MARSHALL COUNTY, MISSISSIPPI AND INCORPORATED AREAS MARSHALL COUNTY COMMUNITY NAME COMMUNITY NUMBER BYHALIA, TOWN OF 280112 HOLLY SPRINGS, CITY OF 280113 MARSHALL COUNTY 280274 (UNINCORPORATED AREAS) POTTS CAMP, TOWN OF 280114 EFFECTIVE: Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER 28093CV000A NOTICE TO FLOOD INSURANCE STUDY USERS Communities participating in the National Flood Insurance Program (NFIP) 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 repository. It is advisable to contact the community repository for any additional data. Selected Flood Insurance Rate Map panels for this community contain information that was previously shown separately on the corresponding Flood Boundary and Floodway Map panels (e.g., floodways, cross sections),. In addition, former flood hazard zone designations have been changed as follows: Old Zone(s) New Zone A1 through A30 AE V1through V30 VE B X C X Part or all of this FIS report may be revised and republished at any time. In addition, part of this FIS report may be revised by the Letter of Map Revision process, which does not involve republication or redistribution of the FIS. It is, therefore, the responsibility of the user to consult with community officials and to check the community repository to obtain the most current FIS report components. Initial Countywide FIS Report Effective Date: Revised Countywide FIS Report Dates: TABLE OF CONTENTS Page 1.0 INTRODUCTION 1 1.1 Purpose of Study 1 1.2 Authority and Acknowledgments 1 1.3 Coordination 2 2.0 AREA STUDIED 2 2.1 Scope of Study 2 2.2 Community Description 3 2.3 Principal Flood Problems 4 2.4 Flood Protection Measures 4 3.0 ENGINEERING METHODS 4 3.1 Hydrologic Analyses 4 3.2 Hydraulic Analyses 5 3.3 Vertical Datum 7 4.0 FLOODPLAIN MANAGEMENT APPLICATIONS 8 4.1 Floodplain Boundaries 8 4.2 Floodways 8 5.0 INSURANCE APPLICATIONS 13 6.0 FLOOD INSURANCE RATE MAP 14 7.0 OTHER STUDIES 16 8.0 LOCATION OF DATA 16 9.0 BIBLIOGRAPHY AND REFERENCES 16 i TABLE OF CONTENTS - continued Page FIGURES Figure 1 - Floodway Schematic 10 TABLES Table 1 - Summary of Discharges 5 Table 2 – Summary of Elevations 5 Table 3 - Floodway Data 11 Table 4 - Community Map History 15 EXHIBITS Exhibit 1 - Flood Profiles Byhalia Creek Panel 01P-03P Nonconnah Creek Lateral B Panel 04P-06P Exhibit 2 - Flood Insurance Rate Map Index Flood Insurance Rate Map ii FLOOD INSURANCE STUDY MARSHALL COUNTY, MISSISSIPPI AND INCORPORATED AREAS 1.0 INTRODUCTION 1.1 Purpose of Study This Flood Insurance Study (FIS) revises and supersedes the FIS reports and/or Flood Insurance Rate Maps (FIRMs) in the geographic area of Marshall County, Mississippi, including the City of Holly Springs, the Towns of Byhalia and Potts Camp, and unincorporated areas of Marshall County (hereinafter referred to collectively as Marshall County). This FIS 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. This information will also be used by Marshall County to update existing floodplain regulations as part of the Regular Phase of the National Flood Insurance Program (NFIP), and by local and regional planners to further promote sound land use and floodplain development. Minimum floodplain management requirements for participation in the 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. 1.2 Authority and Acknowledgments The sources of authority for this FIS report are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. January 17, 1991, FIS Marshall County (Unincorporated Areas) The hydrologic and hydraulic analyses for this study were performed by Spencer- Engineers, Inc./Consultants (the Study Contractor) for the Federal Emergency Management Agency (FEMA), under Contract No. EMW-87-C-2458. This study was completed in September 1988. Detailed flood elevations for Sardis Lake were obtained from the Flood Insurance Study for Lafayette County, Mississippi (FEMA, 1991). This Countywide FIS The hydrologic and hydraulic analyses for this countywide FIS were performed by the State of Mississippi for the Federal Emergency Management Agency (FEMA), under Contract No. EMA-2007-CA-5774. This study was completed in July 2009. The digital base map information files were provided by the U.S. Army Corps of Engineers—Vicksburg District, 4155 East Clay Street, Vicksburg, MS 39183, phone number (601) 631-5053. The digital orthophotography was acquired in March 2006, with the imagery processed to a 2-foot pixel resolution. The digital FIRM was produced using the Mississippi State Plane Coordinate System, East Zone, FIPS ZONE 2301. The horizontal datum was the North American Datum of 1983, GRS 1980 spheroid. Distance units were measured in U.S. feet. The Letter of Map Revision 98-04-091P dated May 28, 1998, has been incorporated into this study. Initially, the LOMC only affected the Marshall County Unincorporated FIRM and not the Town of Byhalia FIRM due to the Town of Byhalia annexing the area affected by the LOMC after the effective dates of the FIRM panels. In this countywide study, the data in the LOMC has been incorporated and affects the Town of Byhalia. 1.3 Coordination An initial Consultation Coordination Officer's (CCO) 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 by detailed methods. A final CCO meeting is held with representatives from FEMA, the community, and the study contractor to review the results of the study. January 17, 1991, Marshall County (Unincorporated Areas) FIS On October 17, 1986, a meeting was held with representatives of FEMA, Marshall County, and the Study Contractor. Letters were sent to various State, Federal, and private agencies informing them of this Study, and requesting any pertinent information available. On February 20, 1990, the results of this Flood Insurance Study were reviewed and accepted at a final coordination meeting attended by representatives of the Study Contractor, FEMA, and the community. This Countywide FIS For this countywide FIS, the Project Scoping Meeting was held on April, 2008 in Holly Springs, MS. Attendees for these meetings included representatives from the Mississippi Department of Environmental Quality, Mississippi Emergency Management Agency, FEMA National Service Provider, Marshall County, the City of Natchez, and the Study Contractor. Coordination with county officials and Federal, State, and regional agencies produced a variety of information pertaining to floodplain regulations, available community maps, flood history, and other hydrologic data. All problems raised in the meetings have been addressed. 2.0 AREA STUDIED 2.1 Scope of Study This FIS covers the geographic area of Marshall County, Mississippi, and its incorporated communities listed in Section 1.1 2 January 17, 1991, Marshall County (Unincorporated Areas) FIS Flooding caused by overflow of Byhalia Creek, Nonconnah Creek Lateral B, and Sardis Lake was studied in detail. Areas having low development potential or minimal flood hazards were previously studied using approximate analyses. The results were shown on the Flood Hazard Boundary Map for Marshall County, Mississippi (Dept. of Housing and Urban Development, 1977), and are incorporated into this Flood Insurance Study. The areas studied were selected with priority given to all known flood hazard areas and areas of projected development or proposed construction through September 1993. The scope and methods study were proposed to and agreed upon by FEMA and Marshall County. This Countywide FIS For this countywide FIS, several flooding sources within the county were studied by approximate methods. Approximate analyses are used to study those areas having a low developmental potential or minimal flood hazards. The scope and methods of study were proposed to, and agreed upon, by FEMA and the State of Mississippi. Floodplain boundaries of streams that have been previously studied by detailed methods were redelineated based on best available topographic information. 2.2 Community Description Marshall County is in north-central Mississippi, about 15 miles southeast of Memphis, Tennessee. The county is bordered on the north by Shelby and Fayette Counties, Tennessee; on the east by Benton and Union Counties, Mississippi; on the south by Lafayette County, Mississippi; and on the west by DeSoto and Tate Counties, Mississippi. Marshall County is served by U.S. Highways 72 and 78; by State Highways 4, 7, 309, 310, 311, 313, and 349; and by the BNSF Railroad and the Canadian National Railroad. The 2007 population of Marshall County was reported to be 36,695 (U.S. Census Bureau, 2009). Byhalia Creek rises in the northwestern part of Marshall County near the town of Byhalia, and flows along the eastern and southern edge of town before leaving the county to its confluence with Pigeon Roost Creek. Byhalia Creek has a broad alluvial valley with an average slope of 10 feet per mile over the detail study reach. Nonconnah Creek Lateral B rises in the northern part of Marshall County and flows westward along the Tennessee border before turning north into Shelby County, Tennessee, to its confluence with Nonconnah Creek, southwest of Collierville, Tennessee. Nonconnah Creek Lateral B is a meandering stream in a broad alluvial valley with an average valley slope of about 9 feet per mile in the study segment.