VOLUME 1 OF 4 GADSDEN COUNTY, FLORIDAportal.nwfwmdfloodmaps.com/NWFWMD_Data/FISReports/...National...

VOLUME 1 OF 4

GADSDEN COUNTY, FLORIDA AND INCORPORATED AREAS

COMMUNITY NAME COMMUNITY NUMBER

CHATTAHOOCHEE, CITY OF 120092

GADSDEN COUNTY, UNINCORPORATED AREAS

120091

GREENSBORO, TOWN OF 120036

GRETNA, CITY OF 120046

HAVANA, TOWN OF 120411

MIDWAY, CITY OF 120026

QUINCY, CITY OF 120093

REVISED: TBD

FLOOD INSURANCE STUDY NUMBER 12039CV001B

Version Number 2.3.3.5

PRELIMINARY

04/11/2018

i

TABLE OF CONTENTS Volume 1

Page

SECTION 1.0 – INTRODUCTION 1 1.1 The National Flood Insurance Program 1 1.2 Purpose of this Flood Insurance Study Report 2 1.3 Jurisdictions Included in the Flood Insurance Study Project 2 1.4 Considerations for using this Flood Insurance Study Report 5

SECTION 2.0 – FLOODPLAIN MANAGEMENT APPLICATIONS 15 2.1 Floodplain Boundaries 15 2.2 Floodways 24 2.3 Base Flood Elevations 25 2.4 Non-Encroachment Zones 25 2.5 Coastal Flood Hazard Areas 26

2.5.1 Water Elevations and the Effects of Waves 26 2.5.2 Floodplain Boundaries and BFEs for Coastal Areas 26 2.5.3 Coastal High Hazard Areas 26 2.5.4 Limit of Moderate Wave Action 26

SECTION 3.0 – INSURANCE APPLICATIONS 26 3.1 National Flood Insurance Program Insurance Zones 26 3.2 Coastal Barrier Resources System 27

SECTION 4.0 – AREA STUDIED 27 4.1 Basin Description 27 4.2 Principal Flood Problems 28 4.3 Non-Levee Flood Protection Measures 29 4.4 Levees 29

SECTION 5.0 – ENGINEERING METHODS 29 5.1 Hydrologic Analyses 30 5.2 Hydraulic Analyses 47 5.3 Coastal Analyses 59

5.3.1 Total Stillwater Elevations 59 5.3.2 Waves 59 5.3.3 Coastal Erosion 59 5.3.4 Wave Hazard Analyses 59

5.4 Alluvial Fan Analyses 59

SECTION 6.0 – MAPPING METHODS 60 6.1 Vertical and Horizontal Control 60 6.2 Base Map 61 6.3 Floodplain and Floodway Delineation 61

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Volume 1 Figures

Page

Figure 1: FIRM Panel Index 7 Figure 2: FIRM Notes to Users 8 Figure 3: Map Legend for FIRM 11 Figure 4: Floodway Schematic 24 Figure 5: Wave Runup Transect Schematic 26 Figure 6: Coastal Transect Schematic 26 Figure 7: Frequency Discharge-Drainage Area Curves 46 Figure 8: 1% Annual Chance Total Stillwater Elevations for Coastal Areas 59 Figure 9: Transect Location Map 59

Volume 1

Tables Page

Table 1: Listing of NFIP Jurisdictions 2 Table 2: Flooding Sources Included in this FIS Report 16 Table 3: Flood Zone Designations by Community 27 Table 4: Coastal Barrier Resources System Information 27 Table 5: Basin Characteristics 27 Table 6: Principal Flood Problems 28 Table 7: Historic Flooding Elevations 28 Table 8: Non-Levee Flood Protection Measures 29 Table 9: Levees 29 Table 10: Summary of Discharges 31 Table 11: Summary of Non-Coastal Stillwater Elevations 46 Table 12: Stream Gage Information used to Determine Discharges 47 Table 13: Summary of Hydrologic and Hydraulic Analyses 48 Table 14: Roughness Coefficients 57 Table 15: Summary of Coastal Analyses 59 Table 16: Tide Gage Analysis Specifics 59 Table 17: Coastal Transect Parameters 59 Table 18: Summary of Alluvial Fan Analyses 60 Table 19: Results of Alluvial Fan Analyses 60 Table 20: Countywide Vertical Datum Conversion 60 Table 21: Stream-by-Stream Vertical Datum Conversion 60 Table 22: Base Map Sources 61 Table 23: Summary of Topographic Elevation Data used in Mapping 62 Table 24: Floodway Data 63

iii

TABLE OF CONTENTS Volume 2

Page

6.4 Coastal Flood Hazard Mapping 128 6.5 FIRM Revisions 128

6.5.1 Letters of Map Amendment 128 6.5.2 Letters of Map Revision Based on Fill 128 6.5.3 Letters of Map Revision 129 6.5.4 Physical Map Revisions 129 6.5.5 Contracted Restudies 129 6.5.6 Community Map History 130

SECTION 7.0 – CONTRACTED STUDIES AND COMMUNITY COORDINATION 131 7.1 Contracted Studies 131 7.2 Community Meetings 136

SECTION 8.0 – ADDITIONAL INFORMATION 140

SECTION 9.0 – BIBLIOGRAPHY AND REFERENCES 141

Volume 2 Tables

Page

Table 25: Flood Hazard and Non-Encroachment Data for Selected Streams 77 Table 26: Summary of Coastal Transect Mapping Considerations 128 Table 27: Incorporated Letters of Map Change 129 Table 28: Community Map History 131 Table 29: Summary of Contracted Studies Included in this FIS Report 132 Table 30: Community Meetings 137 Table 31: Map Repositories 140 Table 32: Additional Information 141 Table 33: Bibliography and References 142

iv

Volume 3Exhibits

Flood Profiles PanelApalachicola River 01-02 PBear Creek 03-04 PDouble Branch 04a-04h PG Creek 04i-04k PG Creek Unnamed Tributary 1 04l-04m PG Creek Unnamed Tributary 2 04n PHammock Creek 04o-04p PHog Creek 04q-04t PHog Creek Unnamed Tributary 04u-04v PHolley Branch 05-07a PHolley Branch Unnamed Tributary 08-08a PHolley Branch Unnamed Tributary 2 08b-08c PHurricane Creek 08d-08f PHurricane Creek Unnamed Tributary 1 08g-08h PHurricane Creek Unnamed Tributary 2 08i-08k PHurricane Creek Unnamed Tributary 3 08l-08m PLake Talquin Unnamed Tributary 09-10b PLittle River 11 PLittle River/Attapulgus Creek/Swamp Creek 12 PMcIntosh Branch 12a PMonroe Creek 13-14a PMonroe Creek Unnamed Tributary 1 14b PMonroe Creek Unnamed Tributary 2 14c-14d PMonroe Creek Unnamed Tributary 3 14e-14g PMonroe Creek Unnamed Tributary 4 14h PMosquito Creek 15 PMosquito Creek Unnamed Tributary 16 POchlockonee River 17-20j POchlockonee River Unnamed Tributary 21-24 POcklawaha Creek 25 PQuincy Creek 26-27 PRichlander Creek 28-29 PRobinson Branch 29a-29b PSalem Branch 29c-29g P

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Volume 4Exhibits

Flood Profiles PanelSouth Mosquito Creek 30 PSouth Mosquito Creek Unnamed Tributary 31-32 PTanyard Branch 33-35 PTanyard Branch Unnamed Tributary 1 36 PTanyard Branch Unnamed Tributary 2 37-37b PTelogia Creek 37ba-37bd PUnnamed Stream 2 37c-37e PUnnamed Stream 3 37f-37g PUnnamed Stream 4 37h-37i PUnnamed Stream 6 37j-37k PSouth Mosquito Creek 30 PSouth Mosquito Creek Unnamed Tributary 31-32 PTanyard Branch 33-35 PTanyard Branch Unnamed Tributary 1 36 PTanyard Branch Unnamed Tributary 2 37-37b PTelogia Creek 37ba-37bd PUnnamed Stream 2 37c-37e PUnnamed Stream 3 37f-37g PUnnamed Stream 4 37h-37i PUnnamed Stream 6 37j-37k PUnnamed Stream 7 37l-37p PUnnamed Stream 8 37q-37r PUnnamed Tributary 1 37s PUnnamed Tributary 2 37t PUnnamed Tributary 3 37u PUnnamed Tributary 4 37v PUnnamed Tributary 5 37w PUnnamed Tributary 6 37x PUnnamed Tributary 7 37y PUnnamed Tributary 8 37z-37aa PUnnamed Tributary 9 37ab-37ac PUnnamed Tributary 10 37ad-37ae PUnnamed Tributary 11 37af-37ag PUnnamed Tributary 12 37ah-37ai PUnnamed Tributary 13 37aj PUnnamed Tributary 14 37ak-37al PUnnamed Tributary 15 37am-37ap PUnnamed Tributary 16 37aq PUnnamed Tributary 17 37ar-37as PUnnamed Tributary 20 37at-37au PUnnamed Tributary 21 37av PUnnamed Tributary to Ochlockonee River Unnamed Tributary 38-39a P

Published Separately

Flood Insurance Rate Map (FIRM)

1

FLOOD INSURANCE STUDY REPORT GADSDEN COUNTY, FLORIDA

SECTION 1.0 – INTRODUCTION

1.1 The National Flood Insurance Program

The National Flood Insurance Program (NFIP) is a voluntary Federal program that enables property owners in participating communities to purchase insurance protection against losses from flooding. This insurance is designed to provide an insurance alternative to disaster assistance to meet the escalating costs of repairing damage to buildings and their contents caused by floods. For decades, the national response to flood disasters was generally limited to constructing flood-control works such as dams, levees, sea-walls, and the like, and providing disaster relief to flood victims. This approach did not reduce losses nor did it discourage unwise development. In some instances, it may have actually encouraged additional development. To compound the problem, the public generally could not buy flood coverage from insurance companies, and building techniques to reduce flood damage were often overlooked. In the face of mounting flood losses and escalating costs of disaster relief to the general taxpayers, the U.S. Congress created the NFIP. The intent was to reduce future flood damage through community floodplain management ordinances, and provide protection for property owners against potential losses through an insurance mechanism that requires a premium to be paid for the protection. The U.S. Congress established the NFIP on August 1, 1968, with the passage of the National Flood Insurance Act of 1968. The NFIP was broadened and modified with the passage of the Flood Disaster Protection Act of 1973 and other legislative measures. It was further modified by the National Flood Insurance Reform Act of 1994 and the Flood Insurance Reform Act of 2004. The NFIP is administered by the Federal Emergency Management Agency (FEMA), which is a component of the Department of Homeland Security (DHS). Participation in the NFIP is based on an agreement between local communities and the Federal Government. If a community adopts and enforces floodplain management regulations to reduce future flood risks to new construction and substantially improved structures in Special Flood Hazard Areas (SFHAs), the Federal Government will make flood insurance available within the community as a financial protection against flood losses. The community’s floodplain management regulations must meet or exceed criteria established in accordance with Title 44 Code of Federal Regulations (CFR) Part 60.3, Criteria for land Management and Use. SFHAs are delineated on the community’s Flood Insurance Rate Maps (FIRMs). Under the NFIP, buildings that were built before the flood hazard was identified on the community’s FIRMs are generally referred to as “Pre-FIRM” buildings. When the NFIP was created, the U.S. Congress recognized that insurance for Pre-FIRM buildings would be prohibitively expensive if the premiums were not subsidized by the Federal

2

Government. Congress also recognized that most of these floodprone buildings were built by individuals who did not have sufficient knowledge of the flood hazard to make informed decisions. The NFIP requires that full actuarial rates reflecting the complete flood risk be charged on all buildings constructed or substantially improved on or after the effective date of the initial FIRM for the community or after December 31, 1974, whichever is later. These buildings are generally referred to as “Post-FIRM” buildings.

1.2 Purpose of this Flood Insurance Study Report

This Flood Insurance Study (FIS) report revises and updates information on the existence and severity of flood hazards for the study area. The studies described in this report developed flood hazard data that will be used to establish actuarial flood insurance rates and to assist communities in efforts to implement sound floodplain management. In some states or communities, floodplain management criteria or regulations may exist that are more restrictive than the minimum Federal requirements. Contact your State NFIP Coordinator to ensure that any higher State standards are included in the community’s regulations.

1.3 Jurisdictions Included in the Flood Insurance Study Project

This FIS Report covers the entire geographic area of Gadsden County, Florida. The jurisdictions that are included in this project area, along with the Community Identification Number (CID) for each community and the 8-digit Hydrologic Unit Codes (HUC-8) sub-basins affecting each, are shown in Table 1. The Flood Insurance Rate Map (FIRM) panel numbers that affect each community are listed. If the flood hazard data for the community is not included in this FIS Report, the location of that data is identified.

Table 1: Listing of NFIP Jurisdictions

Community CID

HUC-8 Sub-

Basin(s) Located on FIRM

Panel(s)

If Not Included, Location of Flood

Hazard Data

Chattahoochee, City of 120092 03130008 03130011

12039C0028C

12039C0029C

12039C0036C

12039C0037C

12039C0050C

Gadsden County, Unincorporated Areas

120091 03120003 03130011

12039C0017C

12039C0019C

12039C0028C

12039C0029C

12039C0036C

12039C0037C

Table 1: Listing of NFIP Jurisdictions continued

3

Community CID

HUC-8 Sub-


Panel(s)


Hazard Data


120091 03120003 03130011

12039C0038C

12039C0039C

12039C0050C

12039C0075D

12039C0100C

12039C0111C

12039C0112C

12039C0113C

12039C0114D

12039C0116C

12039C0117C

12039C0118D

12039C0119D

12039C0125C

12039C0130C

12039C0138D

12039C0139C

12039C0140C

12039C0141C

12039C0143C

12039C0156C

12039C0157C

12039C0159C

12039C0167C

12039C0200D

12039C0225D

12039C0226C

12039C0227C

12039C0228C

12039C0229D

12039C0231C

12039C0232C

12039C0233D

12039C0234C

12039C0237D

12039C0240C

12039C0241D

12039C0242C


4

Community CID

HUC-8 Sub-


Panel(s)


Hazard Data


120091 03120003 03130011

12039C0243D

12039C0244C

12039C0251C

12039C0253C

12039C0255D

12039C0259D

12039C0260D

12039C0261D

12039C0262D

12039C0263D

12039C0264D

12039C0266D

12039C0267D

12039C0268D

12039C0269D

12039C0276C

12039C0277C

12039C0278D

12039C0310D

12039C0335C

12039C0341C

12039C0342D

12039C0343C

12039C0344D

12039C0350D

12039C0351C

12039C0352C

12039C0353D

12039C0354D

12039C0356C

12039C0357C

12039C0358D

12039C0359D

12039C0361D

12039C0362D

12039C0366D

12039C0376C

12039C0377D


5

Community CID

HUC-8 Sub-


Panel(s)


Hazard Data


120091 03120003 03130011

12039C0378C

12039C0379C

12039C0381D

12039C0382D

12039C0383C

Greensboro, Town of 120036 03120003 12039C0200D

12039C0225D

Gretna, City of 120046 03120003 12039C0075D

12039C0225D

Havana, Town of 120411 03120003

12039C0118D

12039C0119D

12039C0260D

Midway, City of 120026 03120003

12039C0244C

12039C0263D

12039C0264D

12039C0268D

12039C0376C

12039C0377D

12039C0381D

12039C0382D

Quincy, City of 120093 03120003

12039C0226C

12039C0227C

12039C0228C

12039C0229D

12039C0231C

12039C0233D

12039C0237D

12039C0240C

12039C0241D

1.4 Considerations for using this Flood Insurance Study Report

The NFIP encourages State and local governments to implement sound floodplain management programs. To assist in this endeavor, each FIS Report provides floodplain data, which may include a combination of the following: 10-, 4-, 2-, 1-, and 0.2-percent annual chance flood elevations (the 1% annual chance flood elevation is also referred to as the Base Flood Elevation (BFE)); delineations of the 1% annual chance and 0.2% annual chance floodplains; and 1% annual chance floodway. This information is presented on the FIRM and/or in many components of the FIS Report, including Flood Profiles, Floodway Data tables, Summary of Non-Coastal Stillwater Elevations tables,

6

and Coastal Transect Parameters tables (not all components may be provided for a specific FIS). This section presents important considerations for using the information contained in this FIS Report and the FIRM, including changes in format and content. Figures 1, 2, and 3 present information that applies to using the FIRM with the FIS Report.

Part or all of this FIS Report may be revised and republished at any time. In addition, part of this FIS Report may be revised by a Letter of Map Revision (LOMR), which does not involve republication or redistribution of the FIS Report. Refer to Section 6.5 of this FIS Report for information about the process to revise the FIS Report and/or FIRM.

It is, therefore, the responsibility of the user to consult with community officials by contacting the community repository to obtain the most current FIS Report components. Communities participating in the NFIP have established repositories of flood hazard data for floodplain management and flood insurance purposes. Community map repository addresses are provided in Table 31, “Map Repositories,” within this FIS Report.

New FIS Reports are frequently developed for multiple communities, such as entire counties. A countywide FIS Report incorporates previous FIS Reports for individual communities and the unincorporated area of the county (if not jurisdictional) into a single document and supersedes those documents for the purposes of the NFIP.

The initial Countywide FIS Report for Gadsden County became effective on February 4, 2009. Refer to Table 28 for information about subsequent revisions to the FIRMs. Since the status of levees is subject to change at any time, the user should contact the appropriate agency for the latest information regarding levees presented in Table 9 of this FIS Report. For levees owned or operated by the U.S. Army Corps of Engineers (USACE), information may be obtained from the USACE national levee database (nld.usace.army.mil). For all other levees, the user is encouraged to contact the appropriate local community.

FEMA has developed a Guide to Flood Maps (FEMA 258) and online tutorials to assist users in accessing the information contained on the FIRM. These include how to read panels and step-by-step instructions to obtain specific information. To obtain this guide and other assistance in using the FIRM, visit the FEMA Web site at http://www.fema.gov/online-tutorials.

The FIRM Index in Figure 1 shows the overall FIRM panel layout within Gadsden County, and also displays the panel number and effective date for each FIRM Panel in the County. Other information shown on the FIRM Index includes community boundaries, flooding sources, watershed boundaries, and United States Geological Survey (USGS) Hydrologic Unit Code-8 codes.

http://www.fema.gov/online-tutorials

0225D0200D

0100C2/4/2009

0075D0050C2/4/2009

0350D

0125C2/4/2009

0335C2/4/20090310D

0130C2/4/2009

0240C2/4/2009

0260D

0140C2/4/2009

0255D

0344D0343C2/4/2009

0362D0361D0341C2/4/2009

0366D0342D

0379C2/4/2009

0378C2/4/2009

0354D 0383C2/4/2009

0353D 0359D0358D

0382D0351C2/4/2009

0377D0376C2/4/2009

0381D0352C2/4/2009

0356C2/4/2009

0357C2/4/2009

0269D0263D 0268D0264D0243D 0244C2/4/2009

0237D 0267D0261D 0266D0167C2/4/2009

0262D0241D 0242C2/4/2009

0259D0228C2/4/2009

0253C2/4/2009

0278D0233D0229D0159C2/4/2009

0234C2/4/2009

0231C2/4/2009

0226C2/4/2009

0157C2/4/2009

0251C2/4/2009

0156C2/4/2009

0277C2/4/2009

0227C2/4/2009

0232C2/4/2009

0276C2/4/2009

0113C2/4/2009

0143C2/4/2009

0138D 0139C2/4/2009

0039C2/4/2009

0119D0118D

0038C2/4/2009

0114D0019C2/4/2009

0017C2/4/2009

0112C2/4/2009

0111C2/4/2009

0036C2/4/2009

0037C2/4/2009

0141C2/4/2009

0116C2/4/2009

0117C2/4/2009

0028C2/4/2009

0029C2/4/2009

90

90

12

267 63

65

12

267

8

8

63CITY OF GRETNA

120046

CITY OF CHATTAHOOCHEE120092

10

10

10

Flat Creek

Bear CreekLittle River

Crooked Creek

Lake Talquin

Cane Creek

Attapulgus Creek

Juniper Creek

Hammock Creek

Hurricane Creek

Hog Creek

Hubbert Branch

Double Branch

Mill Creek

Juniper BranchMule Creek

CITY OF QUINCY120093

TOWN OF HAVANA120411

CITY OF MIDWAY120026

GADSDEN COUNTYUNINCORPORATED AREAS

120091

TOWN OF GREENSBORO120036

HUC8 03120003Lower Ochlockonee Watershed

HUC8 03130011Apalachicola Watershed

HUC8 03130008Lower Flint Watershed

Map Projection:Florida State Plane Single ZoneNorth American Datum 1983 HARN

SEE FLOOD INSURANCE STUDY FOR ADDITIONAL INFORMATION

MAP REVISED

MAP NUMBER12039CIND0B

THE INFORMATION DEPICTED ON THIS MAP AND SUPPORTINGDOCUMENTATION ARE ALSO AVAILABLE IN DIGITAL FORMAT AT

HTTP://MSC.FEMA.GOV

NATIONAL FLOOD INSURANCE PROGRAMFLOOD INSURANCE RATE MAP INDEXGADSDEN COUNTY, FLORIDA and Incorporated AreasPANELS PRINTED: 0017, 0019, 0028, 0029, 0036, 0037,0038, 0039, 0050, 0075, 0100, 0111, 0112, 0113, 0114,0116, 0117, 0118, 0119, 0125, 0130, 0138, 0139, 0140, 0141, 0143, 0156, 0157, 0159, 0167, 0200, 0225, 0226, 0227, 0228, 0229, 0231, 0232, 0233, 0234, 0237, 0240, 0241, 0242, 0243, 0244, 0251, 0253, 0255, 0259, 0260, 0261, 0262, 0263, 0264, 0266, 0267, 0268, 0269, 0276, 0277, 0278, 0310, 0335, 0341, 0342, 0343, 0344, 0350, 0351, 0352, 0353, 0354, 0356, 0357, 0358, 0359, 0361, 0362, 0366, 0376, 0377, 0378, 0379, 0381, 0382, 0383

N 0 16,600 33,2008,300Feet

1 inch = 23,141 feet 1:277,693

Figure 1: FIRM Panel Index

ATTENTION: The corporate limits shown on this FIRM Index are based on thebest information available at the time of publication. As such, they may be morecurrent than those shown on FIRM panels issued before MONTH DAY, YEAR.

GEORGIA

LEON COUNTY

JACKSON COUNTY

LIBERTY COUNTY

COUNTY LOCATOR

PRELIMINARYAPR 11 2018

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Each FIRM panel may contain specific notes to the user that provide additional information regarding the flood hazard data shown on that map. However, the FIRM panel does not contain enough space to show all the notes that may be relevant in helping to better understand the information on the panel. Figure 2 contains the full list of these notes.

Figure 2: FIRM Notes to Users

NOTES TO USERS For information and questions about this map, available products associated with this FIRM including historic versions of this FIRM, how to order products, or the National Flood Insurance Program in general, please call the FEMA Map Information eXchange at 1-877-FEMA-MAP (1-877-336-2627) or visit the FEMA Flood Map Service Center website at msc.fema.gov. Available products may include previously issued Letters of Map Change, a Flood Insurance Study Report, and/or digital versions of this map. Many of these products can be ordered or obtained directly from the website. Users may determine the current map date for each FIRM panel by visiting the FEMA Flood Map Service Center website or by calling the FEMA Map Information eXchange. Communities annexing land on adjacent FIRM panels must obtain a current copy of the adjacent panel as well as the current FIRM Index. These may be ordered directly from the Flood Map Service Center at the number listed above. For community and countywide map dates, refer to Table 28 in this FIS Report. To determine if flood insurance is available in the community, contact your insurance agent or call the National Flood Insurance Program at 1-800-638-6620. PRELIMINARY FIS REPORT: FEMA maintains information about map features, such as street locations and names, in or near designated flood hazard areas. Requests to revise information in or near designated flood hazard areas may be provided to FEMA during the community review period, at the final Consultation Coordination Officer's meeting, or during the statutory 90-day appeal period. Approved requests for changes will be shown on the final printed FIRM.

The map is for use in administering the NFIP. It may not identify all areas subject to flooding, particularly from local drainage sources of small size. Consult the community map repository to find updated or additional flood hazard information. BASE FLOOD ELEVATIONS: For more detailed information in areas where Base Flood Elevations (BFEs) and/or floodways have been determined, consult the Flood Profiles and Floodway Data and/or Summary of Stillwater Elevations tables within this FIS Report. Use the flood elevation data within the FIS Report in conjunction with the FIRM for construction and/or floodplain management. FLOODWAY INFORMATION: Boundaries of the floodways were computed at cross sections and interpolated between cross sections. The floodways were based on hydraulic considerations with regard to requirements of the National Flood Insurance Program. Floodway widths and other pertinent floodway data are provided in the FIS Report for this jurisdiction.

http://msc.fema.gov/


9

FLOOD CONTROL STRUCTURE INFORMATION: Certain areas not in Special Flood Hazard Areas may be protected by flood control structures. Refer to Section 4.3 "Non-Levee Flood Protection Measures" of this FIS Report for information on flood control structures for this jurisdiction.

PROJECTION INFORMATION: The projection used in the preparation of the map was State Plane Lambert Conformal Conic, Florida North Zone; North American Datum 1983 HARN; Western Hemisphere; Vertical Datum: NAVD 88. The horizontal datum was North American Datum 1983 HARN. Differences in datum, spheroid, projection or State Plane zones used in the production of FIRMs for adjacent jurisdictions may result in slight positional differences in map features across jurisdiction boundaries. These differences do not affect the accuracy of the FIRM.

ELEVATION DATUM: Flood elevations on the FIRM are referenced to the North American Vertical Datum of 1988. These flood elevations must be compared to structure and ground elevations referenced to the same vertical datum. For information regarding conversion between the National Geodetic Vertical Datum of 1929 and the North American Vertical Datum of 1988, visit the National Geodetic Survey website at www.ngs.noaa.gov.

Local vertical monuments may have been used to create the map. To obtain current monument information, please contact the appropriate local community listed in Table 31 of this FIS Report.

BASE MAP INFORMATION Base map information shown on this FIRM was derived from digital orthophotography collected by the Digital Aerial Solutions. This imagery was flown in 2016 and was produced with a 6 inch ground sample distance. For information about base maps, refer to Section 6.2 “Base Map” in this FIS Report.

The map reflects more detailed and up-to-date stream channel configurations than those shown on the previous FIRM for this jurisdiction. The floodplains and floodways that were transferred from the previous FIRM may have been adjusted to conform to these new stream channel configurations. As a result, the Flood Profiles and Floodway Data tables may reflect stream channel distances that differ from what is shown on the map.

Corporate limits shown on the map are based on the best data available at the time of publication. Because changes due to annexations or de-annexations may have occurred after the map was published, map users should contact appropriate community officials to verify current corporate limit locations.

NOTES FOR FIRM INDEX REVISIONS TO INDEX: As new studies are performed and FIRM panels are updated within Gadsden County, FL, corresponding revisions to the FIRM Index will be incorporated within the FIS Report to reflect the effective dates of those panels. Please refer to Table 28 of this FIS Report to determine the most recent FIRM revision date for each community. The most recent FIRM panel effective date will correspond to the most recent index date. ATTENTION: The corporate limits shown on this FIRM Index are based on the best information available at the time of publication. As such, they may be more current than those shown on FIRM panels issued before MONTH DAY, YEAR.

SPECIAL NOTES FOR SPECIFIC FIRM PANELS This Notes to Users section was created specifically for Gadsden County, FL, effective 99/99/9999.

http://www.ngs.noaa.gov/


10

FLOOD RISK REPORT: A Flood Risk Report (FRR) may be available for many of the flooding sources and communities referenced in this FIS Report. The FRR is provided to increase public awareness of flood risk by helping communities identify the areas within their jurisdictions that have the greatest risks. Although non-regulatory, the information provided within the FRR can assist communities in assessing and evaluating mitigation opportunities to reduce these risks. It can also be used by communities developing or updating flood risk mitigation plans. These plans allow communities to identify and evaluate opportunities to reduce potential loss of life and property. However, the FRR is not intended to be the final authoritative source of all flood risk data for a project area; rather, it should be used with other data sources to paint a comprehensive picture of flood risk.

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Each FIRM panel contains an abbreviated legend for the features shown on the maps. However, the FIRM panel does not contain enough space to show the legend for all map features. Figure 3 shows the full legend of all map features. Note that not all of these features may appear on the FIRM panels in Gadsden County.

Figure 3: Map Legend for FIRM

SPECIAL FLOOD HAZARD AREAS: The 1% annual chance flood, also known as the base flood or 100-year flood, has a 1% chance of happening or being exceeded each year. Special Flood Hazard Areas are subject to flooding by the 1% annual chance flood. The Base Flood Elevation is the water surface elevation of the 1% annual chance flood. The floodway is the channel of a stream plus any adjacent floodplain areas that must be kept free of encroachment so that the 1% annual chance flood can be carried without substantial increases in flood heights. See note for specific types. If the floodway is too narrow to be shown, a note is shown.

Special Flood Hazard Areas subject to inundation by the 1% annual chance flood (Zones A, AE, AH, AO, AR, A99, V and VE)

Zone A The flood insurance rate zone that corresponds to the 1% annual chance floodplains. No base (1% annual chance) flood elevations (BFEs) or depths are shown within this zone.

Zone AE The flood insurance rate zone that corresponds to the 1% annual chance floodplains. Base flood elevations derived from the hydraulic analyses are shown within this zone, either at cross section locations or as static whole-foot elevations that apply throughout the zone.

Zone AH The flood insurance rate zone that corresponds to the areas of 1% annual chance shallow flooding (usually areas of ponding) where average depths are between 1 and 3 feet. Whole-foot BFEs derived from the hydraulic analyses are shown at selected intervals within this zone.

Zone AO The flood insurance rate zone that corresponds to the areas of 1% annual chance shallow flooding (usually sheet flow on sloping terrain) where average depths are between 1 and 3 feet. Average whole-foot depths derived from the hydraulic analyses are shown within this zone.

Zone AR The flood insurance rate zone that corresponds to areas that were formerly protected from the 1% annual chance flood by a flood control system that was subsequently decertified. Zone AR indicates that the former flood control system is being restored to provide protection from the 1% annual chance or greater flood.

Zone A99 The flood insurance rate zone that corresponds to areas of the 1% annual chance floodplain that will be protected by a Federal flood protection system where construction has reached specified statutory milestones. No base flood elevations or flood depths are shown within this zone.

Zone V The flood insurance rate zone that corresponds to the 1% annual chance coastal floodplains that have additional hazards associated with storm waves. Base flood elevations are not shown within this zone.

Zone VE Zone VE is the flood insurance rate zone that corresponds to the 1% annual chance coastal floodplains that have additional hazards associated with storm waves. Base flood elevations derived from the coastal analyses are shown within this zone as static whole-foot elevations that apply throughout the zone.

Regulatory Floodway determined in Zone AE.


12

OTHER AREAS OF FLOOD HAZARD

Shaded Zone X: Areas of 0.2% annual chance flood hazards and areas of 1% annual chance flood hazards with average depths of less than 1 foot or with drainage areas less than 1 square mile.

Future Conditions 1% Annual Chance Flood Hazard – Zone X: The flood insurance rate zone that corresponds to the 1% annual chance floodplains that are determined based on future-conditions hydrology. No base flood elevations or flood depths are shown within this zone.

Area with Reduced Flood Risk due to Levee: Areas where an accredited levee, dike, or other flood control structure has reduced the flood risk from the 1% annual chance flood.

Area with Flood Risk due to Levee: Areas where a non-accredited levee, dike, or other flood control structure is shown as providing protection to less than the 1% annual chance flood.

OTHER AREAS

Zone D (Areas of Undetermined Flood Hazard): The flood insurance rate zone that corresponds to unstudied areas where flood hazards are undetermined, but possible.

Unshaded Zone X: Areas of minimal flood hazard.

FLOOD HAZARD AND OTHER BOUNDARY LINES

(ortho) (vector)

Flood Zone Boundary (white line on ortho-photography-based mapping; gray line on vector-based mapping)

Limit of Study

Jurisdiction Boundary

Limit of Moderate Wave Action (LiMWA): Indicates the inland limit of the area affected by waves greater than 1.5 feet

GENERAL STRUCTURES

Aqueduct Channel Culvert

Storm Sewer

Channel, Culvert, Aqueduct, or Storm Sewer

__________ Dam Jetty Weir

Dam, Jetty, Weir

Levee, Dike, or Floodwall

Bridge

Bridge

NO SCREEN


13

COASTAL BARRIER RESOURCES SYSTEM (CBRS) AND OTHERWISE PROTECTED AREAS (OPA): CBRS areas and OPAs are normally located within or adjacent to Special Flood Hazard Areas. See Notes to Users for important information.

CBRS AREA 09/30/2009

Coastal Barrier Resources System Area: Labels are shown to clarify where this area shares a boundary with an incorporated area or overlaps with the floodway.

OTHERWISE PROTECTED

AREA 09/30/2009

Otherwise Protected Area

REFERENCE MARKERS

River mile Markers

CROSS SECTION & TRANSECT INFORMATION

Lettered Cross Section with Regulatory Water Surface Elevation (BFE)

Numbered Cross Section with Regulatory Water Surface Elevation (BFE)

Unlettered Cross Section with Regulatory Water Surface Elevation (BFE)

Coastal Transect

Profile Baseline: Indicates the modeled flow path of a stream and is shown on FIRM panels for all valid studies with profiles or otherwise established base flood elevation.

Coastal Transect Baseline: Used in the coastal flood hazard model to represent the 0.0-foot elevation contour and the starting point for the transect and the measuring point for the coastal mapping.

Base Flood Elevation Line (shown for flooding sources for which no cross sections or profile are available)

ZONE AE (EL 16)

Static Base Flood Elevation value (shown under zone label)

ZONE AO (DEPTH 2)

Zone designation with Depth

ZONE AO (DEPTH 2)

(VEL 15 FPS) Zone designation with Depth and Velocity


14

BASE MAP FEATURES

Missouri Creek River, Stream or Other Hydrographic Feature

Interstate Highway

U.S. Highway

State Highway

County Highway

MAPLE LANE

Street, Road, Avenue Name, or Private Drive if shown on Flood Profile

RAILROAD

Railroad

Horizontal Reference Grid Line

Horizontal Reference Grid Ticks

Secondary Grid Crosshairs

Land Grant Name of Land Grant

7 Section Number

R. 43 W. T. 22 N. Range, Township Number

4276000mE Horizontal Reference Grid Coordinates (UTM)

365000 FT Horizontal Reference Grid Coordinates (State Plane)

80 16’ 52.5” Corner Coordinates (Latitude, Longitude)

15

SECTION 2.0 – FLOODPLAIN MANAGEMENT APPLICATIONS

2.1 Floodplain Boundaries

To provide a national standard without regional discrimination, the 1% annual chance (100-year) flood has been adopted by FEMA as the base flood for floodplain management purposes. The 0.2% annual chance (500-year) flood is employed to indicate additional areas of flood hazard in the community. Each flooding source included in the project scope has been studied and mapped using professional engineering and mapping methodologies that were agreed upon by FEMA and Gadsden County as appropriate to the risk level. Flood risk is evaluated based on factors such as known flood hazards and projected impact on the built environment. Engineering analyses were performed for each studied flooding source to calculate its 1% annual chance flood elevations; elevations corresponding to other floods (e.g. 10-, 4-, 2-, 0.2-percent annual chance, etc.) may have also been computed for certain flooding sources. Engineering models and methods are described in detail in Section 5.0 of this FIS Report. The modeled elevations at cross sections were used to delineate the floodplain boundaries on the FIRM; between cross sections, the boundaries were interpolated using elevation data from various sources. More information on specific mapping methods is provided in Section 6.0 of this FIS Report. Depending on the accuracy of available topographic data (Table 23), study methodologies employed (Section 5.0), and flood risk, certain flooding sources may be mapped to show both the 1% and 0.2% annual chance floodplain boundaries, regulatory water surface elevations (BFEs), and/or a regulatory floodway. Similarly, other flooding sources may be mapped to show only the 1% annual chance floodplain boundary on the FIRM, without published water surface elevations. In cases where the 1% and 0.2% annual chance floodplain boundaries are close together, only the 1% annual chance floodplain boundary is shown on the FIRM. Figure 3, “Map Legend for FIRM”, describes the flood zones that are used on the FIRMs to account for the varying levels of flood risk that exist along flooding sources within the project area. Table 2 and Table 3 indicate the flood zone designations for each flooding source and each community within Gadsden County, FL, respectively. Table 2, “Flooding Sources Included in this FIS Report,” lists each flooding source, including its study limits, affected communities, mapped zone on the FIRM, and the completion date of its engineering analysis from which the flood elevations on the FIRM and in the FIS Report were derived. Descriptions and dates for the latest hydrologic and hydraulic analyses of the flooding sources are shown in Table 13. Floodplain boundaries for these flooding sources are shown on the FIRM (published separately) using the symbology described in Figure 3. On the map, the 1% annual chance floodplain corresponds to the SFHAs. The 0.2% annual chance floodplain shows areas that, although out of the regulatory floodplain, are still subject to flood hazards. Small areas within the floodplain boundaries may lie above the flood elevations but cannot be shown due to limitations of the map scale and/or lack of detailed topographic data. The procedures to remove these areas from the SFHA are described in Section 6.5 of this FIS Report.

16

Table 2: Flooding Sources Included in this FIS Report

Flooding Source Community Downstream Limit Upstream Limit

HUC-8 Sub-

Basin(s)

Length (mi) (streams or coastlines)

Area (mi2)

(estuaries or ponding)

Floodway (Y/N)

Zone shown

on FIRM Date of Analysis

All Zone A Streams

Gadsden County and Incorporated Areas

Various Various 03120003 03130011

251.7

N A 2006

Apalachicola River

Chattahoochee, City of; Gadsden County, Unincorporated Areas

Liberty/Calhoun County boundary

Jackson County boundary 03130011 9.2

N AE 1986

Attapulgus Creek Gadsden County, Unincorporated Areas

Confluence with Little River

Confluence with Swamp Creek

03120003 2.1

N AE 1987

Bear Creek Gadsden County, Unincorporated Areas

Confluence with Rocky Comfort Creek

Approximately 150 feet downstream of State Highway 267

03120003 3.6

N AE 1987

Double Branch Gadsden County, Unincorporated Areas

Confluence with Ochlocknee River Oxbow

Approximately 2.4 miles upstream of Unnamed Tributary 12

03120003 7.9

N AE 2015

G Creek Gadsden County, Unincorporated Areas

Approximately 0.8 mile downstream of confluence of G Creek Unnamed Tributary 1

Approximately 1.8 miles upstream of confluence of G Creek Unnamed Tributary 1

03120003 2.7

N AE 2015

G Creek Unnamed Tributary 1

Gadsden County, Unincorporated Areas; Quincy, City of

Confluence with G Creek

Approximately 2,340 feet upstream of Ranch Road

03120003 1.4

N AE 2015




Approximately 1.2 miles upstream of the confluence of G Creek

03120003 1.2

N AE 2015

Hammock Creek Gadsden County, Unincorporated Areas

Confluence with Ochlocknee River

Approximately 2,350 feet upstream of State Highway 267

03120003 2.3

N AE 2015

Hog Creek Gadsden County, Unincorporated Areas


Approximately 4.0 miles upstream of confluence of Ochlocknee River

03120003 4.0

N AE 2015

Hog Creek Unnamed Tributary


Confluence with Hog Creek

Approximately 1.5 miles upstream of confluence of Unnamed Tributary 7

03120003 2.1

N AE 2015

Table 2: Flooding Sources Included in this FIS Report continued

17


HUC-8 Sub-

Basin(s)


Area (mi2)


Floodway (Y/N)

Zone shown


Holley Branch Gadsden County, Unincorporated Areas; Midway, City of

Confluence with the Ochlocknee River

Approximately 4,300 feet upstream of Dupont Road

03120003 2.7

Y AE 2007

Holley Branch Gadsden County, Unincorporated Areas


Approximately 1,300 feet upstream of confluence of Holley Branch Unnamed Tributary 2

03120003 0.2

N AE 2015

Holley Branch Unnamed Tributary

Gadsden County, Unincorporated Areas; Midway, City of

Confluence with Holley Branch

Approximately 4,700 feet upstream of confluence with Holley Branch

03120003 0.8

Y AE 2007





03120003 1.5

N AE 2015

Holley Branch Unnamed Tributary 2



Approximately 1.2 miles upstream of confluence of Holley Branch

03120003 1.2

N AE 2015

Hurricane Creek Gadsden County, Unincorporated Areas

Approximately 2,300 feet downstream of the confluence of Hurricane Creek Tributary 2

Approximately 4,900 feet upstream of the confluence of Hurricane Creek Unnamed Tributary 1

03120003 3.6

N AE 2015

Hurricane Creek Unnamed Tributary 1


Confluence with Hurricane Creek

Approximately 2,390 feet upstream of Penny B Road

03120003 1.7

N AE 2015




Approximately 3,260 feet upstream of Beaver Creek Road

03120003 2.9

N AE 2015



Approximately 750 feet upstream of the confluence of Hurricane Creek

Approximately 4,230 feet upstream of Tallavana Trail

03120003 1.3

N AE 2015

Lake Talquin Gadsden County, Unincorporated Areas

Jackson Bluff Dam Ocklockonee River 03120003 12.5 N AE 1987


18


HUC-8 Sub-

Basin(s)


Area (mi2)


Floodway (Y/N)

Zone shown


Lake Talquin Unnamed Tributary


Confluence with Lake Talquin/Ochlockonee River

Approximately 820 feet upstream of Private Drive

03120003 1.8

Y AE 2007




Approximately 7,120 feet upstream of Private Drive

03120003 1.2

N AE 2015

Little River Gadsden County, Unincorporated Areas; Midway, City of

Confluence with Lake Talquin

Confluence with Attapulgus Creek

03120003 13.2

N AE 1987

McIntosh Branch Gadsden County, Unincorporated Areas

Confluence with Lake Talquin

Approximately 1.0 mile upstream of the confluence with Lake Talquin

03120003 1.0

N AE 2015

Monroe Creek Gadsden County, Unincorporated Areas; Midway, City of


Approximately 700 feet upstream of U.S. Highway 90

03120003 3.8

Y AE 2007

Monroe Creek Gadsden County, Unincorporated Areas


Approximately 1.7 miles upstream of U.S. Highway 90

03120003 1.6

N AE 2015

Monroe Creek Unnamed Tributary 1


Confluence with Monroe Creek

Approximately 0.6 mile upstream of the confluence with Monroe Creek

03120003 0.6

N AE 2015




Approximately 1,250 feet upstream U.S. Highway 90

03120003 2.0

N AE 2015




Approximately 2.4 miles upstream of the confluence of Monroe Creek

03120003 2.4

N AE 2015




Approximately 3,010 feet upstream of the confluence of Monroe Creek

03120003 0.6

N AE 2015


19


HUC-8 Sub-

Basin(s)


Area (mi2)


Floodway (Y/N)

Zone shown


Mosquito Creek Chattahoochee, City of; Gadsden County, Unincorporated Areas

Confluence with Apalachicola River

At U.S. Highway 90 03130011 4.4

N AE 1986

Mosquito Creek Unnamed Tributary

Chattahoochee, City of Confluence with Mosquito Creek

Approximately 4,340 feet upstream of confluence with Mosquito Creek

03130011 0.8

Y AE 2007

Ochlockonee River


Jackson Bluff Dam Grady County boundary 03120003 32.0

Y AE 2015

Ochlockonee River Unnamed Tributary



Approximately 1.6 miles upstream of confluence of Unnamed Tributary to Ochlocknee River Unnamed Tributary

03120003 5.1

Y AE 2007





03120003 0.2

N AE 2015

Ocklawaha Creek Gadsden County, Unincorporated Areas

Confluence with the Ochlockonee River

At State Highway 267 03120003 1.6

N AE 1987

Quincy Creek Gadsden County, Unincorporated Areas; Quincy, City of


Approximately 1.4 miles upstream of State Highway 268

03120003 8.8

Y AE 1987

Richlander Creek Gadsden County, Unincorporated Areas; Quincy, City of

Confluence with the Little River

Approximately 4,050 feet upstream of confluence of Robinson Branch

03120003 5.9

N AE 1987

Richlander Creek Gadsden County, Unincorporated Areas; Quincy, City of



03120003 0.7

N AE 2015

Robinson Branch Gadsden County, Unincorporated Areas

Confluence with Richlander Creek

Approximately 0.9 mile upstream of the Walsh Road

03120003 1.7

N AE 2015


20


HUC-8 Sub-

Basin(s)


Area (mi2)


Floodway (Y/N)

Zone shown


Salem Branch Gadsden County, Unincorporated Areas; Havana, Town of

Approximately 1.1 miles upstream of the confluence with Attapulgus Creek


03120003 5.0

N AE 2015

South Mosquito Creek

Chattahoochee, City of; Gadsden County Unincorporated, Areas

Confluence with Mosquito Creek


03130011 0.6

Y AE 2007

South Mosquito Creek Unnamed Tributary

Chattahoochee, City of; Gadsden County, Unincorporated Areas

Confluence with South Mosquito Creek

Approximately 4,080 feet upstream of Depot Road

03130011 1.3

Y AE 2007

Swamp Creek Gadsden County, Unincorporated Areas


At State Highway 159 03120003 1.6

N AE 1987

Tanyard Branch Gadsden County, Unincorporated Areas; Quincy, City of

Confluence with Quincy Creek

Approximately 150 feet upstream of 7th Street

03120003 2.6

Y AE 2007

Tanyard Branch Unnamed Tributary 1

Quincy, City of Confluence with Tanyard Branch

Approximately 150 feet upstream of Circle Drive

03120003 0.5

Y AE 2007



Confluence with Tanyard Branch

Approximately 145 feet downstream of County Highway 268

03120003 0.9

Y AE 2007




Approximately 320 feet upstream of railroad

03120003 1.9

N AE 2015

Telogia Creek

Gadsden County, Unincorporated, Areas; Greensboro, Town of; Gretna, City of

Liberty County boundary

Approximately 1,850 feet upstream of U.S. Highway 90

03120003 17.0

N AE 2014

Unnamed Stream 2


Confluence with Ochlockonee River

Approximately 2.7 miles upstream of the confluence of Ochlockonee River

03120003 2.7

N AE 2015

Unnamed Stream 3



Approximately 2,350 feet upstream of Reynolds Road

03120003 1.5

N AE 2015


21


HUC-8 Sub-

Basin(s)


Area (mi2)


Floodway (Y/N)

Zone shown


Unnamed Stream 4



Approximately 1,980 feet upstream of Business Park Road

03120003 2.4

N AE 2015

Unnamed Stream 6




03120003 1.5

N AE 2015

Unnamed Stream 7

Gadsden County Unincorporated Areas; Havana, Town of


Approximately 1.2 miles upstream of the confluence if Unnamed Tributary 13

03120003 5.1

N AE 2015

Unnamed Stream 8



Approximately 1.4 miles upstream of the confluence of Ochlocknee River

03120003 1.5

N AE 2015

Unnamed Tributary 1


Confluence with Lake Talquin Unnamed Tributary

Approximately 1,260 feet upstream of Lakeview Point Road

03120003 0.6

N AE 2015

Unnamed Tributary 2



Approximately 4,650 feet upstream of the confluence of Richlander Creek

03120003 0.9

N AE 2015

Unnamed Tributary 3




03120003 0.7

N AE 2015

Unnamed Tributary 4



Approximately 0.8 miles upstream of the confluence of Richlander Creek

03120003 0.8

N AE 2015

Unnamed Tributary 5



Approximately 2,510 feet upstream of Augustine Road

03120003 1.2

N AE 2015


22


HUC-8 Sub-

Basin(s)


Area (mi2)


Floodway (Y/N)

Zone shown


Unnamed Tributary 6


Confluence with Tanyard Branch Unnamed Tributary 2

Approximately 4,640 feet upstream of the confluence of Tanyard Branch Unnamed Tributary 2

03120003 0.9

N AE 2015

Unnamed Tributary 7


Confluence with Hog Creek Unnamed Tributary

Approximately 4,380 feet upstream of the confluence of Hog Creek Unnamed Tributary

03120003 0.8

N AE 2015

Unnamed Tributary 8


Confluence with Hog Creek Unnamed Tributary

Approximately 2.2 miles upstream of the confluence of Hog Creek Unnamed Tributary

03120003 2.2

N AE 2015

Unnamed Tributary 9


Confluence with Double Branch

Approximately 85 feet downstream of Shady Rest Road/State Highway 270

03120003 1.7

N AE 2015

Unnamed Tributary 10




03120003 2.4

N AE 2015




At Robin Lane 03120003 1.6

N AE 2015




Approximately 4,360 feet upstream of Lanier Road

03120003 2.1

N AE 2015



Confluence with Unnamed Stream 7

Approximately 2,050 feet upstream of Eastern Way

03120003 1.1

N AE 2015




Approximately 4,310 feet upstream of Railroad

03120003 2.3

N AE 2015





03120003 4.0

N AE 2015



Confluence with Unnamed Tributary 15

Approximately 1,065 feet upstream of North Quail Hollow Road

03120003 1.1

N AE 2015


23


HUC-8 Sub-

Basin(s)


Area (mi2)


Floodway (Y/N)

Zone shown





Approximately 1,360 feet upstream of Tall Timber Road

03120003 1.3

N AE 2015



Confluence with Unnamed Tributary to Ochlocknee River Unnamed Tributary

Approximately 1.5 miles upstream of the confluence of Unnamed Tributary to Ochlocknee River Unnamed Tributary

03120003 1.5

N AE 2015




Approximately 410 feet upstream of Collins Road II

03120003 0.8

N AE 2015

Unnamed Tributary to Ochlockonee River Unnamed Tributary


Confluence with Ochlockonee River Unnamed Tributary


03120003 1.8

Y AE 2007





03120003 1.7

N AE 2015

24

2.2 Floodways

Encroachment on floodplains, such as structures and fill, reduces flood-carrying capacity, increases flood heights and velocities, and increases flood hazards in areas beyond the encroachment itself. One aspect of floodplain management involves balancing the economic gain from floodplain development against the resulting increase in flood hazard. For purposes of the NFIP, a floodway is used as a tool to assist local communities in balancing floodplain development against increasing flood hazard. With this approach, the area of the 1% annual chance floodplain on a river is divided into a floodway and a floodway fringe based on hydraulic modeling. The floodway is the channel of a stream, plus any adjacent floodplain areas, that must be kept free of encroachment in order to carry the 1% annual chance flood. The floodway fringe is the area between the floodway and the 1% annual chance floodplain boundaries where encroachment is permitted. The floodway must be wide enough so that the floodway fringe could be completely obstructed without increasing the water surface elevation of the 1% annual chance flood more than 1 foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to floodplain development are shown in Figure 4. To participate in the NFIP, Federal regulations require communities to limit increases caused by encroachment to 1.0 foot, provided that hazardous velocities are not produced. The floodways in this project are presented to local agencies as minimum standards that can be adopted directly or that can be used as a basis for additional floodway projects.

Figure 4: Floodway Schematic

25

Floodway widths presented in this FIS Report and on the FIRM were computed at cross sections. Between cross sections, the floodway boundaries were interpolated. For certain stream segments, floodways were adjusted so that the amount of floodwaters conveyed on each side of the floodplain would be reduced equally. The results of the floodway computations have been tabulated for selected cross sections and are shown in Table 24, “Floodway Data.” All floodways that were developed for this Flood Risk Project are shown on the FIRM using the symbology described in Figure 3. In cases where the floodway and 1% annual chance floodplain boundaries are either close together or collinear, only the floodway boundary has been shown on the FIRM. For information about the delineation of floodways on the FIRM, refer to Section 6.3.

2.3 Base Flood Elevations

The hydraulic characteristics of flooding sources were analyzed to provide estimates of the elevations of floods of the selected recurrence intervals. The Base Flood Elevation (BFE) is the elevation of the 1% annual chance flood. These BFEs are most commonly rounded to the whole foot, as shown on the FIRM, but in certain circumstances or locations they may be rounded to 0.1 foot. Cross section lines shown on the FIRM may also be labeled with the BFE rounded to 0.1 foot. Whole-foot BFEs derived from engineering analyses that apply to coastal areas, areas of ponding, or other static areas with little elevation change may also be shown at selected intervals on the FIRM. Cross sections with BFEs shown on the FIRM correspond to the cross sections shown in the Floodway Data table and Flood Profiles in this FIS Report. BFEs are primarily intended for flood insurance rating purposes. For construction and/or floodplain management purposes, users are cautioned to use the flood elevation data presented in this FIS Report in conjunction with the data shown on the FIRM.

2.4 Non-Encroachment Zones

Some States and communities use non-encroachment zones to manage floodplain development. For flooding sources with medium flood risk, field surveys are often not collected and surveyed bridge and culvert geometry is not developed. Standard hydrologic and hydraulic analyses are still performed to determine BFEs in these areas. However, floodways are not typically determined, since specific channel profiles are not developed. To assist communities with managing floodplain development in these areas, a “non-encroachment zone” may be provided. While not a FEMA designated floodway, the non-encroachment zone represents that area around the stream that should be reserved to convey the 1% annual chance flood event. As with a floodway, all surcharges must fall within the acceptable range in the non-encroachment zone. General setbacks can be used in areas of lower risk (e.g. unnumbered Zone A), but these are not considered sufficient where unnumbered Zone A is replaced by Zone AE. The NFIP requires communities to ensure that any development in a non-encroachment area causes no increase in BFEs. Communities must generally prohibit development within the area defined by the non-encroachment width to meet the NFIP requirement. Non-encroachment determinations may be delineated where it is not possible to delineate floodways because specific channel profiles with bridge and culvert geometry

26

were not developed. Any non-encroachment determinations for this Flood Risk Project have been tabulated for selected cross sections and are shown in Table 25, “Flood Hazard and Non-Encroachment Data for Selected Streams.” Areas for which non-encroachment zones are provided show BFEs and the 1% annual chance floodplain boundaries mapped as zone AE on the FIRM but no floodways.

2.5 Coastal Flood Hazard Areas

This section is not applicable to this Flood Risk Project.

2.5.1 Water Elevations and the Effects of Waves


Figure 5: Wave Runup Transect Schematic

[Not Applicable to this Flood Risk Project]

2.5.2 Floodplain Boundaries and BFEs for Coastal Areas


2.5.3 Coastal High Hazard Areas


Figure 6: Coastal Transect Schematic


2.5.4 Limit of Moderate Wave Action


SECTION 3.0 – INSURANCE APPLICATIONS

3.1 National Flood Insurance Program Insurance Zones

For flood insurance applications, the FIRM designates flood insurance rate zones as described in Figure 3, “Map Legend for FIRM.” Flood insurance zone designations are assigned to flooding sources based on the results of the hydraulic or coastal analyses. Insurance agents use the zones shown on the FIRM and depths and base flood elevations in this FIS Report in conjunction with information on structures and their contents to assign premium rates for flood insurance policies. The 1% annual chance floodplain boundary corresponds to the boundary of the areas of special flood hazards (e.g. Zones A, AE, V, VE, etc.), and the 0.2% annual chance floodplain boundary corresponds to the boundary of areas of additional flood hazards. Table 3 lists the flood insurance zones in Gadsden County.

27

Table 3: Flood Zone Designations by Community

Community Flood Zone(s)

Chattahoochee, City of A, AE, X

Gadsden County, Unincorporated Areas A, AE, X

Greensboro, Town of A, AE, X

Gretna, City of A, AE, X

Havana, Town of A, AE, X

Midway, City of A, AE, X

Quincy, City of A, AE, X

3.2 Coastal Barrier Resources System


Table 4: Coastal Barrier Resources System Information


SECTION 4.0 – AREA STUDIED

4.1 Basin Description

Table 5 contains a description of the characteristics of the HUC-8 sub-basins within which each community falls. The table includes the main flooding sources within each basin, a brief description of the basin, and its drainage area.

Table 5: Basin Characteristics

HUC-8 Sub-Basin Name

HUC-8 Sub-Basin Number

Primary Flooding Source Description of Affected Area

Drainage Area

(square miles)

Lower Ochlockonee

03120003 Ochlockonee

River

The Ochlockonee River flows across northwestern Leon County and eastern Gadsden County before it reaches the Lake Talquin Reservoir, the area's largest lake.

1,560

Apalachicola River

03130011 Apalachicola

River

The coastal drainage and associated waters from the Ochlockonee River Basin boundary to and including the Apalachicola River Basin and the drainage into Apalachicola Bay.

1,120

28

4.2 Principal Flood Problems

Table 6 contains a description of the principal flood problems that have been noted for Gadsden County by flooding source.

Table 6: Principal Flood Problems

Flooding Source Description of Flood Problems

All Sources Rainfall associated with the tropical disturbance exceeded 20 inches over a part of the county during September 20 through 23, 1969, and a maximum rainfall of record at Quincy-Havana area exceeded the 1 in 199-year probability (USGS 1972). The Florida Department of Transportation noted 51 sites where the roads were closed due to high water or to the washout of bridges or culverts in the Gadsden County area. Many flood-measurement sites had peak discharges in excess of that of a 50-year flood event. (FEMA 2009)

All Sources September 14-15, 1924 rainfall of record was more than 12 inches at Quincy (USGS 1972).

All Sources September 23-23, 1969 maximum rainfall of record occurred at Quincy with 10.87 inches during a 6-hour period on September 21. The 48-hour maximum rainfall of record was 17.71 inches (USGS 1972). Flood flows were over the road at State Routes 12, 65, and 267 on Quincy Creek. Culvert at County Route 268 on Quincy Creek was washed out (USGS 1972).

Apalachicola River

In March 1929, gaging station at Chattahoochee on the Apalachicola River recorded a stream flow of 293,000 cubic feet per second (cfs), which is the greatest observed flood at this station (USGS 1985). The previous record was a flow of 246,000 cfs recorded in 1925.

Ochlockonee River

February 12, 1986 the Ochlockonee River near Havana crested at flood stage of 33.5 feet. It was the second worst flooding since 1948, when the river reached 35.1 feet (The Post 1986).

Ochlockonee River Valley

October 1, 1957 heavy rains caused two breaks in the Jackson Bluff earthen dam on Lake Taquin, and released waters from the 6,800 acre lake in the Ochlockonee River Valley (Gadsden County Times 1958).

Table 7 contains information about historic flood elevations in the communities within Gadsden County.

Table 7: Historic Flooding Elevations

Flooding Source Location

Historic Peak (Feet NAVD88) Event Date

Approximate Recurrence

Interval (years)

Source of Data

All Sources Quincy-Havana area N/A 09/20/1969-09/23/1969

50 USGS 1972

All Sources Quincy area N/A 09/14/1924-09/15/1924

N/A USGS 1972

Table 7: Historic Flooding Elevations continued

29


Historic Peak (Feet NAVD88) Event Date

Approximate Recurrence

Interval (years)

Source of Data

All Sources Ochlockonee River Valley

N/A 10/01/1957 N/A Gadsden County

Times 1958

Apalachicola River

Gage Station 0235800 Apalachicola River at Chattahoochee

N/A 03/01/1929 N/A USGS 1985

Apalachicola River

Gage Station 0235800 Apalachicola River at Chattahoochee

N/A 1925 N/A USGS 1985

Ochlockonee River

Ochlockonee River near Havana

33.5 02/12/1986 N/A The Post

1986

Ochlockonee River

Ochlockonee River near Havana

35.1 1948 N/A The Post

1986

4.3 Non-Levee Flood Protection Measures

Table 8 contains information about non-levee flood protection measures within Gadsden County such as dams, jetties, and or dikes. Levees are addressed in Section 4.4 of this FIS Report.

Table 8: Non-Levee Flood Protection Measures


4.4 Levees


Table 9: Levees


SECTION 5.0 – ENGINEERING METHODS For the flooding sources in the community, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study. Flood events of a magnitude that are expected to be equaled or exceeded at least once on the average during any 10-, 25-, 50-, 100-, or 500-year period (recurrence interval) have been selected as having special significance for floodplain management and for flood insurance rates. These events, commonly termed the 10-, 25-, 50-, 100-, and 500-year floods, have a 10-, 4-, 2-, 1-, and 0.2% annual chance, respectively, of being equaled or exceeded during any year.

30

Although the recurrence interval represents the long-term, average period between floods of a specific magnitude, rare floods could occur at short intervals or even within the same year. The risk of experiencing a rare flood increases when periods greater than 1 year are considered. For example, the risk of having a flood that equals or exceeds the 100-year flood (1-percent chance of annual exceedance) during the term of a 30-year mortgage is approximately 26 percent (about 3 in 10); for any 90-year period, the risk increases to approximately 60 percent (6 in 10). The analyses reported herein reflect flooding potentials based on conditions existing in the community at the time of completion of this study. Maps and flood elevations will be amended periodically to reflect future changes.

5.1 Hydrologic Analyses

Hydrologic analyses were carried out to establish the peak elevation-frequency relationships for floods of the selected recurrence intervals for each flooding source studied. Hydrologic analyses are typically performed at the watershed level. Depending on factors such as watershed size and shape, land use and urbanization, and natural or man-made storage, various models or methodologies may be applied. A summary of the hydrologic methods applied to develop the discharges used in the hydraulic analyses for each stream is provided in Table 13. Greater detail (including assumptions, analysis, and results) is available in the archived project documentation. A summary of the discharges is provided in Table 10. Stream gage information is provided in Table 12.

31

Table 10: Summary of Discharges


Drainage Area

(Square Miles)

Peak Discharge (cfs)

10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Apalachicola River At Chattahoochee River 17,200 158,000 * 219,000 246,000 310,000

Attapulgus Creek At State Highway 159A 95.6 * * * 29,991 *

Bear Creek About 2,100 feet upstream from mouth

12.8 1,600 * 3,000 3,700 5,600

Bear Creek About 11,300 feet downstream State Highway 267

11.4 1,500 * 2,800 3,450 5,300

Double Branch At the confluence of Unnamed Tributary 9

8.4 1,448 2,156 2,809 3,570 5,847


6.7 1,247 1,857 2,420 3,075 5,033

Double Branch Approximately 400 feet downstream of State Highway 159

6.1 1,167 1,734 2,258 2,866 4,681


4.9 1,018 1,515 1,973 2,505 4,093


4.2 919 1,366 1,777 2,254 3,677


1.7 498 737 955 1,208 1,954

Double Branch Approximately 4,215 feet upstream of the confluence of Unnamed Tributary 12

1.4 452 668 867 1,096 1,773


1.0 347 512 663 837 1,349


0.6 253 373 482 607 975

*Not calculated for this Flood Risk Project

Table 10: Summary of Discharges continued

32


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

G Creek Approximately 1,015 feet upstream of the confluence of Little River

4.7 1,006 1,499 1,954 2,483 4,064

G Creek At the confluence of G Creek Unnamed Tributary 2

3.0 714 1,055 1,366 1,724 2,786


3.0 736 1,094 1,423 1,805 2,942

G Creek

Approximately 2,875 feet downstream of the confluence of G Creek Unnamed Tributary 1

2.5 652 968 1,258 1,595 2,595


1.2 409 605 784 991 1,602

G Creek Approximately 2,575 feet upstream of the confluence of G Creek Unnamed Tributary 1

0.9 326 482 624 788 1,270

G Creek Approximately 6,030 feet upstream of the confluence of G Creek Unnamed Tributary 1

0.5 225 332 429 540 867


At the confluence of G Creek 0.9 320 471 609 767 1,233


Approximately 1,210 feet downstream of Ranch Road

0.6 262 386 499 629 1,010


At the confluence of G Creek 1.3 414 611 791 999 1,612


Approximately 1,350 feet upstream of the confluence of G Creek

0.8 295 434 561 707 1,134


Approximately 3,290 feet upstream of the confluence of G Creek

0.6 247 364 471 593 953


33


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Hammock Creek At the confluence of Ochlockonee River

10.0 1,493 2,183 2,812 3,534 5,661

Hammock Creek Approximately 2,300 feet upstream of the confluence of Ochlockonee River

8.9 1,457 2,156 2,798 3,542 5,755

Hammock Creek Approximately 3,370 feet downstream of the confluence State Highway 267

7.4 1,337 1,992 2,597 3,302 5,409

Hammock Creek Approximately 1,380 feet upstream of the confluence State Highway 267

5.9 1,155 1,720 2,240 2,845 4,653

Hog Creek At the confluence of Ochlockonee River

4.7 1,002 1,494 1,947 2,474 4,051

Hog Creek At the confluence of Hog Creek Unnamed Tributary

2.2 594 882 1,146 1,452 2,360

Hog Creek Approximately 2,800 feet upstream of the confluence of Hog Creek Unnamed Tributary

1.7 516 765 994 1,258 2,041


1.3 432 640 830 1,049 1,699


0.8 316 467 605 764 1,231


At the confluence of Unnamed Tributary 7

0.6 251 371 479 604 971


Approximately 100 feet downstream of a private dam

0.5 138 182 220 259 362

Holley Branch At Ochlockonee River 4.4 617 * 986 1,189 1,729



34


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Holley Branch At the confluence of Holley Branch Unnamed Tributary 2

0.9 315 464 598 753 1,207


At Holley Branch 1.1 336 * 557 670 970


Approximately 2,120 feet downstream of Dupont Road

1.0 336 525 557 670 970


Approximately 850 feet downstream of Dupont Road

0.5 227 335 433 546 876


At the confluence of Holley Branch

0.4 202 297 383 481 769

Hurricane Creek Approximately 1,280 feet downstream of Tallavana Trail Dam

6.9 948 1,320 1,647 2,007 3,019

Hurricane Creek At the confluence of Hurricane Creek Unnamed Tributary 3

5.9 967 1,383 1,756 2,175 3,382

Hurricane Creek


5.7 1,065 1,563 2,017 2,540 4,082


3.2 739 1,090 1,412 1,782 2,877

Hurricane Creek


2.7 682 1,009 1,309 1,655 2,679

Hurricane Creek

Approximately 2,450 feet downstream of the confluence of Hurricane Creek Unnamed Tributary 1

2.2 597 882 1,142 1,443 2,332



35


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Hurricane Creek

Approximately 870 feet downstream of the confluence of Hurricane Creek Unnamed Tributary 1

1.8 495 726 936 1,176 1,881


0.7 246 356 454 566 888

Hurricane Creek


0.6 242 356 460 578 927


At the confluence of Hurricane Creek

0.9 338 498 643 810 1,300


Approximately 1,970 feet downstream of Penny B Road

0.6 258 381 493 621 999



2.2 586 866 1,122 1,418 2,294



1.6 489 724 939 1,187 1,921


Approximately 670 feet downstream of Beaver Creek Road

0.8 307 453 586 739 1,191



0.9 325 478 618 779 1,251


At Lake Talquin 2.1 359 * 617 732 1,020


Approximately 500 feet downstream of Dirt Road

0.9 359 495 617 732 1,020


Approximately 7,700 feet upstream of Dirt Road

0.5 226 333 430 542 870



36


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Little River At mouth 305 * * * 54,827 *

Little River At State Highway 12 237 * * * 48,087 *

McIntosh Branch At the confluence of Ocklawaha Creek

0.7 282 415 535 674 1,081

McIntosh Branch Approximately 2,570 feet upstream of the confluence of Ocklawaha Creek

0.5 236 348 450 567 911

Monroe Creek At Little River 8.1 700 * 1,170 1,380 1,910

Monroe Creek Approximately 700 feet upstream of U.S. Highway 90

2.3 700 816 1,170 1,380 1,910


1.8 528 783 1,015 1,284 2,081

Monroe Creek Approximately 2,240 feet upstream of U.S. Highway 90

1.3 431 638 826 1,044 1,686

Monroe Creek Approximately 4,550 feet upstream of U.S. Highway 90

0.9 319 471 609 769 1,238


At the confluence of Monroe Creek

0.2 138 202 260 327 521



1.6 477 707 918 1,161 1,882



1.4 439 649 840 1,062 1,716



1.0 360 532 689 870 1,404



0.2 106 155 200 251 398



37


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Mosquito Creek At confluence with the Apalachicola River

89.2 * * * 10,500 *

Mosquito Creek At State Highway 269 86.2 * * * 10,200 *

Mosquito Creek At confluence of South Mosquito Creek

58.5 * * * 6,360 *

Mosquito Creek At U.S. Highway 90 58.0 * * * 6,300 *


At Mosquito Creek 0.5 177 * 324 391 563

Ochlockonee River Just downstream of Lake Talquin Dam

530 27,700 42,300 56,300 73,400 129,000

Ochlockonee River Just upstream of Lake Talquin Dam

519 27,300 41,600 55,200 72,000 126,000

Ochlockonee River Just downstream of the confluence of Ocklawaha Creek

495 25,700 38,800 51,400 66,700 116,000

Ochlockonee River Just upstream of confluence of Rocky Comfort Creek

451 24,200 36,300 47,800 61,800 107,000

Ochlockonee River Just upstream of the confluence of Richlander Creek

380 21,000 29,900 37,700 46,400 70,200

Ochlockonee River Approximately 27,530 feet downstream of Interstate 10

261 20,900 29,800 37,600 46,300 70,200

Ochlockonee River Just upstream of Interstate 10 242 20,700 29,600 37,400 46,100 70,000

Ochlockonee River At U.S. Highway 27 211 20,300 29,000 36,700 45,200 68,600

Ochlockonee River Just upstream of the confluence of Ochlockonee River Unnamed Tributary

197 14,543 21,900 29,093 36,992 52,583



38


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Ochlockonee River At the confluence of Lake Iamonia

170 26,211 37,690 48,193 60,157 95,504


At Ochlockonee River 12.9 782 * 1,240 1,430 1,930



1.4 451 668 866 1,095 1,773

Ocklawaha Creek At mouth 31.2 2,600 * 4,900 6,000 9,200

Ocklawaha Creek Just upstream of State Highway 267

29.2 2,550 * 4,800 5,900 9,000

Quincy Creek At mouth 37.8 2,550 * 4,500 5,500 8,100

Quincy Creek About 8,400 feet downstream of old railroad grade

21.6 1,900 * 3,300 3,900 5,700

Quincy Creek Just upstream of State Highway 65

19.7 1,800 * 3,100 3,700 5,400


15.9 1,500 * 2,600 3,100 4,600


6.1 750 * 1,250 1,600 2,200

Quincy Creek About 6,800 feet upstream of State Highway 268

3.5 500 * 800 1,000 1,300

Richlander Creek About 4,500 feet upstream from mouth

9.0 1,300 * 2,400 2,950 4,500

Richlander Creek Just upstream of County Highway 65B

5.8 1,000 * 1,700 2,200 3,300

Richlander Creek Just upstream of Interstate 10 4.0 750 * 1,300 1,650 2,500

Richlander Creek About 9,400 feet upstream of Interstate 10

1.0 240 * 420 500 700



39


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Richlander Creek Approximately 6,630 feet upstream of the confluence of Robinson Branch

1.0 240 343 420 500 700

Richlander Creek Approximately 8,150 feet upstream of the confluence of Robinson Branch

0.5 233 343 443 558 895

Robinson Branch At the confluence of Richlander Creek

1.4 453 670 869 1,100 1,780

Robinson Branch Approximately 4,640 feet upstream of the confluence of Richlander Creek

1.0 363 537 696 879 1,419

Salem Branch Approximately 4,520 feet upstream of the confluence of Little River

4.9 950 1,390 1,790 2,250 3,600

Salem Branch Approximately 5,220 feet upstream of the confluence of Little River

4.5 626 847 1,036 1,239 1,794

Salem Branch Approximately 340 feet downstream of Unnamed Road

4.4 890 1,304 1,682 2,115 3,389

Salem Branch Approximately 3,075 feet upstream of Unnamed Road

3.9 831 1,220 1,574 1,982 3,182


3.5 795 1,174 1,521 1,922 3,109


3.1 734 1,085 1,406 1,777 2,875

Salem Branch Approximately 4,080 feet downstream of State Highway 159

2.7 665 983 1,273 1,609 2,601

Salem Branch Approximately 1,210 feet downstream of State Highway 159

2.2 598 887 1,151 1,456 2,363


40


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Salem Branch Approximately 280 feet upstream of State Highway 159

1.1 374 551 713 899 1,447

Salem Branch Approximately 2,920 feet upstream of State Highway 159

0.8 305 450 582 733 1,179

Salem Branch Approximately 5,400 feet upstream of State Highway 159

0.5 226 332 429 541 867

South Mosquito Creek At Mosquito Creek 24.9 2,310 * 4,250 5,220 7,940


At South Mosquito Creek 2.2 615 * 1,180 1,450 2,200

Swamp Creek At CSX Railroad bridge 53.0 * * * 22,069 *

Tanyard Branch At Quincy Creek 5.2 1,060 * 2,010 2,470 3,760


At Tanyard Branch 0.4 118 * 201 236 319


At Tanyard Branch 3.0 579 * 1,050 1,270 1,850


Approximately 770 feet downstream of the confluence of Unnamed Tributary 6

2.7 579 1,022 1,050 1,270 1,850



1.3 413 611 792 1,001 1,619


Approximately 2,200 feet upstream of the confluence of Unnamed Tributary 6

1.0 356 527 682 862 1,391


Approximately 750 feet upstream of the confluence of Key Farm Road

0.5 226 333 430 541 869



41


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Telogia Creek At the confluence with Juniper Creek

46.9 4,104 * 7,515 9,316 14,570

Telogia Creek Just upstream of County Road 274/ Providence Road

29.0 3,850 * 7,270 9,100 14,500

Telogia Creek Just upstream of State Highway 12/ Greensboro Highway

22.0 2,146 * 3,603 4,326 6,338

Telogia Creek Just upstream County Road 270A/ Flat Creek Road

17.2 1617 * 2,695 3,228 4,700

Telogia Creek Just upstream of Hanna Mill Pond Road

12.8 1210 * 1,990 2,370 3,420

Telogia Creek Just upstream of County Road 268/ Hardaway Highway

7.2 824 * 1,340 1,600 2,290

Telogia Creek Just upstream of U.S. Highway 90

5.0 206 * 335 400 572

Unnamed Stream 2 At the confluence of Ochlockonee River

1.5 421 611 782 976 1,541

Unnamed Stream 2 Approximately 3,600 feet upstream of the confluence of Ochlockonee River

1.0 359 530 686 866 1,395


0.6 242 357 462 582 934


0.8 276 402 516 645 1,020

Unnamed Stream 3 Approximately 1,650 feet downstream of Reynolds Road

0.5 237 349 451 568 912


2.3 621 921 1,196 1,514 2,460



42


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance


1.9 549 815 1,058 1,340 2,175


1.1 382 564 731 923 1,488


0.8 307 453 586 740 1,191


7.0 1,290 1,921 2,502 3,179 5,201


6.6 1,224 1,817 2,363 2,996 4,884


4.1 824 1,199 1,539 1,926 3,058

Unnamed Stream 7 At the confluence of Unnamed Tributary 14

3.0 736 1,091 1,417 1,794 2,914

Unnamed Stream 7 Approximately 610 feet downstream of Rich Bay Road

2.6 663 982 1,275 1,613 2,618

Unnamed Stream 7 Approximately 2,720 feet upstream of Rich Bay Road

2.2 578 856 1,112 1,407 2,283

Unnamed Stream 7 At the confluence of Unnamed Tributary 13

0.9 339 501 648 818 1,317

Unnamed Stream 7 Approximately 2,620 feet upstream of the confluence of Unnamed Tributary 13

0.5 225 332 429 540 867


0.9 327 484 626 791 1,275


43


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Unnamed Tributary 1 At the confluence of Lake Talquin Unnamed Tributary

0.2 117 171 220 276 438

Unnamed Tributary 2 At the confluence of Richlander Creek

0.3 160 235 303 381 607


0.2 104 152 196 245 390


0.4 193 284 367 462 740


1.0 363 537 696 879 1,420

Unnamed Tributary 5 Approximately 230 feet downstream of the confluence of Augustine Road

0.9 325 480 621 784 1,265

Unnamed Tributary 6 At the confluence of Tanyard Branch Unnamed Tributary 2

1.0 345 510 661 834 1,346

Unnamed Tributary 6


0.5 234 345 446 562 902

Unnamed Tributary 7 At the confluence of Hog Creek Unnamed Tributary

0.4 157 219 274 333 500

Unnamed Tributary 8 At the confluence of Hog Creek Unnamed Tributary

0.9 320 472 611 771 1,241

Unnamed Tributary 9 At the confluence of Double Branch

2.1 567 839 1,088 1,375 2,225

Unnamed Tributary 9 Approximately 2,000 feet downstream County Highway 270

1.6 495 733 951 1,203 1,949


1.3 427 631 817 1,031 1,663


44


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Unnamed Tributary 10 Approximately 5,350 feet upstream of the confluence of Double Branch

1.0 340 501 648 818 1,315

Unnamed Tributary 10 Approximately 1,530 feet downstream of the State Highway 159

0.5 224 329 424 534 855


1.0 350 518 671 847 1,367


0.8 303 446 576 726 1,166


2.3 620 920 1,195 1,513 2,458


1.6 496 734 953 1,206 1,955

Unnamed Tributary 12 Approximately 1,830 feet downstream of Lanier Road

0.9 333 492 637 804 1,296

Unnamed Tributary 12 Approximately 1,450 feet upstream of Lanier Road

0.5 225 332 429 540 866

Unnamed Tributary 13 At the confluence of Unnamed Stream 7

0.7 263 386 498 627 1,003

Unnamed Tributary 13 Approximately 1,800 feet upstream of the confluence of Unnamed Stream 7

0.5 228 336 433 546 875


1.0 362 534 691 872 1,405

Unnamed Tributary 14 Approximately 830 feet downstream of Railroad

0.5 236 348 449 565 906


2.3 616 915 1,189 1,507 2,449


45


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance

Unnamed Tributary 15 Approximately 300 feet downstream of Cripple Creek Road

2.0 558 828 1,075 1,362 2,212

Unnamed Tributary 15 At the confluence of Unnamed Tributary 17

1.4 442 654 849 1,073 1,738


0.9 336 496 643 811 1,309


0.3 175 258 333 418 669


0.4 203 299 386 486 778

Unnamed Tributary 20 At the confluence of Unnamed Tributary to Ochlockonee River Unnamed Tributary

1.4 449 664 861 1,088 1,761

Unnamed Tributary 21 At the confluence of Unnamed Tributary to Ochlockonee River Unnamed Tributary

0.3 169 248 320 403 643


At Ochlockonee River Unnamed Tributary

5.6 585 * 969 1,140 1,570



2.2 585 764 969 1,140 1,570



2.0 559 826 1,069 1,349 2,178



1.6 447 652 837 1,048 1,664



46


Drainage Area

(Square Miles)


10% Annual Chance

4% Annual Chance

2% Annual Chance

1% Annual Chance

0.2% Annual Chance



1.5 455 673 871 1,101 1,779



1.0 350 517 669 844 1,362



0.6 240 353 456 574 922

Figure 7: Frequency Discharge-Drainage Area Curves


Table 11: Summary of Non-Coastal Stillwater Elevations


47

Table 12: Stream Gage Information used to Determine Discharges

Flooding Source

Gage Identifier

Agency that Maintains Gage Site Name

Drainage Area

(Square Miles)

Period of Record

From To

Apapachicola River

02358000 USGS Apapachicola River at Chattahoochee, FL

17,200 12/17/1919 04/21/2014

5.2 Hydraulic Analyses

Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the elevations of floods of the selected recurrence intervals. Base flood elevations on the FIRM represent the elevations shown on the Flood Profiles and in the Floodway Data tables in the FIS Report. Rounded whole-foot elevations may be shown on the FIRM in coastal areas, areas of ponding, and other areas with static base flood elevations. These whole-foot elevations may not exactly reflect the elevations derived from the hydraulic analyses. Flood elevations shown on the FIRM are primarily intended for flood insurance rating purposes. For construction and/or floodplain management purposes, users are cautioned to use the flood elevation data presented in this FIS Report in conjunction with the data shown on the FIRM. The hydraulic analyses for this FIS were based on unobstructed flow. The flood elevations shown on the profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. For streams for which hydraulic analyses were based on cross sections, locations of selected cross sections are shown on the Flood Profiles (Exhibit 1). For stream segments for which a floodway was computed (Section 6.3), selected cross sections are also listed on Table 24, “Floodway Data.” A summary of the methods used in hydraulic analyses performed for this project is provided in Table 13. Roughness coefficients are provided in Table 14. Roughness coefficients are values representing the frictional resistance water experiences when passing overland or through a channel. They are used in the calculations to determine water surface elevations. Greater detail (including assumptions, analysis, and results) is available in the archived project documentation.

48

Table 13: Summary of Hydrologic and Hydraulic Analyses

Flooding Source

Study Limits

Downstream Limit

Study Limits

Upstream Limit

Hydrologic Model or

Method Used

Hydraulic Model or

Method Used

Date Analyses

Completed

Flood Zone on

FIRM Special Considerations

All Zone A Streams Various Various Regression Equations

(USGS 1982)

HEC-RAS 3.1.0 (USACE 2002)

06/01/2006 A

Apalachicola River Liberty/Calhoun County boundary

Jackson County boundary

Log-Pearson Type III/Gage

Analysis (USGS 1981

rev 1982)

USGS Step-Backwater

Model E-431 (USGS 1976)

06/01/1986 AE Data taken from the City of Chattahoochee FIS (09/04/1987) (FEMA 1987).

Attapulgus Creek Confluence with Little River

Confluence with Swamp Creek

USGS Regional Analysis Method

(USGS 1966)

HEC-2 (USACE 1984)

11/01/1987 AE

Detailed information can be found in the report, Floods of September 20-23, 1969 in the Gadsden County Area, Florida (USGS1972).

Bear Creek Confluence with Rocky Comfort Creek


Regression Equations

(USGS 1982)

HEC-2 (USACE 1984)

11/01/1987 AE

Double Branch Confluence with Ochlocknee River Oxbow

Approximately 2.4 miles upstream of Unnamed Tributary 12

Regression Equation

(USGS 2006)


04/03/2015 AE

G Creek

Approximately 0.8 mile downstream of confluence of G Creek Unnamed Tributary 1

Approximately 1.8 miles upstream of confluence of G Creek Unnamed Tributary 1

Regression Equation

(USGS 2006)


04/03/2015 AE



Approximately 2,340 feet upstream of Ranch Road

Regression Equation

(USGS 2006)


04/03/2015 AE



Approximately 1.2 miles upstream of the confluence of G Creek

Regression Equation

(USGS 2006)


04/03/2015 AE

Hammock Creek Confluence with Ochlocknee River


Regression Equation

(USGS 2006)


04/03/2015 AE

Table 13: Summary of Hydrologic and Hydraulic Analyses continued

49

Flooding Source

Study Limits

Downstream Limit

Study Limits

Upstream Limit

Hydrologic Model or

Method Used

Hydraulic Model or

Method Used

Date Analyses

Completed

Flood Zone on


Hog Creek Confluence with Ochlocknee River

Approximately 4.0 miles upstream of confluence of Ochlocknee River

Regression Equation

(USGS 2006)


04/03/2015 AE


Confluence with Hog Creek

Approximately 1.5 miles upstream of confluence of Unnamed Tributary 7

Regression Equation

(USGS 2006)


04/03/2015 AE

Holley Branch Confluence with the Ochlocknee River


Rainfall-Runoff Model/

HEC-HMS 3.1.0 (USACE 2006)


09/28/2007 AE w/

Floodway

Holley Branch Approximately 4,300 feet upstream of Dupont Road

Approximately 1,300 feet upstream of confluence of Holley Branch Unnamed Tributary 2

Regression Equation

(USGS 2006)


04/03/2015 AE




Rainfall-Runoff Model/

HEC-HMS 3.1.0 (USACE 2006)


09/28/2007 AE w/

Floodway




Regression Equation

(USGS 2006)


04/03/2015 AE



Approximately 1.2 miles upstream of confluence of Holley Branch

Regression Equation

(USGS 2006)


04/03/2015 AE

Hurricane Creek

Approximately 2,300 feet downstream of the confluence of Hurricane Creek Tributary 2


Regression Equation

(USGS 2006)


04/03/2015 AE



Approximately 2,390 feet upstream of Penny B Road

Regression Equation

(USGS 2006)


04/03/2015 AE


50

Flooding Source

Study Limits

Downstream Limit

Study Limits

Upstream Limit

Hydrologic Model or

Method Used

Hydraulic Model or

Method Used

Date Analyses

Completed

Flood Zone on





Regression Equation

(USGS 2006)


04/03/2015 AE


Approximately 750 feet upstream of the confluence of Hurricane Creek

Approximately 4,230 feet upstream of Tallavana Trail

Regression Equation

(USGS 2006)


04/03/2015 AE

Lake Talquin Jackson Bluff Dam Ocklockonee River


(USGS 1966)

USGS Step-Backwater


11/01/1987 AE


Confluence with Lake Talquin/Ochlockonee River



(USGS 1982)


09/28/2007 AE w/

Floodway



Approximately 7,120 feet upstream of Private Drive

Regression Equation

(USGS 2006)


04/03/2015 AE

Little River Confluence with Lake Talquin



(USGS 1966)

HEC-2 (USACE 1984)

11/01/1987 AE

Detailed information can be found in the report, Floods of September 20-23, 1969 in the Gadsden County Area, Florida (USGS 1972).

McIntosh Branch Confluence with Lake Talquin

Approximately 1.0 mile upstream of the confluence with Lake Talquin

Regression Equation

(USGS 2006)


04/03/2015 AE

Monroe Creek Confluence with Little River



(USGS 1982)


09/28/2007 AE w/

Floodway


Approximately 1.7 miles upstream of U.S. Highway 90

Regression Equation

(USGS 2006)


04/03/2015 AE


51

Flooding Source

Study Limits

Downstream Limit

Study Limits

Upstream Limit

Hydrologic Model or

Method Used

Hydraulic Model or

Method Used

Date Analyses

Completed

Flood Zone on




Approximately 0.6 mile upstream of the confluence with Monroe Creek

Regression Equation

(USGS 2006)


04/03/2015 AE



Approximately 1,250 feet upstream U.S. Highway 90

Regression Equation

(USGS 2006)


04/03/2015 AE



Approximately 2.4 miles upstream of the confluence of Monroe Creek

Regression Equation

(USGS 2006)


04/03/2015 AE




Regression Equation

(USGS 2006)


04/03/2015 AE

Mosquito Creek Confluence with Apalachicola River

At U.S. Highway 90 Regression Equations

(USGS 1982)

USGS Step-Backwater


06/01/1986 AE





(USGS 1982)


09/28/2007 AE w/

Floodway

Ochlockonee River Jackson Bluff Dam Grady County boundary PEAKFQ HEC-RAS 4.1.0 (USACE 2010)

07/01/2015 AE w/

Floodway

Hydrology was calculated using the USGS computer program NSSv5.0 (National Streamflow Statistics).





(USGS 1982)


09/28/2007 AE w/

Floodway


52

Flooding Source

Study Limits

Downstream Limit

Study Limits

Upstream Limit

Hydrologic Model or

Method Used

Hydraulic Model or

Method Used

Date Analyses

Completed

Flood Zone on





Regression Equation

(USGS 2006)


04/03/2015 AE

Ocklawaha Creek Confluence with the Ochlockonee River

At State Highway 267 Regression Equations

(USGS 1982)

HEC-2 (USACE 1984)

11/01/1987 AE

Quincy Creek Confluence with Little River



(USGS 1982)

HEC-2 (USACE 1984)

11/01/1987 AE w/

Floodway

Richlander Creek Confluence with the Little River



(USGS 1982)

HEC-2 (USACE 1984)

11/01/1987 AE

Richlander Creek



Regression Equation

(USGS 2006)


04/03/2015 AE

Robinson Branch Confluence with Richlander Creek

Approximately 0.9 mile upstream of the Walsh Road

Regression Equation

(USGS 2006)


04/03/2015 AE

Salem Branch

Approximately 1.1 miles upstream of the confluence with Attapulgus Creek


Regression Equation

(USGS 2006)


04/03/2015 AE

South Mosquito Creek




(USGS 1982)


09/28/2007 AE w/

Floodway


Confluence with South Mosquito Creek

Approximately 4,080 feet upstream of Depot Road


(USGS 1982)


09/28/2007 AE w/

Floodway


53

Flooding Source

Study Limits

Downstream Limit

Study Limits

Upstream Limit

Hydrologic Model or

Method Used

Hydraulic Model or

Method Used

Date Analyses

Completed

Flood Zone on


Swamp Creek Confluence with Attapulgus Creek

At State Highway 159


(USGS 1966)

HEC-2 (USACE 1984)

11/01/1987 AE

Detailed information can be found in the report, Floods of September 20-23, 1969 in the Gadsden County Area, Florida (USGS 1972).

Tanyard Branch Confluence with Quincy Creek

Approximately 150 feet upstream of 7th Street


(USGS 1982)


09/28/2007 AE w/

Floodway



Approximately 150 feet upstream of Circle Drive


(USGS 1982)


09/28/2007 AE w/

Floodway





(USGS 1982)


09/28/2007 AE w/

Floodway



Approximately 320 feet upstream of railroad

Regression Equation

(USGS 2006)


04/03/2015 AE

Telogia Creek Liberty County boundary

Approximately 1,850 feet upstream of U.S. Highway 90

PEAKFQ HEC-RAS 4.1.0 (USACE 2010)

2014 AE PEAKWin version 5.2.0

Unnamed Stream 2 Confluence with Ochlockonee River

Approximately 2.7 miles upstream of the confluence of Ochlockonee River

Regression Equation

(USGS 2006)


04/03/2015 AE

Unnamed Stream 3 Confluence with Ochlocknee River

Approximately 2,350 feet upstream of Reynolds Road

Regression Equation

(USGS 2006)


04/03/2015 AE


Approximately 1,980 feet upstream of Business Park Road

Regression Equation

(USGS 2006)


04/03/2015 AE



Regression Equation

(USGS 2006)


04/03/2015 AE


54

Flooding Source

Study Limits

Downstream Limit

Study Limits

Upstream Limit

Hydrologic Model or

Method Used

Hydraulic Model or

Method Used

Date Analyses

Completed

Flood Zone on



Approximately 1.2 miles upstream of the confluence if Unnamed Tributary 13

Regression Equation

(USGS 2006)


04/03/2015 AE


Approximately 1.4 miles upstream of the confluence of Ochlocknee River

Regression Equation

(USGS 2006)


04/03/2015 AE

Unnamed Tributary 1 Confluence with Lake Talquin Unnamed Tributary

Approximately 1,260 feet upstream of Lakeview Point Road

Regression Equation

(USGS 2006)


04/03/2015 AE

Unnamed Tributary 2 Confluence with Richlander Creek


Regression Equation

(USGS 2006)


04/03/2015 AE



Regression Equation

(USGS 2006)


04/03/2015 AE


Approximately 0.8 miles upstream of the confluence of Richlander Creek

Regression Equation

(USGS 2006)


04/03/2015 AE


Approximately 2,510 feet upstream of Augustine Road

Regression Equation

(USGS 2006)


04/03/2015 AE

Unnamed Tributary 6 Confluence with Tanyard Branch Unnamed Tributary 2


Regression Equation

(USGS 2006)


04/03/2015 AE


55

Flooding Source

Study Limits

Downstream Limit

Study Limits

Upstream Limit

Hydrologic Model or

Method Used

Hydraulic Model or

Method Used

Date Analyses

Completed

Flood Zone on


Unnamed Tributary 7 Confluence with Hog Creek Unnamed Tributary

Approximately 4,380 feet upstream of the confluence of Hog Creek Unnamed Tributary

Regression Equation

(USGS 2006)


04/03/2015 AE

Unnamed Tributary 8 Confluence with Hog Creek Unnamed Tributary

Approximately 2.2 miles upstream of the confluence of Hog Creek Unnamed Tributary

Regression Equation

(USGS 2006)


04/03/2015 AE

Unnamed Tributary 9 Confluence with Double Branch

Approximately 85 feet downstream of Shady Rest Road/State Highway 270

Regression Equation

(USGS 2006)


04/03/2015 AE




Regression Equation

(USGS 2006)


04/03/2015 AE



At Robin Lane Regression

Equation (USGS 2006)


04/03/2015 AE



Approximately 4,360 feet upstream of Lanier Road

Regression Equation

(USGS 2006)


04/03/2015 AE



Approximately 2,050 feet upstream of Eastern Way

Regression Equation

(USGS 2006)


04/03/2015 AE



Approximately 4,310 feet upstream of Railroad

Regression Equation

(USGS 2006)


04/03/2015 AE




Regression Equation

(USGS 2006)


04/03/2015 AE



Approximately 1,065 feet upstream of North Quail Hollow Road

Regression Equation

(USGS 2006)


04/03/2015 AE


56

Flooding Source

Study Limits

Downstream Limit

Study Limits

Upstream Limit

Hydrologic Model or

Method Used

Hydraulic Model or

Method Used

Date Analyses

Completed

Flood Zone on




Approximately 1,360 feet upstream of Tall Timber Road

Regression Equation

(USGS 2006)


04/03/2015 AE



Approximately 1.5 miles upstream of the confluence of Unnamed Tributary to Ochlocknee River Unnamed Tributary

Regression Equation

(USGS 2006)


04/03/2015 AE



Approximately 410 feet upstream of Collins Road II

Regression Equation

(USGS 2006)


04/03/2015 AE


Confluence with Ochlockonee River Unnamed Tributary



(USGS 1982)


09/28/2007 AE w/

Floodway




Regression Equation

(USGS 2006)


04/03/2015 AE

57

Table 14: Roughness Coefficients

Flooding Source Channel “n” Overbank “n”

All Zone A Streams * *

Apalachicola River 0.030 0.135

Attapulgus Creek 0.030 0.135

Bear Creek 0.030-0.035 0.120

Double Branch 0.045 0.120

G Creek 0.045 0.110-0.120

G Creek Unnamed Tributary 1 0.035-0.050 0.080-0.120

G Creek Unnamed Tributary 2 0.035-0.050 0.120

Hammock Creek 0.040 0.120

Hog Creek 0.045 0.120

Hog Creek Unnamed Tributary 0.035-0.045 0.120

Holley Branch 0.044-0.045 0.120-0.143

Holley Branch Unnamed Tributary 0.035-0.045 0.120-0.143

Holley Branch Unnamed Tributary 2 0.035-0.045 0.120

Hurricane Creek 0.030-0.050 0.060-0.120


0.040-0.045 0.100-0.120


0.040-0.050 0.120


0.035-0.050 0.060-0.120

Lake Talquin Unnamed Tributary 0.042-0.075 0.096-0.150

Little River 0.030 0.135

McIntosh Branch 0.045 0.120

Monroe Creek 0.031-0.047 0.090-0.120

Monroe Creek Unnamed Tributary 1 0.045 0.120

Monroe Creek Unnamed Tributary 2 0.045 0.120

Monroe Creek Unnamed Tributary 3 0.045-0.050 0.120

Monroe Creek Unnamed Tributary 4 0.040-0.045 0.120

Mosquito Creek 0.035 0.100

Mosquito Creek Unnamed Tributary 0.044-0.053 0.093-0.118

Ocholockonee River 0.040-0.050 0.016-0.200


0.021-0.074 0.119-0.139

* Date not available

Table 14: Roughness Coefficients continued

58


Ocklawaha Creek 0.035 0.100

Quincy Creek 0.030-0.060 0.100-0.180

Richlander Creek 0.030-0.050 0.060-0.150

Robinson Branch 0.035-0.050 0.090-0.120

Salem Branch 0.040-0.055 0.070-0.120

South Mosquito Creek 0.044 0.118


0.044-0.055 0.093-0.118

Swamp Creek 0.030 0.135

Tanyard Branch 0.068-0.131 0.104-0.140


0.064-0.067 0.097-0.101


0.004-0.131 0.060-0.139

Telogia Creek 0.030-0.135 0.070-0.217

Unnamed Stream 2 0.040-0.050 0.120

Unnamed Stream 3 0.040-0.050 0.120

Unnamed Stream 4 0.045 0.120


Unnamed Stream 7 0.045-0.055 0.120


Unnamed Tributary 1 0.045 0.120

Unnamed Tributary 2 0.030-0.050 0.060-0.120





Unnamed Tributary 7 0.035-0.045 0.120








Table 14: Roughness Coefficients continued

59








0.035-0.074 0.080-0.138

5.3 Coastal Analyses


Table 15: Summary of Coastal Analyses


5.3.1 Total Stillwater Elevations


Figure 8: 1% Annual Chance Total Stillwater Elevations for Coastal Areas


Table 16: Tide Gage Analysis Specifics


5.3.2 Waves


5.3.3 Coastal Erosion


5.3.4 Wave Hazard Analyses


Table 17: Coastal Transect Parameters


Figure 9: Transect Location Map


5.4 Alluvial Fan Analyses


60

Table 18: Summary of Alluvial Fan Analyses


Table 19: Results of Alluvial Fan Analyses


SECTION 6.0 – MAPPING METHODS

6.1 Vertical and Horizontal Control

All FIS Reports and FIRMs are referenced to a specific vertical datum. The vertical datum provides a starting point against which flood, ground, and structure elevations can be referenced and compared. Until recently, the standard vertical datum used for newly created or revised FIS Reports and FIRMs was the National Geodetic Vertical Datum of 1929 (NGVD29). With the completion of the North American Vertical Datum of 1988 (NAVD88), many FIS Reports and FIRMs are now prepared using NAVD88 as the referenced vertical datum. Flood elevations shown in this FIS Report and on the FIRMs are referenced to NAVD88. These flood elevations must be compared to structure and ground elevations referenced to the same vertical datum. For information regarding conversion between NGVD29 and NAVD88 or other datum conversion, visit the National Geodetic Survey website at www.ngs.noaa.gov. Temporary vertical monuments are often established during the preparation of a flood hazard analysis for the purpose of establishing local vertical control. Although these monuments are not shown on the FIRM, they may be found in the archived project documentation associated with the FIS Report and the FIRMs for this community. Interested individuals may contact FEMA to access these data. To obtain current elevation, description, and/or location information for benchmarks in the area, please contact information services Branch of the NGS at (301) 713-3242, or visit their website at www.ngs.noaa.gov. The datum conversion locations and values that were calculated for Gadsden County are provided in Table 20.

Table 20: Countywide Vertical Datum Conversion

Quadrangle Name Quadrangle

Corner Latitude Longitude

Conversion from NGVD29 to

NAVD88 (feet)

Average Conversion from NGVD29 to NAVD88 = -0.530 feet

Table 21: Stream-by-Stream Vertical Datum Conversion




61

6.2 Base Map

The FIRMs and FIS Report for this project have been produced in a digital format. The flood hazard information was converted to a Geographic Information System (GIS) format that meets FEMA’s FIRM database specifications and geographic information standards. This information is provided in a digital format so that it can be incorporated into a local GIS and be accessed more easily by the community. The FIRM Database includes most of the tabular information contained in the FIS Report in such a way that the data can be associated with pertinent spatial features. For example, the information contained in the Floodway Data table and Flood Profiles can be linked to the cross sections that are shown on the FIRMs. Additional information about the FIRM Database and its contents can be found in FEMA’s Guidelines and Standards for Flood Risk Analysis and Mapping, www.fema.gov/guidelines-and-standards-flood-risk-analysis-and-mapping. Base map information shown on the FIRM was derived from the sources described in Table 22.

Table 22: Base Map Sources

Data Type Data Provider Data Date Data Scale Data Description

County Boundary

Gadsden County, FL 04/30/2014 N/A S_Pol_Ar. County Boundary.

Digital Orthophoto

Florida Department of Transportation

04/02/2013 N/A

S_Base_Index table contains information about the raster data used as a base map for the study area.

Digital Orthophoto

Merrick & Company 12/31/2012 N/A

S_Base_Index table contains information about the raster data used as a base map for the study area.

Incorporated Communities Boundaries

Federal Emergency Management Agency

02/04/2009 N/A

S_Pol_Ar. Corporate Boundaries. S_PLSS_AR, S_Pol_AR, and S_Trnsport_Ln. U.S. Public Land Survey System areas within the study area, county boundary areas associated within the study area, and railroads within the study area.

Surface Water Features

Federal Emergency Management Agency

02/04/2009 N/A S_Wtr_Ln and S_Wtr_Ar.

Transportation Features

U.S. Census Bureau, Geography Division

07/05/2013 N/A S_Trnsport_Ln. All roads and railroads within the study area.

6.3 Floodplain and Floodway Delineation

The FIRM shows tints, screens, and symbols to indicate floodplains and floodways as well as the locations of selected cross sections used in the hydraulic analyses and floodway computations.

http://www.fema.gov/guidelines-and-standards-flood-risk-analysis-and-mapping

http://www.fema.gov/guidelines-and-standards-flood-risk-analysis-and-mapping

62

For riverine flooding sources, the mapped floodplain boundaries shown on the FIRM have been delineated using the flood elevations determined at each cross section; between cross sections, the boundaries were interpolated using the topographic elevation data described in Table 23. In cases where the 1% and 0.2% annual chance floodplain boundaries are close together, only the 1% annual chance floodplain boundary has been shown. Small areas within the floodplain boundaries may lie above the flood elevations but cannot be shown due to limitations of the map scale and/or lack of detailed topographic data. The floodway widths presented in this FIS Report and on the FIRM were computed for certain stream segments on the basis of equal conveyance reduction from each side of the floodplain. Floodway widths were computed at cross sections. Between cross sections, the floodway boundaries were interpolated. Table 2 indicates the flooding sources for which floodways have been determined. The results of the floodway computations for those flooding sources have been tabulated for selected cross sections and are shown in Table 24, “Floodway Data.” Certain flooding sources may have been studied that do not have published BFEs on the FIRMs, or for which there is a need to report the 1% annual chance flood elevations at selected cross sections because a published Flood Profile does not exist in this FIS Report. These streams may have also been studied using methods to determine non-encroachment zones rather than floodways. For these flooding sources, the 1% annual chance floodplain boundaries have been delineated using the flood elevations determined at each cross section; between cross sections, the boundaries were interpolated using the topographic elevation data described in Table 23. All topographic data used for modeling or mapping has been converted as necessary to NAVD88. The 1% annual chance elevations for selected cross sections along these flooding sources, along with their non-encroachment widths, if calculated, are shown in Table 25, “Flood Hazard and Non-Encroachment Data for Selected Streams.”

Table 23: Summary of Topographic Elevation Data used in Mapping

Source for Topographic Elevation Data

Community Flooding Source Description

Vertical Accuracy

Horizontal Accuracy Citation

Gadsden County and Incorporated Areas

All Streams in HUC

03120003

Light Detection and Ranging data (LiDAR)

N/A N/A Merrick & Company

2009

BFEs shown at cross sections on the FIRM represent the 1% annual chance water surface elevations shown on the Flood Profiles and in the Floodway Data tables in the FIS Report. Rounded whole-foot elevations may be shown on the FIRM in coastal areas, areas of ponding, and other areas with static base flood elevations.

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