00 426.3 3.03 5.81 91.7 20+25.3 20+48.7 61+17.0 1.11 0.58 -47.7 6.93 4.19 -39.5 19+97.8 20+23.7 61+42.0 1.14 0.40 -64.9 6.91 3.51 -49.2 19+67.5 19+96.7 61+69.0 0.32 1.42 343.8 3.86 5.75 49.0 19+34.8 19+66.2 61+99.5 0.60 0.82 36.7 5.16 5.06 -1.9 18+93.2 19+30.7 62+35.0 0.81 0.77 -4.9 5.92 4.95 -16.4 18+52.8 18+78.7 62+87.0 0.09 0.60 566.7 2.02 4.24 109.9 17+89.0 18+07.7 63+58.0 0.95 0.32 -66.3 6.35 2.67 -58.0 16+98.3 17+31.7 64+34.0 0.29 0.20 -31.0 3.64 2.37 -34.9 15+89.1 16+30.6 65+35.0 0.56 0.71 26.8 4.99 4.14 -17.0 15+81.3 16+07.4 65+58.3 0.20 0.13 -35.0 2.88 2.23 -22.6 15+34.3 15+68.7 65+97.0 0.83 0.32 -61.4 5.51 3.39 -38.5 14+71.4 14+96.7 66+69.0 0.43 0.59 37.2 4.04 4.59 13.6 14+11.6 14+32.7 67+33.0 0.68 0.85 25.0 5.07 5.33 5.1 13+75.3 13+95.7 67+70.0 0.50 0.66 32.0 4.25 4.54 6.8 13+40.9 13+36.7 68+02.0 0.32 0.82 156.3 3.49 4.34 24.4 12+48.3 12+45.7 69+20.0 0.30 0.39 30.0 3.34 3.13 -6.3 12+23.0 12+19.7 69+46.0 0.17 0.33 94.1 2.57 3.04 18.3 11+91.9 11+89.7 69+76.0 0.46 0.54 17.4 4.18 3.72 -11.0 11+60.5 11+59.7 70+06.0 0.45 0.40 -11.1 4.21 2.85 -32.3 11+09.4 11+18.7 70+47.0 1.01 0.52 -48.5 5.95 3.67 -38.3 10+69.5 10+70.7 70+95.0 0.10 0.75 650.0 2.12 4.11 93.9 10+39.5 10+32.7 71+33.0 0.63 0.33 -47.6 4.78 2.93 -38.7 10+00.4 9+97.7 71+68.0 0.46 0.31 -32.6 4.17 2.90 -30.5 9+87.9 9+70.7 71+95.0 0.57 0.25 -56.1 4.63 2.63 -43.2

91 BayLand Consultants & Designers, Inc.

Upper Mill Creek Design Development Report

Table 30 – East Tributary 10-Year Storm Event Existing and Proposed Shear Stresses and Velocities Existing Proposed Change in Existing Proposed Change in Existing Proposed Proposed Shear Shear Shear Velocity Velocity Velocity (%) River River Alignment Stress Stress Stress (%) (ft/s) (ft/s) Station Station Station (lb/sq ft) (lb/sq ft) 9+39.5 9+30.7 72+35.0 0.32 0.35 9.4 3.45 3.12 -9.6 9+15.6 8+95.7 72+70.0 0.11 0.28 154.5 2.17 2.44 12.4 8+36.5 8+29.7 73+36.0 0.26 0.70 169.2 3.26 4.36 33.7 7+95.5 7+50.7 74+15.0 0.32 0.28 -12.5 3.55 2.89 -18.6 7+19.1 6+89.7 74+76.0 1.29 0.41 -68.2 6.92 2.89 -58.2 6+58.9 6+35.7 75+30.0 0.19 0.22 15.8 2.82 2.52 -10.6 6+11.1 5+78.7 75+87.0 1.32 0.32 -75.8 6.99 3.02 -56.8 5+51.3 5+21.7 76+44.0 0.26 0.32 23.1 3.29 3.05 -7.3 5+24.6 4+80.7 76+85.0 0.21 0.43 104.8 2.91 3.22 10.7 5+06.0 4+69.7 76+96.0 0.39 0.22 -43.6 3.99 2.78 -30.3 4+96.9 4+58.7 77+07.0 0.18 0.18 0.0 2.79 2.18 -21.9 4+66.2 4+22.7 77+43.0 0.16 0.42 162.5 3.29 3.75 14.0 3+69.1 3+39.7 78+26.0 0.13 1.64 1161.5 3.06 5.93 93.8 3+27.0 2+97.7 78+68.0 0.09 0.06 -33.3 2.54 1.25 -50.8 3+01.4 2+68.7 78+97.0 0.16 0.08 -50.0 3.38 1.56 -53.8 2+61.3 2+30.7 79+35.0 0.06 0.27 350.0 2.06 2.72 32.0 2+36.6 1+98.7 79+67.0 0.30 0.19 -36.7 4.47 2.03 -54.6 1+82.3 1+59.7 80+06.0 0.08 0.22 175.0 2.45 2.58 5.3 1+43.0 1+21.7 80+44.0 0.13 0.15 15.4 3.03 2.15 -29.0 0+91.6 0+79.7 80+86.0 0.16 0.21 31.3 3.30 2.55 -22.7 0+31.2 0+10.7 81+55.0 0.06 0.08 33.3 2.15 1.47 -31.6

92 BayLand Consultants & Designers, Inc.

Upper Mill Creek Design Development Report

2-Dimensional Modeling

HEC-RAS (5.0.5) has the ability to perform two-dimensional (2D) hydrodynamic routing under unsteady flow conditions. Using either the 2D Saint-Venant or 2D Diffusion Wave equations, the program uses an Implicit Finite Volume algorithm to calculate hydraulic parameters over a user defined mesh size and time step. The program uses an unstructured computation mesh with cells consisting of 3-8 sides (cell faces) and a cell bottom. The cell faces are pre-processed into detailed hydraulic property tables that govern the movement of flow between adjacent cells, while each computational cell bottom is based on the details of the underlying terrain. This allows the application of larger cells to speed up processing times without losing the details of the site topography.

A 2-dimensional model was developed to determine the efficacy of the proposed design and to ensure that increased floodplain connectivity would not produce erosive shear stresses or velocities. Unit hydrographs developed during the hydrologic analysis were routed through both models to compare the effects of the proposed design and to identify areas of potential concern.

The model results showed that all storm events accessed the floodplain, with the half year recurrence interval storm accessing the floodplain and the one-year recurrence interval storm expanding across the entire valley width for most of the project area. Shear stresses and velocities were evaluated for all storm events along the stream channel. High shear stresses were identified at a few locations due to changes in valley or channel slope, roughness, or valley morphology, and design measures were taken (i.e. valley grade controls) to ensure channel and floodplain stability. The model results confirmed that the proposed design will increase floodplain connectivity, safely convey all storm flows up to the 100-YR event and will provide sufficient saturation for wetland enhancement and expansion.

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11. FUNCTION BASED ASSESSMENT (UM-1 through UM-9)

Introduction

The Stream Functions Pyramid Framework (SFPF) from A Function-Based Framework for Stream Assessment and Restoration Projects (Harman et al., 2012) was utilized throughout the entire Project process to ensure that the most appropriate design approach would be selected.

It should be noted that Anne Arundel County has conducted biological monitoring since 2010 at four sampling locations along Mill Creek, three of which are within the Study Area. The monitoring effort consists of benthic macroinvertebrate sampling, physical habitat assessments, geomorphology assessments including pebble counts and cross sections, and in-situ water quality measurements. Monitoring results from 2010 to 2014 are provided in the report Biological Monitoring Report for Targeted Sites in the Dividing Creek, Mill Creek, and Reference Reach Watersheds (Baughman, et al., 2016), and monitoring results from 2016 are provided in Targeted Sites and CIP Stream Restoration Sites Biological Monitoring For the 2016 Index Period (Anne Arundel County, 2016). The monitoring results were evaluated and included as part of the functional pyramid assessment.

Table 31 shows the assessment parameters by SFPF pyramid level that were evaluated as part of this Project. Table 31 also includes the measurement method(s) used to quantify the existing function-based condition.

Table 31 – Assessment Parameters by Pyramid Level Level and Category Parameter Measurement Method Flow Regime (Flashiness) Level 1 – Hydrology Runoff Concentrated Flow Bank Height Ratio Floodplain Connectivity Level 2 – Hydraulics Entrenchment Ratio Flow Dynamics Stream Velocity BEHI/NBS Level 3 – Geomorphology Bank Migration/Lateral Stability Actual Lateral Erosion Rate (Cross Sections for UM-2, UM-4, and UM-9 only) Nutrients Laboratory Analysis Conductivity (µS/cm) DO (mg/L) Level 4 – Physicochemical Water Quality (for UM-2, UM-4, pH and UM-9 only) Temperature (ºC) Turbidity (NTUs)

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Table 31 – Assessment Parameters by Pyramid Level Level and Category Parameter Measurement Method MBSS Habitat Assessment EPA Habitat Assessment RBP Score (for UM-2, UM-4 and Macroinvertebrate & Level 5 – Biology UM-9 only) Fish Communities PHI Score (for UM-2, UM-4 and UM-9 only) BIBI Score (for UM-2, UM-4 and UM-9 only)

Reach Scale Function Based Assessment

Using the above assessment parameters and associated measurement methods, the existing function-based condition for each reach was quantified. Each measurement method value was rated either “Functioning,” “Functioning at Risk” or “Not Functioning” based on a set of performance standards. Documentation supporting the specific assessment parameters, measurement methods and performance standards for the Project are provided in Appendix M.

A summary of the overall existing condition rating for each reach is shown in Table 32. Detailed explanations of the ratings are included in Appendix M.

Table 32 – Pre-Restoration Condition Rating Overall Pre-Restoration Level Reach Condition Rating UM-1, UM-2, UM-3, UM-4, UM-5, Level 1 – Hydrology Not Functioning UM-6, UM-7, UM-8, UM-9 UM-1, UM-2, UM-3, UM-4, UM-5, Level 2 – Hydraulics Not Functioning UM-6, UM-7, UM-8, UM-9 UM-1, UM-2, UM-3, UM-4, UM-6, Functioning at Risk Level 3 – Geomorphology UM-7, UM-8, UM-9 UM-5 Functioning UM-1, UM-2, UM-3, UM-4, UM-5, Level 4 – Physicochemical Not Functioning UM-6, UM-7, UM-8, UM-9 UM-1, UM-2, UM-3, UM-4, UM-5, Functioning at Risk Level 5 – Biology UM-6, UM-7, UM-8 UM-9 Not Functioning

Design Objectives

Design objectives are quantifiable and describe how the Project will be implemented (Harman et al., 2012). The design objectives for the Project are shown in Table 33. The floodplain connectivity design objective will help achieve the programmatic goal of establishment or reconnection with riparian wetlands and optimize floodplain reconnection volume. The bank stabilization design objective will help achieve the

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programmatic goal of providing a significant reduction in annual mass sediments and attached nutrients originating from on-site channel degradation. The installation of riffle grade control structures will promote denitrification during base flow and enhance stream ecological function. Additionally, multiple design objectives will provide water quality credit towards Anne Arundel County’s NPDES MS4 permit and assist in meeting the County’s WLA towards the Bay TMDL.

Table 33 – Design Objectives Level and Parameter Objectives Reach Designation Category Reduce hydrograph peaks and UM-1, UM-2, UM-3, Flow Regime increase duration compared to UM-4, UM-5, UM-6, Level 1 – existing conditions UM-7, UM-8, UM-9 Hydrology UM-1, UM-2, UM-3, Concentrated Reduce potential for concentrated UM-4, UM-5, UM-6, Flows flow to impair reach restoration site UM-7, UM-8, UM-9 UM-1, UM-2, UM-3, Achieve a bank height ratio ≤ 1.0 UM-4, UM-5, UM-6, Floodplain UM-7, UM-8, UM-9 Connectivity UM-1, UM-2, UM-3, Level 2 – Achieve an entrenchment ratio > 2.2 UM-4, UM-5, UM-6, Hydraulics UM-7, UM-8, UM-9 Reduce stream velocities to non- UM-1, UM-2, UM-4, erosive conditions UM-5, UM-7, UM-8 Flow Dynamics Stabilize bed and banks where UM-1, UM-2, UM-4, stream velocities cannot be reduced UM-5, UM-7, UM-8 UM-1, UM-2, UM-3, Level 3 – Stabilize banks (bank Lateral Stability UM-4, UM-6, UM-7, Geomorphology migration/lateral stability) UM-8, UM-9

Proposed Design Approach

Typical design approaches used in Maryland to restore function in highly degraded stream systems include: natural channel design (NCD), legacy sediment removal, analytical design, regenerative stream conveyance design (RSC) and valley restoration. Each design approach was evaluated for suitability for the Project.

The NCD approach is founded on form-based classification determined by measured morphological relations associated with bankfull flow, geomorphic valley type and geomorphic stream type. Natural channel design involves designing channel dimension, pattern and profile based on reference reach data. However, since NCD uses bankfull or effective discharge as the design discharge and maximum floodplain reconnection is a central Project goal, NCD will not be utilized.

The legacy sediment removal approach typically involves wide-scale, aggressive sediment removal across the floodplain. Considering the extensive wetland and tree impacts that would be required to implement this technique, the legacy sediment removal approach was removed from consideration. Additionally, the Project is within

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the Critical Area and permit requirements generally discourage this design approach due to the extensive tree removal necessary to implement.

The analytical design approach is founded on the theory that channel dimensions can be calculated from physically based equations including continuity, hydraulic resistance and sediment transport. It is a process-based classification that involves identifying factors that directly control the imbalance or balance between applied forces and boundary resistance in order to understand alluvial channel behavior and channel response to disturbances. As discussed previously, there are likely no major external sources of sediment to the study reaches were restoration work is proposed. Therefore, sediment transport capacity will not be a major concern after stabilization and the analytical design approach for alluvial channels will not apply.

RSC systems consist of a series of cobble-standstone steps strategically placed in an incised perennial stream to safely transition flow down steep gradient channels. RSC systems are designed to carry the 100-year storm event to ensure floodplain stability where valleys are narrow with a steep longitudinal gradient. Since some of the study reaches are characterized by steep gradient channels and valleys, RSC systems will be utilized.

Valley restoration involves reconstruction of the stream channel and floodplain to re- establish floodplain connectivity and hyporheic exchange. The approach is based on the design of valley topography to produce a high frequency, high duration and large extent of surface and groundwater exchange between the channel and floodplain and to promote the retention of organic matter, sediment, nutrients and water within the channel and floodplain. This approach has been highly successful in eastern U.S. headwater streams with valley slopes between 0.03 percent and 3.00 percent (Starr et al., 2015), although it is not limited to slopes within that range.

Valley restoration is the recommended primary Project approach since it will result in the highest ecological uplift and it will achieve most Project goals, including floodplain re-connection. It will also result in the highest amount of TMDL credit for the Project. RSC systems will be utilized in combination with the valley restoration approach where manipulation of the floodplain is not practicable.

Proposed Design

General Design Approach

The overall design approach utilizes valley restoration wherever possible as this approach most successfully achieves the goals of the Project. As mentioned in Section 9.6., there is a low upstream sediment supply to the project reaches. Therefore, sediment transport modeling was not necessary and was not a major component of the valley restoration approach. Instead, a combination of geomorphic principles (reference data) with hydrologic and hydraulic models was utilized. Reference reaches within the Western Coastal Plain physiographic region including Cat Branch and Jabez Branch

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were utilized to help determine appropriate channel dimensions for a baseflow channel. These reaches are in dynamic equilibrium and have good floodplain connectivity which is in agreement with multiple Project design goals. Hydraulic modeling, including HEC- RAS modeling, was also performed to verify channel and floodplain dimension stability by determining resistance to shear stress. Additional information regarding the design criteria is provided below and the design development plans are provided in Appendix N.

The impaired project reaches were designed using bankfull dimensions and ratios from reference reaches, but with additional floodplain connectivity. The existing base flow channel will generally be filled using on-site material and select borrow, and a new channel will be created. The resulting bank height ratio and increased water table will help establish and support riparian and floodplain plant communities while providing a high capacity to store sediment. Additionally, reconnecting the channel to its floodplain will encourage the development of a system highly resilient to disturbance as flood flows are spread out across the valley and shear stress is minimized. The existing planform will be modified to create a more sustainable channel planform and radius of curvature. The proposed planform will also avoid impacts to large trees and jurisdictional wetlands wherever possible. Log-cobble riffles and log grade controls are proposed to provide grade control and promote stream stability and hydraulic diversity. Clay channel blocks will be installed in strategic locations within the existing channel to improve groundwater recharge and floodplain wetland hydrology. Valley-wide grade controls will also be utilized to mitigate erosion shears across the floodplain. Cobble-sandstone steps will be utilized in series at the upstream end of the East Tributary (Reach UM-1), the upstream end of the Upper Mill Creek Main Stem (Reach UM-6), intermittent channel #1 and intermittent channel #2, to convey flow safely down the steep valley slope.

In-Stream and Floodplain Stabilization Structures

Brief descriptions of the in-stream and floodplain structures proposed for use at Upper Mill Creek are provided below.

Log-Cobble Riffles

Log-Cobble riffles are proposed in areas where riffle features would normally occur, including cross-overs. Log-Cobble riffles are weirs composed of bed material with proposed logs at the riffle crests. The bed material has a proposed gradation sized to remain immobile at design flows. Log-Cobble riffles are intended to emulate existing riffles and maintain or improve floodplain access due to slight increases in bed elevation at the crest of the riffle. The structures will be keyed into the existing/proposed bed and banks to prevent flanking or undermining.

Log Grade Control Structures

Log grade control structures are proposed in place of log-cobble riffles where water surface slopes are low gradient or, more specifically, where the proposed change in elevation between proposed structures is equal to or less than four inches. Compared to

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log-cobble riffles, log grade control structures are a more natural and economical way to provide grade control. Log grade control structures are only utilized in perennial stream channels to ensure logs remain constantly submerged and maintain structural integrity.

Clay Channel Blocks

Clay channel blocks are proposed in areas where the proposed channel diverges from the existing channel. Low hydraulic conductivities associated with clay promote increased groundwater tables, support floodplain reconnection and enhanced riparian vegetation/wetlands.

Cobble-Sandstone Steps

Cobble-sandstone steps consist of weirs placed in an incised intermittent or perennial channel to encourage upstream sedimentation and connection of the channel with the adjacent floodplain. A series of Cobble-sandstone steps sized to carry the 100-year storm event is referred to is an RSC system.

Valley Grade Controls

Valley grade controls (VGCs) are proposed where hydraulic modeling indicated shear stresses across the floodplain greater than 1.5 pounds per square foot. The structures either consist of riprap wrapped in non-woven geotextile fabric placed subgrade across the floodplain with smaller material washed in to minimize void space, or they consist of logs. VGCs prevent potential head cuts from mitigating upstream and prevent the down- valley migration of the channel during higher flow events.

Large Woody Debris

Large Woody Debris (LWD) consists of felled trees with rootwads attached placed in the floodplain to increase floodplain roughness and floodplain flow diversity, as well as create habitat.

Channel Design Criteria

Ultimately, bankfull discharge estimates predicted by the USFWS Western Coastal Plain Regional Curve, which are less than the 1-year storm event developed using TR- 20 hydrologic modeling, were determined to be the most reliable for the Project. However, the project reaches were designed with channel dimensions to flood prior to the design discharge to increase floodplain connectivity and minimize channel shear stress. The valley restoration approach does not include an analysis to estimate bankfull discharge or dimensions, however, valley restoration channels are generally one-third to one-half the area of the bankfull channel associated with the local bankfull regional curve (Starr, R. et al., 2015), and this was taken into consideration during design of the channel.

Channel plan form and bed form diversity are not specifically described in the valley restoration approach. Therefore, plan form sinuosity was designed to yield a slope that

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minimizes shear stress. Generally, sinuosity was increased upstream of the confluence in order to account for rapid variation in the existing valley slope. Per USACE (1991), the degree of scour along a bend is proportional to the ratio of the radius of curvature (RC) to the channel width (W), and scour problems usually develop when ratios (RC/W) are between 2.5 to 3.0, becoming severe at ratios less than 2.5. Therefore, adjusted meander geometry was based on a minimum radius of curvature to bankfull channel width ratio of three. The planform that will be utilized for the proposed channel has RC/W ratios between 3.0 and 6.

General concepts for the layout of the longitudinal profile and the location of bed features were developed based on the planform and reference reach data. After the proposed channel planform and longitudinal profile were completed, preliminary channel dimensions were developed. A summary of pertinent design criteria utilized is provided in Table 34.

Channel dimensions were generally based on stable reference reaches (Table 34), and channel and floodplain stability was verified using HEC-RAS and 2D modeling. Boundary shear stress and critical shear stress were analyzed in conjunction with the existing and proposed substrate materials. The maximum threshold depth and shear stress was calculated for particle mobility of the median (D50) particle size. Particle mobility was limited by not exceeding a shear stress that would move particles between the D35 and D50.

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Table 34 – Design Criteria Proposed Main Proposed Main Proposed East Stem Upstream Stem Downstream Existing Reference Tributary Variable Symbol Units of Confluence of Confluence Channel Reach Channel Channel Channel Dimensions Dimensions Dimensions Drainage Area DA mi2 0.22 – 0.44 0.34 0.36 0.44 0.84 Bankfull Width Wbkf feet 5.0 – 11.7 5.7 4.0 4.0 6.0 Bankfull Mean dbkf feet 0.6 – 1.0 0.9 0.2 – 0.4 0.2 – 0.4 0.2 – 0.4 Depth Width/Depth Ratio Wbkf/dbkf N/A 5.1 – 20.2 6.1 9.1 – 21.1 9.1 – 21.1 13.1 – 31.0

Bankfull Cross- 2 Abkf ft 4.8 – 10.9 5.4 0.7 – 1.8 0.7 – 1.8 1.2 – 2.8 sectional Area Bankfull Mean Vbkf ft/sec 2.3 – 3.5 3.4 0.8 – 2.9 0.8 – 2.9 1.0 – 3.1 Velocity Bankfull Discharge Qbkf cfs 14.7 – 28.5 18.2 0.8 – 5.1 0.8 – 5.1 1.1 – 8.4 Bankfull Maximum dmax feet 0.7 – 1.5 1.3 0.2 – 0.5 0.2 – 0.5 0.2 – 0.5 Depth Max depth/Mean dmax/dbkf N/A 1.17 – 1.67 1.4 1.0 – 1.25 1.0 – 1.25 1.0 – 1.25 Depth Width of Flood Wfpa feet 6.7 – 14.7 60.0 15.2 – 200.0 14.8 – 200.0 18.0 – 200.0 Prone Area Entrenchment Ratio Wfpa/Wbkf N/A 1.0 – 1.5 10.4 > 3.8 > 3.7 > 3.0 Ratio of Radius of Curvature to Rc/Wbkf N/A 0.47 – 208.33 1.0 – 2.6 3.5 – 6.0 3.5 – 6.0 3.5 – 6.0 Bankfull Width Sinuosity K N/A 1.04 – 2.80 1.15 1.21 1.25 1.1 Valley Slope Sval ft/ft 0.005 – 0.016 0.009 0.005 – 0.016 0.005 – 0.016 0.005 – 0.016 Average Water 0.0027 – 0.001 – 0.030 0.005 – 0.030 0.015 – 0.030 (Riffle Savg ft/ft 0.008 Surface Slope 0.0082 (Riffle Slopes) (Riffle Slopes) Slopes)

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Stone Sizing Computations

Log-Cobble Riffles

Log-Cobble Riffles will utilize a gradation of stone and salvaged bed sediments to help embed the interlocking stone matrix and create a stable grade control that mimics a more natural substrate. Stone size was calculated using a critical shear stress relationship developed by Shields (1936) and Andrews (1983). Since a gradation of stone will be utilized, the incipient stone size derived from the Shields equation for uniform stream beds was not appropriate. The competence relationships developed by Andrews provide a more accurate estimation of the threshold of movement for stream beds varying gradations of stone and thus is more applicable. The Di/D50 ratio of bed armor for the Andrews equation can vary from 0.3 to 4.2, depending on the mix of the stone. However, an armor ratio of 2.5 can be substituted in the Andrews equation to form the “Modified Andrews Equation” that establishes a relationship between surface bed sediment size and critical shear stress. For the purpose of these calculations the void space is assumed to be 30 percent and the furnished stone is assumed to be immobile. Critical shear stress (ζci) was set equal to shear stress (ζ) and was taken from the HEC-RAS model at the appropriate sections where structures are to be placed. The maximum shear stress for each section was generally used for the calculation. A Factor of Safety (FS) of 1.25 was used to increase the modeled shear stress and account for natural variations in the bed and localized jumps in bed shear. Equations and relationships used to calculate the constructed riffle stone size, as well as the proposed pool bed material are as follows:

Andrews Equation, ζci* = 0.0834(Di/Ds50)-0.872 Modified Andrews Equation (1), ζci* = 0.0375(Di/Ds50)-0.872 Shields Shear Stress Equation (2), ζci = ζci*(ρs-ρw)g*di Where,

g = 9.81 (m/sec2) Di = D30 (m) D50 = D30/0.3 (m) ρs = 2600 (kg/m3) ρw = 1000 (kg/m3)

Solve for dimensionless critical shear stress,

ζci* = 0.0375(0.3 D50/ Ds50)-0.887

Solve for critical shear stress, ζci = 15700ζci* d30

Reduce and solve Equation (2) for critical shear stress,

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ζci* = 0.107

Reduce and solve equation (1) for D30,

D30 = 0.000594ζci

Shear stress is converted from lbs/ft2 to Pa by multiplying by 47.8803, and this value is multiplied by a factor of safety of 1.25

ζci(Pa)= [ζci (in lbs/ft2 from HEC-RAS)*1.25]*47.88 Therefore,

D30 = ζci(Pa)*0.000594

and,

D50 = D30 / 0.3

Stone mixes for the constructed material were based on the calculated D50 stone diameter. A graphical representation of the proposed percent by weight destitution was compared to the standard Anne Arundel County riprap specifications to determine a suitable, well-graded mix that would promote interlocking of the particles and increase the structures resistance to flood flows.

Although the material sized for the structures is presumed to be immobile, scour depth computations will be conducted at the 90 percent design phase to ensure stone will be installed deep enough to protect the integrity of grade control in areas where localized scour may occur.

Functional Uplift

This approach, if implemented, will result in quantitative functional uplift for Level 2- hydraulics, Level 3-geomorphology. Although only functional uplift for Levels 2 and 3 can be constructed and are therefore considered definitive Project goals, it is important to consider the effect the uplift will have on higher level functions, Level 4- physicochemical and Level 5-biology. Level 4 functionality will likely be improved by achieving annual mass nutrient and sediment reduction credit. Level 5 functionality will likely be increased by improvements in aquatic and terrestrial habitats through floodplain re-establishment and stable riffle-pool sequences.

Proposed Condition

The proposed condition is the highest level of restoration or functional list that can be achieved given the watershed health, reach-level function-based condition, stressors and constraints (Harman et al., 2012). Therefore, it was determined that Levels 2 and 3 (Hydraulics and Geomorphology), will be restored to fully functional levels for all project reaches (Table 35). Typically, lift for higher level functions cannot be constructed and

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relies on the functionality of lower level functions. Therefore, higher level functions will likely have partial-functional lift.

Table 35 – Proposed Condition Level Reach Existing Condition Proposed Condition UM-1, UM-2, UM- Level 1 – 3, UM-4, UM-5, Not Functioning Functioning at Risk Hydrology UM-6, UM-7, UM- 8, UM-9 UM-1, UM-2, UM- Level 2 – 3, UM-4, UM-5 Not Functioning Functioning Hydraulics UM-6, UM-7, UM- 8, UM-9 UM-1, UM-2, UM- Level 3 – 3, UM-4, UM-6, Functioning at Risk Functioning Geomorphology UM-7, UM-8, UM-9 UM-5 Functioning

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12. PROPOSED DESIGN – UM-10

General Design Approach

The retrofit approach for UM-10 is in agreement with the County’s preferred design approach to stabilize the intermittent channel and breach the existing SWM pond using regenerative storm conveyance (RSC) systems. The decommissioned pond will no longer be subject to MD-378 design standards and maintenance requirements. Installation of the RSC systems will facilitate outfall channel stability and improve water quality treatment of stormwater while removing maintenance responsibilities of Pond 824.

The RSC system design was based upon the Regenerative Step Pool Storm Conveyance (SPSC) – aka Coastal Plain Outfalls (CPO) guidance document developed by Anne Arundel County (2012). A SPSC system is a series of open-channel conveyance structures installed in ephemeral channels to convert, through attenuation ponds and a sand seepage filter, surface storm flow to shallow groundwater flow. These systems safely convey, attenuate and treat the quality of storm flow. SPSC systems utilize a series of constructed aquatic pools, cobble-sandstone steps, native vegetation and an underlying sand/woodchip mix filter bed media (Figure 12).

An RSC is similar to a SPSC system, except it is installed in an intermittent and/or perennial channels so storm flow is treated primary through attenuation instead of a sand seepage filter. RSC systems consist of a series of constructed aquatic pools, cobble-sandstone steps, native vegetation and select borrow, typical of site conditions, instead of sand/woodchip mix filter bed media.

Figure 12 – Typical Step-Pool Storm Conveyance Profile

At UM-10, the in-line pond (Pond 824) will be replaced with an RSC that has additional capacity above baseflow conditions to treat the one inch storm event.

Flow will discharge from Outfall S15O012 to an inflow swale followed by two RSC systems; RSC #1 and RSC #2. RSC #1 will convey flow approximately 144 linear feet

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over a 3-foot change in elevation using a series of four riffle-weirs and pools. The proposed weirs for RSC #1 are designed to safely convey the 100-year storm event discharge of 43.4 cubic feet per second. The weirs will be 12 feet long, 13 feet wide and 1.3 feet deep with 5 to 1 side slopes. The proposed pools following the riffle-weirs will be 24 feet long and 2 feet deep and will have varying widths.

From RSC #1, flow will be conveyed to RSC #2, which is sized to convey additional flow from Outfall S15O014. RSC #2 will convey flow approximately 468 linear feet over a 13.5-foot change in elevation using a series of 13 riffle-weirs and pools. The proposed weirs for the RSC system are designed to safely convey the 100-year storm event discharge of 59.4 cubic feet per second. The weirs will be 12 feet long, 15 feet wide and 1.5 feet deep with 5 to 1 side slopes. The proposed pools following the riffle-weirs will be 24 feet long and 2 feet deep and will have varying widths.

From RSC #2, flow will be conveyed over two cobble-sandstone step-pools in series before reaching the confluence with the Main Stem. The RSC design computations are provided in Appendix O.

Since the ephemeral channel downstream of Outfall S15O014 is steep and narrow, the installation of a SPSC system is not feasible. Therefore, channel stabilization is proposed through the installation of a storm drain system. An Anne Arundel County Standard Type ‘B’ (shallow) manhole will be installed at the end of the existing 18-inch CMP. From the shallow manhole, an 18-inch High Performance Polyethylene (HPPE) pipe is proposed to convey flow 89 linear feet over a 12.6-foot drop in elevation from the first proposed manhole (PR M-1) to a second proposed Anne Arundel County Standard Type ‘B’ (shallow) manhole (PR M-2). From the second manhole, a proposed 18-inch HPPE pipe will be installed to convey flow 29 linear feet at a 0.6 percent slope to the tie- in with proposed RSC #2. An end wall will be installed at the end of the 18-inch HPPE and flow will discharge into a confluence pool lined with boulders on all sides. The 18- inch HPPE pipes were sized to convey the 10-year storm discharge. Supporting computations are provided in Appendix O.

Water Quality Computations

The unified stormwater sizing criteria including water quality volume (WQv) and channel protection volume (CPv) as described in the MDE 2000 Maryland Stormwater Design Manual, Volumes I and II were the basis for design enhancements for the decommissioning of Pond 824. WQv is the storage required to catch and treat the stormwater runoff from 90 percent of the average annual rainfall. The volume is based on the percent of imperviousness, drainage area and annual rainfall (1.0 inches). Since Pond 824 was designed prior to current stormwater regulations as a quantity extended detention facility, it provides little to no WQv. As part of the retrofit, WQv will be provided to the maximum extent practicable (MEP). Using a 1-inch design storm, the target WQv for Pond 824 is 0.43 acre-feet.

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The RSC systems are located within an intermittent channel and therefore will not include a sand-seepage system to promote subsurface flow, so the primary source of water quality treatment will be provided by temporary ponding of stormwater within the pools above baseflow elevation. The existing drainage area to Pond 824 is composed of 4.5 acres of impervious area and 0.43 acre-feet of water quality volume is required to treat the first inch of runoff. The total water quality volume treated by the proposed RSC systems above baseflow is 0.52 acre-feet, over 100 percent of the required WQv treatment for the contributing drainage area.

Table 36 below summarizes the target and provided WQv for the drainage area. The target and provided WQv computations can be found in Appendix O.

Table 36 – WQv Summary Target Storage Provided Storage

(acre-feet) (acre-feet) WQv 0.43 0.52

Facility Hydraulics

A reduced CN was computed for the 1-, 10- and 100-year storm events based on the storage provided within the proposed RSC systems above baseflow and TR-20 was utilized to determine the proposed discharges from the RSC systems. Tables 37 and 38 summarize the existing and proposed conditions facility models. Existing hydraulic computations associated with Pond 824 are provided in Appendix G and proposed condition hydraulic computations are located in Appendix P.

Table 37 – Hydraulic Summary: Existing Pond 824 Provided Elevation To Facility From Facility Design Storm Storage (feet) (cfs) (cfs) (acre-feet) 1-year (Cpv) 0.21 51.87 13.5 11.4 10-year 0.49 52.76 58.6 50.3 100-year 1.00 54.11 105.9 73.3

Table 38 – Hydraulic Summary: Proposed RSC System Provided Original CN/ To Facility From Facility Design Storm Storage Reduced CN (cfs) (cfs) (acre-feet) 1-year (Cpv) 71/63 0.52 13.5 9.9 10-year 71/68 0.52 58.6 51.9 100-year 71/68 0.52 105.9 97.5

The proposed RSC system will not increase downstream discharges for the 1-year storm event, although discharges associated with the 10-year and 100-year storm events will be increased. The proposed RSC system is designed to convey the 100-year

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storm event, but it will not fully attenuate the peak discharge associated with the 10-year or 100-year storm events so overbank flood protection (10-year) and extreme flood control (100-year) will not be provided. Anne Arundel County Stormwater Management Practices and Procedures Manual (2012) Section 7.2.2 states overbank flood protection (10-year) is not required if: 1) historical flooding problems do not exist; 2) the site discharges to floodplain areas on County owned land or on parcels that preclude development; and 3) the site discharges to a location that is deemed to have an adequate outfall. Similar criteria exist for providing extreme flood control (100-year). The RSC system was included in the proposed conditions HEC-RAS model to ensure that the additional flow being transported downstream will not adversely impact the Upper Mill Creek Main Stem and floodplain.

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13. POLLUTANT REMOVAL

Interim pollutant load removal and efficiency for the proposed design was estimated using methodology from Final Recommendations of the Expert Panel to Define Removal Rates for Individual Stream Restoration Projects (Schueler, T., Stack, B., 2014). Credit was obtained for Protocol 1 (Prevented Sediment During Storm Flow), Protocol 2 (Instream Denitrification) and Protocol 3 (Floodplain Reconnection).

To estimate the credit for Protocol 1, multiple boring samples were obtained along the length of the Project, spaced approximately 500 linear feet apart. The soil samples were then sent to a laboratory for analysis to determine TN and TP concentration. The laboratory test results report is provided in Appendix Q. TN and TP concentrations were then multiplied by sediment loading rates to determine nutrient loading. As mentioned in Section 9.8, sediment loading rates were obtained from pre-project stream bank erosion rates determined using the Bank Assessment for Non-point source Consequences of Sediment (BANCS) method. It should be noted that the measured bulk densities and nutrient concentrations are lower than the default values from Rosgen (1996, 2001) and Walter et. al (2007), respectively, that were used during concept design (125 pounds per cubic ton bulk density, 1.05 pounds P per ton of sediment and 2.28 pounds of N per ton sediment) (Table 39). One reason for the lower measured bulk density values is due to a high percentage of stream bank area occupied by tree and plant roots. The mass load reduction was discounted 50 percent to account for the fact that some sediment transport occurs naturally in a stable stream channel.

To estimate credit for Protocol 2, denitrification was assumed to occur within a “box” extending the length of the restored reach with a bank height ratio of one or less. The cross-sectional area of the box was estimated to have a maximum depth of 5 feet beneath the stream invert and a width associated with the median base flow channel plus 5 feet on either side of the stream bank. The hyporheic box volume was then multiplied by the default unit denitrification rate (1.06 x 10-4 pounds/ton/day of soil).

Credit for Protocol 3 was estimated by calculating the pre- and post- restoration volumes of runoff that access the floodplain on an average annual basis. A ratio of the net increase in floodplain volume to the total runoff volume was then determined and multiplied by the total pollutant load across the watershed, minus the load treated by upstream BMP practices. Finally, pollutant removal was assumed to be 20 percent of the N load, 30 percent of the P load and 20 percent of the sediment load.

The estimated pollutant load removal and efficiency using the aforementioned assumptions is shown below in Table 39. Supporting computations are provided in Appendix Q.

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Table 39 – Interim Pollutant Load Removal Efficiencies Total Nitrogen Total Phosphorous Total Sediment Protocol Credit (lbs N/yr) Credit (lbs P/yr) Credit (tons/yr) 1-Estimated Credit for Prevented Sediment 556 347 584 During Storm Flow 2-Credit for In-Stream and Riparian Nutrient Processing within the 1,267 N/A N/A Hyporheic Zone during Base Flow 3- Credit for Floodplain 883 74 13 Reconnection Volume Total 2,706 421 597

The impervious area treated was assessed using criteria in the MDE guidance document Accounting for Stormwater Wasteload Allocations and Impervious Acres Treated, (August 2014) which indicates that there is a 0.01 impervious acre equivalent credit for every 1,000 linear feet of stream restoration. Therefore, the Project will treat 82.4 acres of impervious area.

In addition to receiving credit under protocol 1 as detailed above, UM-10 will receive credit as a BMP retrofit based on the criteria in the Maryland Department of the Environment (MDE) guidance document Accounting for Stormwater Wasteload Allocations and Impervious Acres Treated, (August 2014). The alternative BMP performs similar to a wet pond so the associated nitrogen, phosphorus and suspended sediment removal efficiencies per 1 inch of rainfall treated were applied to the drainage area. When less than 1 inch of rainfall is treated, the percent of impervious area receiving water quality treatment will be credited along with the associated prorated pollutant removal rates for structural practices.

The proposed RSC system at UM-10 provides 0.52 acre-feet of storage which equates to 1.2 inches of rainfall. Table 40 shows the total pollutant removal and impervious area treated per the MDE guidance documentation.

Table 40 – Pollutant Removal and Impervious Area Treated (UM-10) Pollutant Removal Proposed Annual Pollutant Impervious Efficiencies Load Removal BMP Area Treated TN TP TSS TN TP TSS (acres) (%) (%) (%) (lbs/yr) (lbs/yr) (tons/yr) RSC 35.0 54.5 70.0 92.4 8.4 2.3 4.7

Supporting MS4 and TDML credit computations are included in Appendix Q.

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14. PERMITTING

The proposed Project will require local, state and federal permits for disturbance to existing wetlands. A Joint Federal/State Application for the Alteration of any Floodplain, Water, Tidal or Non-Tidal Wetland in Maryland, submitted to the MDE/ACOE, will be prepared as part of the Project. Also, an Anne Arundel County Grading Permit will be required for land disturbance greater than 5,000 square feet (SF).

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15. COST ANALYSIS

The estimated cost of construction for all proposed improvements is $4,433,434. The cost of the stream restoration is $3,529,451 (before contingencies). This is approximately $465 per linear foot of restoration. The cost of the RSC systems is $165,077 (before contingencies). An itemized construction cost estimate is included in Appendix R.

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16. CONCLUSION

The Upper Mill Creek project reaches have been significantly influenced by historical channel alterations and increasing urbanization of the watershed. There is geomorphic evidence of active stream degradation and hydrologic evidence of floodplain disconnection. Stabilization of the reaches is needed to protect critical public infrastructure, as well as enhance overall watershed health.

The stream restoration design alternative will promote floodplain reconnection; provide design features that promote denitrification during baseflow; provide a reduction in annual mass of sediment and attached nutrients originating from on-site channel degradation and upstream loss being delivered to downstream receiving waters; provide water quality credit towards Anne Arundel County’s NPDES MS4 permit watershed restoration requirement; and assist in meeting Anne Arundel County’s wasteload allocation towards the Chesapeake Bay TMDL. Also, it will limit the extent of grading needed and impacts to the existing riparian vegetation and wetlands.

The proposed RSC system at UM-10 will provide over 100 percent of the target WQv within the contributing drainage area and will assist AA County in meeting its NPDES MS4 permit requirements. Retrofitting the intermittent channel and Pond 824 into a RSC system will relieve the facility from MD-378 maintenance requirements and minimize disturbance to environmental features and adjacent private property.

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