HUMBOLDT COUNTY, PRELIMINARY CALIFORNIA October 27, 2015 AND INCORPORATED AREAS COMMUNITY NAME COMMUNITY NUMBER ARCATA, CITY OF 060061 BLUE LAKE, CITY OF 060438 EUREKA, CITY OF 060062 FERNDALE, CITY OF 060445 FORTUNA, CITY OF 060063 HUMBOLDT COUNTY (UNINCORPORATED AREAS) 060060 RIO DELL, CITY OF 060064 TRINIDAD, TOWN OF* 060436 *NOT PARTICIPATING IN THE NFIP Humboldt County REVISED Month, Day, Year Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER 06023CV000A 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. Part or all of this FIS may be revised and republished at any time. In addition, part of this FIS may be revised by the Letter of Map Revision process, which does not involve republication or redistribution of the FIS. It is, therefore, the responsibility of the user to consult with community officials and to check the community repository to obtain the most current FIS components. 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 and cross sections). In addition, former flood hazard zone designations have been changed as follows. Old Zone(s) New Zone A1 through A30 AE V1 through V30 VE B X C X This FIS report was revised on (Insert Date). 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 this FIS report. Therefore, users of this FIS 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 Countywide FIS Effective Date: (Insert Date) Revised Countywide FIS Date: (Insert Date) First Revision This preliminary FIS report does not include unrevised Floodway Data Tables and unrevised Flood Profiles. These Floodway Data Tables and Flood Profiles will appear in the final FIS report. TABLE OF CONTENTS 1.0 INTRODUCTION ................................................................................................................ 3 1.1 Purpose of Study ..................................................................................................... 3 1.2 Authority and Acknowledgments ........................................................................... 3 1.3 Coordination ........................................................................................................... 6 2.0 AREA STUDIED .................................................................................................................. 7 2.1 Scope of Study ........................................................................................................ 7 2.2 Community Description .......................................................................................... 8 2.3 Principal Flood Problems ...................................................................................... 11 2.4 Flood Protection Measures ................................................................................... 22 3.0 ENGINEERING METHODS ............................................................................................ 24 3.1 Hydrologic Analyses ............................................................................................. 25 3.2 Hydraulic Analyses ............................................................................................... 35 3.3 Coastal Hazard Analyses ...................................................................................... 41 3.4 Coastal Analyses for the Insert Date Revision to the Countywide FIS ................ 43 3.5 Vertical Datum ...................................................................................................... 67 4.0 FLOODPLAIN MANAGEMENT APPLICATIONS ..................................................... 68 4.1 Floodplain Boundaries .......................................................................................... 68 4.2 Floodways ............................................................................................................. 69 5.0 INSURANCE APPLICATIONS ....................................................................................... 78 6.0 FLOOD INSURANCE RATE MAP ................................................................................. 80 7.0 OTHER STUDIES .............................................................................................................. 82 8.0 LOCATION OF DATA ...................................................................................................... 83 9.0 BIBLIOGRAPHY AND REFERENCES ......................................................................... 85 10.0 REVISION DESCRIPTIONS ............................................................................................ 88 10.1 First Revision (insert date) .................................................................................... 88 i TABLE OF CONTENTS - continued FIGURES Figure 1 - TRANSECT SCHEMATIC 42 Figure 2 - COASTAL REACH ASSIGNMENT FOR SPATIAL APPLICATION OF TIDE GAUGE ANALYSES RESULTS 44 Figure 3 – TRANSECT LOCATION MAPS FOR THE OPEN PACIFIC COAST STUDY AREA 51 Figure 4 - FLOODWAY SCHEMATIC 78 TABLES Table 1 – INITIAL AND FINAL CCO MEETINGS 7 Table 2 - FLOODING SOURCES STUDIED BY DETAILED METHODS 7 Table 3 - SUMMARY OF DISCHARGES 31 Table 4 - SUMMARY OF STILLWATER ELEVATIONS 33 Table 5 - MANNING'S "n" VALUES 41 Table 6 – SPATIAL APPLICATION OF TIDE GAUGE ANALYSES RESULTS 44 Table 7 – SUMMARY OF REGIONAL SWELs AT TIDE GAUGES 45 Table 8 – TRANSECT LOCATION DESCRIPTIONS FOR THE OPEN PACIFIC COAST STUDY 47 Table 9 – OPEN PACIFIC COAST STUDY TRANSECT DATA AND TWLs 65 Table 10 - FLOODWAY DATA TABLES 72 Table 11 - COMMUNITY MAP HISTORY 81 Table 12 - MAP REPOSITORIES 84 EXHIBITS Exhibit 1 - Flood Profiles Dave Power’s Creek Panel 01P-02P Eastside Channel Panel 03P Eel River Panels 04P-15P Francis Creek Panels 16P-17P Freshwater Creek Panels 18P-21P Hillside Creek Panel 22P Jacoby Creek Panels 23P-25P Janes Creek Panels 26P-28P Mad River Panels 29P-31P Mad River (at Blue Lake) Panels 32P-35P Martin Slough Panels 36P-39P Martin Slough Tributary C Panels 40P-41P North Fork Mad River Panels 42P-43P Rohner Creek Panels 44P-47P South Fork Eel River Panels 48P-50P Strongs Creek Panels 51P-52P Trinity River Panels 53P-55P Van Duzen River Panels 56P-59P Williams Creek Panels 60P-61P Exhibit 2 - Flood Insurance Rate Map Index Flood Insurance Rate Maps ii FLOOD INSURANCE STUDY HUMBOLDT COUNTY, CALIFORNIA AND INCORPORATED AREAS 1.0 INTRODUCTION 1.1 Purpose of Study This countywide 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 Humboldt County, California, including: the Cities of Arcata, Blue Lake, Eureka, Ferndale, Fortuna, and Rio Dell, and the unincorporated areas of Humboldt County (hereinafter referred to collectively as Humboldt County). Humboldt County also includes the Town of Trinidad, which is not participating in the National Flood Insurance Program. This FIS aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. This FIS 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 Humboldt County to update existing floodplain regulations as part of the Regular Phase of the National Flood Insurance Program (NFIP), and will also be used 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 are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. This FIS was prepared to include the unincorporated areas of, and incorporated communities within, Humboldt County in 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. Arcata, City of: the hydrologic and hydraulic analyses from the original FIS report dated November 5, 1997, were performed by Anderson-Nichols and Company, Inc., for the Federal Emergency Management Agency (FEMA), under Contract No. H-4821. That work, which was completed in July 1980, covered all 3 significant flooding sources affecting Arcata. In the November 5, 1997, revision, the hydrologic and hydraulic analyses were prepared by Ensign & Buckley Consulting Engineers, the study contractor, for FEMA, under Contract No. EMW-90-C-3133. Blue Lake, City of: the hydrologic and hydraulic analyses