THORNTON CREEK WATERSHED CHARACTERIZATION REPORT CONTENTS ACRONYMS GLOSSARY EXECUTIVE SUMMARY PART 1: WELCOME TO THE WATERSHED Chapter 1: Introduction...............................................................................................................................................................1-1 1.1 Thornton Creek Watershed.................................................................................................. 1-1 1.2 Focus on Non-Point Pollution............................................................................................... 1-2 1.3 Thornton Creek Watershed Action Planning .......................................................................... 1-5 1.4 Impacts of Development on Streams and Watersheds ........................................................... 1-7 PART 2: WATERSHED CHARACTER AND CONDITION Chapter 2: People of the Watershed.........................................................................................................................................2-1 2.1 Historical Settlement............................................................................................................ 2-1 2.2 Population........................................................................................................................... 2-8 2.3 Watershed Survey ............................................................................................................. 2-15 Chapter 3: Water and Land ........................................................................................................................................................3-1 3.1 The Natural Environment ..................................................................................................... 3-1 3.2 Thornton Creek Flows ......................................................................................................... 3-8 3.3 Diversions for Human Use ................................................................................................. 3-18 3.4 Three Major Creek Sections ............................................................................................... 3-18 3.5 Minor Thornton Creek Watersheds (Sub-basins) ................................................................. 3-22 3.6 Land Use.......................................................................................................................... 3-22 3.7 Impervious Surfaces .......................................................................................................... 3-36 Chapter 4: Aquatic and Terrestrial Resources (Fish, Wildlife, and Habitat)..................................................................4-1 4.1 Overview of Watershed Habitat ............................................................................................ 4-1 4.2 Terrestrial Habitat and Wildlife.............................................................................................. 4-2 4.3 Aquatic Habitat.................................................................................................................... 4-5 4.4 Aquatic Wildlife.................................................................................................................. 4-11 4.5 Habitat Assessments......................................................................................................... 4-19 4.6 Watershed-wide Habitat Problems...................................................................................... 4-23 4.7 Sub-basin Description and Specific Habitat Problems .......................................................... 4-24 Chapter 5: Water and Sediment Quality..................................................................................................................................5-1 5.1 Stream Uses and Standards ................................................................................................ 5-1 5.2 Review of Government Water Quality Data ........................................................................... 5-5 5.3 Review of Other Water Quality Data ................................................................................... 5-19 5.4 Sediment Quality............................................................................................................... 5-23 5.5 Fish Tissue ....................................................................................................................... 5-25 5.6 Benthic Macro-invertebrate Sampling.................................................................................. 5-26 5.7 Groundwater Quality.......................................................................................................... 5-27 5.8 Exceedance of Surface Water Quality Standards................................................................. 5-29 5.9 Water Quality Trends ......................................................................................................... 5-30 iii THORNTON CREEK WATERSHED CHARACTERIZATION REPORT PART 3: WATERSHED PROTECTION ACTIVITIES Chapter 6: Government Laws and Policies ............................................................................................................................6-1 6.1 Federal Government............................................................................................................ 6-1 6.2 Tribal Government............................................................................................................... 6-4 6.3 Washington State Government............................................................................................. 6-5 6.4 Interjursidictional Approaches............................................................................................. 6-10 6.5 King County ...................................................................................................................... 6-11 6.6 City of Seattle.................................................................................................................... 6-12 6.7 City of Shoreline................................................................................................................ 6-24 6.8 Watersed Management Committee Concerns ..................................................................... 6-29 Chapter 7: Non-government Organizations, Schools, and Other Organizations...............................................................7-1 7.1 Non-Government Organizations ........................................................................................... 7-1 7.2 Schools .............................................................................................................................. 7-6 7.3 Government-Affiliated Organizations..................................................................................... 7-7 Chapter 8: Stormwater Management .......................................................................................................................................8-1 8.1 Responsibility for Stormwater Management........................................................................... 8-1 8.2 Stormwater Infrastructure..................................................................................................... 8-3 8.3 Drainage Operation and Maintenance Programs ................................................................... 8-9 8.4 Drainage Capital Improvement Programs............................................................................ 8-13 8.5 Assessment of Stormwater Management Programs............................................................. 8-20 Chapter 9: Non-point Pollution Prevention and Control Programs .................................................................................9-1 9.1 Sources of Non-point Pollution ............................................................................................. 9-1 9.2 Comprehensive Government Non-point Pollution Programs ................................................... 9-3 9.3 Citizen-oriented Non-point Pollution Prevention Programs...................................................... 9-5 9.4 Business Non-point Pollution Prevention Programs ............................................................... 9-8 9.5 Government Maintenance Non-point Pollution Prevention Programs..................................... 9-10 9.6 Research and Monitoring ................................................................................................... 9-12 9.7 Non-point Pollution Program Assessment ........................................................................... 9-13 Chapter10: Wildlife and Habitat Programs ..........................................................................................................................10-1 10.1 Maps, Inventories, and Studies......................................................................................... 10-1 10.2 Coordination of Habitat Projects ....................................................................................... 10-6 10.3 Open Space and Land Acquisition .................................................................................... 10-7 10.4 Tree and Native Plant Programs..................................................................................... 10-10 10.5 Community Restoration Projects .................................................................................... 10-13 10.6 Habitat Related Capital Improvement Projects (CIPS)...................................................... 10-17 10.7 Assessment of Existing