TIFT COUNTY, GEORGIA AND INCORPORATED AREAS. Tift County. Revised: September 29, 2010 FLOOD INSURANCE STUDY NUMBER 13277CV000A

Transcription

1 TIFT COUNTY, GEORGIA AND INCORPORATED AREAS Community Name Community Number Tift County OMEGA, CITY OF TIFT COUNTY (UNINCORPORATED AREAS) TIFTON, CITY OF TY TY, CITY OF Revised: September 29, 2010 FLOOD INSURANCE STUDY NUMBER 13277CV000A

2 NOTICE TO FLOOD INSURANCE STUDY USERS Communities participating in the National Flood Insurance Program have established repositories of flood hazard data for floodplain management and flood insurance purposes. This Flood Insurance Study (FIS) report may not contain all data available within the Community Map Repository. Please contact the Community Map Repository for any additional data. The Federal Emergency Management Agency (FEMA) may revise and republish part or all of this FIS report at any time. In addition, FEMA may revise part of this FIS report by the Letter of Map Revision process, which does not involve republication or redistribution of the FIS report. Therefore, users should consult with community officials and check the Community Map Repository to obtain the most current FIS report components. Initial Countywide FIS Effective Date: August 17, 1998 Revised Countywide FIS Effective Dates: September 29, 2010

3 TABLE OF CONTENTS 1.0 INTRODUCTION Purpose of Study Authority and Acknowledgments Coordination AREA STUDIED Scope of Study Community Description Principal Flood Problems Flood Protection Measures ENGINEERING METHODS Hydrologic Analyses Hydraulic Analyses Vertical Datum FLOODPLAIN MANAGEMENT APPLICATIONS Floodplain Boundaries Floodways INSURANCE APPLICATIONS FLOOD INSURANCE RATE MAP OTHER STUDIES LOCATION OF DATA BIBLIOGRAPHY AND REFERENCES i

4 TABLE OF CONTENTS (Continued) FIGURES Figure 1 - Floodway Schematic TABLES Table 1 - Streams Studied by Detailed Methods... 4 Table 2 - Summary of Discharges... 9 Table 3 - Vertical Datum Conversion Table 4 - Floodway Data Table 5 - Community Map History Exhibit 1 - Flood Profiles EXHIBITS Channel A Panel 01P Channel A-1 Panels 02P-05P Channel A-2 Panel 06P Channel B Panels 07P-10P Channel B-1 Panel 11P Channel C Panel 12P Channel D Panel 13P Channel D-1 Panel 14P Channel E Panels 15P-16P Channel E-1 Panel 17P Channel G Panel 18P Gum Creek Panels 19P-20P Little River Panel 21P New River Panels 22P-26P Exhibit 2 - Flood Insurance Rate Map Index Flood Insurance Rate Map ii

5 FLOOD INSURANCE STUDY TIFT COUNTY, GEORGIA AND INCORPORATED AREAS 1.0 INTRODUCTION 1.1 Purpose of Study This Flood Insurance Study (FIS) revises and updates information on the existence and severity of flood hazards in the geographic area of Tift County, including the Cities of Omega, Tifton, and Ty Ty; and the unincorporated areas of Tift County (referred to collectively herein as Tift County), and aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of This study has developed flood-risk data for various areas of the community that will be used to establish actuarial flood insurance rates and to assist the community in its efforts to promote sound floodplain management. Minimum floodplain management requirements for participation in the National Flood Insurance Program (NFIP) are set forth in the Code of Federal Regulations at 44 CFR, Please note that the City of Omega is geographically located in Tift and Colquitt Counties. The City of Omega is included in its entirety in this FIS report. In some states or communities, floodplain management criteria or regulations may exist that are more restrictive or comprehensive than the minimum Federal requirements. In such cases, the more restrictive criteria take precedence and the State (or other jurisdictional agency) will be able to explain them. The Digital Flood Insurance Rate Map (DFIRM) and FIS report for this countywide study have been produced in digital format. Flood hazard information was converted to meet the Federal Emergency Management Agency (FEMA) DFIRM database specifications and Geographic Information System (GIS) format requirements. The flood hazard information was created and is provided in a digital format so that it can be incorporated into a local GIS and be accessed more easily by the community. 1.2 Authority and Acknowledgments The sources of authority for this FIS are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of

6 Precountywide FIS Report Information on the authority and acknowledgements for each jurisdiction included in this countywide FIS, as compiled from their previously printed FIS reports, is shown below: Tifton, City of: Tift County (Unincorporated Areas): The hydrologic and hydraulic analyses for Channels A, B-1, C, D, and D-1, for the FIS report dated December 3, 1982, were prepared by the U.S. Army Corps of Engineer (USACE), Jacksonville District, for the Federal Insurance Administration (FIA), under Inter- Agency Agreement No. IAA-H-16-75, Project Order No. 19, and Inter-Agency Agreement No. IAA-H-7-76, Project Order No. 4. The work was completed in December 1976 (FIA, 1982). The hydrologic and hydraulic analyses for Gum Creek, Little River, and New River for the FIS report dated December 1, 1981, were performed by the USACE, Jacksonville District, for FEMA, under Inter-Agency Agreement No. IAA-H-9-70, Project Order No. 5. The work was completed in October 1980 (FEMA, 1981). The authority and acknowledgements for the City of Omega and the City of Ty Ty are not included because there were no previously printed FIS reports for areas within Tift County for those communities. August 17, 1998 Initial Countywide FIS Report For the initial countywide August 17, 1998, FIS report, the hydrologic and hydraulic analyses for Channel A-1, Channel A-2, Channel B, Channel E, Channel E-1, Channel G, and the New River, from railroad to approximately 1,300 feet upstream of U.S. Highway 41, were prepared for FEMA by W.L. Jorden & Co., Inc., under Contract No. EMW-94-C The work was completed on January 8, 1996 (FEMA, 1998). 2

7 This Countywide FIS Report The redelineation for detailed studied streams and hydrologic and hydraulic analyses for streams studied by approximate methods for this countywide FIS were performed by Post, Buckley, Schuh, & Jernigan, Inc. (PBS&J), for the Georgia Department of Natural Resources (DNR), under contract No. EMA CA The work was completed in July Base map information shown on the Flood Insurance Rate Map (FIRM) was derived from the National Agriculture Imagery Program produced at a scale of 1:12,000, photography dated 2007 or later. The projection used in the preparation of this map is State Plane Georgia West, and the horizontal datum used is North American Datum 1983 (NAD83). 1.3 Coordination An initial meeting is held with representatives from FEMA, the community, and the study contractor to explain the nature and purpose of a FIS, and to identify the streams to be studied or restudied. A final meeting is held with representatives from FEMA, the community, and the study contractor to review the results of the study. Precountywide Analyses The initial and final meeting dates for previous FIS reports for Tift County and the City of Tifton are listed in the following table: Community FIS Date Initial Meeting Final Meeting Tifton, City of May 1, 1978 August 21, 1975 February 8, 1977 Tift County (Unincorporated Areas) June 1, 1982 November 13, 1978 July 7, 1981 August 17, 1998 Initial countywide FIS Report For the August 17, 1998, countywide FIS, the initial meeting was held on August 12, 1994, and attended by representatives of FEMA, the USACE, and the county and communities. A final meeting was held on June 11, 1997, and was attended by representatives of FEMA, the study contractor, the county and communities. 3

8 2.0 AREA STUDIED This Countywide Revision For this revision, the initial meeting was held on August 20, 2008, and attended by representatives of the Georgia DNR, South Georgia Regional Development Center, and the communities. The results of the study were reviewed at the final meeting held on October 15, 2009, and attended by representatives of PBS&J, FEMA, Georgia DNR, and the communities. All problems raised at that meeting have been addressed. 2.1 Scope of Study This FIS covers the geographic area of Tift County, Georgia, including the incorporated communities listed in Section 1.1. The areas studied by detailed methods were selected with priority given to all known flood hazards and areas of projected development or proposed construction. The streams studied by detailed methods are listed in Table 1. Table 1 Streams Studied by Detailed Methods Stream Channel A Channel A-1 Reach From approximately 800 feet downstream of Interstate Highway 75 to approximately 90 feet upstream from Lake Drive From confluence with New River to approximately 250 feet upstream of State Highway 125/North Tift Avenue Channel A-2 From confluence with Channel A-1 to approximately 3,000 feet upstream of East Fortieth Street Channel B From confluence with Little River to approximately 350 feet upstream from South Victory Drive Channel B-1 Channel C Channel D From confluence with Channel B to approximately 40 feet upstream of West Fourth Street From approximately 2,300 feet downstream from South College Avenue to approximately 250 feet upstream from West Seventh Street From approximately 4,000 feet upstream of Interstate Highway 75 to approximately 900 feet upstream of East Thirteenth Street 4

9 Table 1 Streams Studied by Detailed Methods (Continued) Stream Reach Channel D-1 Channel E From approximately 800 feet downstream of Railroad to approximately 450 feet upstream of Main Street From confluence with New River to Fulwood Road Channel E-1 From confluence with Channel E to approximately 1,200 feet upstream of West Thirtieth Street Channel G Gum Creek Little River New River From confluence with New River to approximately 300 feet upstream of Love Avenue From approximately 2,800 feet upstream of Parker Road to approximately 2,500 feet upstream of U.S. Highway 41 From U.S. Highway 319 to approximately 3,500 feet upstream of Upper Ty Ty Road From approximately 9,500 feet upstream of Lower Brookfield Road to approximately 1,100 feet upstream of West Twentieth Street The limits of detailed study are indicated on the Flood Profiles (Exhibit 1) and on the FIRM (Exhibit 2). August 17, 1998 Initial Countywide FIS Report Channel A-1, Channel A-2, Channel B, Channel E, Channel E-1, Channel G, and New River were newly studied or revised as part of the August 17, 1998, initial countywide FIS. This Countywide Revision For this countywide revision, all areas studied by detailed methods were redelienated based on updated topography. All areas studied by approximate methods were either newly studied or revised based on updated hydrologic and hydraulic models. Also the vertical datum was converted from the National Geodetic Vertical Datum of 1929 (NGVD) to the North American Vertical Datum of 1988 (NAVD). The projection used in the preparation of this map is State Plane Georgia West. In addition, the Transverse Mercator, State Plane coordinates, previously referenced to the North American Datum of 1927 (NAD27), are now referenced to NAD83. Approximate analyses were used to study those areas having low development potential or minimal flood hazards. The scope and methods of study were proposed to and agreed by FEMA and the communities. 5

10 2.2 Community Description Tift County, which is located in southern Georgia, is bordered on the north by Turner County, on the east by Irwin and Berrien Counties, on the south by Cook and Colquitt Counties, and on the west by Worth County. The City of Tifton is the county seat. According to the 2000 Census, the population of Tift County was 38,407. The county has a total land area of 265 square miles (U.S. Census Bureau, 2009). The average high temperature, 90 degrees Fahrenheit ( F), occurs in July. The average low temperature is 59 F and occurs in January. Tift County receives an average of 47.0 inches of rainfall per year (The Weather Channel, 2009). 2.3 Principal Flood Problems Floods in Tift County occur most frequently during the late spring or early summer as a result of intense thunderstorms, or during late summer and early autumn as a result of tropical storms. Large floods occurred on the Little River in August 1928, April 1948, and April Records were available for only the latter flood, which reached a peak elevation of feet NAVD and had an estimated recurrence interval of approximately twenty-five years. Floods on the New River, Gum Creek, and tributaries of those streams occurred in 1948, 1958, 1961, and Elevations or discharges are unavailable for these floods because these streams have no gaging stations. Based on recent flood-related state and federal disaster declarations, Tift County has experienced flooding associated with severe storms, tropical storms, heavy winds and torrential rains, severe low pressure systems, torrential downpours, and severe thunderstorms (Georgia Emergency Management Agency, 2009). 2.4 Flood Protection Measures Flood protection measures are not known to exist within Tift County. 3.0 ENGINEERING METHODS For the flooding sources studied by detailed methods 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 once on the average during any 10-, 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-, 50-, 100-, and 500-year floods, have a 10-, 2-, 1-, and 0.2-percent chance, respectively, of being equaled or exceeded during any year. Although the recurrence interval represents the long-term, 6

11 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 1-percent-annual-chance (100-year) flood in any 50-year period is approximately 40 percent (4 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. 3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish peak discharge-frequency relationships for each flooding source studied by detailed methods affecting the community. Precountywide Analyses Rainfall-frequency estimates were obtained using the statistical analyses of rainfall records prepared by the National Weather Bureau in Technical Paper No. 40 (National Weather Service, 1961). Runoff Curve Numbers developed by the Soil Conservation Service (SCS) were used to calculate the infiltration losses based on the soil type and land use (SCS, 1969). The hydrologic analyses of the New River, from approximately 3,150 feet downstream Railroad to Railroad, Gum Creek, and Channel A were performed using the Massachusetts Institute of Technology Catchment (MITCAT) model computer program (Resources Analysis, Inc., 1976). The MITCAT model was checked by comparing it to flows computed by the TRACOR Method (TRACOR, Inc., 1968). The Gum Creek hydrologic analysis was checked against the hydrologic analysis found in the Georgia Department of Transportation (GDOT) drainage manual (GDOT, 1975). The hydrologic analysis of the New River was obtained from Chart 5-28 in the GDOT publication entitled Manual on Drainage Design for Highways (GDOT, 1975). The 0.2-annual-percent-chance frequency was derived from a straight-line extrapolation on probability paper of the 10-, 2-, and 1-percent-annual-chance frequencies. Chart 5-28 was derived from a preliminary study of small rural watersheds in south Georgia by the U.S. Geological Survey (USGS) (USGS, 1973). A unit hydrograph for the New River was synthetically produced by the Snyder Method from the nearby Ochlockonee River basin. The results of this hydrograph compared favorably with Chart For the New River, in the City of Tifton, the SCS provided gage records for the years 1969 through 1973 at the Old Ocilla Road Bridge (SCS, 1973). 7

12 The hydrologic analysis of the Little River was derived from the USGS regional regression equation for Georgia (USGS, 1979). Regression equations estimate peak discharges for ungauged streams based on the characteristics of nearby gauged streams. In the City of Tifton, the hydrologic analyses of Channels A, D, and D-1 were performed using the TRACOR Method (TRACOR, Inc., 1968). The hydrologic analyses of Channels B-1, and C were performed using the rational method (Q=CIA) in accordance with the GDOT drainage manual (GDOT, 1975). The 0.2- percent-annual-chance flood discharge determined by extrapolation of the rainfall intensity-duration curve. August 17, 1998 Initial Countywide Analyses For the initial countywide FIS, the hydrologic analyses for Channels A-1, A-2, B, E, E-1, and G, and the New River, were performed using the USACE Hydrologic Engineering Center s (HEC) HEC-1 computer program (HEC, 1990). The HEC-1 hydrologic model was used to develop runoff hydrographs. Precipitation data were obtained from the National Weather Service (NWS) publication TR-40 (NWS, 1961). The precipitation totals were distributed based on the SCS Type II distribution, and the estimate of rainfall-runoff relationship was developed using SCS Runoff Curve Numbers, which relate rainfall to direct runoff (SCS, 1969). The Runoff Curve Numbers were incorporated into the HEC-1 input data. The dimensionless unit hydrograph was used with the Muskingham Routing option to route the hydrograph through the watersheds. Muskingham coefficients were calibrated using the velocities obtained from the HEC-2 model (HEC, 1991). The final flow rates were compared with the USGS Urban Regression Equations for Georgia (USGS, 1979) as a verification. This Countywide Revision For this countywide revision, discharges for the approximate analysis streams were estimated using the published USGS regional regression equations for rural areas in Georgia (Stamey and Hess, 1993). Regression equations estimate the peak discharges for unguaged streams based on characteristics of nearby gauged streams. Drainage areas were developed from the USGS 30-meter Digital Elevation Models (DEMs). Peak discharge-drainage area relationships for each flooding source studied in detail are presented in Table 2. 8

13 Table 2 - Summary of Discharges Peak Discharges (cubic feet per second) Flooding Source and Location Drainage Area (square miles) 10-Percent- Annual-Chance 2-Percent- Annual-Chance 1-Percent- Annual-Chance 0.2-Percent- Annual-Chance CHANNEL A At Alabama Drive At Lake Drive CHANNEL A-1 At approximately 600 feet ,163 1,686 2,025 3,002 upstream of U.S. Highway 319 / State Highway 35 At Ferry Lakes Road ,079 1,570 1,913 2,916 At Old Ocilla Road ,108 1,502 2,306 At confluence of Channel ,066 1,455 2,235 A-2 At East Twenty-Eighth Street ,133 CHANNEL A-2 At confluence with Channel A ,222 CHANNEL B At confluence with Little ,504 2,122 2,518 3,364 River At U.S. Highway ,074 1,498 1,766 2,337 Approximately 300 feet downstream of Interstate Highway ,054 1,352 CHANNEL B-1 At West Second Street At West Fourth Street CHANNEL C At South College Avenue At West Seventh Street CHANNEL D At East Thirteenth Street CHANNEL D-1 At Main Street CHANNEL E At confluence with New ,296 River At West Twenty-Fourth ,012 Street At Wilson Avenue CHANNEL E-1 At West Twenty-Sixth Street CHANNEL G At Belmont Avenue ,090 1,420 At Prince Avenue ,280 At North Tift Avenue ,100 9

14 Table 2 - Summary of Discharges (Continued) Peak Discharges (cubic feet per second) Flooding Source and Location Drainage Area (square miles) 10-Percent- Annual-Chance 2-Percent- Annual-Chance 1-Percent- Annual-Chance 0.2-Percent- Annual-Chance GUM CREEK At Tifton El Dorado Road ,100 1,770 2,120 2,990 At State Highway At Vernon Drive At Railroad LITTLE RIVER At U.S. Highway 82 West ,490 5,530 5,530 9,100 NEW RIVER At Railroad ,329 4,745 5,656 7,606 At approximately 600 feet ,199 4,552 5,422 7,285 downstream of U.S. Highway 82 At West Old Brookfield ,136 4,463 5,315 7,142 Road At approximately 700 feet ,082 2,933 3,475 4,631 upstream of U.S. Highway 319 At approximately 400 feet ,013 2,838 3,364 4,482 downstream of Ferry Lake Road At Tyson Avenue ,636 2,305 2,733 3,640 At Old Ocilla Road ,480 2,092 2,483 3,314 At Tift Avenue North ,138 1,609 1,909 2,548 At approximately 200 feet downstream of North Central Avenue ,064 1, 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. Users should be aware that flood elevations shown on the FIRM represent rounded whole-foot elevations and may not exactly reflect the elevations shown on the Flood Profiles or in the Floodway Data Table in the FIS report. 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. Precountywide Analyses For Channels A, B-1, C, D, D-1, Gum Creek, Little River, and New River, cross sections were obtained from field and aerial surveys (USACE, 1980). Water-surface elevations (WSELs) of floods of the selected recurrence intervals were computed using the USACE HEC-2 step-backwater computer program (HEC, 1991). 10

15 Starting WSELs were determined using the slope-area method. August 17, 1998 Initial Countywide Analyses For Channels A-1, A-2, B, E, E-1, and G, and the New River, cross sections were obtained from aerial photography (Hoffman & Co., Inc., undated). WSELs of floods of the selected recurrence intervals were computed using the USACE HEC-2 step-backwater computer program (HEC, 1991). Starting WSELs were determined using the slope-area method. Large portions of both Channel E and Channel E-1 include an underground storm water pipe system. The surcharged capacity of these pipes was evaluated using the HYDRAIN pipe analyzing program (GKY and Associates, Inc., 1993). The pipe system capacity was subtracted from the total flow estimated by the HEC-1 hydrologic analysis, and the remaining flow was routed over the surface using the HEC-2 program to determine the limits of the floodplains for the streams. Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles (Exhibit 1). For stream segments for which a floodway was computed (Section 4.2), selected cross section locations are also shown on the FIRM (Exhibit 2). This Countywide Revision For this countywide revision, cross section data for the streams newly studied by approximate methods was obtained from the USGS 10-meter DEMs. Hydraulically significant roads were modeled as bridges, with opening data gathered from available inventory data or approximated from the imagery. Top of road elevations were estimated from the best available topography. The studied streams were modeled using the computer program, HEC-RAS, version (HEC, 2008). Channel roughness factors (Mannings n ) used in the hydraulic computations were chosen by field survey. The Manning s n values for all detailed studied streams are listed in the following table: Manning's "n" Values Stream Channel n Overbank n Channel A Channel A Channel A Channel B Channel B

16 Manning's "n" Values (Continued) Stream Channel n Overbank n Channel C Channel D Channel D Channel E Channel E Channel G Gum Creek Little River New River Vertical Datum 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 in use for newly created or revised FIS reports and FIRMs was NGVD. With the finalization of NAVD, many FIS reports and FIRMs are being prepared using NAVD as the referenced vertical datum. All flood elevations shown in this FIS report and on the FIRM are referenced to NAVD. Structure and ground elevations in the community must, therefore, be referenced to NAVD. It is important to note that adjacent communities may be referenced to NGVD. This may result in differences in Base Flood Elevations (BFEs) across the corporate limits between the communities. Some of the data used in this study were taken from the prior effective FIS reports and adjusted to NAVD. The average conversion factor that was used to convert the data in this FIS report to NAVD was calculated using the National Geodetic Survey s (NGS) VERTCON online utility (NGS, 2009). The data points used to determine the conversion are listed in Table 3. Table 3 - Vertical Datum Conversion Conversion from Quad Name Corner Latitude Longitude NGVD to NAVD Ashburn SE Bethel SE Sumner SE Chula SE Waterloo SE Ty Ty SE Tifton West SE Tifton East SE Average:

17 For additional information regarding conversion between NGVD and NAVD, visit the NGS website at or contact the NGS at the following address: Vertical Network Branch, N/CG13 National Geodetic Survey, NOAA Silver Spring Metro Center East-West Highway Silver Spring, Maryland (301) 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 Technical Support Data Notebook associated with the FIS report and FIRM for this community. Interested individuals may contact FEMA to access these data. To obtain current elevation, description, and/or location information for benchmarks shown on this map, please contact the Information Services Branch of the NGS at (301) , or visit their website at FLOODPLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local governments to adopt sound floodplain management programs. Therefore, each FIS provides 1-percent-annual-chance (100- year) flood elevations and delineations of the 1- and 0.2-percent-annual-chance (500- year) floodplain boundaries and 1-percent-annual-chance floodway to assist communities in developing floodplain management measures. This information is presented on the FIRM and in many components of the FIS report, including Flood Profiles, Floodway Data Table, and Summary of Stillwater Elevations Table. Users should reference the data presented in the FIS report as well as additional information that may be available at the local map repository before making flood elevation and/or floodplain boundary determinations. 4.1 Floodplain Boundaries To provide a national standard without regional discrimination, the 1-percentannual-chance flood has been adopted by FEMA as the base flood for floodplain management purposes. The 0.2-percent-annual-chance flood is employed to indicate additional areas of flood risk in the community. For all streams studied by detailed methods, the 1- and 0.2-percent-annualchance floodplain boundaries have been delineated using the flood elevations determined at each cross section. Between cross sections, the boundaries were interpolated using topographic maps at a scale of 1:100, with a contour interval of two feet (Mark Hurd Aerial Surveys, Inc., 2003). 13

18 For all streams studied by approximate methods except, Arnold Creek, Channel A-1, Channel A-2, Channel C, Cow House Branch, Little Creek, Little River, Little River Tributary 13, Little River Tributary 18, Little River Tributary 20, New River, and New River Tributary 8, between modeled cross sections, the boundaries were delineated using the USGS 10-meter DEMs (USGS, 2009). For Arnold Creek, Channel A-1, Channel A-2, Channel C, Cow House Branch, Little Creek, Little River, Little River Tributary 13, Little River Tributary 18, Little River Tributary 20, New River, and New River Tributary 8, between modeled cross sections, the boundaries were interpolated using topographic maps at a scale of 1:100, with a contour interval of two feet (Mark Hurd Aerial Surveys, Inc., 2003). The 1- and 0.2-percent-annual-chance floodplain boundaries are shown on the FIRM (Exhibit 2). On this map, the 1-percent-annual-chance floodplain boundary corresponds to the boundary of the areas of special flood hazards (Zones A and AE), and the 0.2-percent-annual-chance floodplain boundary corresponds to the boundary of areas of moderate flood hazards. In cases where the 1- and 0.2-percent-annual-chance floodplain boundaries are close together, only the 1-percent-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. For the streams studied by approximate methods, only the 1-percent-annualchance floodplain boundary is shown on the FIRM (Exhibit 2). 4.2 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 this aspect of floodplain management. Under this concept, the area of the 1-percent-annual-chance floodplain is divided into a floodway and a floodway fringe. The floodway is the channel of a stream, plus any adjacent floodplain areas, that must be kept free of encroachment so that the 1-percent-annual-chance flood can be carried without substantial increases in flood heights. Minimum Federal standards limit such increases to 1 foot, provided that hazardous velocities are not produced. The floodways in this study are presented to local agencies as minimum standards that can be adopted directly or that can be used as a basis for additional floodway studies. The floodways presented in this FIS report and on the FIRM were computed for certain stream segments on the basis of equal-conveyance reduction from each 14

19 side of the floodplain. Floodway widths were computed at cross sections. Between cross sections, the floodway boundaries were interpolated. The results of the floodway computations have been tabulated for selected cross sections (Table 4). In cases where the floodway and 1-percent-annual-chance floodplain boundaries are either close together or collinear, only the floodway boundary has been shown. The area between the floodway and 1-percent-annual-chance floodplain boundaries is termed the floodway fringe. The floodway fringe encompasses the portion of the floodplain that could be completely obstructed without increasing the water surface elevation of the 1-percent-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 1. Figure 1 - Floodway Schematic 15

20 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) CHANNEL A SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) A B C 1, D 2, Feet above Limit of Detailed Study (Approximately 790 feet downstream of Interstate Highway 75) TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA CHANNEL A

21 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) CHANNEL A-1 SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) A 3, , B 5, , C 6, D 7, , E 8, , F 10, G 11, , H 11, , I 12, , J 14, K 15, , L 16, M 16, , N 17, , O 19, , P 19, Q 20, Feet above confluence with New River TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA CHANNEL A-1

22 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) CHANNEL A-2 SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) A B 1, C 2, D 3, E 5, F 5, Feet above confluence with Channel A-1 TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA CHANNEL A-2

23 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) CHANNEL B SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) A 2, , B 2, , C 3, , D 5, , E 6, , F 8, , G 10, , H 10, , I 12, J 13, K 13, L 15, M 16, , N 16, O 17, P 18, Q 18, R 19, S 19, T 19, Feet above confluence with Little River TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA CHANNEL B

24 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) CHANNEL B-1 A B 1, C 1, Feet above confluence with Channel B TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA CHANNEL B-1

25 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) CHANNEL C A 3, B 5, C 5, D 6, E 7, Feet above confluence with Channel D TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA CHANNEL C

26 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) CHANNEL D A 4, B 4, C 5, Feet above Interstate Highway 75 TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA CHANNEL D

27 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) CHANNEL D-1 A 1, , B 1, , C 2, , Feet above Limit of Detailed Study (Limit of Detailed Study is approximately 800 feet downstream of Railroad) TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA CHANNEL D-1

28 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) CHANNEL E SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) A , B C 1, D 1, E 2, F 2, G 3, H 4, I 4, J 4, K 6, L 7, M 7, N 8, Feet above confluence with New River TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA CHANNEL E

29 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) CHANNEL E-1 A B C 1, D 2, E 2, Feet above confluence with Channel E TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA CHANNEL E-1

30 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) CHANNEL G A 2, B 3, C 3, D 4, E 4, F 5, G 5, H 5, Feet above confluence with New River TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA CHANNEL G

31 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) GUM CREEK SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) A 2, , B 5, , C 6, , D 8, , E 8, , F 9, , G 10, , H 11, , I 12, , J 13, , K 14, L 15, M 17, N 18, O 19, P 20, Q 20, R 21, S 21, Feet above Parker Road TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA GUM CREEK

32 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) LITTLE RIVER SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) A 1,320 1,328 7, B 4,330 1,084 7, C 7, , D 11,194 1,558 9, E 14,573 1,157 7, F 17,635 1,760 13, G 21,912 1,371 6, H 23,813 1,374 8, I 25,714 1,653 10, J 30,786 1,282 10, K 33, , L 36,115 1,119 9, M 39, , Feet above U.S. Highway 319 / State Highway 35 TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA LITTLE RIVER

33 FLOODING SOURCE CROSS SECTION DISTANCE 1 WIDTH (FEET) NEW RIVER SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION WITHOUT WITH INCREASE (FEET) A 9, , B 11, , C 16, , D 17, , E 19, , F 24, G 26, , H 26, , I 26, J 27, , K 28, L 29, , M 31, N 32, O 32, P 33, Q 34, R 35, S 36, T 36, Feet above Lower Brookfield Road TABLE 4 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS DATA NEW RIVER

34 5.0 INSURANCE APPLICATIONS For flood insurance rating purposes, flood insurance zone designations are assigned to a community based on the results of the engineering analyses. These zones are as follows: Zone A Zone A is the flood insurance risk zone that corresponds to the 1-percent-annual-chance floodplains that are determined in the FIS by approximate methods. Because detailed hydraulic analyses are not performed for such areas, no BFEs or base flood depths are shown within this zone. Zone AE Zone AE is the flood insurance risk zone that corresponds to the 1-percent-annual-chance floodplains that are determined in the FIS by detailed methods. In most instances, wholefoot BFEs derived from the detailed hydraulic analyses are shown at selected intervals within this zone. Zone X Zone X is the flood insurance risk zone that corresponds to areas outside the 0.2-percentannual-chance floodplain, areas within the 0.2-percent-annual-chance floodplain, areas of 1-percent-annual-chance flooding where average depths are less than 1 foot, areas of 1- percent-annual-chance flooding where the contributing drainage area is less than 1 square mile, and areas protected from the 1-percent-annual-chance flood by levees. No BFEs or base flood depths are shown within this zone. 6.0 FLOOD INSURANCE RATE MAP The FIRM is designed for flood insurance and floodplain management applications. For flood insurance applications, the map designates flood insurance risk zones as described in Section 5.0 and, in the 1-percent-annual-chance floodplains that were studied by detailed methods, shows selected whole-foot BFEs or average depths. Insurance agents use the zones and BFEs in conjunction with information on structures and their contents to assign premium rates for flood insurance policies. For floodplain management applications, the map shows by tints, screens, and symbols, the 1- and 0.2-percent-annual-chance floodplains, floodways, and the locations of selected cross sections used in the hydraulic analyses and floodway computations. The countywide FIRM presents flooding information for the entire geographic area of Tift County. Previously, FIRMs were prepared for each incorporated community and the 30

35 unincorporated areas of the County identified as flood-prone. Historical data relating to the maps prepared for each community are presented in Table OTHER STUDIES This report either supersedes or is compatible with all previous studies on streams studied in this report and should be considered authoritative for purposes of the NFIP. 8.0 LOCATION OF DATA Information concerning the pertinent data used in the preparation of this study can be obtained by contacting FEMA, Federal Insurance and Mitigation Division, Koger Center Rutgers Building, 3003 Chamblee Tucker Road, Atlanta, Georgia BIBLIOGRAPHY AND REFERENCES Federal Emergency Management Agency, Flood Insurance Study, Tift County, Georgia (Unincorporated Areas), Flood Insurance Study Report, December 1, 1981; Flood Insurance Rate Map, June 1, Federal Emergency Management Agency, Flood Insurance Study, Tift County, Georgia and Incorporated Areas, August 17, Federal Insurance Administration, Flood Insurance Study, City of Tifton, Tifton County, Georgia, December 3, Georgia Department of Transportation, Manual on Drainage Design for Highways, Chapter 5, Charts 5-28, Georgia Emergency Management Agency, Georgia Disaster History. Retrieved April 16, 2009, from GKY and Associates, Inc., HYDRAIN Integrated Drainage Design Computer System, Version 4.1, Springfield, Virginia, April Hoffman & Co., Inc., Aerial Photography, Atlanta, Georgia, undated. Hydrologic Engineering Center, HEC-1 Flood Hydrograph Package, U.S. Army Corps of Engineers, Davis, California, September Hydrologic Engineering Center, HEC-2 Water Surface Profiles, U.S. Army Corps of Engineers, Davis, California, May Hydrologic Engineering Center, HEC-RAS River Analysis System, Version 4.0, U.S. Army Corps of Engineers, Davis, California, March

36 Table 5 - Community Map History COMMUNITY NAME INITIAL IDENTIFICATION FLOOD HAZARD BOUNDARY MAP REVISION DATE FIRM EFFECTIVE DATE FIRM REVISION DATE Omega, City of September 29, 2010 None September 29, 2010 None Tift County (Unincorporated Areas) February 17, 1978 None June 1, 1982 None Tifton, City of January 17, 1975 July 9, 1976 May 1, 1978 December 3, 1982 Ty Ty, City of August 22, 1975 None September 4, 1985 None TABLE 5 FEDERAL EMERGENCY MANAGEMENT AGENCY TIFT COUNTY, GA AND INCORPORATED AREAS COMMUNITY MAP HISTORY

37 Mark Hurd Aerial Surveys, Inc., Aerial Photography & Contour Mapping, Approximate Photo Scale, 1:100, Contour Interval 2 Feet; Tifton, Georgia, National Geodetic Survey, VERTCON-North American Vertical Datum Conversion Utility. Retrieved April 3, 2009, from National Weather Service, Rainfall Frequency Atlas of the United States, 30-Minute to 24-Hour Durations, 1- to 100-Year Return Periods, Technical Paper 40, U.S. Department of Commerce, Resources Analysis, Inc., MITCAT Computer Program, Waltham, Massachusetts, July Soil Conservation Service, National Engineering Handbook, Section 4, Hydrology, U.S. Department of Agriculture, 1964, revised Soil Conservation Service, Gage Records, New River, Old Ocilla Road Bridge, U.S. Department of Agriculture, Stamey, T.C. and C. W. Hess, Techniques for Estimating Magnitude and Frequency of Floods in Rural Basins of Georgia, USGS Water Resources Investigation Report , The Weather Channel, Monthly Averages for Tifton, Georgia. Retrieved on March 13, 2009, from TRACOR, Inc., The Effects of Urbanization on Unit Hydrographs for Small Watersheds, Houston, Texas, , Austin, Texas, September 25, U.S. Army Corps of Engineers, Jacksonville District, Stream Cross Sections, Continental Aerial Surveys, Alcoa, Tennessee. Aerial Photography flown on January 24, U.S. Census Bureau, American Fact Finder, Tift County, Georgia, Retrieved March 13, 2009, from U.S. Geological Survey, Preliminary Flood Frequency Relations for Small Streams in Georgia, U.S. Geological Survey, Floods in Georgia, Magnitudes and Frequency, October U.S. Geological Survey, Seamless Data Distribution System 10-meter Digital Elevation Model. Downloaded March 2009, from 33