SKAGIT COUNTY, WASHINGTON AND INCORPORATED AREAS Community Community Name Number ANACORTES, CITY OF 530317 BURLINGTON, CITY OF 530153 CONCRETE, TOWN OF 530154 HAMILTON, TOWN OF 530155 LA CONNER, TOWN OF 530156 LYMAN, TOWN OF 530157 MOUNT VERNON, CITY OF 530158 SAUK-SUIATTLE INDIAN TRIBE 530340 SEDRO-WOOLLEY, CITY OF 530159 SKAGIT COUNTY (UNINCORPORATED AREAS) 530151 SWINOMISH INDIAN TRIBAL COMMUNITY 530222 *UPPER SKAGIT INDIAN TRIBE 530013 *Non-floodprone Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER 53057CV000A 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 may not contain all data available within the repository. It is advisable to contact the community repository for any additional data. Selected Flood Insurance Rate Map panels for this community contain information that was previously shown separately on the corresponding Flood Boundary and Floodway Map panels (e.g., floodways, cross sections). In addition, former flood hazard zone designations have been changes as follows: Old Zone(s) New Zone A1 through A30 AE V1 through V30 VE B X C X The Federal Emergency Management Agency (FEMA) may revise and republish part of 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. This FIS report was revised on TBD. Users should refer to Section 10.0, Revisions Description for further information. Section 10.0 is intended to present the most up-to-date information for specific portions of the FIS report. Therefore, users of this report should be aware that the information presented in Section 10.0 supersedes information in Sections 1.0 through 9.0 of this FIS report. Initial Effective Date: TBD i 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 ...................................................................................................... 5 2.3 Principal Flood Problems .................................................................................................. 18 2.4 Flood Protection Measures ................................................................................................ 22 3.0 ENGINEERING METHODS ..................................................................................................... 25 3.1 Hydrologic Analyses ......................................................................................................... 25 3.2 Hydraulic Analyses ........................................................................................................... 33 3.3 Vertical Datum .................................................................................................................. 39 4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS .............................................................. 40 4.1 Floodplain Boundaries ...................................................................................................... 40 4.2 Floodways ......................................................................................................................... 42 5.0 INSURANCE APPLICATION ................................................................................................... 56 6.0 FLOOD INSURANCE RATE MAP ........................................................................................... 57 7.0 OTHER STUDIES ....................................................................................................................... 59 8.0 LOCATION OF DATA ............................................................................................................... 59 9.0 BIBLIOGRAPHY AND REFERENCES ................................................................................... 60 10.0 REVISIONS DESCRIPTION ..................................................................................................... 63 10.1 First Revision .................................................................................................................... 63 ii TABLE OF CONTENTS (Cont’d) Page FIGURES Figure 1 – Floodway Schematic .................................................................................................................. 43 TABLES Table 1 – Streams Studied by Detailed Methods ........................................................................................... 4 Table 2 – Population Figures for Skagit County and Incorporated Cities ..................................................... 6 Table 3 – Peak Discharges on the Skagit River near Sedro-Woolley .......................................................... 19 Table 4 – Observed and Historic Floods in Skagit County ......................................................................... 19 Table 5 – Storage Characteristics of Existing Reservoirs ............................................................................ 24 Table 6 – Summary of Stillwater Elevations ............................................................................................... 26 Table 7 – Historical Floods for the Skagit River near Concrete .................................................................. 28 Table 8 – Summary of Discharges .............................................................................................................. 32 Table 9 – Floodway Data ............................................................................................................................ 44 Table 10 – Flood Insurance Zones within Each Community ....................................................................... 57 Table 11 – Community Map History ........................................................................................................... 58 EXHIBITS Exhibit 1 - Flood Profiles Baker River Panels 01P – 02P Cascade River Panels 03P – 05P Samish River Panels 06P – 12P Sauk River Panels 13P – 19P Skagit River Delta Overbank Flowpath 1 Panels 20P – 21P Skagit River Delta Overbank Flowpath 2 Panels 22P – 25P Skagit River Delta Overbank Flowpath 3 Panels 26P – 28P North Fork Skagit River Panels 29P – 31P South Fork Skagit River Panels 32P – 33P Main Stem Skagit River Panels 34P – 39P Skagit River Panels 40P – 63P Skagit River Split Flow Panel 64P Suiattle River Panels 65P – 70P PUBLISHED SEPARATELY: Flood Insurance Rate Map Index Flood Insurance Rate Map iii FLOOD INSURANCE STUDY SKAGIT COUNTY, WASHINGTON AND INCORPORATED AREAS 1.0 INTRODUCTION 1.1 Purpose of Study This Flood Insurance Study (FIS) revises and updates information on the existence and severity of flood hazards in the geographic area of Skagit County, Washington, including the Cities of Anacortes, Burlington, Mount Vernon, Sedro-Woolley; the Towns of Concrete, Hamilton, La Conner, Lyman; the Sauk-Suiattle Indian Tribe, Swinomish Indian Tribal Community, Upper Skagit Indian Tribe, and the unincorporated areas of Skagit County (referred to collectively herein as Skagit County), and 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 and to assist the communities in their efforts to promote sound floodplain management. Minimum floodplain management requirements for participation in the National Flood Insurance Program (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. Pre-Countywide Analyses The original hydrologic and hydraulic analyses for the City of Anacortes were performed by the United States Corps of Engineers (USACE), Seattle District, and Dames & Moore, for FEMA, under Inter-Agency Agreement No. IAA-H-7-76, Project Order No. 13, and Contract No. EMW-C-0542. That study was completed in December 1982 and was published for the unincorporated areas of Skagit County, Washington (Reference 1). The original hydrologic and hydraulic analyses for