VOLUME 1 OF 4 GADSDEN COUNTY, FLORIDAportal.nwfwmdfloodmaps.com/NWFWMD_Data/FISReports/...National...
Transcript of 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
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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
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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
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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)
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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
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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
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Community CID
HUC-8 Sub-
Basin(s) Located on FIRM
Panel(s)
If Not Included, Location of Flood
Hazard Data
Gadsden County, Unincorporated Areas
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
Table 1: Listing of NFIP Jurisdictions continued
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Community CID
HUC-8 Sub-
Basin(s) Located on FIRM
Panel(s)
If Not Included, Location of Flood
Hazard Data
Gadsden County, Unincorporated Areas
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
Table 1: Listing of NFIP Jurisdictions continued
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Community CID
HUC-8 Sub-
Basin(s) Located on FIRM
Panel(s)
If Not Included, Location of Flood
Hazard Data
Gadsden County, Unincorporated Areas
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,
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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.
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.
Figure 2: FIRM Notes to Users
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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.
Figure 2: FIRM Notes to Users
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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.
Figure 3: Map Legend for FIRM
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
Figure 3: Map Legend for FIRM
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
Figure 3: Map Legend for FIRM
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
G Creek Unnamed Tributary 2
Gadsden County, Unincorporated Areas
Confluence with G Creek
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
Confluence with Ochlocknee River
Approximately 4.0 miles upstream of confluence of Ochlocknee River
03120003 4.0
N AE 2015
Hog Creek Unnamed Tributary
Gadsden County, Unincorporated Areas
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
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
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 4,300 feet upstream of Dupont Road
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
Holley Branch Unnamed Tributary
Gadsden County, Unincorporated Areas
Approximately 4,700 feet upstream of confluence with Holley Branch
Approximately 5,600 feet upstream of Dupont Road
03120003 1.5
N AE 2015
Holley Branch Unnamed Tributary 2
Gadsden County, Unincorporated Areas
Confluence with Holley Branch
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
Gadsden County, Unincorporated Areas
Confluence with Hurricane Creek
Approximately 2,390 feet upstream of Penny B Road
03120003 1.7
N AE 2015
Hurricane Creek Unnamed Tributary 2
Gadsden County, Unincorporated Areas
Confluence with Hurricane Creek
Approximately 3,260 feet upstream of Beaver Creek Road
03120003 2.9
N AE 2015
Hurricane Creek Unnamed Tributary 3
Gadsden County, Unincorporated Areas
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
Table 2: Flooding Sources Included in this FIS Report continued
18
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
Lake Talquin Unnamed Tributary
Gadsden County, Unincorporated Areas
Confluence with Lake Talquin/Ochlockonee River
Approximately 820 feet upstream of Private Drive
03120003 1.8
Y AE 2007
Lake Talquin Unnamed Tributary
Gadsden County, Unincorporated Areas
Approximately 820 feet upstream of Private Drive
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
Confluence with Little River
Approximately 700 feet upstream of U.S. Highway 90
03120003 3.8
Y AE 2007
Monroe Creek Gadsden County, Unincorporated Areas
Approximately 700 feet upstream of U.S. Highway 90
Approximately 1.7 miles upstream of U.S. Highway 90
03120003 1.6
N AE 2015
Monroe Creek Unnamed Tributary 1
Gadsden County, Unincorporated Areas
Confluence with Monroe Creek
Approximately 0.6 mile upstream of the confluence with Monroe Creek
03120003 0.6
N AE 2015
Monroe Creek Unnamed Tributary 2
Gadsden County, Unincorporated Areas
Confluence with Monroe Creek
Approximately 1,250 feet upstream U.S. Highway 90
03120003 2.0
N AE 2015
Monroe Creek Unnamed Tributary 3
Gadsden County, Unincorporated Areas; Midway, City of
Confluence with Monroe Creek
Approximately 2.4 miles upstream of the confluence of Monroe Creek
03120003 2.4
N AE 2015
Monroe Creek Unnamed Tributary 4
Gadsden County, Unincorporated Areas; Midway, City of
Confluence with Monroe Creek
Approximately 3,010 feet upstream of the confluence of Monroe Creek
03120003 0.6
N AE 2015
Table 2: Flooding Sources Included in this FIS Report continued
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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
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
Gadsden County, Unincorporated Areas; Midway, City of
Jackson Bluff Dam Grady County boundary 03120003 32.0
Y AE 2015
Ochlockonee River Unnamed Tributary
Gadsden County, Unincorporated Areas
Confluence with the Ochlocknee River
Approximately 1.6 miles upstream of confluence of Unnamed Tributary to Ochlocknee River Unnamed Tributary
03120003 5.1
Y AE 2007
Ochlockonee River Unnamed Tributary
Gadsden County, Unincorporated Areas
Approximately 1.6 miles upstream of confluence of Unnamed Tributary to Ochlocknee River Unnamed Tributary
Approximately 1.8 miles upstream of confluence of Unnamed Tributary to Ochlocknee River Unnamed Tributary
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
Confluence with Little River
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
Approximately 4,050 feet upstream of confluence of Robinson Branch
Approximately 7,520 feet upstream of confluence of Robinson Branch
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
Table 2: Flooding Sources Included in this FIS Report continued
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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
Salem Branch Gadsden County, Unincorporated Areas; Havana, Town of
Approximately 1.1 miles upstream of the confluence with Attapulgus Creek
Approximately 1.7 miles upstream of State Highway 159
03120003 5.0
N AE 2015
South Mosquito Creek
Chattahoochee, City of; Gadsden County Unincorporated, Areas
Confluence with Mosquito Creek
Approximately 3,270 feet upstream of 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
Confluence with Attapulgus Creek
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
Tanyard Branch Unnamed Tributary 2
Gadsden County, Unincorporated Areas; Quincy, City of
Confluence with Tanyard Branch
Approximately 145 feet downstream of County Highway 268
03120003 0.9
Y AE 2007
Tanyard Branch Unnamed Tributary 2
Gadsden County, Unincorporated Areas; Quincy, City of
Approximately 145 feet downstream of County Highway 268
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
Gadsden County, Unincorporated Areas
Confluence with Ochlockonee River
Approximately 2.7 miles upstream of the confluence of Ochlockonee River
03120003 2.7
N AE 2015
Unnamed Stream 3
Gadsden County, Unincorporated Areas
Confluence with Ochlocknee River
Approximately 2,350 feet upstream of Reynolds Road
03120003 1.5
N AE 2015
Table 2: Flooding Sources Included in this FIS Report continued
21
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
Unnamed Stream 4
Gadsden County, Unincorporated Areas; Midway, City of
Confluence with Ochlockonee River
Approximately 1,980 feet upstream of Business Park Road
03120003 2.4
N AE 2015
Unnamed Stream 6
Gadsden County, Unincorporated Areas
Confluence with Ochlockonee River
Approximately 40 feet downstream of State Highway 270
03120003 1.5
N AE 2015
Unnamed Stream 7
Gadsden County Unincorporated Areas; Havana, Town of
Confluence with Ochlocknee River
Approximately 1.2 miles upstream of the confluence if Unnamed Tributary 13
03120003 5.1
N AE 2015
Unnamed Stream 8
Gadsden County, Unincorporated Areas
Confluence with Ochlocknee River
Approximately 1.4 miles upstream of the confluence of Ochlocknee River
03120003 1.5
N AE 2015
Unnamed Tributary 1
Gadsden County, Unincorporated Areas
Confluence with Lake Talquin Unnamed Tributary
Approximately 1,260 feet upstream of Lakeview Point Road
03120003 0.6
N AE 2015
Unnamed Tributary 2
Gadsden County, Unincorporated Areas
Confluence with Richlander Creek
Approximately 4,650 feet upstream of the confluence of Richlander Creek
03120003 0.9
N AE 2015
Unnamed Tributary 3
Gadsden County, Unincorporated Areas
Confluence with Richlander Creek
Approximately 3,490 feet upstream of the confluence of Richlander Creek
03120003 0.7
N AE 2015
Unnamed Tributary 4
Gadsden County, Unincorporated Areas
Confluence with Richlander Creek
Approximately 0.8 miles upstream of the confluence of Richlander Creek
03120003 0.8
N AE 2015
Unnamed Tributary 5
Gadsden County, Unincorporated Areas
Confluence with Richlander Creek
Approximately 2,510 feet upstream of Augustine Road
03120003 1.2
N AE 2015
Table 2: Flooding Sources Included in this FIS Report continued
22
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
Unnamed Tributary 6
Gadsden County, Unincorporated Areas; Quincy, City of
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
Gadsden County, Unincorporated Areas
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
Gadsden County, Unincorporated Areas
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
Gadsden County, Unincorporated Areas
Confluence with Double Branch
Approximately 85 feet downstream of Shady Rest Road/State Highway 270
03120003 1.7
N AE 2015
Unnamed Tributary 10
Gadsden County, Unincorporated Areas
Confluence with Double Branch
Approximately 2,260 feet upstream of State Highway 159
03120003 2.4
N AE 2015
Unnamed Tributary 11
Gadsden County, Unincorporated Areas
Confluence with Double Branch
At Robin Lane 03120003 1.6
N AE 2015
Unnamed Tributary 12
Gadsden County, Unincorporated Areas
Confluence with Double Branch
Approximately 4,360 feet upstream of Lanier Road
03120003 2.1
N AE 2015
Unnamed Tributary 13
Gadsden County, Unincorporated Areas
Confluence with Unnamed Stream 7
Approximately 2,050 feet upstream of Eastern Way
03120003 1.1
N AE 2015
Unnamed Tributary 14
Gadsden County, Unincorporated Areas
Confluence with Unnamed Stream 7
Approximately 4,310 feet upstream of Railroad
03120003 2.3
N AE 2015
Unnamed Tributary 15
Gadsden County, Unincorporated Areas
Confluence with Unnamed Stream 7
Approximately 1.6 miles upstream of State Highway 153
03120003 4.0
N AE 2015
Unnamed Tributary 16
Gadsden County, Unincorporated Areas
Confluence with Unnamed Tributary 15
Approximately 1,065 feet upstream of North Quail Hollow Road
03120003 1.1
N AE 2015
Table 2: Flooding Sources Included in this FIS Report continued
23
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
Unnamed Tributary 17
Gadsden County, Unincorporated Areas
Confluence with Unnamed Tributary 15
Approximately 1,360 feet upstream of Tall Timber Road
03120003 1.3
N AE 2015
Unnamed Tributary 20
Gadsden County, Unincorporated Areas
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
Unnamed Tributary 21
Gadsden County, Unincorporated Areas
Confluence with Unnamed Tributary to Ochlocknee River Unnamed Tributary
Approximately 410 feet upstream of Collins Road II
03120003 0.8
N AE 2015
Unnamed Tributary to Ochlockonee River Unnamed Tributary
Gadsden County Unincorporated Areas; Havana, Town of
Confluence with Ochlockonee River Unnamed Tributary
Approximately 2,330 feet upstream of State Highway 12
03120003 1.8
Y AE 2007
Unnamed Tributary to Ochlockonee River Unnamed Tributary
Gadsden County Unincorporated Areas; Havana, Town of
Approximately 2,330 feet upstream of State Highway 12
Approximately 2.2 miles upstream of State Highway 12
03120003 1.7
N AE 2015
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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
This section is not applicable to this Flood Risk Project.
Figure 5: Wave Runup Transect Schematic
[Not Applicable to this Flood Risk Project]
2.5.2 Floodplain Boundaries and BFEs for Coastal Areas
This section is not applicable to this Flood Risk Project.
2.5.3 Coastal High Hazard Areas
This section is not applicable to this Flood Risk Project.
Figure 6: Coastal Transect Schematic
[Not Applicable to this Flood Risk Project]
2.5.4 Limit of Moderate Wave Action
This section is not applicable to this Flood Risk Project.
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
This section is not applicable to this Flood Risk Project.
Table 4: Coastal Barrier Resources System Information
[Not Applicable to this Flood Risk Project]
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
Flooding Source Location
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
[Not Applicable to this Flood Risk Project]
4.4 Levees
This section is not applicable to this Flood Risk Project.
Table 9: Levees
[Not Applicable to this Flood Risk Project]
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
Flooding Source Location
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
Double Branch At the confluence of Unnamed Tributary 10
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
Double Branch At the confluence of Unnamed Tributary 11
4.9 1,018 1,515 1,973 2,505 4,093
Double Branch At the confluence of Unnamed Tributary 11
4.2 919 1,366 1,777 2,254 3,677
Double Branch At the confluence of Unnamed Tributary 12
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
Double Branch Approximately 5,645 feet upstream of the confluence of Unnamed Tributary 12
1.0 347 512 663 837 1,349
Double Branch Approximately 8,915 feet upstream of the confluence of Unnamed Tributary 12
0.6 253 373 482 607 975
*Not calculated for this Flood Risk Project
Table 10: Summary of Discharges continued
32
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
G Creek At the confluence of G Creek Unnamed Tributary 2
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
G Creek At the confluence of G Creek Unnamed Tributary 1
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
G Creek Unnamed Tributary 1
At the confluence of G Creek 0.9 320 471 609 767 1,233
G Creek Unnamed Tributary 1
Approximately 1,210 feet downstream of Ranch Road
0.6 262 386 499 629 1,010
G Creek Unnamed Tributary 2
At the confluence of G Creek 1.3 414 611 791 999 1,612
G Creek Unnamed Tributary 2
Approximately 1,350 feet upstream of the confluence of G Creek
0.8 295 434 561 707 1,134
G Creek Unnamed Tributary 2
Approximately 3,290 feet upstream of the confluence of G Creek
0.6 247 364 471 593 953
Table 10: Summary of Discharges continued
33
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
Hog Creek Approximately 5,240 feet upstream of the confluence of Hog Creek Unnamed Tributary
1.3 432 640 830 1,049 1,699
Hog Creek Approximately 8,040 feet upstream of the confluence of Hog Creek Unnamed Tributary
0.8 316 467 605 764 1,231
Hog Creek Unnamed Tributary
At the confluence of Unnamed Tributary 7
0.6 251 371 479 604 971
Hog Creek Unnamed Tributary
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
*Not calculated for this Flood Risk Project
Table 10: Summary of Discharges continued
34
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
Holley Branch Unnamed Tributary
At Holley Branch 1.1 336 * 557 670 970
Holley Branch Unnamed Tributary
Approximately 2,120 feet downstream of Dupont Road
1.0 336 525 557 670 970
Holley Branch Unnamed Tributary
Approximately 850 feet downstream of Dupont Road
0.5 227 335 433 546 876
Holley Branch Unnamed Tributary 2
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
Approximately 1,240 feet upstream of the confluence of Hurricane Creek Unnamed Tributary 3
5.7 1,065 1,563 2,017 2,540 4,082
Hurricane Creek At the confluence of Hurricane Creek Unnamed Tributary 2
3.2 739 1,090 1,412 1,782 2,877
Hurricane Creek
Approximately 3,880 feet upstream of the confluence of Hurricane Creek Unnamed Tributary 2
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
*Not calculated for this Flood Risk Project
Table 10: Summary of Discharges continued
35
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
Hurricane Creek At the confluence of Hurricane Creek Unnamed Tributary 1
0.7 246 356 454 566 888
Hurricane Creek
Approximately 2,000 feet upstream of the confluence of Hurricane Creek Unnamed Tributary 1
0.6 242 356 460 578 927
Hurricane Creek Unnamed Tributary 1
At the confluence of Hurricane Creek
0.9 338 498 643 810 1,300
Hurricane Creek Unnamed Tributary 1
Approximately 1,970 feet downstream of Penny B Road
0.6 258 381 493 621 999
Hurricane Creek Unnamed Tributary 2
At the confluence of Hurricane Creek
2.2 586 866 1,122 1,418 2,294
Hurricane Creek Unnamed Tributary 2
Approximately 3,420 feet upstream of Beaver Creek Road
1.6 489 724 939 1,187 1,921
Hurricane Creek Unnamed Tributary 2
Approximately 670 feet downstream of Beaver Creek Road
0.8 307 453 586 739 1,191
Hurricane Creek Unnamed Tributary 3
At the confluence of Hurricane Creek
0.9 325 478 618 779 1,251
Lake Talquin Unnamed Tributary
At Lake Talquin 2.1 359 * 617 732 1,020
Lake Talquin Unnamed Tributary
Approximately 500 feet downstream of Dirt Road
0.9 359 495 617 732 1,020
Lake Talquin Unnamed Tributary
Approximately 7,700 feet upstream of Dirt Road
0.5 226 333 430 542 870
*Not calculated for this Flood Risk Project
Table 10: Summary of Discharges continued
36
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
Monroe Creek Approximately 730 feet upstream of U.S. Highway 90
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
Monroe Creek Unnamed Tributary 1
At the confluence of Monroe Creek
0.2 138 202 260 327 521
Monroe Creek Unnamed Tributary 2
At the confluence of Monroe Creek
1.6 477 707 918 1,161 1,882
Monroe Creek Unnamed Tributary 3
At the confluence of Monroe Creek
1.4 439 649 840 1,062 1,716
Monroe Creek Unnamed Tributary 3
Approximately 5,090 feet upstream of the confluence of Monroe Creek
1.0 360 532 689 870 1,404
Monroe Creek Unnamed Tributary 4
At the confluence of Monroe Creek
0.2 106 155 200 251 398
*Not calculated for this Flood Risk Project
Table 10: Summary of Discharges continued
37
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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 *
Mosquito Creek Unnamed Tributary
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
*Not calculated for this Flood Risk Project
Table 10: Summary of Discharges continued
38
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
Ochlockonee River Unnamed Tributary
At Ochlockonee River 12.9 782 * 1,240 1,430 1,930
Ochlockonee River Unnamed Tributary
At the confluence of Unnamed Tributary 18
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
Quincy Creek Just upstream of State Highway 267
15.9 1,500 * 2,600 3,100 4,600
Quincy Creek Just upstream of State Highway 268
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
*Not calculated for this Flood Risk Project
Table 10: Summary of Discharges continued
39
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
Salem Branch Approximately 6,110 feet upstream of Unnamed Road
3.5 795 1,174 1,521 1,922 3,109
Salem Branch Approximately 8,520 feet upstream of Unnamed Road
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
Table 10: Summary of Discharges continued
40
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
South Mosquito Creek Unnamed Tributary
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
Tanyard Branch Unnamed Tributary 1
At Tanyard Branch 0.4 118 * 201 236 319
Tanyard Branch Unnamed Tributary 2
At Tanyard Branch 3.0 579 * 1,050 1,270 1,850
Tanyard Branch Unnamed Tributary 2
Approximately 770 feet downstream of the confluence of Unnamed Tributary 6
2.7 579 1,022 1,050 1,270 1,850
Tanyard Branch Unnamed Tributary 2
At the confluence of Unnamed Tributary 6
1.3 413 611 792 1,001 1,619
Tanyard Branch Unnamed Tributary 2
Approximately 2,200 feet upstream of the confluence of Unnamed Tributary 6
1.0 356 527 682 862 1,391
Tanyard Branch Unnamed Tributary 2
Approximately 750 feet upstream of the confluence of Key Farm Road
0.5 226 333 430 541 869
*Not calculated for this Flood Risk Project
Table 10: Summary of Discharges continued
41
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
Unnamed Stream 2 Approximately 8,150 feet upstream of the confluence of Ochlockonee River
0.6 242 357 462 582 934
Unnamed Stream 3 At the confluence of Ochlockonee River
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
Unnamed Stream 4 At the confluence of Ochlockonee River
2.3 621 921 1,196 1,514 2,460
*Not calculated for this Flood Risk Project
Table 10: Summary of Discharges continued
42
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
10% Annual Chance
4% Annual Chance
2% Annual Chance
1% Annual Chance
0.2% Annual Chance
Unnamed Stream 4 Approximately 5,920 feet upstream of the confluence of Ochlockonee River
1.9 549 815 1,058 1,340 2,175
Unnamed Stream 6 Approximately 3,360 feet upstream of the confluence of Ochlockonee River
1.1 382 564 731 923 1,488
Unnamed Stream 6 Approximately 5,770 feet upstream of the confluence of Ochlockonee River
0.8 307 453 586 740 1,191
Unnamed Stream 7 At the confluence of Ochlockonee River
7.0 1,290 1,921 2,502 3,179 5,201
Unnamed Stream 7 Approximately 3,450 feet upstream of the confluence of Ochlockonee River
6.6 1,224 1,817 2,363 2,996 4,884
Unnamed Stream 7 Approximately 6,010 feet upstream of the confluence of Ochlockonee River
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
Unnamed Stream 8 At the confluence of Ochlockonee River
0.9 327 484 626 791 1,275
Table 10: Summary of Discharges continued
43
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
Unnamed Tributary 3 At the confluence of Richlander Creek
0.2 104 152 196 245 390
Unnamed Tributary 4 At the confluence of Richlander Creek
0.4 193 284 367 462 740
Unnamed Tributary 5 At the confluence of Richlander Creek
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
Approximately 3,300 feet upstream of the confluence of Tanyard Branch Unnamed Tributary 2
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
Unnamed Tributary 10 At the confluence of Double Branch
1.3 427 631 817 1,031 1,663
Table 10: Summary of Discharges continued
44
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
Unnamed Tributary 11 At the confluence of Double Branch
1.0 350 518 671 847 1,367
Unnamed Tributary 11 Approximately 2,950 feet upstream of the confluence of Double Branch
0.8 303 446 576 726 1,166
Unnamed Tributary 12 At the confluence of Double Branch
2.3 620 920 1,195 1,513 2,458
Unnamed Tributary 12 Approximately 3,130 feet upstream of the confluence of Double Branch
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
Unnamed Tributary 14 At the confluence of Unnamed Stream 7
1.0 362 534 691 872 1,405
Unnamed Tributary 14 Approximately 830 feet downstream of Railroad
0.5 236 348 449 565 906
Unnamed Tributary 15 At the confluence of Unnamed Stream 7
2.3 616 915 1,189 1,507 2,449
Table 10: Summary of Discharges continued
45
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
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
Unnamed Tributary 15 At the confluence of Unnamed Tributary 16
0.9 336 496 643 811 1,309
Unnamed Tributary 16 At the confluence of Unnamed Tributary 15
0.3 175 258 333 418 669
Unnamed Tributary 17 At the confluence of Unnamed Tributary 15
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
Unnamed Tributary to Ochlockonee River Unnamed Tributary
At Ochlockonee River Unnamed Tributary
5.6 585 * 969 1,140 1,570
Unnamed Tributary to Ochlockonee River Unnamed Tributary
Approximately 2,410 feet upstream of State Highway 12
2.2 585 764 969 1,140 1,570
Unnamed Tributary to Ochlockonee River Unnamed Tributary
Approximately 3,340 feet upstream of State Highway 12
2.0 559 826 1,069 1,349 2,178
Unnamed Tributary to Ochlockonee River Unnamed Tributary
Approximately 3,610 feet upstream of State Highway 12
1.6 447 652 837 1,048 1,664
*Not calculated for this Flood Risk Project
Table 10: Summary of Discharges continued
46
Flooding Source Location
Drainage Area
(Square Miles)
Peak Discharge (cfs)
10% Annual Chance
4% Annual Chance
2% Annual Chance
1% Annual Chance
0.2% Annual Chance
Unnamed Tributary to Ochlockonee River Unnamed Tributary
Approximately 4,830 feet upstream of State Highway 12
1.5 455 673 871 1,101 1,779
Unnamed Tributary to Ochlockonee River Unnamed Tributary
Approximately 6,160 feet upstream of State Highway 12
1.0 350 517 669 844 1,362
Unnamed Tributary to Ochlockonee River Unnamed Tributary
Approximately 10,530 feet upstream of State Highway 12
0.6 240 353 456 574 922
Figure 7: Frequency Discharge-Drainage Area Curves
[Not Applicable to this Flood Risk Project]
Table 11: Summary of Non-Coastal Stillwater Elevations
[Not Applicable to this Flood Risk Project]
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
Approximately 150 feet downstream of State Highway 267
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)
HEC-RAS 4.1.0 (USACE 2010)
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)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
G Creek Unnamed Tributary 1
Confluence with G Creek
Approximately 2,340 feet upstream of Ranch Road
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
G Creek Unnamed Tributary 2
Confluence with G Creek
Approximately 1.2 miles upstream of the confluence of G Creek
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Hammock Creek Confluence with Ochlocknee River
Approximately 2,350 feet upstream of State Highway 267
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
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
FIRM Special Considerations
Hog Creek Confluence with Ochlocknee River
Approximately 4.0 miles upstream of confluence of Ochlocknee River
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Hog Creek Unnamed Tributary
Confluence with Hog Creek
Approximately 1.5 miles upstream of confluence of Unnamed Tributary 7
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Holley Branch Confluence with the Ochlocknee River
Approximately 4,300 feet upstream of Dupont Road
Rainfall-Runoff Model/
HEC-HMS 3.1.0 (USACE 2006)
HEC-RAS 3.1.3 (USACE 2005)
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)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Holley Branch Unnamed Tributary
Confluence with Holley Branch
Approximately 4,700 feet upstream of confluence with Holley Branch
Rainfall-Runoff Model/
HEC-HMS 3.1.0 (USACE 2006)
HEC-RAS 3.1.3 (USACE 2005)
09/28/2007 AE w/
Floodway
Holley Branch Unnamed Tributary
Approximately 4,700 feet upstream of confluence with Holley Branch
Approximately 5,600 feet upstream of Dupont Road
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Holley Branch Unnamed Tributary 2
Confluence with Holley Branch
Approximately 1.2 miles upstream of confluence of Holley Branch
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Hurricane Creek
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
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Hurricane Creek Unnamed Tributary 1
Confluence with Hurricane Creek
Approximately 2,390 feet upstream of Penny B Road
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Table 13: Summary of Hydrologic and Hydraulic Analyses continued
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
FIRM Special Considerations
Hurricane Creek Unnamed Tributary 2
Confluence with Hurricane Creek
Approximately 3,260 feet upstream of Beaver Creek Road
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Hurricane Creek Unnamed Tributary 3
Approximately 750 feet upstream of the confluence of Hurricane Creek
Approximately 4,230 feet upstream of Tallavana Trail
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Lake Talquin Jackson Bluff Dam Ocklockonee River
USGS Regional Analysis Method
(USGS 1966)
USGS Step-Backwater
Model E-431 (USGS 1976)
11/01/1987 AE
Lake Talquin Unnamed Tributary
Confluence with Lake Talquin/Ochlockonee River
Approximately 820 feet upstream of Private Drive
Regression Equations
(USGS 1982)
HEC-RAS 3.1.3 (USACE 2005)
09/28/2007 AE w/
Floodway
Lake Talquin Unnamed Tributary
Approximately 820 feet upstream of Private Drive
Approximately 7,120 feet upstream of Private Drive
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Little River Confluence with Lake Talquin
Confluence with Attapulgus 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 (USGS 1972).
McIntosh Branch Confluence with Lake Talquin
Approximately 1.0 mile upstream of the confluence with Lake Talquin
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Monroe Creek Confluence with Little River
Approximately 700 feet upstream of U.S. Highway 90
Regression Equations
(USGS 1982)
HEC-RAS 3.1.3 (USACE 2005)
09/28/2007 AE w/
Floodway
Monroe Creek Approximately 700 feet upstream of U.S. Highway 90
Approximately 1.7 miles upstream of U.S. Highway 90
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Table 13: Summary of Hydrologic and Hydraulic Analyses continued
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
FIRM Special Considerations
Monroe Creek Unnamed Tributary 1
Confluence with Monroe Creek
Approximately 0.6 mile upstream of the confluence with Monroe Creek
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Monroe Creek Unnamed Tributary 2
Confluence with Monroe Creek
Approximately 1,250 feet upstream U.S. Highway 90
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Monroe Creek Unnamed Tributary 3
Confluence with Monroe Creek
Approximately 2.4 miles upstream of the confluence of Monroe Creek
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Monroe Creek Unnamed Tributary 4
Confluence with Monroe Creek
Approximately 3,010 feet upstream of the confluence of Monroe Creek
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Mosquito Creek Confluence with Apalachicola River
At U.S. Highway 90 Regression Equations
(USGS 1982)
USGS Step-Backwater
Model E-431 (USGS 1976)
06/01/1986 AE
Mosquito Creek Unnamed Tributary
Confluence with Mosquito Creek
Approximately 4,340 feet upstream of confluence with Mosquito Creek
Regression Equations
(USGS 1982)
HEC-RAS 3.1.3 (USACE 2005)
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).
Ochlockonee River Unnamed Tributary
Confluence with the Ochlocknee River
Approximately 1.6 miles upstream of confluence of Unnamed Tributary to Ochlocknee River Unnamed Tributary
Regression Equations
(USGS 1982)
HEC-RAS 3.1.3 (USACE 2005)
09/28/2007 AE w/
Floodway
Table 13: Summary of Hydrologic and Hydraulic Analyses continued
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
FIRM Special Considerations
Ochlockonee River Unnamed Tributary
Approximately 1.6 miles upstream of confluence of Unnamed Tributary to Ochlocknee River Unnamed Tributary
Approximately 1.8 miles upstream of confluence of Unnamed Tributary to Ochlocknee River Unnamed Tributary
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
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
Approximately 1.4 miles upstream of State Highway 268
Regression Equations
(USGS 1982)
HEC-2 (USACE 1984)
11/01/1987 AE w/
Floodway
Richlander Creek Confluence with the Little River
Approximately 4,050 feet upstream of confluence of Robinson Branch
Regression Equations
(USGS 1982)
HEC-2 (USACE 1984)
11/01/1987 AE
Richlander Creek
Approximately 4,050 feet upstream of confluence of Robinson Branch
Approximately 7,520 feet upstream of confluence of Robinson Branch
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Robinson Branch Confluence with Richlander Creek
Approximately 0.9 mile upstream of the Walsh Road
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Salem Branch
Approximately 1.1 miles upstream of the confluence with Attapulgus Creek
Approximately 1.7 miles upstream of State Highway 159
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
South Mosquito Creek
Confluence with Mosquito Creek
Approximately 3,270 feet upstream of confluence with Mosquito Creek
Regression Equations
(USGS 1982)
HEC-RAS 3.1.3 (USACE 2005)
09/28/2007 AE w/
Floodway
South Mosquito Creek Unnamed Tributary
Confluence with South Mosquito Creek
Approximately 4,080 feet upstream of Depot Road
Regression Equations
(USGS 1982)
HEC-RAS 3.1.3 (USACE 2005)
09/28/2007 AE w/
Floodway
Table 13: Summary of Hydrologic and Hydraulic Analyses continued
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
FIRM Special Considerations
Swamp Creek Confluence with Attapulgus Creek
At State Highway 159
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 (USGS 1972).
Tanyard Branch Confluence with Quincy Creek
Approximately 150 feet upstream of 7th Street
Regression Equations
(USGS 1982)
HEC-RAS 3.1.3 (USACE 2005)
09/28/2007 AE w/
Floodway
Tanyard Branch Unnamed Tributary 1
Confluence with Tanyard Branch
Approximately 150 feet upstream of Circle Drive
Regression Equations
(USGS 1982)
HEC-RAS 3.1.3 (USACE 2005)
09/28/2007 AE w/
Floodway
Tanyard Branch Unnamed Tributary 2
Confluence with Tanyard Branch
Approximately 145 feet downstream of County Highway 268
Regression Equations
(USGS 1982)
HEC-RAS 3.1.3 (USACE 2005)
09/28/2007 AE w/
Floodway
Tanyard Branch Unnamed Tributary 2
Approximately 145 feet downstream of County Highway 268
Approximately 320 feet upstream of railroad
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
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)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Stream 3 Confluence with Ochlocknee River
Approximately 2,350 feet upstream of Reynolds Road
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Stream 4 Confluence with Ochlockonee River
Approximately 1,980 feet upstream of Business Park Road
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Stream 6 Confluence with Ochlockonee River
Approximately 40 feet downstream of State Highway 270
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Table 13: Summary of Hydrologic and Hydraulic Analyses continued
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
FIRM Special Considerations
Unnamed Stream 7 Confluence with Ochlocknee River
Approximately 1.2 miles upstream of the confluence if Unnamed Tributary 13
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Stream 8 Confluence with Ochlocknee River
Approximately 1.4 miles upstream of the confluence of Ochlocknee River
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
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)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 2 Confluence with Richlander Creek
Approximately 4,650 feet upstream of the confluence of Richlander Creek
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 3 Confluence with Richlander Creek
Approximately 3,490 feet upstream of the confluence of Richlander Creek
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 4 Confluence with Richlander Creek
Approximately 0.8 miles upstream of the confluence of Richlander Creek
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 5 Confluence with Richlander Creek
Approximately 2,510 feet upstream of Augustine Road
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 6 Confluence with Tanyard Branch Unnamed Tributary 2
Approximately 4,640 feet upstream of the confluence of Tanyard Branch Unnamed Tributary 2
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Table 13: Summary of Hydrologic and Hydraulic Analyses continued
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
FIRM Special Considerations
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)
HEC-RAS 4.1.0 (USACE 2010)
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)
HEC-RAS 4.1.0 (USACE 2010)
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)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 10
Confluence with Double Branch
Approximately 2,260 feet upstream of State Highway 159
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 11
Confluence with Double Branch
At Robin Lane Regression
Equation (USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 12
Confluence with Double Branch
Approximately 4,360 feet upstream of Lanier Road
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 13
Confluence with Unnamed Stream 7
Approximately 2,050 feet upstream of Eastern Way
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 14
Confluence with Unnamed Stream 7
Approximately 4,310 feet upstream of Railroad
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 15
Confluence with Unnamed Stream 7
Approximately 1.6 miles upstream of State Highway 153
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 16
Confluence with Unnamed Tributary 15
Approximately 1,065 feet upstream of North Quail Hollow Road
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Table 13: Summary of Hydrologic and Hydraulic Analyses continued
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
FIRM Special Considerations
Unnamed Tributary 17
Confluence with Unnamed Tributary 15
Approximately 1,360 feet upstream of Tall Timber Road
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 20
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
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary 21
Confluence with Unnamed Tributary to Ochlocknee River Unnamed Tributary
Approximately 410 feet upstream of Collins Road II
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
04/03/2015 AE
Unnamed Tributary to Ochlockonee River Unnamed Tributary
Confluence with Ochlockonee River Unnamed Tributary
Approximately 2,330 feet upstream of State Highway 12
Regression Equations
(USGS 1982)
HEC-RAS 3.1.3 (USACE 2005)
09/28/2007 AE w/
Floodway
Unnamed Tributary to Ochlockonee River Unnamed Tributary
Approximately 2,330 feet upstream of State Highway 12
Approximately 2.2 miles upstream of State Highway 12
Regression Equation
(USGS 2006)
HEC-RAS 4.1.0 (USACE 2010)
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
Hurricane Creek Unnamed Tributary 1
0.040-0.045 0.100-0.120
Hurricane Creek Unnamed Tributary 2
0.040-0.050 0.120
Hurricane Creek Unnamed Tributary 3
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
Ochlockonee River Unnamed Tributary
0.021-0.074 0.119-0.139
* Date not available
Table 14: Roughness Coefficients continued
58
Flooding Source Channel “n” Overbank “n”
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
South Mosquito Creek Unnamed Tributary
0.044-0.055 0.093-0.118
Swamp Creek 0.030 0.135
Tanyard Branch 0.068-0.131 0.104-0.140
Tanyard Branch Unnamed Tributary 1
0.064-0.067 0.097-0.101
Tanyard Branch Unnamed Tributary 2
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 6 0.045 0.120
Unnamed Stream 7 0.045-0.055 0.120
Unnamed Stream 8 0.050 0.150
Unnamed Tributary 1 0.045 0.120
Unnamed Tributary 2 0.030-0.050 0.060-0.120
Unnamed Tributary 3 0.045 0.120
Unnamed Tributary 4 0.040-0.045 0.080-0.120
Unnamed Tributary 5 0.045 0.120
Unnamed Tributary 6 0.045 0.120
Unnamed Tributary 7 0.035-0.045 0.120
Unnamed Tributary 8 0.035-0.045 0.120
Unnamed Tributary 9 0.045 0.120
Unnamed Tributary 10 0.035-0.045 0.120
Unnamed Tributary 11 0.035-0.055 0.120
Unnamed Tributary 12 0.045 0.120
Unnamed Tributary 13 0.035-0.050 0.090-0.120
Unnamed Tributary 14 0.035-0.050 0.080-0.120
Table 14: Roughness Coefficients continued
59
Flooding Source Channel “n” Overbank “n”
Unnamed Tributary 15 0.040-0.050 0.090-0.120
Unnamed Tributary 16 0.040-0.045 0.100-0.120
Unnamed Tributary 17 0.035-0.050 0.060-0.120
Unnamed Tributary 20 0.035-0.045 0.100-0.120
Unnamed Tributary 21 0.045-0.050 0.120
Unnamed Tributary to Ochlockonee River Unnamed Tributary
0.035-0.074 0.080-0.138
5.3 Coastal Analyses
This section is not applicable to this Flood Risk Project.
Table 15: Summary of Coastal Analyses
[Not Applicable to this Flood Risk Project]
5.3.1 Total Stillwater Elevations
This section is not applicable to this Flood Risk Project.
Figure 8: 1% Annual Chance Total Stillwater Elevations for Coastal Areas
[Not Applicable to this Flood Risk Project]
Table 16: Tide Gage Analysis Specifics
[Not Applicable to this Flood Risk Project]
5.3.2 Waves
This section is not applicable to this Flood Risk Project.
5.3.3 Coastal Erosion
This section is not applicable to this Flood Risk Project.
5.3.4 Wave Hazard Analyses
This section is not applicable to this Flood Risk Project.
Table 17: Coastal Transect Parameters
[Not Applicable to this Flood Risk Project]
Figure 9: Transect Location Map
[Not Applicable to this Flood Risk Project]
5.4 Alluvial Fan Analyses
This section is not applicable to this Flood Risk Project.
60
Table 18: Summary of Alluvial Fan Analyses
[Not Applicable to this Flood Risk Project]
Table 19: Results of Alluvial Fan Analyses
[Not Applicable to this Flood Risk Project]
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
[Not Applicable to this Flood Risk Project]
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.
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.