GREATER OREGON CITY WATERSHED ASSESSMENT P REPARED FOR: Greater Oregon City Watershed Council Oregon City, OR Contact: Rita Baker P REPARED BY: ICF International 317 Alder Street, Suite 800 Portland, OR 97204 Contact: John Runyon 503/525‐6153 & Watershed Professionals Network Corvallis, OR April 2010 ICF International. 2010. Greater Oregon City Watershed Assessment. (ICF Project 00223.09.) Portland, OR. Prepared for the Greater Oregon City Watershed Council, Oregon City, OR. Acknowledgements Primary funding for this project was provided by the Oregon Watershed Enhancement Board. We thank Wendy Hudson, Willamette Basin Program Representative, for her support and guidance. Additional funding was provided by the Clackamas County Soil and Water Conservation District. The group of dedicated volunteers, from the watershed council members, the technical advisory committee, and agency staff, attended meetings and provided thoughtful review comments on the draft assessment. The final product is much stronger due to their dedication and commitment to this project. We thank: Council: Eric Hand, Chair Cara Hughes, Vice‐Chair Doug Neeley, Treasurer Alison Heimowitz, Secretary Sarah Miller, Past Chair, Citizen‐at‐large Sammy Warner, Watershed Resident Dan Tooze, Watershed Resident Jeff Stott, Citizen‐at‐large Technical Assistance Committee: Mark Mouser, Clackamas County Department of Transportation and Development Isaac Sanders, ODFW‐North Willamette Watershed District Doug Cramer, Portland General Electric Dave Phipps, Stonecreek Golf Course Anders Rasmussen, HDR Contributors: Jeffrey Kee, Past TAC Chair Clair Klock, Clackamas County Soil & Watershed Conservation District Brian Vaughn, Metro Tonia Burns, Clackamas County Parks Coordinator, Rita Baker Greater Oregon City Watershed Council April 2010 i Greater Oregon City Watershed Assessment ICF 00223.09 Contents List of Tables and Figures ...................................................................................................................... iv List of Acronyms and Abbreviations ...................................................................................................... vi Introduction and Purpose .................................................................................................................... 1 Watershed Overview ........................................................................................................................... 3 Watershed Assessment Area ................................................................................................................. 3 Land Use and Land Cover ....................................................................................................................... 6 Natural Areas ................................................................................................................................. 10 Geology .......................................................................................................................................... 10 Riparian and Wetland Areas .............................................................................................................. 13 Introduction .......................................................................................................................................... 13 Riparian Area Assessment .................................................................................................................... 13 Invasive Plant Species ........................................................................................................................... 16 Forested Riparian Areas and Contributions of Large Wood ................................................................. 17 Stream Shade ....................................................................................................................................... 18 Wetland Habitat Loss ........................................................................................................................... 19 Floods and Water Use ........................................................................................................................ 22 Introduction .......................................................................................................................................... 22 Streamflow Patterns ............................................................................................................................. 22 Flood History ........................................................................................................................................ 25 Water Use ............................................................................................................................................. 27 Locations of Water Withdrawals ................................................................................................... 28 Withdrawal Rates ........................................................................................................................... 29 Effects of Water Withdrawals on Flow Regime ............................................................................. 31 Surface Erosion and Stream Sediment ................................................................................................ 32 Introduction .......................................................................................................................................... 32 Bank Erosion ......................................................................................................................................... 32 Upland Surface Erosion ........................................................................................................................ 32 Water Quality .................................................................................................................................... 35 Introduction .......................................................................................................................................... 35 Relationship to Land Use ...................................................................................................................... 36 Water Temperature .............................................................................................................................. 37 Toxics .................................................................................................................................................... 37 Greater Oregon City Watershed Council April 2010 ii Greater Oregon City Watershed Assessment ICF 00223.09 Stormwater Quality .............................................................................................................................. 38 pH ................................................................................................................................................... 39 Total Dissolved Solids ..................................................................................................................... 39 Total Suspended Solids .................................................................................................................. 40 Aquatic Habitat and Fish Populations ................................................................................................. 45 Introduction .......................................................................................................................................... 45 Overview of Fish Presence and Distribution ........................................................................................ 45 Coho Salmon .................................................................................................................................. 47 Winter Steelhead ........................................................................................................................... 48 Cutthroat Trout .............................................................................................................................. 48 Lamprey and Other Fish Species .................................................................................................... 49 Abernethy Creek: Fish Use and Habitat ............................................................................................... 50 Backwatering in Abernethy Creek and Fish Use ............................................................................ 52 Abernethy Tributary Streams ........................................................................................................ 54 Beaver Creek: Fish Use and Habitat ..................................................................................................... 57 Fish Passage Barriers ............................................................................................................................ 57 Dams .............................................................................................................................................. 58 Road Crossings ............................................................................................................................... 59 Summary and Recommendations....................................................................................................... 62 References ......................................................................................................................................... 65 Appendix A. Water Quality Data Sources, Criteria, and Stormwater