Bay View Watershed Stormwater Management Plan March 2006 Draft Board of County Commissioners Ken Dahlstedt, Chair Don Munks Ted Anderson Skagit County Public Works Chal A. Martin, PE, Director/County Engineer David R. Brookings, Public Works Administrator Ric Boge, Surface Water Manager Janice Flagan, Assistant Surface Water Manager Erick Aurand, Drainage Utility Coordinator Consultants Semrau Engineering & Surveying, PLLC TetraTech/KCM, Inc. Technical Contributors Dike & Drainage District No. 12 Drainage District No. 14 Drainage District No. 19 Port of Skagit County Skagit Conservation District Padilla Bay National Estuarine Research Reserve i Bay View Watershed Stormwater Management Plan March 2006 ii Table of Contents Chapter 1 Executive Summary....................................................................................1.1 Chapter 2 Introduction.................................................................................................2.1 A. Purpose and Scope ...........................................................................................................................2.1 B. Stakeholders Purpose and Objectives ..............................................................................................2.1 1. Skagit County............................................................................................................................... 2.1 2. Drainage District No. 14.............................................................................................................. 2.1 3. Drainage District No. 19.............................................................................................................. 2.2 4. Dike and Drainage District No. 8 ................................................................................................ 2.2 5. Dike and Drainage District No. 12 .............................................................................................. 2.2 6. Port of Skagit County................................................................................................................... 2.3 7. City of Burlington........................................................................................................................ 2.3 8. Large Tract Land Owners ............................................................................................................ 2.3 9. Washington State Department of Ecology................................................................................... 2.3 10. Washington State Department of Fish and Wildlife.................................................................. 2.4 11. Washington State Department of Transportation ...................................................................... 2.4 12. Federal Aviation Administration ............................................................................................... 2.4 C. Related Planning Documents ...........................................................................................................2.4 1. Padilla Bay/Bay View Watershed Non-Point Action Plan.......................................................... 2.5 2. Port of Skagit County Stormwater Management Master Plan..................................................... 2.5 3. Hydrologic and Hydraulic Model of the No Name Slough Drainage ......................................... 2.6 4. Bayview Ridge Subarea Plan....................................................................................................... 2.6 5. Joe Leary Slough Drainage Study................................................................................................ 2.7 6. Tide Gate and Pump Station Study.............................................................................................. 2.7 7. No Name Slough Watershed Characterization Report ................................................................ 2.8 Chapter 3 Study Area ..................................................................................................3.1 A. Land Use and Development.............................................................................................................3.1 1. Historical Development ............................................................................................................... 3.1 2. Skagit County Planning Efforts ................................................................................................... 3.3 B. Natural Features ...............................................................................................................................3.3 1. Topography.................................................................................................................................. 3.4 2. Soil ............................................................................................................................................... 3.4 3. Climate......................................................................................................................................... 3.4 C. Critical Areas....................................................................................................................................3.5 1. Aquifer Recharging Areas ........................................................................................................... 3.5 2. Flood Hazard Areas ..................................................................................................................... 3.5 3. Wetlands ...................................................................................................................................... 3.5 4. Port of Skagit County Wetlands Management Plan .................................................................... 3.6 5. Priority Habitat............................................................................................................................. 3.6 iii Bay View Watershed Stormwater Management Plan Chapter 4 Storm Drainage Facilities ...........................................................................4.1 A. No Name Slough Basin....................................................................................................................4.1 B. Joe Leary Slough Basin....................................................................................................................4.2 C. Indian Slough Basin .........................................................................................................................4.3 Chapter 5 Stormwater Quantity Analysis....................................................................5.1 A. Modeling Methodology....................................................................................................................5.1 1. Computer Hydraulic Model ......................................................................................................... 5.1 2. Model Input.................................................................................................................................. 5.1 3. Model Basin Descriptions............................................................................................................ 5.2 B. Modeling Results..............................................................................................................................5.4 1. No Name Slough.......................................................................................................................... 5.4 2. Joe Leary Slough.......................................................................................................................... 5.6 3. Little Indian Slough ..................................................................................................................... 5.9 4. Big Indian Slough ...................................................................................................................... 5.10 Chapter 6 Stormwater Quality and Treatment ............................................................6.1 A. Bay View Area Stormwater Quality ................................................................................................6.1 B. Contamination Sources and Management Strategies.......................................................................6.2 1. Pavement Runoff and Roadside Ditches...................................................................................... 6.2 2. Septic Tanks................................................................................................................................. 6.2 3. Agricultural Activities ................................................................................................................. 6.3 C. Stormwater Treatment Techniques ..................................................................................................6.4 1. Stormwater Ponds and Bioswales................................................................................................ 6.4 2. Wetlands ...................................................................................................................................... 6.4 D. West Nile Virus................................................................................................................................6.5 Chapter 7 Storm Drainage Alternatives Analysis .......................................................7.1 A. Storm Drainage Structures...............................................................................................................7.1 1. Open Channels............................................................................................................................