THURSTON COUNTY, WASHINGTON AND INCORPORATED AREAS Community Community Name Number BUCODA, TOWN OF 530189 LACEY, CITY OF 530190 OLYMPIA, CITY OF 530191 RAINIER, CITY OF 530260 TENINO, CITY OF 530302 THURSTON COUNTY 530188 TUMWATER, CITY OF 530192 YELM, CITY OF 530310 Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER 53067CV000A NOTICE TO FLOOD INSURANCE STUDY USERS Communities participating in the National Flood Insurance Program have established repositories of flood hazard data for floodplain management and flood insurance purposes. This Flood Insurance Study (FIS) may not contain all data available within the repository. It is advisable to contact the community repository for any additional data. The Federal Emergency Management Agency (FEMA) may revise and republish part or all of this FIS report at any time. In addition, FEMA may revise part of this FIS Report by the Letter of Map Revision process, which does not involve republication or redistribution of the FIS report. Therefore, users should consult with community officials and check the Community Map Repository to obtain the most current FIS report components. Selected Flood Insurance Rate Map (FIRM) panels for this community contain information that was previously shown separately on the corresponding Flood Boundary and Floodway Map (FBFM) panels (e.g., floodways and cross sections). In addition, former flood hazard zone designations have been changed as follows: Old Zone(s) New Zone(s) A1 through A30 AE V1 through V30 VE B X C X Initial Countywide FIS Effective Date: TABLE OF CONTENTS Page 1.0 INTRODUCTION ...................................................................................................................... 1 1.1 Purpose of Study ............................................................................................................... 1 1.2 Authority and Acknowledgments ...................................................................................... 1 1.3 Coordination ...................................................................................................................... 3 2.0 AREA STUDIED ....................................................................................................................... 4 2.1 Scope of Study .................................................................................................................. 4 2.2 Community Description .................................................................................................... 8 2.3 Principal Flood Problems .................................................................................................. 9 2.4 Flood Protection Measures .............................................................................................. 11 3.0 ENGINEERING METHODS................................................................................................... 11 3.1 Hydrologic Analyses ....................................................................................................... 12 3.2 Hydraulic Analyses ......................................................................................................... 18 3.3 Vertical Datum ................................................................................................................ 22 4.0 FLOODPLAIN MANAGEMENT APPLICATIONS .............................................................. 23 4.1 Floodplain Boundaries .................................................................................................... 23 4.2 Floodways ....................................................................................................................... 24 5.0 INSURANCE APPLICATIONS .............................................................................................. 42 6.0 FLOOD INSURANCE RATE MAP ........................................................................................ 43 7.0 OTHER STUDIES ................................................................................................................... 43 8.0 LOCATION OF DATA ........................................................................................................... 43 9.0 BIBLIOGRAPHY AND REFERENCES ................................................................................ 45 i TABLE OF CONTENTS - continued Page FIGURES Figure 1 - Floodway Schematic ......................................................................................................... 25 TABLES Table 1 – Initial and Final CCO Meetings ............................................................................................ 3 Table 2 – Streams Studied By Detailed Methods ................................................................................. 4 Table 3 – Areas Studied By Approximate Methods ............................................................................. 5 Table 4 – USGS Gages Used in Hydrologic Analysis ........................................................................ 14 Table 5 – Summary of Discharges ...................................................................................................... 16 Table 6 – Summary of Elevations ....................................................................................................... 17 Table 7 – Manning’s n Values ............................................................................................................ 22 Table 8 – Floodway Data ............................................................................................................... 26-41 Table 9 – Community Map History .................................................................................................... 44 EXHIBITS Exhibit 1 – Flood Profiles Black River Chehalis River Deschutes River Outlet of Black Lake Percival Creek Scatter Creek Scatter Creek Tributary Skookumchuck River Woodland Creek Yelm Creek Exhibit 2 – Flood Insurance Rate Map Index Flood Insurance Rate Map ii FLOOD INSURANCE STUDY THURSTON COUNTY, WASHINGTON AND INCORPORATED AREAS 1.0 INTRODUCTION 1.1 Purpose of Study This Flood Insurance Study (FIS) investigates the existence and severity of flood hazards in, or revises and updates previous FISs/Flood Insurance Rate Maps (FIRMS) for the geographic area of Thurston County, including the Cities of Lacey, Olympia, Rainier, Tenino, Tumwater, Yelm; the Town of Bucoda, and the unincorporated areas of Thurston County (hereinafter referred to collectively as Thurston County). Within Thurston County, the Chehalis Indian Reservation and the Nisqually Indian Reservation are non-participating communities in the NFIP. This FIS aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. This study has developed flood-risk data for various areas of the county that will be used to establish actuarial flood insurance rates. This information will also be used by the communities of Thurston County to update existing floodplain regulations as part of the Regular Phase of the National Flood Insurance Program (NFIP), and by local and regional planners to further promote sound land use and floodplain development. Minimum floodplain management requirements for participation in the NFIP are set forth in the Code of Federal Regulations at 44 CFR, 60.3. In some States or communities, floodplain management criteria or regulations may exist that are more restrictive or comprehensive than the minimum Federal requirements. In such cases, the more restrictive criteria take precedence, and the State (or other jurisdictional agency) will be able to explain them. 1.2 Authority and Acknowledgments The sources of authority for this FIS report are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. This FIS was prepared to include the incorporated communities within Thurston County into a countywide format. Information on the authority and acknowledgments for each jurisdiction included in this countywide FIS, as compiled from their previously printed FIS reports, is shown below. Bucoda, Town of: The hydrologic and hydraulic analyses for this study were performed by the U.S. Geological Survey, for the Federal Insurance Administration, under Inter-Agency Agreement No. IAA-H-9-77, Project Order No. 2. This work, which was completed in August 1979, covered all significant flooding sources affecting the Town of Bucoda. Lacey, City of: The hydrologic and hydraulic analyses for this study were performed by the U.S. Geological Survey for the Federal Insurance 1 Administration, under Inter-Agency Agreement No. IAA-H-9-77, Project Order No. 2. This work, which was completed in April 1979, covered all significant flooding sources affecting the City of Lacey. Olympia, City of: The hydrologic and hydraulic analyses for this study were performed by the U.S. Geological Survey, for the Federal Emergency Management Agency, under Inter-Agency Agreement No. IAA-H-9-77, Project Order No. 2. This work, which was completed in July 1980, covered all significant flooding sources affecting the City of Olympia. Tenino, City of: The hydrologic and hydraulic analyses for this study were performed by the U.S. Geological Survey, for the Federal Insurance Administration, under Inter-Agency Agreement No. IAA-H-9-77, Project Order No. 2. This work, which was completed in November 1978, covered all significant flooding sources affecting the City of Tenino. Thurston County, Unincorporated: The hydrologic and hydraulic analyses for this study were performed by the U.S. Geological