Snohomish County Planning & Development Services Revised Draft Summary of Best Available Science for Critical Areas March 2006 Snohomish County Planning & Development Services Craig R. Ladiser, Director REPORT INQUIRIES AND COMMENTS Inquiries, comments, and suggestions about this report may be directed to: Critical Areas Update Snohomish County Department of Planning and Development Services 3000 Rockefeller Avenue, M/S 604, Everett, WA 98201 [email protected] ACKNOWLEDGEMENTS This document was produced through cooperative efforts with State agencies, other local jurisdictions, and several departments within Snohomish County government. Snohomish County Planning and Development Services extends its gratitude to the individuals who assisted in this effort, and especially to the scientists, engineers, and planners who gathered and evaluated the material presented in this document. Vaughn Collins, Jalyn Cummings, Jeff Kirtland, Bill Leif, Frank Leonetti, Randy Middaugh, Randy Sleight, and Darrell Smith all provided valuable expertise. Terri Strandberg served as the project manager and Linda Lyshall as the primary editor. Some of the background material for this document was borrowed from King County’s Best Available Science, Volume 1, A Review of Science Literature, King County Executive Report, February 2004, and Pentec Environmental’s Review Draft, Appendix B, Use of Best Available Science in Critical Area Protection in Snohomish County, June 9, 2004. Chapter 5 was taken in its entirety from the Washington Department of Ecology’s Wetlands Volume 1: A Synthesis of the Science, March 2005. RECOMMENDED CITATION Snohomish County, 2006. Revised Draft Summary of Best Available Science for Critical Areas. March 2006. Snohomish County Planning and Development Services. Everett, WA. Table of Contents EXECUTIVE SUMMARY .......................................................................................................... 1 PURPOSE OF UPDATE ................................................................................................................... 2 THE ROLE OF BEST AVAILABLE SCIENCE .................................................................................... 2 IDENTIFYING BEST AVAILABLE SCIENCE ..................................................................................... 2 SUMMARY OF BEST AVAILABLE SCIENCE RULES ........................................................................ 4 SUMMARY OF THE FIVE CRITICAL AREAS CHAPTERS .................................................................. 5 CHAPTER 1 – CRITICAL AQUIFER RECHARGE AREAS .............................................. 13 INTRODUCTION .......................................................................................................................... 13 METHODS FOR DETERMINING CRITICAL AQUIFER RECHARGE AREAS ....................................... 21 SPECIAL AREAS OR ISSUES OF CONCERN ................................................................................... 23 SUMMARY .................................................................................................................................. 29 CHAPTER 2 – FREQUENTLY FLOODED AREAS ............................................................. 35 INTRODUCTION .......................................................................................................................... 35 FLOOD HAZARDS, DAMAGES, AND METHODS OF DELINEATION ................................................ 36 COASTAL FLOODING .................................................................................................................. 38 OTHER FLOOD HAZARDS ........................................................................................................... 40 SUMMARY .................................................................................................................................. 41 CHAPTER 3 – FISH AND WILDLIFE HABITAT CONSERVATION AREAS ................ 47 INTRODUCTION .......................................................................................................................... 47 AQUATIC AREAS ........................................................................................................................ 47 STORMWATER MANAGEMENT AND AQUATIC AREAS ................................................................ 73 WILDLIFE HABITAT CONSERVATION ......................................................................................... 85 THREATENED AND ENDANGERED SPECIES ................................................................................. 93 SUMMARY ................................................................................................................................ 105 CHAPTER 4 – GEOLOGICALLY HAZARDOUS AREAS ............................................... 129 INTRODUCTION ........................................................................................................................ 129 SEISMIC HAZARD AREAS ......................................................................................................... 129 EROSION HAZARD AREAS ........................................................................................................ 138 LANDSLIDE HAZARD AREAS .................................................................................................... 147 VOLCANIC HAZARD AREAS ..................................................................................................... 151 ABANDONED MINE HAZARD AREAS ........................................................................................ 155 SUMMARY ................................................................................................................................ 159 CHAPTER 5 – WETLANDS ................................................................................................... 167 PROVIDED ON CD .................................................................................................................... 167 APPENDIX A – STORMWATER MITIGATION MEASURES ........................................ 169 Revised Draft Summary of Best Available Science for Critical Areas, March 2006 Snohomish County Planning and Development Services Executive Summary Snohomish County’s historical initiative and abiding concern for environmental quality has led to responsible and aggressive protection of environmentally sensitive areas. These front-line actions have been central in sustaining the natural beauty and quality of life in this region. Working in partnership with the tribes, community groups, and state and federal agencies, the County has preserved and restored salmon habitat to ensure the perseverance of this vital cultural, economic, and ecological natural resource. The County’s implementation of buffers on aquatic areas has protected essential fish and wildlife habitat and natural functions. The County has made significant progress in protecting the natural environment, but as demands on these resources grow we need to take additional actions. The primary challenge facing environmental protection in Snohomish County is finding the balance between the demands of growth, the requirements of functioning natural systems, and our need for productive agricultural and forestry lands. The decisions we make today will affect available resources, the sense of place that we value, and the legacy we leave to following generations. Through regulatory and non-regulatory efforts, the County is continually striving to minimize environmental impacts to preserve the clean air and water, forested mountains, and thriving economy we all enjoy. Some human activities in our sensitive natural environment need to be avoided, while others can be mitigated. The County is committed to working together with the citizens of this region for the common good of all. Snohomish County has created environmental policies and regulations and implemented land use law to protect natural resources for more than three decades. In the early 1970s the County adopted the Shoreline Management Master Program and began utilizing the State Environmental Policy Act regulations to protect environmentally sensitive areas. In the 1980s the storm and surface water utility was established to protect water quality and quantity and the Aquatic Resource Protection Program was initiated, and then repealed by citizen referendum shortly after adoption in 1990. Also in the 1990s, a groundwater advisory committee was formed and the Stillaguamish Clean Water District was established. Recognizing the need for further protection of limited natural resources, Snohomish County adopted its first Critical Area Regulations (CAR) in 1995. Critical Area Regulations (CAR) that designate and protect environmentally critical areas’ functions and values are required under Washington State’s Growth Management Act (GMA), which was enacted in 1990. The GMA defines critical areas as wetlands, critical aquifer recharge areas, fish and wildlife habitat areas, frequently flooded areas, and geologically hazardous areas. The County is currently reviewing and updating CARs to include Best Available Science (BAS), as required by the GMA. Integrating new scientific understanding with current regulations, incentives, and educational and stewardship efforts provides a cohesive program of environmental protection. There are trade- offs; each part of the strategy has pros and cons, but as an interconnected plan the pieces work together to achieve the goal of adequately protecting our natural resources