2020 Flood Insurance Study
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FAIRBANKS NORTH STAR BOROUGH, ALASKA COMMUNITY COMMUNITY NAME NUMBER FAIRBANKS NORTH STAR BOROUGH 025009 REVISED: SEPTEMBER 18, 2020 Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER 02090CV000B 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. Selected Flood Insurance Rate Map panels for the 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 changed as follows: Old Zone 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 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. This FIS report was revised on September 18, 2020. 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 may supersede information in Sections 1.0 through 9.0 of this FIS report. Boroughwide Effective Date: March 17, 2014 Revised Date: September 18, 2020 i Table of Contents 1.0 INTRODUCTION .............................................................................................................. 1 1.1 Purpose of Study .............................................................................................................. 1 1.2 Authority and Acknowledgments..................................................................................... 1 1.3 Coordination ..................................................................................................................... 1 2.0 AREA STUDIED................................................................................................................ 3 2.1 Scope of Study ................................................................................................................. 3 2.2 Community Description ................................................................................................... 3 2.3 Principal Flood Problems ................................................................................................. 5 2.4 Flood Protection Measures ............................................................................................... 7 3.0 ENGINEERING METHODS ............................................................................................. 7 3.1 Hydrologic Analyses ........................................................................................................ 8 3.2 Hydraulic Analyses ........................................................................................................ 10 3.3 Vertical Datum ............................................................................................................... 13 4.0 FLOODPLAIN MANAGEMENT APPLICATIONS ...................................................... 15 4.1 Floodplain Boundaries ................................................................................................... 15 4.2 Floodways ...................................................................................................................... 15 5.0 INSURANCE APPLICATION ........................................................................................ 29 6.0 FLOOD INSURANCE RATE MAP ................................................................................ 30 7.0 OTHER STUDIES ............................................................................................................ 32 8.0 LOCATION OF DATA .................................................................................................... 32 9.0 BIBLIOGRAPHY AND REFERENCES ......................................................................... 32 10.0 REVISIONS DESCRIPTION ........................................................................................... 35 10.1 Partial Boroughwide Revision (March 17, 2014)……………………………………....35 10.2 Partial Boroughwide Revision – Chena Slough (Date September 18, 2020) ................. 51 Figures Figure 1: Floodway Schematic ......................................................................................................................... 17 Figure 2: FIRM Notes to Users......................................................................................................................... 55 Figure 3: Map Legend for FIRM ...................................................................................................................... 57 Tables Table 1: Fairbanks Area Stream Gaging Stations .......................................................................... 8 Table 2: Summary of Discharges .................................................................................................. 10 Table 3: Floodway Data .................................................................................................................18 Table 4: Community Map History ..................................................................................................31 Table 5: 1-Percent-Annual-Chance Rainfall-Depth-Duration Quantiles Estimate …………...…38 at Fairbanks International Airport Table 6: Flows and Stages of Tanana and Chena Rivers Applied to ……………………...…….43 Groundwater Contours Table 7: Channel-A Seepage Capture Efficiencies (as per DM 12) ………………………...…. 46 Table 8: Revised Detailed Flooding Sources…………………………………………………….51 Table 9: Initial Peak Discharges for Chena Slough Surface Runoff…………………………….52 ii Exhibits Exhibit 1: Flood Profiles Chena River 01P - 04P Chena Slough 05P – 17P Little Chena River 18P - 19P Noyes Slough 20P Tanana River 21P - 26P Exhibit 2: Flood Insurance Rate Map Index Flood Insurance Rate Map iii FLOOD INSURANCE STUDY FAIRBANKS NORTH STAR BOROUGH, ALASKA 1.0 INTRODUCTION 1.1 Purpose of Study This Flood Insurance Study (FIS) revises and updates a previous Flood Insurance Study/Flood Insurance Rate Map for Fairbanks North Star Borough, Alaska (Reference 1). This information will be used by Fairbanks North Star Borough to update existing floodplain regulations as part of the Regular Phase of the National Flood Insurance Program (NFIP). The information will also be used by local and regional planners to further promote sound land use and floodplain development. 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. The hydrologic and hydraulic analyses for the original study were performed by the U.S. Army Corps of Engineers (COE), Alaska District, for the Federal Insurance Administration under Interagency Agreement No. IAA-H-8-70, Project Order No. 8. This work, which was completed in March 1969, covered flooding from the Chena River, from its mouth to mile 13.6, Noyes Slough, and the Tanana River. The remaining flooding sources in Fairbanks North Star Borough were studied by approximate methods by Michael Baker, Jr., Inc. The hydrologic and hydraulic analyses for the restudy were performed by the COE, Alaska District, the study contractor, for the Federal Emergency Management Agency (FEMA), under Interagency Agreement No. EMW-84-E-1506, Project Order No. 1, Amendment 30. This study was completed in August 1988. 1.3 Coordination On September 26, 1983, during a Community Assistance and Program Evaluation meeting between Fairbanks North Star Borough and FEMA, the Borough requested an updated Flood Insurance Study with base flood elevations for the community. In the following coordination meeting, the Borough agreed to obtain and provide the detailed topography as a cost-shared item if FEMA would fund the remainder of the update. Under the Interagency Agreement with FEMA, the COE, Alaska District, began holding meetings with the Borough to discuss the study process, of which the mapping would be 1 a key item. At a meeting with the Borough on April 4, 1985, mapping requirements were discussed and priority areas were identified so the study could begin. A meeting with the Borough on July 9, 1985, was held to discuss the various components of the study and demonstrate how the information would be used to regulate development in the flood- prone areas. A public meeting was held in the Steamboat Landing Subdivision on August 28, 1985, where residents were informed of the study and how the results would determine the degree to which their property is flood prone. Prior to and throughout the study there was significant public concern