Pacific County, Washington and Incorporated Areas
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PACIFIC COUNTY, WASHINGTON AND INCORPORATED AREAS COMMUNITY NAME COMMUNITY NUMBER ILWACO, TOWN OF 530127 LONG BEACH, TOWN OF 530128 PACIFIC COUNTY, 530126 UNINCORPORATED AREAS RAYMOND, CITY OF 530129 SHOALWATER BAY INDIAN TRIBE 530341 SOUTH BEND, CITY OF 530130 Pacific County PRELIMINARY: AUGUST 30, 2013 FLOOD INSURANCE STUDY NUMBER 53049CV000A 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) report may not contain all data available within the Community Map Repository. Please contact the Community Map 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, cross sections). In addition, former flood hazard zone designations have been changed as follows: Old Zone(s) New Zone Al through A30 AE B X C X Initial Countywide FIS Effective Date: To Be Determined TABLE OF CONTENTS 1.0 INTRODUCTION ........................................................................................................ 1 1.1 Purpose of Study ................................................................................................ 1 1.2 Authority and Acknowledgments ...................................................................... 1 1.3 Coordination ...................................................................................................... 2 2.0 AREA STUDIED .......................................................................................................... 3 2.1 Scope of Study ................................................................................................... 3 2.2 Community Description ..................................................................................... 4 2.3 Principal Flood Problems ................................................................................... 6 2.4 Flood Protection Measures ................................................................................ 8 3.0 ENGINEERING METHODS ...................................................................................... 9 3.1 Hydrologic Analyses .......................................................................................... 9 3.2 Hydraulic Analyses .......................................................................................... 11 3.3 Wave Height Analysis ..................................................................................... 14 3.4 Vertical Datum ................................................................................................. 28 4.0 FLOODPLAIN MANAGEMENT APPLICATIONS .............................................. 31 4.1 Floodplain Boundaries ..................................................................................... 31 4.2 Floodways ........................................................................................................ 33 4.3 Base Flood Elevations ..................................................................................... 34 4.4 Velocity Zones ................................................................................................. 34 5.0 INSURANCE APPLICATIONS................................................................................ 40 6.0 FLOOD INSURANCE RATE MAP ......................................................................... 40 7.0 OTHER STUDIES ...................................................................................................... 43 8.0 LOCATION OF DATA .............................................................................................. 43 9.0 BIBLIOGRAPHY AND REFERENCES ................................................................. 43 i TABLE OF CONTENTS – (Continued) FIGURES Figure 1 – Transect Schematic ................................................................................................... 18 Figure 2 – Transect Location Map ............................................................................................. 19 Figure 3 – Floodway Schematic ................................................................................................ 35 TABLES Table 1 – Initial and Final CCO Meetings ................................................................................... 3 Table 2 – Areas Studied by Detailed Methods ............................................................................ 3 Table 3 – Major Floods Occurring on the Naselle and Willapa Rivers ....................................... 6 Table 4 – Summary of Discharges ............................................................................................. 10 Table 5 – Summary of Stillwater Elevations ............................................................................. 11 Table 6 – Manning’s “n” Values ............................................................................................... 13 Table 7 – Transect Descriptions ................................................................................................ 20 Table 8 – Transect Data Table ................................................................................................... 26 Table 9 – Vertical Datum Conversion for Naselle River ........................................................... 29 Table 10 – Vertical Datum Conversion for Salmon Creek ........................................................ 29 Table 11 – Vertical Datum Conversion for South Fork Naselle River ...................................... 30 Table 12 – Vertical Datum Conversion for Willapa River ........................................................ 30 Table 13 – Floodway Data Table ............................................................................................... 36 Table 14 – Community Map History ......................................................................................... 42 EXHIBITS Exhibit 1 – Flood Profiles Naselle River Panels 01P Salmon Creek Panels 02P-03P South Fork Naselle River Panels 04P-05P Willapa River Panels 06P Exhibit 2 – Flood Insurance Rate Map Index Flood Insurance Rate Map ii FLOOD INSURANCE STUDY PACIFIC COUNTY, WASHINGTON AND INCORPORATED AREAS 1.0 INTRODUCTION 1.1 Purpose of Study This Flood Insurance Study (FIS) report investigates the existence and severity of flood hazards in the geographic area of Pacific County, Washington, including the Cities of Raymond and South Bend; the Towns of Ilwaco and Long Beach; the Shoalwater Bay Indian Tribe; and the Unincorporated Areas of Pacific County (referred to collectively herein as Pacific County). 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 community that will be used to establish actuarial flood insurance rates and to assist the community in its 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. The Digital Flood Insurance Rate Map (DFIRM) and FIS report for this countywide study have been produced in digital format. Flood hazard information was converted to meet the Federal Emergency Management Agency (FEMA) DFIRM database specifications and Geographic Information System (GIS) format requirements. The flood hazard information was created and is provided in a digital format so that it can be incorporated into a local GIS and be accessed more easily by the community. 1.2 Authority and Acknowledgments The sources of authority for this FIS are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. This FIS was prepared to include all jurisdictions within Pacific County into a countywide format FIS. Information on the authority and acknowledgements for each of the previously printed FISs for communities within Pacific County was compiled, and is shown below. Ilwaco, Town of The hydrologic and hydraulic analyses for the August 1978 study were performed by Tippetts-Abbett-McCarthy-Stratton, Engineers and Planners, for the Federal Insurance Administration (FIA), under Contract No. H-4022. This work was completed in April 1977 (Reference 1). 1 Raymond, City of The hydrologic and hydraulic analyses for the January 1979 study were performed by CH2M HILL, Inc., for FIA, under Contract No. H-3815. This work was completed in January 1978 (Reference 2). South Bend, City The hydrologic and hydraulic analyses for the May 1979 study of were performed by CH2M HILL, Inc., for FIA, under Contract No. H-3815.