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FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED AREAS) ROME, CITY OF 130081 Revised: September 25, 2009 FLOOD INSURANCE STUDY NUMBER 13115CV000A

FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

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Page 1: FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED AREAS) ROME, CITY OF 130081

Revised: September 25, 2009

FLOOD INSURANCE STUDY NUMBER 13115CV000A

Page 2: FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

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 9, 2000 Revised Countywide Dates: September 25, 2009

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TABLE OF CONTENTS

1.0 INTRODUCTION ...................................................................................................................1

1.1 Purpose of Study................................................................................................................1

1.2 Authority and Acknowledgments ......................................................................................1

1.3 Coordination ......................................................................................................................3

2.0 AREA STUDIED .....................................................................................................................4

2.1 Scope of Study ...................................................................................................................4

2.2 Community Description.....................................................................................................7

2.3 Principal Flood Problems...................................................................................................8

2.4 Flood Protection Measures ................................................................................................9

3.0 ENGINEERING METHODS ...............................................................................................10

3.1 Hydrologic Analyses........................................................................................................10

3.2 Hydraulic Analyses..........................................................................................................17

3.3 Vertical Datum.................................................................................................................19

4.0 FLOODPLAIN MANAGEMENT APPLICATIONS ........................................................20

4.1 Floodplain Boundaries .....................................................................................................21

4.2 Floodways........................................................................................................................22

5.0 INSURANCE APPLICATIONS ..........................................................................................40

6.0 FLOOD INSURANCE RATE MAP ....................................................................................41

7.0 OTHER STUDIES .................................................................................................................41

8.0 LOCATION OF DATA.........................................................................................................43

9.0 BIBLIOGRAPHY AND REFERENCES ............................................................................43

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TABLE OF CONTENTS (Continued)

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FIGURES

Figure 1 – Floodway Schematic ....................................................................................................... 40

TABLES

Table 1 – Redelineated Streams.......................................................................................................... 5 Table 2 – Streams Studied by Limited Detailed Methods .................................................................. 6 Table 3 – Streams Studied by Detailed Methods................................................................................ 7 Table 4 – Summary of Discharges.................................................................................................... 13 Table 5 – Vertical Datum Conversion .............................................................................................. 19 Table 6 – Floodway Data.................................................................................................................. 23 Table 7 – Community Map History.................................................................................................. 42

EXHIBITS

Exhibit 1 - Flood Profiles Armuchee Creek Panels 01P-02P Big Dry Creek Panels 03P-04P Big Dry Creek Tributary 1 Panels 05P-07P Big Dry Creek Tributary 2 Panel 08P Booze Creek Panels 09P-10P Burwell Creek Panel 11P Coosa River Panels 12P-13P Dykes Creek Panels 14P-16P Etowah River Panels 17P-22P Horseleg Creek Panels 23P-25P Little Armuchee Creek Panels 26P-27P Little Cedar Creek Panels 28P-29P Little Dry Creek Panels 30P-33P Mill Race Creek Panel 34P Oostanaula River Panels 35P-36P Prentis Branch Panel 37P Silver Creek Panels 38P-41P South Fork Horseleg Creek Panel 42P South Fork Little Dry Creek Panels 43P-44P Tributary A Panel 45P Unnamed Tributary to Silver Creek Panel 46P Exhibit 2 - Flood Insurance Rate Map Index

Flood Insurance Rate Map

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FLOOD INSURANCE STUDY FLOYD 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 Floyd County, including the Cities of Cave Spring and Rome; and the unincorporated areas of Floyd County (referred to collectively herein as Floyd County), and aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. 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, 60.3. In some states or communities, floodplain management criteria or regulations may exist that are more restrictive or comprehensive than the minimum Federal requirements. In such cases, the more restrictive criteria take precedence and the State (or other jurisdictional agency) will be able to explain them. 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 1973. Information on the authority and acknowledgements for each jurisdiction included in this countywide FIS report, as compiled from their previously printed FIS reports, is shown below.

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Cave Spring, City of: The hydrologic and hydraulic analyses for the original February 5, 1985, FIS report, and the May 1, 1985, Flood Insurance Rate Map (FIRM) (hereinafter referred to as the 1985 FIS report) (Reference 1), were performed by the U.S. Army Corps of Engineers (USACE), Mobile District, for FEMA, under Inter-Agency Agreement No. EMW-E-1153, Project Order No. 1. The study was completed in January 1984.

Floyd County (Unincorporated Areas):

The hydrologic and hydraulic analyses for the original May 19, 1987, FIS (Reference 2) were performed by the USACE, Mobile District, for FEMA, under Inter-Agency Agreement No. EMW-E-1153, Project Order No. 1. The study was completed in January 1985.

Rome, City of:

The hydrologic and hydraulic analyses for the original March 15, 1978, FIS report, and September 15, 1978, FIRM (hereinafter referred to as the 1978 FIS report) (Reference 3) were performed by the USACE, Mobile District, for the Federal Insurance Administration, under Inter-Agency Agreement No. IAA-H-1-75. The work, which was completed in October 1976, covered all significant flooding sources affecting the City of Rome. For the November 4, 1998, FIS report (Reference 4), the hydraulic analyses were prepared by the USACE, Atlanta District. FEMA reviewed and accepted the data for the purposes of the revision.

For the initial countywide FIS report (Reference 5), the hydrologic and hydraulic analyses for Little Dry Creek were prepared by the USACE, for FEMA, under Inter-Agency Agreement No. EMW-E-1153, Project Order No. 1. The work was completed in 1995. The hydraulic analyses for the Coosa and Etowah Rivers were prepared by Braswell Engineering, for FEMA, under Contract No. EMW-96-00-021. The work was completed in November 1997. The hydrologic and hydraulic analyses for portions of Horseleg Creek and South Fork Horseleg Creek within the unincorporated areas of Floyd County were prepared by the

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USACE, Mobile District, and taken from the FIS for the City of Rome (Reference 4). For this countywide revision, the analyses for the streams studied by limited detailed methods and the work done for the streams redelineated based on new topography in this FIS report were performed by PBS&J, for the Georgia Department of Natural Resources (DNR), under Contract No. EMA-2003-GR-569 with FEMA. The work was completed in April 2005. Also for this countywide revision, the analyses for Big Dry Creek and Tributaries 1 and 2 were provided by the USACE, Mobile District. The analyses were prepared in response to a request from Floyd County and under the authority provided in Section 206 of the 1960 Flood Control Act, as amended. The work was completed in September 1998 (Reference 6).

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. The initial and final meeting dates for the previous FIS reports for Floyd County and its communities are listed in the following table:

Community FIS Date Initial Meeting Final Meeting

Cave Spring, City of February 5, 1985 April 14, 1993 September 27, 1984 Floyd County

(Unincorporated Areas)

May 19, 1987 N/A July 8, 1986

Rome, City of March 15, 1978 January 22, 1975 October 12, 1976 These meetings were attended by representatives of the communities, FEMA, the USACE, and Georgia DNR. The City of Rome meetings were also attended by representatives of the Coosa Valley Area Planning and Development Commission. For the initial countywide FIS report dated August 9, 2000, the Cities of Cave Spring and Rome, and Floyd County were notified by a letter on August 21, 1998, that their FIS reports and FIRMs would be revised into a countywide format. For this countywide revision, a scoping meeting was held on September 21, 2004, and attended by representatives of Floyd County, the Cities of Cave Spring and Rome, the Georgia DNR, FEMA, Black and Veatch, and PBS&J.

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For this countywide revision, a final meeting was held on September 20, 2005, and attended by representatives from FEMA, the Georgia DNR, PBS&J, and the communities.

2.0 AREA STUDIED

2.1 Scope of Study

This FIS report covers the geographic area of Floyd 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 at the time of the study. The following streams are studied by detailed methods: Armuchee Creek, Big Dry Creek, Big Dry Creek Tributary 1, Big Dry Creek Tributary 2, Booze Creek, Burwell Creek, Coosa River, Dykes Creek, Etowah River, Horseleg Creek, Little Armuchee Creek, Little Cedar Creek, Little Dry Creek, Mill Race Creek, Oostanaula River, Prentis Branch, Silver Creek, South Fork Horseleg Creek, South Fork Little Dry Creek, Tributary A, and Unnamed Tributary to Silver Creek. The limits of detailed study are indicated on the Flood Profiles (Exhibit 1) and on the FIRM (Exhibit 2). Letters of Map Revision dated March 2, 1994, and November 21, 1997, both for Little Dry Creek in the City of Rome, were incorporated into the initial countywide FIS report and FIRM. 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 upon by FEMA and Floyd County. For this countywide revision, reaches of streams that have been studied by detailed methods were selected for redelineation based on more recent topography. Floyd County and the City of Rome provided digital topography for the entire county. This data has a 2-foot contour interval for areas within the City of Rome and a 5-foot contour interval for areas outside the City of Rome (Reference 7). Only stream reaches that had 2-foot contours available were candidates for redelineation. The streams reaches redelineated are listed in Table 1.

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Table 1 – Redelineated Streams

Stream Reach Description

Burwell Creek From the confluence with Oostanaula River to approximately 1,585 feet upstream of Norfolk Southern Railway

Coosa River From approximately 23,000 feet upstream of the confluence of Webb Creek to the confluence of Etowah and Oostanaula Rivers

Etowah River From the confluence with Coosa River and Oostanaula River to approximately 200 feet upstream of East Rome Bypass / State Highway 1L

Horseleg Creek From the confluence with Coosa River to Billy Pyle Road

Little Dry Creek From the confluence with Oostanaula River to Redmond Gap Road

Oostanaula River From the confluence with Coosa River and Etowah River to approximately 3,000 feet upstream of the confluence of Big Dry Creek

Silver Creek From the confluence with Etowah River to approximately 5,935 feet upstream of Old Rockmart Road

South Fork Horseleg Creek From the confluence with Horseleg Creek to approximately 50 feet upstream of Hearthwood Drive

Tributary A From the confluence with Etowah River to approximately 550 feet upstream of Valley Brook Drive

Unnamed Tributary to Silver Creek From the confluence with Silver Creek to approximately 550 feet upstream of Norfolk Southern Railway

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The areas studied by limited detailed methods were selected with priority given to all known flood hazards and areas of projected development or proposed construction. The streams studied by limited detailed methods are listed in Table 2.

Table 2 – Streams Studied by Limited Detailed Methods

Stream Reach Description

Big Cedar Creek From approximately 4, 445 feet

downstream of Fosters Mill Road / State Highway 100 to approximately 5,270 feet upstream of Spout Springs Road Southwest

Big Dry Creek From approximately 11,270 feet upstream of the confluence with the Oostanaula River to approximately 34,200 feet upstream of the confluence with the Oostanaula River

Johns Creek From approximately 950 feet upstream of the confluence with Oostanaula River to approximately 1,010 feet upstream of State Highway 156 / New Rosedale Road Northeast

Zuber Creek From approximately 130 feet upstream of the confluence with Dozier Creek to approximately 150 feet upstream of Calhoun Road Northeast

Zuber Creek Tributary 1 From the confluence with Zuber Creek to approximately 180 feet upstream of Camp Street

The analyses for Big Dry Creek and Tributaries cover approximately 5.6 miles within Floyd County. The topographic mapping was developed from aerial photographs taken in January 1998 at a scale of 1:6,000 and a contour interval of 5 feet (Reference 6). Table 3 lists the extents of the new detailed studies.

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Table 3 – Streams Studied by Detailed Methods

Stream Reach Description

Big Dry Creek From the confluence with Oostanaula River to the confluence of Big Dry Creek Tributary 1

Big Dry Creek Tributary 1 From the confluence with Big Dry Creek to approximately 2,450 feet upstream of CCC Road Northwest

Big Dry Creek Tributary 2 From the confluence with Big Dry Creek Tributary 1 to approximately 130 feet upstream of Lindsey Road Northwest

2.2 Community Description Floyd County, located in northwestern Georgia, is bordered by Chattooga County on the northwest, Gordon County on the northeast, Bartow County on the east, Polk County on the south, and Cherokee County, Alabama, on the west. The population of Floyd County according to the 2000 U.S. Census was 90,565 (Reference 8). The county’s two incorporated communities are the City of Cave Spring, located in the southwestern portion of the county, and the City of Rome, which is located in the south-central portion of the county. Floyd County has three major rivers: the Oostanaula, Etowah, and Coosa Rivers. The headwaters of the Oostanaula and Etowah Rivers originate in the mountains of north-central Georgia. The rivers generally flow southwesterly toward the City of Rome where they join to form the Coosa River. The Coosa River then flows westerly toward the Alabama River. Dykes, Little Cedar, Silver, Booze, Armuchee, Little Armuchee, and Little Cedar Creek are major tributaries to these rivers. Little Cedar Creek, from its headwaters on the northeastern slopes of Indian Mountain in Polk County, Georgia, flows 12 miles in a northerly direction through Cave Spring to join Big Cedar Creek, a tributary of the Coosa River, about 2.5 miles north of the city. The 23-square-mile watershed of Little Cedar Creek is approximately 9 miles long and has a maximum width of 4 miles. The channel banks of the creek are generally 4 to 8 feet in height and vary in width from 20 to 80 feet. The channel has an average slope of about 14 feet per mile. The climate of Floyd County consists of warm, humid summers, mild winters, and abundant rainfall. Summer temperatures average 84 degrees Fahrenheit (ºF)

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and winter temperatures average 55°F. On average, July is the warmest month with the highest mean monthly temperature of 78°F, while January is the coolest month with the lowest mean monthly temperature of 39°F (Reference 9). The average annual precipitation in Floyd County is 56 inches. The wettest month is March with an average of 6.67 inches of precipitation while October is the driest with 3.40 inches (Reference 9).

2.3 Principal Flood Problems

The headwaters of the Oostanaula and Etowah Rivers are in the mountains of north-central Georgia. These streams flow from the mountains into the wide valleys of the Valley and Ridge physiographic province. The two rivers join at Rome to form the Coosa River, which flows west into the Alabama River. The physical characteristics of the basin are favorable to the production of high rates of runoff. The speed with which runoff concentrates in the main channel of the Etowah River is illustrated by the major flood of April 1938 and several minor floods in 1939, in which stages at Canton and Kingston, east of Rome, began to rise 3 hours after the beginning of the intense rainfall and peaked 9 to 12 hours after its end (Reference 10). The gradient of the Oostanaula River is not as steep as the Etowah River; therefore, the peak discharges at Rome from the Etowah River usually precede those from the Oostanaula River. This interval between peak flows tends to prolong the duration of floods. Floods usually occur in winter and spring due to frontal system movements; prior to construction of Allatoona Lake Dam, the frequency was an average of one flood per year. The largest flood on record was in 1886, when the Oostanaula River reached a level of 40.4 feet North American Vertical Datum of 1988 (NAVD88). Some of the most damaging floods occurred in 1892, 1916, 1919, 1921, 1932, 1936, 1938, 1946, 1947, and 1972. Recurrence intervals cannot be estimated for these floods because flood control projects have changed the flood characteristics of the area (Reference 11). Relatively minor floods occur frequently in Rome, usually in the late spring and summer as a result of thunderstorms. These floods usually result in flooded streets with little property damage. The most recent flood occurred on April 1, 1976, when the river reached a crest of 28 feet. The physical characteristics of the Little Cedar Creek basin promote high rates of storm runoff, which can occur with little or no warning as heavy rainstorms move over the basin. Over the years, runoff has gradually increased as a result of periodic commercial and residential developments and clearing to expand

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agricultural production. This is a typical problem in all drainage basins with any increase in population or economic growth. Floods have occurred on Little Cedar Creek; the creek overflows its banks on average of twice a year. The highest floods of record occurred in 1951, 1977, and 1980 and caused considerable flood damages.

2.4 Flood Protection Measures

No significant structural flood protection measures exist in the City of Cave Spring. However, the city carefully maintains the channels and bridge openings to avoid debris buildup, siltation, or other restrictions to the normal flow patterns of the creek. For the City of Rome, following the floods of 1886 and the early 1900s, local merchants began taking the first measures in preventing flood damage by raising portions of Broad Street as high as 15 feet. Allatoona Lake Dam is located on the Etowah River, approximately 48 miles upstream of Rome. Congress authorized construction of Allatoona Dam in August 1941, but construction did not begin until February 1946. The flood control operation of the dam, which began in December 1949, has prevented major damage to the city since that time. In addition, the flood control operation of Carters Dam, combined with Allatoona Dam in a system operation, will further reduce the probability of major flood damage in the vicinity of Rome. Carters Dam is located approximately 75 miles upstream of Rome on the Coosawattee River, a tributary of the Oostanaula River. After three floods in December 1932 and four floods within three months during 1936, Congress appropriated $330,000 for a 2-mile levee to be constructed on the north side of the Oostanaula and Coosa Rivers. The project consists of a system of earthen levees west of Wilson Avenue. The structures are located in areas from the confluence of the Oostanaula River and the Etowah River to a point approximately 2.3 miles downstream, along the left bank of the Coosa River (Reference 12). This levee was completed in 1939 and in the past protected the fourth ward area of Rome from flooding caused by the Coosa River. Levees exist in the study area that provide the county with some degree of protection against flooding. However, it has been ascertained that some of these levees may not protect the community from rare events such as the 1-percent-annual-chance flood. The criteria used to evaluate protection against the 1-percent-annual-chance flood are 1) adequate design, including freeboard, 2) structural stability, and 3) proper operation and maintenance. Levees that do not

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protect against the 1-pecent-annual-chance flood are not considered in the hydraulic analysis of the 1-percent-annual-chance floodplain. The South Rome Levee System has been certified to provide protection against the 1-percent-annual-chance flood. Areas behind the levee system have two ponding areas with pumping stations to control flooding resulting from interior drainage.

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, 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

Each jurisdiction within Floyd County has a previously printed FIS report narrative. The hydrologic analyses described in those reports have been compiled and are summarized below. The streams in Floyd County vary from large main stem streams, which are regulated by upstream multi-purpose dams, to small tributary streams with no available gage data. Therefore, the discharge frequencies were computed on a case-by-case basis with the method of selection dependent on available data.

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Data from available studies were used to determine discharge frequencies on the three main rivers. Discharge frequencies on the Oostanaula and the Etowah Rivers were based on a study made to analyze the effects of the operation of the Allatoona Lake and Carters Dams (Reference 13). A study titled, Montgomery to Gadsden Coosa River Channel was used to compute discharge frequencies for the tributaries (Reference 14). The equations used were from Flood Frequency Analysis for Small Streams in Georgia, (Reference 15). The Sauer Method was used to estimate the effect of urbanization on Little Dry Creek. Discharge frequencies on the Oostanaula River were obtained by prorating between the Rome and Resaca discharge-frequency curves, which had been adjusted for the flood control effects from Carters Dam (Reference 13). Since flows attenuate from Resaca to Rome, the prorations between the gages were patterned after flows from the runoff model described in the Allatoona Lake Dam study (Reference 13). Discharge frequencies on the Etowah River were obtained by prorating between the Rome and Kingston frequency curves, which had been adjusted for the flood control effect from Allatoona Lake Dam (Reference 13). The flows between the gages were prorated by the drainage area ratio since they increase in the downstream direction of this reach. The discharge-frequency curve for the Mayos Bar Gage, adjusted for regulation by the Carters and Allatoona Lake Dams, was used to obtain discharge frequencies for the Coosa River (Reference 13). Discharge-frequency information was obtained for the lower end of the study reach at State Highway 100 by applying the drainage area ration to the Mayos Bar curve. Discharges from the Mayos Bar curve were considered appropriate for use at the confluence of the Oostanaula and the Etowah Rivers and in upstream portions. The HEC-1 hydrologic computer program was used to model the Silver Creek drainage basin (Reference 16). For this analysis, the total Silver Creek basin of 40.3 square miles was divided into 14 subbasins ranging in size from 1.2 square miles to approximately 5.6 square miles. The model computes runoff from each subbasin by the U.S. Department of Agriculture, Soil Conservation Service, unit-hydrograph method (Reference 16). The discharges are routed across each succeeding basin and the discharges are combined at the lower reach of each subbasin. Discharges throughout the upper portion of the entire basin and along the entire length of the Prentis Branch were routed by the Muskingum method (Reference 16). Discharges downstream of Booze Mountain Road, on both Silver and Booze Creeks, were routed using storage values produced by a HEC-2 model of that area (Reference 17). A second discharge-frequency estimate was made using regional regression equations, since there is little historical data available to corroborate results of the HEC-1 model.

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Results of these equations were adjusted to account for urban development by the Sauer method. Discharge frequencies derived from the regional equations were used to verify the final calibration of the HEC-1 model. The HEC-1 model was then used to estimate current discharge frequencies. Rainfall volumes for the 10-, 2-, 1-, and 0.2-percent-annual-chance frequencies were taken from Technical Paper No. 40 (Reference 18). The National Weather Service (NWS), HYDRO-35 was used to compute 30-minute amounts. The regression equations for the hydrologic Region One in the report titled Flood Frequency Analysis for Small Streams in Georgia (Reference 15) were used to compute the discharge frequencies for all other ungaged tributary streams. Drainage areas required for the regression equations were measured using topographic maps and verified against points where drainage areas were available from the latest U.S. Geological Survey (USGS) drainage area study (Reference 19). The USGS areas were used where they were available. The Little Dry Creek drainage basin was the only one with significant development. The development areas were measured using the above-mentioned topographic maps and classified as to land use. The Sauer equation was then applied to determine the modified flows. Regional regression equations relating drainage area to discharge for each recurrence interval were used to determine discharges for Prentis Branch, Tributary A, Horseleg Creek, South Fork Horseleg Creek, and Burwell Creek (Reference 20). Adjustments were made for streams with developed watersheds. Because adequate stream gage data were not available for analysis in the Little Cedar Creek basin, in the City of Cave Spring, it was necessary to compute the discharge-frequency relationships from regional equations, using drainage area as the main input parameter in the City of Cave Spring. Regional equations from the Frequency Analysis for Small Natural Streams in Georgia were selected for this purpose (Reference 15). Initial Countywide FIS (August 9, 2000) For the August 9, 2000, countywide FIS report, revision, the peak flows from the November 4, 1988 FIS report for the City of Rome were used to study the Etowah and the Coosa Rivers in detail. Flow data at the USGS Etowah River gage at Rome has been regulated by storage in Allatoona Lake since December 1949. Upon the request of Water Resources and Coastal Engineering, the USGS Water Resources Division, Georgia District, performed a standard frequency analysis based on 45 years of peak flows between 1950 and 1994 at this site. A comparison of the results revealed that the peak flow estimate prepared by the USGS are nearly identical to those peak flows used in preparation of the existing FIS report. The difference, therefore, can be neglected for such large flow rates.

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The peak flows from the existing FIS report were used in the initial countywide FIS report. This Countywide Revision For this countywide revision, the discharges for Big Dry Creek, Big Dry Creek Tributary 1, and Big Dry Creek Tributary 2 were computed using regional equations published by the USGS (Reference 21). Also for this revision, for the streams studied by limited detailed methods, regression equations were used to compute the peak discharges for the 1-percent-annual-chance flood (Reference 21). Floyd County and the City of Rome provided digital topographic data, which had contour intervals of 2 and 5 feet (Reference 7). The watershed areas for the selected streams were calculated using USGS 30 meter resolution Digital Elevation Models (DEMs) gathered from the National Elevation Dataset (NED) (Reference 22). Peak discharge-drainage area relationships for the 10-, 2-, 1-, and 0.2-percent-annual-chance floods for each stream studied by detailed methods in Floyd County are shown in Table 4.

Table 4 – 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

ARMUCHEE CREEK

At confluence with Oostanaula River

226 14,500 22,100 24,300 32,700

Just upstream of the confluence of Lavender Creek

201 13,400 20,300 22,500 30,200

Just downstream of confluence of Little Armuchee Creek

196 13,100 20,000 22,100 29,700

Just upstream of the confluence of Little Armuchee Creek

113 9,000 13,700 15,200 20,500

BIG DRY CREEK

At the confluence with Oostanaula River

14.98 2,574 4,139 4,907 7,023

BIG DRY CREEK TRIBUTARY 1

At the confluence with Big Dry Creek

6.61 1,551 2,544 3,043 4,431

Just upstream of the confluence of Big Dry Creek Tributary 2

3.30 1,009 1,683 2,028 2,997

At CCC Road Northwest 2.93 938 1,568 1,892 2,802

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Table 4 – Summary of Discharges (Continued)

14

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

BIG DRY CREEK TRIBUTARY 2

At confluence with Big Dry Creek Tributary 1

2.24 794 1,336 1,618 2,409

At Selman Road Northwest 1.24 551 940 1,145 1,727 BOOZE CREEK

At confluence with Silver Creek

3.0 1,283 1,885 2,078 2,600

Just upstream of Booze Mountain Road

2.1 872 1,311 1,471 1,800

BURWELL CREEK

Just upstream of confluence with Oostanaula River

3.63 1,175 1,650 1,800 2,250

Approximately 95 feet upstream of Norfolk Southern Railway (upstream crossing)

2.19 825 1,150 1,250 1,600

COOSA RIVER

At State Highway 100 / Fosters Mill Road

* 49,800 64,100 71,200 87,400

At Mayo Bar Dam gauge 4,040 49,000 63,000 70,000 86,000 DYKES CREEK

At confluence with the Etowah River

17.5 2,490 3,790 4,290 5,770

Just downstream of State Highway 293

16.4 2,370 3,610 4,090 5,490

Just upstream of State Highway 293

15.1 2,240 3,410 3,860 5,190

Just downstream of Gentry Road

5.7 1,140 1,740 1,990 2,680

ETOWAH RIVER

At Rome Gage 1,310 25,000 35,000 40,000 52,000 At Freeman Ferry * 24,500 34,500 39,400 51,600 Just upstream of the

confluence of Dykes Creek * 24,200 34,200 39,300 51,400

Just upstream of the confluence of Spring Creek

* 22,900 32,900 38,100 50,400

Approximately 1,850 feet upstream of the confluence of Young’s Mill Creek

* 22,800 32,800 38,000 50,300

HORSELEG CREEK

Approximately 105 feet upstream of Horseleg Creek Road Southwest

6.30 1,750 2,400 2,650 3,300

*Data not available

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Table 4 – Summary of Discharges (Continued)

15

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

HORSELEG CREEK (Cont’d)

Approximately 0.5 mile downstream of Burnett Ferry Road Southwest

5.08 1,500 2,050 2,250 2,850

Approximately 105 feet upstream of Deerbrook Drive

0.66 350 482 529 674

LITTLE ARMUCHEE CREEK

At confluence with Armuchee Creek

82.6 7,230 11,000 12,300 16,500

Just upstream of the confluence of Heath Creek

58.0 5,670 8,630 9,650 13,000

LITTLE CEDAR CREEK

At Sprout Springs Road Southwest

23.2 3,011 4,587 5,174 6,956

At U.S. Highway 411 / Rome Road / State Highway 53

19.8 2,699 4,112 4,646 6,245

At State Highway 100 / Mill Street

15.2 2,249 3,426 3,881 5,218

LITTLE DRY CREEK

Just upstream of Redmond Road

5.2 1,280 1,870 2,130 2,800

Approximately 1.4 miles upstream of Redmond Road

1.4

1,040

1,530

1,740

2,290 Approximately 3.1 miles

upstream of Redmond Road

3.1

580

880

1,010

1,350 Approximately 4.0 miles

upstream of Redmond Road

4.0

360

550

640

860 MILL RACE CREEK

At confluence with Little Cedar Creek

3.4 805 1,227 1,410 1,896

OOSTANAULA RIVER

At Rome Gage 2,120 32,000 40,000 44,000 54,000 PRENTIS BRANCH

Just upstream of Norfolk Southern Railway

8.90 2,100 2,750 3,050 3,900

Just downstream of Eden Valley Road

6.76 1,700 2,300 2,600 3,200

SILVER CREEK

At confluence with the Etowah River

40.3 4,871 7,935 8,748 11,500

Just upstream of Crescent Avenue

38.9 4,828 7,884 8,691 11,000

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Table 4 – Summary of Discharges (Continued)

16

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

SILVER CREEK (Cont’d)

Just downstream of confluence of Prentis Branch

37.0 4,792 8,005 8,878 11,300

Just upstream of confluence of Prentis Branch

28.2 4,028 6,459 7,098 9,000

Just downstream of confluence of Booze Creek

26.6 4,137 6,431 7,055 9,000

Just upstream of confluence of Booze Creek

23.6 3,984 6,161 6,487 8,500

SOUTH FORK HORSELEG

CREEK

Just upstream of the confluence with Horseleg Creek

1.77 675 925 1,050 1,275

Approximately 105 feet upstream of East Creek View Drive

7.76

1,950 2,750 3,000 3,750

Approximately 50 downstream of Hearthwood Drive

5.52 1,500 2,150 2,350 2,900

SOUTH FORK LITTLE DRY

CREEK

Approximately 1,110 feet upstream of the confluence with Little Dry Creek

1.60 500 750 800 1,050

Approximately 370 feet upstream of North Division Street

1.34

450

650

725

900

TRIBUTARY A

Just downstream of Turner Chapel Road Southeast

3.49 1,025 1,400 1,650 2,000

Approximately 105 feet upstream of Valley Brook Drive

3.04 900 1,250 1,450 1,750

UNNAMED TRIBUTARY TO

SILVER CREEK

Approximately 1,000 feet upstream of the confluence with Silver Creek

0.90 350 540 600 750

Approximately 1,270 feet upstream of Cedar Avenue

0.43 230 320 350 440

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17

3.2 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. 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 Cross sections for the flooding sources studied by detailed methods were obtained from field surveys. All bridges, dams, and culverts were field surveyed to obtain elevation data and structural geometry. The USACE HEC-2 step backwater computer program (Reference 17) was used to calculate the WSELs of floods of the selected recurrence intervals for all streams in the pre-countywide analyses. Initial Countywide FIS (August 9, 2000) Eight new field-run cross sections were taken with emphasis on areas that experienced recent development. These cross sections were inserted into the HEC-2 models reflecting current conditions at developed areas (Reference 17). The streams studied in detail include the portions of the Etowah and the Coosa Rivers that flow within the city limits of Rome. The existing HEC-2 model for the City of Rome was used as reference for the initial countywide revision. Water surface elevations (WSELs) of floods of the selected recurrence intervals were computed using the USACE HEC-2 step backwater computer program (Reference 17). Flood profiles were drawn showing the computed WSELs for floods of the selected recurrence intervals. The water surface profiles for Silver Creek for the 10-, 2-, 1-, and 0.2-percent-annual-chance floods were computed using the HEC-2 step-backwater computer program (Reference 17). The USACE provided topographic maps used to revise the cross sections and Manning’s “n” values to better reflect existing conditions (Reference 23). The flood profiles and the Special Flood Hazard Area (SFHA) of Prentis Branch were revised to accommodate the higher backwater from Silver Creek. Starting WSELs for all streams were developed by the slope/area method or by a coincidental flow analysis in backwater areas where peak discharges occur at nearly the same time, and adjusted for backwater conditions.

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Roughness factors (Manning’s “n”) used in the hydraulic computations were based on field conditions. For the Coosa and Etowah Rivers, the channel “n” ranged from 0.036 to 0.040 and the overbank “n” ranged from 0.100 to 0.130. For detailed studied streams in the unincorporated areas, the channel “n” ranged from 0.030 to 0.055 and the overbank “n” ranged from 0.10 to 0.15. The Manning’s “n” values for Little Cedar Creek and Mill Race Creek ranged from 0.030 to 0.040 for the channels and 0.040 to 0.150 for the overbanks in the City of Cave Spring. For the City of Rome, the channel “n” ranged from 0.035 to 0.070 and the overbank “n” ranged from 0.100 to 0.150. The Oostanaula River values ranged from 0.040 to 0.060 for the channel and 0.040 to 0.200 for the overbanks. This Countywide Revision Cross section data for Big Dry Creek, Big Dry Creek Tributary 1, and Big Dry Creek Tributary 2 were obtained from field surveys. WSELs of the selected recurrence intervals were computed using the USACE’s HEC-RAS (version 3.1.1) hydraulic model (Reference 24). Starting WSELs were computed using normal depth calculations. A Manning’s “n” value of 0.040 was used for the channels while a value of 0.060 was used for the overbanks. Also for this revision, cross sections for the flooding sources studied by limited detailed methods were obtained using digital topography and field surveys. The 1-percent-annual-chance WSELs were computed using the USACE’s HEC-RAS (version 3.1.2) hydraulic model (Reference 25), and HEC-GeoRAS was used to delineate the 1-percent-annual-chance floodplain (Reference 26). The hydraulic model was prepared using digital elevation data from the County along with data from the NED (References 22), without surveying bathymetric data. Where bridge or culvert data were readily available, these data were reflected in the hydraulic model. Where these structural data were not readily available, field measurements of these structures were made to approximate their geometry in the hydraulic models. This model does not include field surveys that determine specifics on channel and floodplain characteristics. A limited detailed study is a “buildable” product that can be upgraded to a full detailed study at a later date by verifying stream channel characteristics, bridge and culvert opening geometry, and by analyzing multiple recurrence intervals. Flood profiles have been developed for streams studied by limited detailed methods to be used for floodplain management and flood insurance rating purposes. The flood profiles for the streams studied by limited detailed methods were published separately from this FIS report. Please contact your local floodplain administrator for more information.

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The hydraulic analyses for this study were based on unobstructed flow. The flood elevations shown on the Flood Profiles (Exhibit 1) are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. 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).

3.3 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 the National Geodetic Vertical Datum of 1929 (NGVD29). With the finalization of the NAVD88, many FIS reports and FIRMs are being prepared using NAVD88 as the referenced vertical datum. All flood elevations shown in this FIS report and on the FIRM are referenced to NAVD88. Structure and ground elevations in the community must, therefore, be referenced to NAVD88. It is important to note that adjacent communities may be referenced to NGVD29. This may result in differences in Base Flood Elevations (BFEs) across the corporate limits between the communities. The average conversion factor that was used to convert the data in this FIS report to NAVD88 was calculated using the National Geodetic Survey’s (NGS) VERTCON online utility (Reference 27). The data points used to determine the conversion are listed in Table 5.

Table 5 – Vertical Datum Conversion

Conversion from Quad Name Corner Latitude Longitude NGVD29 to NAVD88

Sugar Valley NW 34.625 -85.125 0.089 feet Sugar Valley SW 34.500 -85.125 0.105 feet

Plainville SE 34.375 -85.000 0.085 feet Plainville SW 34.375 -85.125 0.075 feet Armuchee SW 34.375 -85.250 0.108 feet

Summerville SW 34.375 -85.375 0.072 feet Chattoogaville SW 34.250 -85.500 0.112 feet Rock Mountain SW 34.250 -85.375 0.072 feet Rock Mountain SE 34.250 -85.250 0.131 feet

Rome North SE 34.250 -85.125 0.115 feet Shannon SE 34.250 -85.000 0.089 feet

Wax SW 34.125 -85.125 0.187 feet

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Table 5 – Vertical Datum Conversion (Continued)

20

Conversion from Quad Name Corner Latitude Longitude NGVD29 to NAVD88

Rome South SW 34.125 -85.250 0.217 feet Livingston SW 34.125 -85.375 0.210 feet

Average: 0.119 feet

For additional information regarding conversion between NGVD and NAVD, visit the NGS website at www.ngs.noaa.gov, or contact the NGS at the following address:

Vertical Network Branch, N/CG13 National Geodetic Survey, NOAA Silver Spring Metro Center 3 1315 East-West Highway Silver Spring, Maryland 20910 (301) 713-3191

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) 713-3242, or visit their website at www.ngs.noaa.gov.

4.0 FLOODPLAIN MANAGEMENT APPLICATIONS

The NFIP encourages State and local governments to adopt sound floodplain management programs. Therefore, each FIS report 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.

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4.1 Floodplain Boundaries

To provide a national standard without regional discrimination, the 1-percent-annual-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 each stream studied by detailed methods, the 1- and 0.2-percent-annual-chance floodplain boundaries have been delineated using the flood elevations determined at each cross section. Between cross sections, the boundaries were interpolated using 1982 photographic topographic maps at a scale of 1:200, with a contour interval of 2 feet, and topographic maps at a scale of 1:24,000, with a contour interval of 10 and 20 feet (Reference 19 and Reference 28). Between cross sections, the boundaries were interpolated using topographic maps at a scale of 1:4,800 and a contour interval of 4 feet in the City of Cave Spring (Reference 29). For the initial countywide revision, the 1- and 0.2-percent-annual-chance floodplain boundaries and the 1-percent-annual-chance floodway were delineated using the computed flood elevations plotted along surveyed cross sections using aerial topographic maps, provided by the City of Rome, reproduced at a scale of 1:200, with a contour interval of 2 feet (Reference 28). The floodplain for the Coosa River was revised using 2 foot contour mapping provided by Williams, Sweitzer, and Barnum, Inc., reducing the SFHA behind the levee system (Reference 12). For this revision, floodplain boundaries for Burwell Creek, Coosa River, Etowah River, Etowah River Tributary 1, Horseleg Creek, Little Dry Creek, Oostanaula River, Silver Creek, Silver Creek Tributary 1, and South Fork Horseleg Creek were redelineated based on revised topography. The digital topography was provided by the City of Rome has contour intervals of 2 feet within the City of Rome and 5-foot outside of Rome (Reference 30). Only portions of the stream within the 2-foot contour area were redelineated. The streams studied by limited detailed methods were delineated as Zone A floodplain boundaries based on the topography provided by Floyd County and the City of Rome. The floodplain boundaries for Big Dry Creek, Big Dry Creek Tributary 1, and Big Dry Creek Tributary 2 were interpolated between cross sections using topographic mapping at a scale of 1:6,000 and a contour interval of 5 feet (Reference 6).

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

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22

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 and limited detailed methods, only the 1-percent-annual-chance 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 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 6). 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 WSEL 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.

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FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

ARMUCHEE CREEK A 2,400 3,658 21,162 1.1 602.3 597.02 598.0 1.0 B 5,300 1,767 13,799 1.8 602.3 599.22 600.2 1.0 C 8,350 1,472 14,840 1.6 602.3 600.62 601.6 1.0 D 10,000 1,718 16,314 1.5 602.3 601.92 602.9 1.0 E 13,500 991 8,908 2.7 603.4 603.4 604.4 1.0 F 16,000 846 8,882 2.8 604.3 604.3 605.3 1.0 G 20,200 836 9,267 2.6 606.4 606.4 607.4 1.0 H 25,000 611 6,463 3.7 609.9 609.9 610.9 1.0 I 29,000 821 11,098 2.1 612.2 612.2 613.2 1.0 J 32,920 622 8,194 2.9 613.4 613.4 614.4 1.0 K 33,700 388 6,190 3.8 613.7 613.7 614.7 1.0 L 35,000 293 5,150 4.6 614.4 614.4 615.4 1.0 M 36,000 313 4,841 4.9 615.2 615.2 616.2 1.0 N 36,700 518 7,567 3.1 616.7 616.7 617.7 1.0 O 37,700 829 12,513 1.9 617.5 617.5 618.4 0.9 P 41,000 1,900 28,601 0.8 618.0 618.0 619.0 1.0 Q 46,600 457 5,955 3.7 618.8 618.8 619.8 1.0 R 53,535 250 4,141 3.7 623.7 623.7 624.7 1.0 S 55,400 1,056 14,823 1.0 624.4 624.4 625.4 1.0 T 58,400 1,014 12,621 1.2 624.9 624.9 625.9 1.0 U 60,230 1,345 15,925 1.0 625.2 625.2 626.2 1.0

1 Feet above confluence with Oostanaula River 2 Elevation computed without consideration of backwater effects from Oostanaula River

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

ARMUCHEE CREEK

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FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

ARMUCHEE CREEK (CONT’D)

V 61,800 1,205 10,897 1.4 625.4 625.4 626.4 1.0 W 64,000 866 6,656 2.3 626.4 626.4 627.4 1.0 X 68,500 888 6,688 2.3 631.0 631.0 632.0 1.0 Y 71,200 680 5,841 2.6 634.1 634.1 635.1 1.0 Z 73,300 984/02 9,752 1.6 636.2 636.2 637.2 1.0

1 Feet above confluence with Oostanaula River 2 Total width/width within county

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

ARMUCHEE CREEK

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FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

BIG DRY CREEK A 8,2871 120 725 4.2 596.6 582.02 582.2 0.2 B 9,8941 297 1,475 2.1 596.6 582.72 583.0 0.3

BIG DRY CREEK

TRIBUTARY 1

A 3,1563 167 490 6.2 596.6 585.92 586.9 1.0 B 7,5243 171 826 2.5 596.6 596.12 597.1 1.0 C 10,7133 286 1,835 1.0 604.5 604.5 605.2 0.7 D 13,0113 24 204 9.3 604.5 604.5 605.4 0.9

BIG DRY CREEK

TRIBUTARY 2

A 6874 198 1,477 1.1 596.6 593.82 594.2 0.4 B 1,7154 181 857 1.9 596.6 593.92 594.3 0.4 C 2,9464 291 1,614 0.7 598.3 598.3 598.4 0.1 D 5,6064 196 946 1.2 603.1 603.1 603.9 0.8

1 Feet above confluence with Oostanaula River 4Feet above confluence with Big Dry Creek Tributary 1 2Elevation computed without consideration of backwater effects from Oostanaula River 3Feet above confluence with Big Dry Creek

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS BIG DRY CREEK – BIG DRY CREEK TRIBUTARY 1 –

BIG DRY CREEK TRIBUTARY 2

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FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

BOOZE CREEK A 1,175 275 2,402 0.9 642.4 642.4 643.4 1.0 B 1,685 180 1,084 1.9 642.8 642.8 643.8 1.0 C 2,215 41 252 8.2 644.3 644.3 645.2 0.9 D 4,580 58 382 5.4 660.0 660.0 661.0 1.0 E 5,275 193 993 2.1 663.9 663.9 664.8 0.9 F 5,655 374 1,847 1.1 664.6 664.6 665.5 0.9 G 6,893 291 1,217 1.7 671.7 671.7 672.7 1.0

1 Feet above confluence with Silver Creek

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

BOOZE CREEK

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FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

BURWELL CREEK A 3,2201 3002 11,947 0.2 596.3 596.3 597.1 0.8 B 5,7551 968 8,845 0.2 596.3 596.3 597.1 0.8 COOSA RIVER A 203 553 15,052 4.7 585.4 585.4 586.4 1.0 B 7,4003 4,576 42,431 1.7 586.7 586.7 587.6 0.9 C 12,6003 4,112 51,854 1.4 587.2 587.2 588.2 1.0 D 17,0003 4,634 54,416 1.3 587.5 587.5 588.5 1.0 E 22,2003 3,754 37,150 1.9 588.0 588.0 589.0 1.0 F 28,8003 3,437 53,713 1.3 588.6 588.6 589.6 1.0 G 33,6003 2,119 28,893 2.5 589.1 589.1 590.1 1.0 H 36,8003 2,591 34,682 2.1 589.6 589.6 590.6 1.0 I 43,6003 1,466 27,411 2.6 590.6 590.6 591.6 1.0 J 46,2003 1,361 28,565 2.5 590.9 590.9 591.9 1.0 K 48,3003 1,442 20,262 3.5 591.3 591.3 592.3 1.0 L 54,2003 1,858 29,380 2.4 592.3 592.3 593.3 1.0 M 60,2003 1,179 21,943 3.1 592.9 592.9 593.9 1.0 N 64,6003 1,270 22,167 3.0 593.4 593.4 594.4 1.0 O 67,8003 1,659 24,105 2.8 593.9 593.9 594.9 1.0 P 73,8003 1,640 24,050 2.8 594.6 594.6 595.6 1.0

1 Feet above confluence with Oostanaula River 2 Actual floodway width differs from modeled floodway width due to redelineation

3Feet above State Highway 100

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

BURWELL CREEK – COOSA RIVER

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FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

COOSA RIVER (CONT’D)

Q 76,4001 1,713 26,307 2.5 594.9 594.9 595.9 1.0 R 79,8201 1,449 19,925 3.4 595.3 595.3 596.3 1.0 S 83,9801 869 18,523 3.6 595.7 595.7 596.7 1.0 DYKES CREEK A 6002 98 941 4.6 605.5 598.63 599.6 1.0 B 1,0852 271 3,432 1.2 605.5 599.23 600.1 0.9 C 3,2002 282 2,573 1.7 605.5 599.83 600.8 1.0 D 5,2002 218 1,114 3.9 605.5 603.73 604.7 1.0 E 7,0002 124 872 4.9 610.3 610.3 611.3 1.0 F 9,0002 110 748 5.2 615.4 615.4 615.9 0.5 G 10,8002 100 660 5.8 623.2 623.2 623.8 0.6 H 12,4002 156 809 4.8 627.7 627.7 628.6 0.9 I 13,1002 169 1,110 3.5 631.1 631.1 632.1 1.0 J 16,2002 90 518 6.6 639.4 639.4 640.3 0.9 K 16,9002 455 969 3.5 644.5 644.5 645.4 0.9 L 18,2002 180 1,256 2.7 652.9 652.9 653.6 0.7 M 19,8002 251 1,517 2.2 657.6 657.6 658.6 1.0 N 22,2002 288 1,248 2.4 662.9 662.9 663.9 1.0

1 Feet above State Highway 100 2 Feet above confluence with Etowah River 3 Elevation computed without consideration of backwater effects from Etowah River

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

COOSA RIVER – DYKES CREEK

Page 33: FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

DYKES CREEK (CONT’D)

O 25,1201 88 519 5.1 673.6 673.6 674.6 1.0 P 28,4001 80 455 4.7 691.2 691.2 691.9 0.7 Q 34,8801 96 479 4.2 735.6 735.6 736.2 0.6 ETOWAH RIVER A 8202 324 10,946 3.7 596.2 596.2 597.2 1.0 B 2,0702 298 7,983 5.0 596.3 596.3 597.2 0.9 C 3,1102 327 9,096 4.4 596.6 596.6 597.4 0.8 D 4,2202 278 8,186 4.9 596.9 596.9 597.7 0.8 E 5,1722 330 9,075 4.4 597.1 597.1 597.9 0.8 F 6,3152 581 10,294 3.9 597.4 597.4 598.1 0.7 G 7,2552 361 7,616 5.3 597.4 597.4 598.1 0.7 H 8,4592 268 8,614 4.6 597.8 597.8 598.5 0.7 I 9,2852 315 8,419 4.8 598.0 598.0 598.7 0.7 J 10,3562 262 8,473 4.7 598.5 598.5 599.0 0.5 K 11,7952 401 9,745 4.1 598.8 598.8 599.1 0.3 L 14,2122 426 10,629 3.8 599.0 599.0 599.4 0.4 M 16,2402 424 17,930 2.2 599.1 599.1 600.1 1.0 N 21,7402 360 9,180 4.4 600.2 600.2 601.2 1.0

1 Feet above confluence with Etowah River 2 Feet above confluence with Coosa River and Oostanaula River

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

DYKES CREEK – ETOWAH RIVER

Page 34: FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

ETOWAH RIVER (CONT’D)

O 26,540 280 7,856 5.1 601.5 601.5 602.5 1.0 P 32,740 305 8,558 4.6 603.3 603.3 604.3 1.0 Q 38,440 400 9,102 4.3 604.8 604.8 605.8 1.0 R 43,940 360 8,791 4.5 606.6 606.6 607.6 1.0 S 49,940 370 8,409 4.7 608.9 608.9 609.8 0.9 T 55,340 409 8,793 4.3 610.8 610.8 611.8 1.0 U 60,540 410 8,297 4.6 612.4 612.4 613.4 1.0 V 65,240 380 8,388 4.5 614.3 614.3 615.3 1.0 W 70,140 400 9,343 4.1 616.2 616.2 617.1 0.9

1 Feet above confluence with Coosa River and Oostanaula River

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

ETOWAH RIVER

Page 35: FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

HORSELEG CREEK A 581 109 2,816 0.9 596.0 596.0 596.0 0.0 B 2,534 111 1,383 1.9 596.2 596.2 596.2 0.0 C 4,171 173 1,221 2.1 597.1 597.1 597.4 0.3 D 5,966 148 677 3.8 599.0 599.0 599.8 0.8 E 7,656 166 956 2.4 603.5 603.5 604.5 1.0 F 8,184 80 593 3.4 604.8 604.8 605.8 1.0 G 10,138 32 206 6.3 608.6 608.6 609.2 0.6 H 11,563 41 201 6.5 615.6 615.6 615.9 0.3 I 13,992 1202 1,181 0.6 628.5 628.5 628.9 0.4 J 14,520 180 949 0.8 628.8 628.8 629.3 0.5 K 16,474 27 132 4.0 634.6 634.6 635.5 0.9

1 Feet above confluence with Coosa River 2 Actual floodway width differs from modeled floodway width due to redelineation

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

HORSELEG CREEK

Page 36: FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

LITTLE ARMUCHEE CREEK

A 2,200 1,013 4,307 2.9 621.8 617.52 618.5 1.0 B 6,000 910 3,783 2.6 621.8 621.42 622.4 1.0 C 8,340 620 3,249 3.0 624.2 624.2 625.2 1.0 D 10,800 140 1,529 6.3 627.6 627.6 628.6 1.0 E 14,200 498 4,033 2.4 630.9 630.9 631.9 1.0 F 15,200 128 2,181 4.4 632.6 632.6 633.6 1.0 G 16,000 128 2,109 4.6 633.0 633.0 634.0 1.0 H 17,000 444 4,717 2.0 633.7 633.7 634.7 1.0 I 18,600 823 6,375 1.5 634.3 634.3 635.3 1.0 J 21,000 851 5,388 1.8 635.1 635.1 636.1 1.0 K 22,600 493 4,128 2.3 636.1 636.1 637.1 1.0

1 Feet above confluence with Armuchee Creek 2 Elevation computed without consideration of backwater effects from Armuchee Creek

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

LITTLE ARMUCHEE CREEK

Page 37: FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

LITTLE CEDAR CREEK A 1,355 68 676 7.7 607.7 607.7 608.7 1.0 B 3,900 115 698 7.4 615.0 615.0 616.0 1.0 C 4,600 80 700 7.4 618.2 618.2 619.0 0.8 D 7,200 209 1,653 3.1 623.5 623.5 624.5 1.0 E 9,930 126 921 5.6 628.7 628.7 629.7 1.0 F 10,655 124 759 6.8 630.3 630.3 631.3 1.0 G 11,710 430 2,488 2.1 633.2 633.2 634.2 1.0 H 12,750 140 847 5.5 635.1 635.1 635.9 0.8 I 13,950 150 1,040 4.5 637.2 637.2 638.2 1.0 J 14,300 145 1,110 4.2 638.1 638.1 639.1 1.0 K 14,770 186 1,424 3.3 638.6 638.6 639.6 1.0 L 15,500 210 1,564 3.0 639.8 639.8 640.8 1.0 M 16,400 110 950 4.9 640.7 640.7 641.7 1.0 N 16,970 267 1,649 2.8 642.3 642.3 643.3 1.0 O 17,410 180 1,405 2.8 643.8 643.8 644.8 1.0 P 17,800 115 912 4.3 644.1 644.1 645.1 1.0 Q 18,189 115 785 4.9 645.0 645.0 646.0 1.0 R 19,765 102 652 5.9 650.2 650.2 651.1 0.9

1 Feet above confluence with Big Cedar Creek

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

LITTLE CEDAR CREEK

Page 38: FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

LITTLE DRY CREEK A 2,851 261 2,494 1.2 596.2 585.33 586.3 1.0 B 4,594 269 1,620 1.9 596.2 586.63 587.6 1.0 C 6,758 528 7,032 0.3 597.3 597.3 598.3 1.0 D 9,100 571 6,712 0.3 599.9 599.9 600.9 1.0 E 10,400 4102 5,462 0.4 599.9 599.9 600.9 1.0 F 12,100 415 3,275 0.7 600.0 600.0 601.0 1.0 G 14,650 261 1,420 1.5 600.4 600.4 601.4 1.0 H 17,000 139 625 3.4 603.1 603.1 604.1 1.0 I 20,000 203 1,040 1.7 608.5 608.5 609.5 1.0 J 22,900 108 539 2.5 612.3 612.3 613.3 1.0 K 24,900 111 540 1.9 615.3 615.3 616.3 1.0 L 27,600 75 329 3.1 619.4 619.4 620.4 1.0 M 29,500 83 322 3.1 627.4 627.4 628.4 1.0 N 31,700 311 857 0.7 631.7 631.7 632.7 1.0 O 35,100 30 111 5.8 637.6 637.6 638.5 0.9 P 38,400 81 302 2.1 652.9 652.9 653.8 0.9

1 Feet above confluence with Oostanaula River 2 Actual floodway width differs from modeled floodway width due to redelineation

3 Elevation computed without consideration of backwater effects from Coosa River

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

LITTLE DRY CREEK

Page 39: FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

MILL RACE CREEK A 5001 60 279 5.1 643.9 643.9 644.8 0.9 B 1,1001 57 183 7.7 647.3 647.3 647.3 0.0 C 1,8001 60 229 6.2 652.3 652.3 652.7 0.4 OOSTANAULA RIVER A 3272 383 10,941 4.0 596.2 ∗ ∗ ∗ B 6342 3203 11,896 3.7 596.2 ∗ ∗ ∗ C 2,2182 2403 9,377 4.7 596.2 ∗ ∗ ∗ D 3,5382 440 13,771 3.2 596.2 ∗ ∗ ∗ E 6,8502 976 15,899 2.8 596.2 595.54 596.5 1.0 F 9,1502 1,863 25,818 1.7 596.2 595.74 596.7 1.0 G 11,1502 345 9,885 4.5 596.2 595.84 596.8 1.0 H 11,5502 345 9,917 4.4 596.2 595.94 596.9 1.0 I 15,7502 1,631 25,606 1.7 596.6 596.6 597.6 1.0 J 21,7502 1,950 24,502 1.8 597.2 597.2 598.2 1.0 K 26,7502 956 16,415 2.7 597.7 597.7 598.7 1.0 L 31,9502 1,724 25,746 1.7 598.5 598.5 599.5 1.0 M 37,1502 1,908 26,597 1.7 599.2 599.2 600.2 1.0 N 42,1502 2,512 31,762 1.4 599.6 599.6 600.6 1.0 O 46,3502 325 7,893 5.6 599.9 599.9 600.9 1.0 P 52,7502 985 16,627 2.6 601.2 601.2 602.2 1.0

1 Feet above confluence with Little Cedar Creek ∗ Data not available 2 Feet above confluence with Coosa River and Etowah River 3 Actual floodway width differs from modeled floodway width due to redelineation

4 Elevation computed without consideration of backwater effects from Coosa River

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

MILL RACE CREEK – OOSTANAULA RIVER

Page 40: FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

OOSTANAULA RIVER (CONT’D)

Q 54,7501 1,599 22,136 2.0 601.6 601.6 602.6 1.0 R 62,9501 1,420 17,062 2.6 602.6 602.6 603.6 1.0 S 68,7501 1,816 26,426 1.7 603.4 603.4 604.4 1.0 T 72,5501 1,379 17,741 2.5 604.0 604.0 605.0 1.0 PRENTIS BRANCH A 3172 4703 3,631 2.4 609.1 609.1 609.9 0.8 B 1,3202 9803 4,604 1.9 610.0 610.0 610.9 0.9 C 2,9572 349 1,519 1.9 614.4 614.4 615.4 1.0 D 5,0692 173 766 3.9 621.3 621.3 622.1 0.8 E 9,2932 201 770 3.4 638.6 638.6 639.6 1.0

1 Feet above confluence with Coosa River and Etowah River 2 Feet above confluence with Silver Creek 3 Combined floodway width with Silver Creek

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

OOSTANAULA RIVER – PRENTIS BRANCH

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FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE1 WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

SILVER CREEK A 1,530 352 993 8.8 596.4 596.4 597.4 1.0 B 2,268 215 3,205 2.7 597.4 597.4 598.2 0.8 C 3,400 195 3,127 2.8 597.9 597.9 598.9 1.0 D 4,000 370 5,846 1.5 598.6 598.6 599.6 1.0 E 5,200 424 5,508 1.6 598.9 598.9 599.9 1.0 F 6,044 97 1,273 6.8 598.9 598.9 599.9 1.0 G 6,400 165 2,152 4.0 600.4 600.4 601.4 1.0 H 8,100 651 5,273 1.6 601.8 601.8 602.8 1.0 I 9,080 790 7,667 1.1 604.7 604.7 605.7 1.0 J 11,200 239 2,247 3.9 605.6 605.6 606.6 1.0 K 12,400 299 2,772 3.1 606.6 606.6 607.6 1.0 L 14,000 4703 3,631 2.4 609.1 609.1 609.9 0.8 M 15,000 9803 4,604 1.9 610.0 610.0 610.9 0.9 N 16,100 537 3,456 2.1 611.2 611.2 612.2 1.0 O 17,300 702 1,349 5.3 614.8 614.8 615.8 1.0 P 19,100 1452 2,529 2.8 619.2 619.2 620.2 1.0 Q 21,000 658 3,798 1.9 622.1 622.1 623.1 1.0 R 22,150 404 2,118 3.3 625.4 625.4 626.4 1.0 S 23,960 403 2,334 3.0 630.9 630.9 631.9 1.0 T 26,700 117 1,878 3.5 648.3 648.3 649.3 1.0

1 Feet above confluence with Etowah River 2 Actual floodway width differs from modeled floodway width due to redelineation

3 Combined floodway width with Prentis Branch

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

SILVER CREEK

Page 42: FLOYD COUNTY, GEORGIA · FLOYD COUNTY, GEORGIA AND INCORPORATED AREAS Community Community Name Number CAVE SPRING, CITY OF 130080 FLOYD COUNTY 130079 Floyd County (UNINCORPORATED

FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

SILVER CREEK (CONT’D)

U 27,8001 386 5,252 1.2 648.9 648.9 649.9 1.0 V 29,2001 233 2,229 2.9 650.8 650.8 651.8 1.0 W 30,5001 140 1,299 5.3 653.0 653.0 653.9 0.9 X 32,5201 360 2,169 3.2 659.4 659.4 660.4 1.0 Y 34,9801 246 1,725 4.0 667.1 667.1 668.1 1.0 Z 35,9201 293 1,836 3.8 671.8 671.8 672.8 1.0

SOUTH FORK HORSELEG CREEK

A 2,6932 134 783 1.3 621.8 621.8 622.8 1.0 B 3,1152 47 209 3.6 623.6 623.6 623.9 0.3 C 5,0162 33 142 5.3 629.5 629.5 630.0 0.5

1 Feet above confluence with Etowah River 2 Feet above confluence with Horseleg Creek

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

SILVER CREEK – SOUTH FORK HORSELEG CREEK

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FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION

CROSS SECTION DISTANCE WIDTH (FEET)

SECTION AREA

(SQUARE FEET)

MEAN VELOCITY (FEET PER SECOND)

REGULATORY (FEET NAVD)

WITHOUT FLOODWAY (FEET NAVD)

WITH FLOODWAY (FEET NAVD)

INCREASE (FEET)

SOUTH FORK LITTLE DRY CREEK

A 1,1091 525 6,054 0.1 596.7 596.7 597.7 1.0 B 3,3261 165 836 0.9 597.0 597.0 598.0 1.0 C 3,6431 239 2,086 0.4 602.5 602.5 602.6 0.1 D 6,2301 28 152 3.4 605.1 605.1 606.0 0.9 E 7,5501 21 109 3.9 610.6 610.6 611.0 0.4 F 8,4481 12 91 3.0 616.0 616.0 616.2 0.2 TRIBUTARY A A 2,9042 416 3,550 0.5 599.7 599.43 599.4 0.0 B 5,2802 156 876 1.7 601.9 601.9 602.1 0.2

UNNAMED TRIBUTARY TO SILVER CREEK

A 1,0034 508 5,165 0.1 600.0 600.0 600.2 0.2 B 1,2674 482 3,254 0.2 600.0 600.0 600.2 0.2 C 2,0064 94 400 0.9 601.1 601.1 602.1 1.0 D 2,4294 36 131 2.7 601.5 601.5 602.5 1.0

1 Feet above confluence with Little Dry Creek 2 Feet above confluence with Etowah River 3 Elevation computed without consideration of backwater effects from Etowah River

4 Feet above confluence with Silver Creek

FLOODWAY DATA

TAB

LE 6

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS SOUTH FORK LITTLE DRY CREEK – TRIBUTARY A –

UNNAMED TRIBUTARY TO SILVER CREEK

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Figure 1 – Floodway Schematic

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 BFE 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, whole-

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foot 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-percent-annual-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 Floyd County. Previously, FIRMs were prepared for each incorporated community and the unincorporated areas of the County identified as flood-prone. This countywide FIRMs also includes flood-hazard information that was presented separately on Flood Boundary and Floodway Maps, where applicable. Historical data relating to the maps prepared for each community are presented in Table 7.

7.0 OTHER STUDIES

There are Flood Profiles for the streams studied by limited detailed methods, which were published separately from this FIS report.

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COMMUNITY NAME INITIAL IDENTIFICATION

FLOOD HAZARD BOUNDARY MAP REVISION DATE

FIRM EFFECTIVE DATE

FIRM REVISION DATE

Cave Spring, City of June 14, 1974 February 13, 1976 May 1, 1985 None

Floyd County

(Unincorporated Areas) April 30, 1976 None May 19, 1987 None

Rome, City of May 17, 1974 January 30, 1976 September 15, 1978 November 4, 1988

TAB

LE 7

FEDERAL EMERGENCY MANAGEMENT AGENCY

FLOYD COUNTY, GA AND INCORPORATED AREAS

COMMUNITY MAP HISTORY

Table 7 – Community Map History

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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, 3003 Chamblee Tucker Road, Atlanta, Georgia 30341.

9.0 BIBLIOGRAPHY AND REFERENCES

1. Federal Emergency Management Agency, Flood Insurance Study, City of Cave Spring, Floyd County, Georgia, FIS Report published February 5, 1985, FIRM published May 1, 1985.

2. Federal Emergency Management Agency, Flood Insurance Study, Floyd

County, Georgia (Unincorporated Areas), May 19, 1987.

3. Federal Insurance Administration, Flood Insurance Study, City of Rome, Floyd County, Georgia, FIS Report published March 15, 1978, FIRM published September 15, 1978.

4. Federal Emergency Management Agency, Flood Insurance Study, City of

Rome, Floyd County, Georgia, November 4, 1988.

5. Federal Emergency Management Agency, Flood Insurance Study, Floyd County and Incorporated Areas, August 9, 2000.

6. U.S. Army Corps of Engineers, Mobile District, Special Flood Hazard

Evaluation, Big Dry Creek and Tributaries, Floyd County, Georgia, September 1998.

7. Floyd County, Georgia, Digital Topographic Data and Orthophotos, City of

Rome and outside areas, Floyd County, Georgia, 2 foot and 5 foot contour intervals, March 2004.

8. 2000 U.S. Census: Floyd County, Georgia, Retrieved on April 14, 2005, from http://factfinder.census.gov.

9. Monthly Averages for Rome, Georgia, Retrieved on April 15, 2005, from

http://www.weather.com.

10. U.S. Army Corps of Engineers, Mobile District, Flood Hazard Information Report, Etowah River from Allatoona Dam to Vicinity of Rome, Georgia, July 1975.

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11. U.S. Army Corps of Engineers, Mobile District, Special Flood Hazard Information Report Coosa River – Etowah River Oostanaula River – Rome, Floyd County, Georgia, February 1973.

12. Williams, Sweitzer, and Barnum, Inc., Topographic Mapping, The South Rome Development Area – Phase II, Study Map Proposed Levee System, Rome, Georgia, December 1983.

13. U.S. Army Corps of Engineers, Mobile District, Review Study (conducted under the Authority of the Flood Control Act of 1970, Section 216), Public Law 91-611.

14. U.S. Army Corps of Engineers, Montgomery to Gadsden Coosa River Channel, Alabama Design Memorandum No. 1, General Design, May 1982.

15. Georgia Department of Transportation, Research Project No. 6303, Flood Frequency Analysis for Small Streams in Georgia, 1976.

16. U.S. Army Corps of Engineers, Hydrologic Engineering Center, HEC-1, Flood

Hydrograph Package, Computer Program 823-X-L2610, Davis, California, January 1973.

17. U.S. Army Corps of Engineers, Hydrologic Engineering Center, HEC-2 Water Surface Profiles, Users Manual for Computer Program 723-X6-L202A, Davis, California, April 1984.

18. U.S. Department of Commerce, Weather Bureau, Technical Paper No. 40, Rainfall Frequency Atlas of the United States, January 1963.

19. U.S. Department of the Interior, Geological Survey, 7.5-Minute Series

Topographic Maps, Scale 1:24,000, Contour Interval 10 feet: Livingston, Georgia, 1967; Plainville, Georgia, 1968; Rome North, Georgia, 1967; Melson, Georgia-Alabama, 1967; Contour Interval 20 feet: Armuchee, Georgia, 1968; Cedartown East, Georgia, 1967; photorevised 1980; Cedartown West, Georgia, 1967; photorevised 1980; Chattoogaville, Georgia-Alabama, 1967; Indian Mountain, Alabama-Georgia, 1967; photoinspected 1976; Rock Mountain, Georgia, 1967; Rockmart North, Georgia, 1973; Rockmart South, Georgia, 1973; Rome South, Georgia, 1968; Shannon, Georgia, 1968; Subligna, Georgia, 1967; Sugar Valley, Georgia 1967; Summerville, Georgia, 1967; Wax, Georgia, 1968.

20. U.S. Department of the Interior, Geological Survey, Water Resources Division,

Preliminary Flood Frequency Relationships for Urban Streams, Metropolitan Atlanta, Georgia, Doraville, Georgia, October 1975.

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21. Stamey, T.C. and C.W. Hess, USGS Water Resources Investigations Report 93-4016, Techniques for Estimating Magnitude and Frequency of Floods in Rural Basins of Georgia, 1993.

22. U.S. Geological Survey, National Elevation Dataset, Southeast Atlanta, Redan,

Jonesboro, Stockbridge, Kelleytown, Hampton, McDonough, and Ola Quads, 7.5-minute series, Contour Interval 10 feet, USGS EROS Data Center, Sioux Falls, South Dakota, 1999.

23. U.S. Army Corps of Engineers, Mobile District, Silver Creek, Detailed Project

Report, Rome, Georgia, January 1983.

24. U.S. Army Corps of Engineers, Hydrologic Engineering Center, HEC-RAS River Analysis System, Version 3.1.1, Davis, California, May 2003.

25. U.S. Army Corps of Engineers, Hydrologic Engineering Center, HEC-RAS

River Analysis System, Version 3.1.2, Davis, California, April 2004.

26. U.S. Army Corps of Engineers, Hydrologic Engineering Center, HEC-GeoRAS, Version BETA 6.0, April 2004.

27. NGS, VERTCON-North American Vertical Datum Conversion Utility,

Retrieved on March 24, 2005, from http://www.ngs.noaa.gov/.

28. Hoffman and Company, City of Rome Topographic Mapping Photograph, Scale 1:200, Contour Interval 2 feet, Smyrna, Georgia, 1982.

29. U.S. Army Corps of Engineers, Mobile District, Topographic Maps, Scale

1:4,800, Contour Interval 4 feet, 1983.

30. City of Rome, Digital Topography, Contour Interval 2 and 5 feet, date unavailable.

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