Volume II Eno River Watershed Improvement Plan Improvement Plan Durham, North Carolina December 2018 PREPARED FOR: City of Durham Public Works Department Stormwater & GIS Services Division 101 City Hall Plaza, Third Floor Durham, North Carolina 27701 This page left blank intentionally Eno River Watershed Improvement Plan City of Durham Stormwater & GIS Services Division Public Works Department 101 City Hall Plaza, Third Floor Durham, North Carolina 27701 This page left blank intentionally AECOM Acknowledgments The Eno River Watershed Improvement Plan represents the combined effort of staff from the City of Durham, AECOM, Kimley Horn and Associates, and Three Oaks Engineering. City of Durham Team Paul Wiebke, Assistant Director, Public Works Kelly Hartman Sandra Wilbur, Project Manager Dana Hornkohl Lance Fontaine, Assistant Project Manager J.V. Loperfido Jonathan Baker Don O’Toole Christine Cailleret Laura Smith Charlotte Dawn Megan Walsh Erin Harrison Michelle Woolfolk AECOM Team AECOM Technical Services of North Carolina Sujit Ekka, Project Manager Michelle Mayfield Brian Jacobson, Deputy Project Manager Karthik Narayanaswamy Matthew Burnette Alex Nice Diana Burke Hernan Rodriguez Brad Courtney Jason Sites Manasa Damera Zack Twigg Beth Kerby Cyndy Yu-Robinson Kimley-Horn and Associates Three Oaks Engineering Beth Reed Tom Dickinson Jason Hartshorn Nathan Howell Andrew Jones Kate Monteith Sevick Jennifer Murphy Chris Sheats This page left blank intentionally AECOM Table of Contents Acronyms and Abbreviations ......................................................................................................................................... v 1 Introduction ......................................................................................................................................................... 1-1 1.1 Background ................................................................................................................................................................................... 1-1 1.2 Goals ................................................................................................................................................................................................ 1-2 1.3 Organization ................................................................................................................................................................................. 1-3 2 Watershed Assessment ....................................................................................................................................... 2-1 2.1 Watershed Characteristics ....................................................................................................................................................... 2-1 2.1.1 Data Inventory ............................................................................................................................................................. 2-1 2.1.2 Summary of Previous Studies................................................................................................................................ 2-2 2.1.3 Hydrology...................................................................................................................................................................... 2-3 2.1.4 Topography .................................................................................................................................................................. 2-4 2.1.5 Geology and Soils ...................................................................................................................................................... 2-4 2.1.6 Floodplains ................................................................................................................................................................... 2-5 2.1.7 Land Use and Impervious Cover .......................................................................................................................... 2-6 2.2 Water Quality Conditions ........................................................................................................................................................ 2-8 2.2.1 Surface Water Classifications................................................................................................................................. 2-8 2.2.2 Water Quality Monitoring....................................................................................................................................... 2-9 2.2.3 Sediment Monitoring .............................................................................................................................................2-12 2.3 Watershed Impacts and Sources of Pollution ...............................................................................................................2-13 3 Stream Inventory and Assessment and Project Opportunities .................................................................... 3-1 3.1 Stream Field Inventory and Assessment Methodology ............................................................................................... 3-1 3.2 Results of Stream Field Assessments .................................................................................................................................. 3-1 3.3 Potential Stream Project Opportunities ............................................................................................................................. 3-3 4 Stormwater Control Measure Inventory, Assessment, and Project Opportunities ................................... 4-1 4.1 SCM Field Assessment Methodology ................................................................................................................................. 4-1 4.2 Retrofit Opportunities to Existing SCMs ............................................................................................................................ 4-2 4.3 Potential New SCMs .................................................................................................................................................................. 4-4 5 Evaluation of Watershed Improvement Scenarios ......................................................................................... 5-1 5.1 Pilot Study Areas ......................................................................................................................................................................... 5-1 5.2 Stormwater Management Modeling................................................................................................................................... 5-1 5.3 Scenarios ........................................................................................................................................................................................ 5-2 5.3.1 Scenario Methodology ............................................................................................................................................ 5-2 5.3.2 Scenario Results ........................................................................................................................................................5-10 6 Prioritization of Watershed Improvement Projects....................................................................................... 6-1 6.1 Prioritization Criteria .................................................................................................................................................................. 6-1 Eno River Watershed Improvement Plan, Volume II i AECOM 6.2 High-Priority Watershed Improvement Projects ............................................................................................................ 6-3 6.2.1 High-Priority SCM Projects..................................................................................................................................... 6-3 6.2.2 High Priority Stream Improvement Projects ................................................................................................... 6-4 7 Public Outreach and Involvement .................................................................................................................... 7-1 7.1 Public Information Sessions ................................................................................................................................................... 7-1 7.1.1 First Public Information Session: March 21, 2017 ......................................................................................... 7-1 7.1.2 Second Public Information Session: November 2, 2017............................................................................. 7-1 7.1.3 Third Public Information Session: July 31, 2018............................................................................................. 7-2 7.2 Eno Watershed River Improvement Plan Webpage...................................................................................................... 7-3 7.3 Eno River Watershed Improvement Plan Social Media Updates ............................................................................. 7-3 7.4 Project Fact Sheets ..................................................................................................................................................................... 7-3 7.5 Educational Radio Spots .......................................................................................................................................................... 7-3 7.6 Educational