Chehalis River Basin Comprehensive Flood Hazard Management Plan June 2010 Prepared for: Prepared by: Chehalis River Basin Flood Authority ESA Adolfson Chehalis River Basin Comprehensive Flood Hazard Management Plan ACRONYMS AF acre feet BA Biological Assessment BE Biological Evaluation BMC Bucoda Municipal Code BMP Best Management Practice CEQ Council on Environmental Quality CFHMP Comprehensive Flood Hazard Management Plan CFR Code of Federal Regulations CFRP Centralia Flood Reduction Project cfs cubic feet per second CMC Chehalis Municipal Code COE U.S. Army Corps of Engineers Corps U.S. Army Corps of Engineers CMZ Channel Migration Zone CRS Community Rating System CTED Community, Trade, and Economic Development CWA Clean Water Act CWPO Closed Without Payment DOE Department of Ecology DST Decision Support Tool Ecology Washington State Department of Ecology EIS Environmental Impact Statement EO Executive Order EPA Environmental Protection Agency ER Emergency Response ESA Endangered Species Act ESSB Engrossed Substitute Senate Bill FCAAP Flood Control Assistance Account Program FEMA Federal Emergency Management Association FERC Federal Energy Regulatory Commission FHWA Federal Highway Administration FIA Federal Insurance Administration FIRM Flood Insurance Rate Map FMA Flood Mitigation Assistant grant program FONSI Finding of No Significant Impact GI General Investigation GIS Geographic Information System GMA Growth Management Act GO General Obligation HEC-RAS Hydrologic Engineering Centers River Analysis System HHS Human Health & Safety HPA Hydraulic Project Approval LCC Lewis County Code June 2010 A-1 Chehalis River Basin Comprehensive Flood Hazard Management Plan LID local improvement district LiDAR Light Detection and Ranging LLC Limited Liability Company LWD large woody debris MI Major Infrastructure NEPA National Environmental Policy Act NF North Fork NFIP National Flood Insurance Program nhc Northwest Hydraulics Consultants NHMP Natural Hazards Mitigation Plan NMFS National Marine Fisheries Service NOAA National Oceanic and Atmospheric Administration NPDES National Pollutant Discharge Elimination System NRCS Natural Resource Conservation Service NSIP National Streamflow Information Program NWS National Weather Service O&M operation and maintenance OHWM ordinary high water mark OMC Oakville Municipal Code PCB polychlorinated biphenyl PL Public Law PUD Lewis County Public Utility District RCW Revised Code of Washington RM River Mile SaSI Salmonid Stock Inventory SBA Small Business Administration SEPA State Environmental Policy Act SFHA Special Flood Hazard Area SMA Shoreline Management Act SMP Shoreline Master Program SR State Route SRF State Revolving Fund TCC Thurston County Code TMDL Total Maximum Daily Load USACE U.S. Army Corps of Engineers USC U.S. Code USDA U.S. Department of Agriculture USFSW U.S. Fish and Wildlife Services USGS United States Geological Survey WDFW Washington Department of Fish and Wildlife WRDA Water Resources Development Act WRIA Water Resource Inventory Area WSDOT Washington State Department of Transportation WWTP Wastewater Treatment Plant A-2 June 2010 Chehalis River Basin Comprehensive Flood Hazard Management Plan TABLE OF CONTENTS Acronyms ................................................................................................................................... A-1 Chapter 1 Introduction and Goals ............................................................................................ 1-1 BACKGROUND ................................................................................................................................ 1-1 Major Flooding Issues in the Basin ................................................................................... 1-1 Authority and Scope for the Chehalis River Basin CFHMP .............................................. 1-1 PLAN DEVELOPMENT PROCESS ...................................................................................................... 1-2 Summary of Public Involvement and Agency Coordination .............................................. 1-2 DEFINING GOALS ........................................................................................................................... 1-3 RELATED PLANS ............................................................................................................................ 1-4 NEXT STEPS ................................................................................................................................... 1-5 CFHMP Adoption .............................................................................................................. 1-5 SEPA Review ..................................................................................................................... 1-5 Chapter 2 Study Area Characteristics ..................................................................................... 2-1 STUDY AREA DESCRIPTION ........................................................................................................... 2-1 PHYSICAL CHARACTERISTICS ........................................................................................................ 2-5 Climate ............................................................................................................................. 2-5 Geology ............................................................................................................................. 2-6 Topography ........................................................................................................................ 2-6 Soils ............................................................................................................................. 2-7 Hydrology .......................................................................................................................... 2-7 Wetlands .......................................................................................................................... 2-18 Fish and Wildlife.............................................................................................................. 2-19 Endangered Species Act Issues ........................................................................................ 2-22 Water Quality .................................................................................................................. 2-22 LAND USE CHARACTERISTICS ...................................................................................................... 2-23 POPULATION ................................................................................................................................ 2-24 Chapter 3 Regulatory Overview ............................................................................................... 3-1 SUMMARY OF EXISTING REGULATIONS ......................................................................................... 3-1 KEY FEDERAL REGULATIONS ........................................................................................................ 3-1 National Flood Insurance Program ................................................................................... 3-1 Clean Water Act ................................................................................................................. 3-6 Rivers and Harbors Act, Section 10 ................................................................................... 3-9 Executive Order 11988 - Floodplains ................................................................................ 3-9 Executive Order 11990 - Wetlands .................................................................................. 3-10 Endangered Species Act................................................................................................... 3-11 National Environmental Policy Act ................................................................................. 3-12 KEY STATE REGULATIONS ........................................................................................................... 3-13 Floodplain Management Program .................................................................................. 3-13 Hydraulic Code ................................................................................................................ 3-13 Other State Programs Implemented at the Local level .................................................... 3-13 FLOOD AUTHORITY REGULATORY SUMMARY ............................................................................. 3-14 Chapter 4 Previous Studies........................................................................................................ 4-1 U.S. ARMY CORPS OF ENGINEERS ACTIVITIES ............................................................................... 4-1 1930-1976 .......................................................................................................................... 4-1 1972-1982 .......................................................................................................................... 4-2 1990s-Present .................................................................................................................... 4-4 2007 Project Authorization ................................................................................................ 4-8 Corps Twin Cities Flood Damage Reduction Project........................................................ 4-9 2009-Chehalis River Basin General Investigation ............................................................ 4-9 FEMA REGION X INTERAGENCY