VOLUSIA COUNTY, FLORIDA AND INCORPORATED AREAS

Transcription

1 VOLUSIA COUNTY, FLORIDA AND INCORPORATED AREAS VOLUSIA COUNTY Community Name Community Number DAYTONA BEACH, CITY OF DAYTONA BEACH SHORES, CITY OF DeBARY, CITY OF DELAND, CITY OF DELTONA, CITY OF EDGEWATER, CITY OF FLAGLER BEACH, CITY OF HOLLY HILL, CITY OF LAKE HELEN, CITY OF NEW SMYRNA BEACH, CITY OF OAK HILL, CITY OF ORANGE CITY, CITY OF ORMOND BEACH, CITY OF PIERSON, TOWN OF PONCE INLET, TOWN OF PORT ORANGE, CITY OF SOUTH DAYTONA, CITY OF VOLUSIA COUNTY (UNINCORPORATED AREAS) REVISED: February 19, 2014 Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER 12127CV000C

2 NOTICE TO FLOOD INSURANCE STUDY USERS Communities participating in the National Flood Insurance Program have established repositories of flood hazard data for floodplain management and flood insurance purposes. This Flood Insurance Study (FIS) may not contain all data available within the repository. It is advisable to contact the community 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, part of this FIS 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 Map Repository to obtain the most current FIS components. This FIS report was revised on February 19, 2003, September 29, 2011 and February 19, Users should refer to Section 10.0, Revisions Description, for further information. Section 10.0 is intended to present the most up-to-date information for specific portions of this FIS report. Therefore, users of this report should be aware that the information presented in Section 10.0 supersedes information in Sections 1.0 through 9.0 of this FIS report. Initial Countywide FIS Effective Date: April 15, 2002 Revised FIS Dates: February 19, 2003 September 29, 2011 February 19, 2014

3 TABLE OF CONTENTS Page 1.0 INTRODUCTION Purpose of Study Authority and Acknowledgments Coordination AREA STUDIED Scope of Study Community Description Principal Flood Problems Flood Protection Measures ENGINEERING METHODS Riverine Hydrologic Analyses Riverine Hydraulic Analyses Coastal Hydrologic Analyses Coastal Hydraulic Analyses Vertical Datum FLOODPLAIN MANAGEMENT APPLICATIONS Floodplain Boundaries Floodways INSURANCE APPLICATIONS FLOOD INSURANCE RATE MAP OTHER STUDIES LOCATION OF DATA BIBLIOGRAPHY AND REFERENCES REVISION DESCRIPTIONS First Revision (Revised February 19, 2003) Second Revision (Revised September 29, a. Acknowledgments 52 i

4 TABLE OF CONTENTS continued b. Coordination 52 c. Scope 52 d. Hydrologic and Hydraulic Analyses 52 e. Floodplain Boundaries 53 f. Floodways 53 g. Bibliography and References Third Revision (Revised February 19, 2014) 53 a. Acknowledgments 53 b. Coordination 54 c. Scope 54 d. Hydrologic and Hydraulic Analyses 56 e. Floodplain Boundaries 60 f. Floodways 60 g. Bibliography and References 64 FIGURES Figure 1 - Transect Location Map 22 Figure 2 - Transect Schematic 29 Figure 3 - Floodway Schematic 40 TABLES Table 1 - Flooding Sources Studied by Detailed Methods 5 Table 2 - Initial Countywide Scope 5-6 Table 3 - Summary of Discharges Table 4 - Summary of Stillwater Elevations 15 Table 5 - Manning s n Values 18 Table 6 - Summary of Coastal Stillwater Elevations 20 Table 7 - Transect Descriptions Table 8 - Transect Data 29 Table 9 - Floodway Data Table 10 - Community Map History Table 11 - First Revision Summary of Stillwater Elevations Table 12 - Third Revision Detailed Study Scope Table 13 - Incorporated LOMRs ii

5 TABLES continued Table 14 - Revised Summary of Discharges Table 15 Third Revision Summary of Stillwater Elevations 58 Table 16 - Revised Hydraulic Model Boundary Conditions 59 Table 17 - Revised Manning s n Values 59 Table 18 - Revised Floodway Data EXHIBITS Exhibit 1 - Flood Profiles B-19 Canal Panels 01P-03P B-19 Canal Tributary No. 1 Panel 04P B-19 Canal Tributary No. 2 Panel 05P B-19 Canal Tributary No. 7 Panel 06P B-27 Canal North Panel 07P B-27 Canal South Panel 08P Bulow Creek Panel 09P Canal Between Panel 10P E Canal Panel 11P Eleventh Street Canal Panel 12P Eleventh Street Canal Tributary No. 2 Panel 13P Groover Branch Panels 14P-15P Halifax Canal Panels 16P-17P Laurel Creek Panels 18P-19P LPGA Canal Panel 20P Little Tomoka River Panels 21P-22P Misner Branch Panels 23P-24P Nova Canal North Reach 1 Panels 25P Nova Canal North Reach 2 Panels 26P-27P Nova Canal South Reach 1 Panels 28P-29P Nova Canal South Reach 2 Panels 30P St. Johns River Panels 31P-34P Shooting Range Canal/Eleventh Street Canal Tributary No. 2/Eleventh Street Canal Tributary No. 2A Panels 35P-37P South Canal Panel 38P Spruce Creek Panels 39P-40P Spruce Creek Tributary No. 1 Panel 41P Spruce Creek Tributary No. 2 Panel 42P Spruce Creek Tributary A Panel 43P Thompson Creek Panels 44P Tomoka River Panels 45P-48P Wally Hoffmeyer Canal Panel 49P Exhibit 2 - Flood Insurance Rate Map Index Flood Insurance Rate Map iii

6 1.0 INTRODUCTION FLOOD INSURANCE STUDY VOLUSIA COUNTY, FLORIDA AND INCORPORATED AREAS 1.1 Purpose of Study This Flood Insurance Study (FIS) revises and supersedes the FIS reports and Flood Insurance Rate Maps (FIRMs) in the geographic area of Volusia County, Florida, including: the Cities of Daytona Beach, Daytona Beach Shores, DeBary, Deland, Deltona, Edgewater, Flagler Beach, Holly Hill, Lake Helen, New Smyrna Beach, Oak Hill, Orange City, Ormond Beach, Port Orange, and South Daytona; the Towns of Pierson and Ponce Inlet; and the unincorporated areas of Volusia County (hereinafter referred to collectively as Volusia County), and aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of This study has developed flood risk data for various areas of the county that will be used to establish actuarial flood insurance rates. This information will also be used by Volusia 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, Please note that the City of Flagler Beach is geographically located in Volusia and Flagler Counties. For this FIS only the portions of the City of Flagler Beach within Volusia County are included. The portions of the City of Flagler Beach that are geographically located within Flagler County are included in the Flagler County FIS. 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 are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of This FIS was prepared to include the unincorporated areas of, and incorporated communities within Volusia County into a countywide FIS. Information on the authority and acknowledgments for all of the incorporated communities within, and the unincorporated areas of, Volusia County, as compiled from their previously printed FIS reports, is shown below. Daytona Beach, City of: the hydrologic and hydraulic analyses for the FIS report dated June 4, 1990, were obtained from the June 4, 1990, FIS for the unincorporated areas of Volusia County and the study titled Tomoka River and B-19 Canal 100- year Flood Results for the City of Daytona Beach (References 1 and 2). 1

7 Daytona Beach Shores, City of: the coastal analyses were conducted for the Wave Height Analysis dated March 16, DeBary, City of: Edgewater, City of: New Smyrna Beach, City of: Oak Hill, City of: Ormond Beach, City of: Ponce Inlet, Town of: Port Orange, City of: South Daytona, City of: the hydrologic and hydraulic analyses for the FIS report dated February 2, 1996, were obtained from the June 4, 1990, FIS for the unincorporated areas of Volusia County (Reference 1). the hydrologic and hydraulic analyses for the FIS report dated June 4, 1990, were performed for FEMA and completed in August Additional coastal analyses were performed by FEMA to provide sufficient information for delineation of the floodplain boundaries for the City of Edgewater. the coastal analyses were conducted for the Wave Height Analysis dated March 16, the hydrologic and hydraulic analyses for the FIS report dated June 4, 1990, were obtained from the June 4, 1990, FIS for the unincorporated areas of Volusia County (Reference 1). the hydrologic and hydraulic analyses for the FIS report dated June 4, 1990, were obtained from the June 4, 1990, FIS for the unincorporated areas of Volusia County and the study titled Tomoka River Flood Plain Management Study - Tributaries to the Tomoka River (References 1 and 3). the coastal analyses were conducted for the Wave Height Analysis dated March 16, the hydrologic and hydraulic analyses for the FIS report dated June 4, 1990, were obtained from the June 4, 1990, FIS for the unincorporated areas of Volusia County and the study titled Tomoka River and B-19 Canal 100- year Flood Results for the City of Daytona Beach (References 1 and 2). the hydrologic and hydraulic analyses for the FIS report dated June 4, 1990, were obtained from the June 4, 1990, FIS for the unincorporated areas of Volusia County (Reference 1). Additional coastal analyses were performed by FEMA to provide sufficient 2

8 information for delineation of the flood elevation boundaries for the City of South Daytona. Volusia County (unincorporated areas): the hydrologic and hydraulic analyses for the FIS report dated June 4, 1990, for the Tomoka River from its mouth to Eleventh Street, Spruce Creek, Spruce Creek Tributaries Nos. 1 and 2, and Bulow Creek, prepared by Gee & Jenson Engineers-Architects-Planners, Inc., for FEMA, under Contract No. EMW-C-0951; the Tomoka River, from Eleventh Street to Interstate 4, was obtained from a report by Camp Dresser & McKee, Inc. (CDM); St. Johns River, were taken from the Lake and Seminole Counties FIS reports; Bulow Creek, were taken from the Flagler County FIS; Spruce Creek Tributary A, obtained from a report submitted by Zev Cohen & Associates, Inc.; Shooting Range Canal, Eleventh Street Canal Tributaries No. 2 and 2A, were taken from a Soil Conservation Service (SCS, now Natural Resources Conservation Service [NRCS]) report; and B-19 Canal Tributaries Nos. 1 and 2, were performed by the SCS (References 2, 4, 5, 6, 7, 3, and 8). The authority and acknowledgments for the Cities of Deland, Deltona, Holly Hill, Lake Helen, Orange City, and the Town of Pierson are not included because there were no previously printed FIS reports for those communities. For the April 15, 2002, countywide FIS, the hydrologic and hydraulic analyses were prepared by Taylor Engineering, Inc., for FEMA, under Contract No. EMW-95-C Daniel W. Cory, Surveyor, Inc., and Morgan & Eklund, Inc., performed riverine and beach/nearshore surveying, respectively, under contract to Taylor Engineering, Inc. That work was completed in August Planimetric base map files were provided in digital format by the County of Volusia Information Technology Group, Geographic Information Services, 123 West Indiana Avenue, Deland, Florida These files were compiled at a scale of 1:4,800 from orthophotos. The coordinate system used for the production of the FIRM is Universal Transverse Mercator (UTM), North American Datum of 1927 (NAD27), Clarke 1866 spheroid. 1.3 Coordination The initial Consultation Coordination Officer (CCO) meeting was held on September 16, 1994, and attended by representatives of FEMA, Volusia County; several municipalities; local consulting engineering companies; and Taylor Engineering, Inc. Numerous other contacts for coordination and data acquisition were made with appropriate agencies and groups throughout the course of the study, including the following: 3

9 2.0 AREA STUDIED Applied Technology and Management, Inc. McKim and Creed, Inc. Dyer, Riddle & Associates, Inc. Marshall, Provost & Associates Camp Dresser & McKee, Inc. Cities of Daytona Beach, Ormond Beach, New Smyrna Beach, and Port Orange U.S. Army Corps of Engineers (USACE), Jacksonville District USACE Waterways Experiment Station Dewberry & Davis Volusia County Council, Department of Planning and Zoning, Department of Public Works, and Geographic Information Services Florida Department of Environmental Protection (FDEP), and Department of Transportation (FDOT) National Ocean Service National Weather Service St. Johns River Water Management District (SJRWMD) The News-Journal U.S. Department of Agriculture, NRCS U.S. Environmental Protection Agency USGS, Tallahassee, Jacksonville, and Orlando Subdistricts An inventory of available data pertinent to the countywide FIS was collected from local, county, regional, and state agencies and firms, as well as from the general public. Five field reconnaissances were performed: June 30, July 12-14, July 27, August 4, and August 12, A meeting was held on September 6, 1995, and on March 6, 1996, and attended by representatives of Taylor Engineering, Inc., and FEMA to discuss study progress, methods, and preliminary results. On April 9, 1996, Taylor Engineering, Inc. met with SJRWMD staff to discuss available information and District rainfall studies pertinent to the countywide FIS (References 9 and 10). The District s rainfall depths have been used in countywide stormwater studies in lieu of NOAA TP-40 rainfall depths (Reference 11). The results of that meeting and pertinent District rainfall reports and data were forwarded to FEMA for evaluation. Based on technical review, FEMA selected the NOAA rainfall depths for use in this FIS. The results of the study were reviewed at the final CCO meeting held on August 4, 1999, and attended by representatives of FEMA, the State, the communities, and the study contractor. All problems raised at that meeting have been addressed. 2.1 Scope of Study This FIS covers the geographic area of Volusia County, Florida. All or portions of the flooding sources listed in Table 1, Flooding Sources Studied by Detailed Methods, were studied by detailed methods. Limits of detailed study are indicated on the Flood Profiles (Exhibit 1) and on the FIRM (Exhibit 2) where applicable. 4

10 TABLE 1 FLOODING SOURCES STUDIED BY DETAILED METHODS Atlantic Ocean Halifax River B-19 Canal Little Tomoka River B-19 Canal Tributary No. 1 Misner Branch B-19 Canal Tributary No.2 Mosquito Lagoon B-19 Canal Tributary No.7 St. Johns River Bulow Creek Shooting Range Canal Canal Between South Canal Crescent Lake Spruce Creek Indian River North Spruce Creek Tributary No. 1 Intracoastal Waterway Spruce Creek Tributary No. 2 E Canal Spruce Creek Tributary A Eleventh Street Canal Thompson Creek Eleventh Street Canal Tributary No.2 Tomoka River Eleventh Street Canal Tributary No. 2A Wally Hoffmeyer Canal Groover Branch As part of the April 15, 2002, countywide FIS, new or revised detailed analyses were included for the flooding sources shown in Table 2, Initial Countywide Scope. TABLE 2 INITIAL COUNTYWIDE SCOPE FLOODING SOURCE NAME Atlantic Ocean Eleventh Street Canal Eleventh Street Canal Tributary No. 2 Halifax River Indian River North Mosquito Lagoon LIMITS OF NEW OR REVISED DETAILED STUDY For its entire coastline within Volusia County. From the confluence with the Tomoka River to a point approximately 2,800 feet upstream of Clyde Morris Boulevard North. From the confluence with the Eleventh Street Canal to confluence of Eleventh Street Canal Tributary No. 2A. From a point approximately 100 feet southwest of the intersection of John Anderson Drive and Highbridge Road to the intersection of Ocean Drive and Peninsula Avenue North. From a point approximately 1,500 feet east of the intersection of Conrad Drive and Redland Drive to a point approximately 1,500 feet southwest of the intersection of South Street and State Route AlA. For the entire shoreline within Volusia County. B-19 Canal From a point approximately 1 mile downstream of Taylor Road to a point approximately 110 feet upstream of Belville Road. B-19 Canal Tributary No. 7 From the confluence with B-19 Canal to a point approximately 150 feet upstream of Bellville Road. Groover Branch From the confluence with the Tomoka River to a point approximately 85 feet upstream of Tymber Creek Road North. 5

11 TABLE 2 INITIAL COUNTYWIDE SCOPE (continued) FLOODING SOURCE NAME Little Tomoka River Misner Branch Shooting Range Canal/Eleventh Street Canal Tributary No. 2/Eleventh Street Canal Tributary No. 2 Thompson Creek Tomoka River LIMITS OF NEW OR REVISED DETAILED STUDY From the confluence with the Tomoka River to a point approximately 100 feet upstream of State Route 40. From the confluence with the Tomoka River to a point approximately 50 feet upstream of Hand Avenue. From the confluence with the Tomoka River to Clyde Morris North / From Clyde Morris Boulevard North to confluence of Eleventh Street Canal Tributary No. 2 / From to a point approximately 2,600 feet upstream of the confluence with Eleventh Street Canal Tributary No. 2. Confluence. From a point approximately 475 feet downstream of U.S. Highway 1 to just downstream of Division Road. From a point approximately 3.3 miles downstream of U.S. Highway 1 to a point approximately 0.96 mile upstream of U.S. Route 92. In addition, detailed analyses of Crescent Lake have been incorporated for the April 15, 2002, countywide FIS. The areas studied by detailed methods were selected with priority given to all known flood hazard areas and areas of projected development and proposed construction. The April 15, 2002, countywide FIS reflects annexations by the Cities of Daytona Beach, Daytona Beach Shores, DeBary, Deland, Deltona, Edgewater, Holly Hill, New Smyrna Beach, Oak Hill, Orange City, Ormond Beach, Port Orange, and South Daytona and the Town of Ponce Inlet. For the purpose of the April 15, 2002, FIS, and all future FISs, the stream once known as Tributary No. 7 will now be known as B-19 Canal Tributary No.7. For the April 15, 2002, FIS, a Letter of Map Revision (LOMR) dated July 21, 1992, in the City of Ormond Beach, and a letter dated January 31, 1991, for the unincorporated areas of Volusia County, both for the Little Tomoka River were incorporated into the FIRM. A Letter of Map Amendment dated February 19, 1992, for a 492-acre parcel of undeveloped land within the unincorporated areas of Volusia County was incorporated into the FIRM. Numerous flooding sources in the county were studied by approximate methods. Approximate analyses were used to study those areas having a low development potential or minimal flood hazards. The scope and methods of study were proposed to, and agreed upon by, FEMA and Volusia County. 2.2 Community Description Volusia County is located in the central portion of the Florida east coast and is 6

12 bordered by Flagler County to the north, Putnam County to the northwest, Lake County to the west, Seminole County to the southwest, Brevard County to the southeast, and the Atlantic Ocean to the east. The land area of Volusia County comprises approximately 1,210 square miles with 50 miles of Atlantic Ocean shoreline. Along the eastern side of the county, the Halifax River and Indian River North/Mosquito Lagoon form long, narrow estuaries which separate the county s mainland from its barrier island. Ponce DeLeon Inlet, located near the middle of the coastline, serves as the county s only inlet through the barrier island and the major passage through which Atlantic Ocean tides and hurricane surges propagate into the estuaries. Although the City of Deland, located in the western central portion of the county, serves as the county seat, the county s eastern incorporated areas support most of the county s population and the highest concentration of residential and commercial land use. The U.S. Census Bureau reports a Volusia County population of 443,343 in Several major transportation routes serve the county, including Interstates 4 and 95; U.S. Routes 1, 17, and 92; State Routes AlA, 40, and 44; the Intracoastal Waterway; and the Florida East Coast Railway. Volusia County has a subtropical climate, with long, warm, and humid summers and short, mild winters. The average annual precipitation is approximately 48 inches. Over half of this rainfall occurs during the hurricane season. Based on data, the seasonal distribution of rainfall ranges from a high of 29.4 inches (June- October) to a low of 10.5 inches (December-March). The terrain of Volusia County varies considerably. In the western portion of the county, rolling forested hills and moderately steep slopes with numerous small lakes characterize the terrain. Elevations in these areas generally range from approximately 9 to 99 feet North American Vertical Datum of 1988 (NAVD88) (Reference 12). In the central and eastern portions of the county, low lying, mildly sloping terrain with extensive swamps generally characterize the land. Much of this terrain is covered with somewhat impermeable, poorly-drained soil formations with a consistently high water table that varies from 6 feet to less than one foot from the surface. The predominant soils associated with this flat terrain include Myakka-Smyrna-Immokalee, Daytona- Paola-Astatula, Palm Beach-Paola-Canaveral, Hydraquents-Turnbull, and Pomona- Wauchula. The predominant hydrologic soil groups are A/D, B/D, and D (References 13, 14, 15, 16, 17, 18, and 19). Elevations in these areas generally range from -1 to 34 feet NAVD88 (Reference 12). The St. Johns River, the largest stream in the county, is the state s largest wholly contained river with a drainage area of 9,430 square miles and length of approximately 285 miles. Otherwise, most of the major streams are located in the eastern portion of the county. Of these, the two largest are the Tomoka River and Spruce Creek. The Tomoka River drains approximately 159 square miles of the northeastern and central eastern portions of the county, including much of the coastal Cities of Ormond Beach and Daytona Beach. The Tomoka River flows south to north draining several significant tributaries and empties into the Halifax River through the Tomoka Basin where it is subject to coastal surge flooding. Spruce Creek flows south to north, then west to east, and empties into the Halifax River through Strickland Bay, where it is also subject to coastal surge flooding. Spruce Creek drains approximately 91 square miles of the southeastern portion of the county, including Spruce Creek Swamp and significant tributaries such as Turnbull Creek and B-19 Canal. The 7

13 floodplains of these rivers are characterized by low, heavily vegetated swamping areas that extend several hundred feet across in some areas. 2.3 Principal Flood Problems Flooding in Volusia County results from tidal surges associated with hurricanes, northeasters, and tropical storm activity and from overflow of streams and swamps associated with rainfall runoff. Major rainfall events occur from hurricanes, tropical storms, and thundershowers associated with frontal systems. Some of the worst floods to occur in the area recently were the result of high intensity rainfall during hurricanes or tropical storms such as Gordon and Faye in 1994 and Having a relatively short time of concentration, the smaller streams tend to reach peak flood flow concurrently with elevated tailwater conditions associated with the coastal storm surge. This greatly increases the likelihood of inundation of low lying areas along the coast observed on several occasions. Areas along the Halifax River, Indian River North, and Mosquito Lagoon are particularly vulnerable to this flooding. In the eastern portion of the county, most of the flood-prone areas feature relatively impermeable soil, a high water table, and flat terrain. These characteristics contribute significantly to flooding problems. Furthermore, the flat slopes and heavily vegetated floodplains promote backwater effects and aggravate the flood problems by preventing the rapid drainage of floodwaters. However, the vast extent of some floodplains, particularly those of the Tomoka River, serve to mitigate some of the flooding and lower peak discharges by providing overbank storage of floodwaters. The USGS, NOAA, and the Florida Department of Transportation have installed discharge and stage gages at several locations throughout the county. Limited periods of record and availability of data reduce the usefulness of many county gages for evaluation of major historical flooding. However, USGS stream gages for the Tomoka River and B-19 Canal provide some significant historical flood data. Locations and periods of record for those gages considered in this FIS are listed below. TR11 Tomoka River at Eleventh Street (1964-present) TR92 Tomoka River at U.S. Highway 92 ( ) B19WR B-19 Canal at Willow Run ( ) B19415 B-19 Canal at State Route 415 ( ) Storm events and relevant data recorded at these stream gages are shown in the following tabulation. Elevation Daily Mean Date Gage (feet NAVD) Discharge (cfs) September 11, 1964 TRII ,170 8

14 October 19, 1968 TRII ,100 October 8, 1969 TRII ,200 June 5, 1976 TRII ,750 November 17, 1994 TRII ,050 December 11, 1983 TR * September 27, 1984 TR * December 12, 1983 B19415 * 170 January 22, 1989 B October 10, 1989 B August 15, 1991 B June 21, 1991 B19WR *Data not available Major flooding events recorded by the Tomoka River gage to date include the 1964, 1968, and 1976 storms. Of these, the 1964 (associated with Hurricane Dora) and 1968 storms were the largest and similar in magnitude. At the Eleventh Street gaging station near Holly Hill, the Tomoka River reached elevations of 11.6 and 11.8 feet NAVD, respectively. For this location, the return period of these storms is approximately five years (based on the discharge-frequency analysis results of this FIS). No other Tomoka River gage records were found for these storms. In B-19 Canal, the largest storm recorded by the gage at State Route 415 occurred in This storm produced a peak daily-averaged flow rate of 267 cfs and a stage of 17.8 feet NAVD. For this location, the return period for the 1989 storm is approximately five years. Floods caused by Crescent Lake can occur in unpredictable cycles. It is possible for the cumulative effect of slightly above-normal rainfall for several consecutive years to cause greater floods than those caused by one year of exceedingly high rainfall. However, a combination of high lake levels; high ground-water levels; and exceedingly high rainfall, which are associated either with several consecutive summer thunderstorms or with a hurricane, can produce extreme flooding. Any unusual combination of meteorologic and hydrologic conditions can produce a rise in the level of Crescent Lake and can result in inundation of the areas adjacent to its normal shoreline (Reference 20). The coastal areas of Volusia County are subject to flooding from tidal surges associated with hurricanes and northeasters. Observed/recorded high water marks from coastal hurricane surge flooding include those from Hurricane Dora on September 9, The surge elevation at Ponce De Leon Inlet exceeded 5.9 feet NAVD. At the Seabreeze Bridge on the Halifax River, the surge reached 3.9 feet NAVD (Reference 21). 2.4 Flood Protection Measures Other than small oceanfront seawalls and numerous, small, man-made canals, no major flood protection structures are known to exist within Volusia County. However, floodplain management measures within the county are extensive. Flooding problems led county and municipal officials to initiate and adopt a series of comprehensive stormwater management plans. Completed in 1995, these plans identified and prioritized flooding problems and developed structural and nonstructural solutions to mitigate flooding while planning for future growth. Structural improvements include 9

15 subdivision swales, berms, and pumping; additional culverts, detention ponds, channel improvements, and weirs. Nonstructural improvements include ordinances which restrict floodplain development. Although the recommended structural improvements have begun, they are not expected to significantly impact this FIS. Available data and results from these stormwater management plans were evaluated and incorporated into this FIS. 3.0 ENGINEERING METHODS For the flooding sources studied by detailed methods in Volusia County, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study. Flood events of a magnitude which 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 which equals or exceeds the 1-percent-annual-chance 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 Volusia County at the time of completion of this study. Maps and flood elevations will be amended periodically to reflect future changes. 3.1 Riverine Hydrologic Analyses Hydrologic analyses were carried out to establish the peak discharge-frequency relationships and peak elevation-frequency relationships for each flooding source studied in detail affecting Volusia County. Precountywide Analyses For B-19 Canal, Tomoka River, Canal Between, Eleventh Street Canal, and Wally Hoffmeyer Canal in the City of Daytona Beach, the runoff block of the EPA Stormwater Management Model (SWMM), as modified by Camp Dresser & McKee, Inc., was used to generate runoff hydrographs and to perform simplified lake/channel/conduit routing (References 22 and 23). Detailed information on the hydrologic parameters is contained in the study Tomoka River and B-19 Canal 100- year Flood Results for the City of Daytona Beach (Reference 2). The drainage areas were obtained from this model. The EXTRAN model performs hydraulic routing in the downstream reaches of the watershed (Reference 24). Discharges were obtained from the EXTRAN model. For the St. Johns River in the City of DeBary and the unincorporated areas of Volusia County, the flood profiles were taken from the Lake and Seminole Counties FISs (References 4 and 5). The 10-, 1-, and 0.2-percent annual chance flood profiles in the FISs were determined from an analysis of gage records on the St. Johns River, which also involved stream routings to correlate past storm events at the stream gage locations. Peak discharge data are therefore unavailable for the St. Johns River. 10

16 For E Canal and South Canal in the City of Edgewater, peak discharge-frequency relationships for floods of the selected recurrence intervals were estimated from a regional flood-frequency analysis based on the gage records of three stations, with lengths of record of 25 years, 15 years, and 12 years. The gaging stations are located at the mouth of South Canal, at the mouth of E Canal, and at Fern Palm Drive on E Canal. The regional flood-frequency analysis provides two curves; the first expresses the flood discharge-time relation, showing variation of peak discharge expressed as a ratio to the mean annual flood, with recurrence interval. The second relates the mean annual flood to drainage area (Reference 25). Thus, by delineating drainage areas of South Canal and E Canal, peak discharges for the selected recurrence intervals could be estimated. For Eleventh Street Canal Tributary Nos. 2 and 2A, and Shooting Range Canal in the City of Ormond Beach; and B-19 Canal Tributary Nos. 1 and 2, and Spruce Creek in the City of Port Orange and the unincorporated areas of Volusia County, regionalized regression equations, developed by the USGS, in cooperation with the FDOT, were used for deriving peak discharge-frequency relationships (Reference 26). These equations were slightly modified to represent the extensive swamp areas within the drainage basins of the streams by adjusting the lake storage term of the equation so that the computed peak discharges of the selected recurrence intervals agree closely with the peak discharges resulting from the log-pearson Type III analysis for the streamflow records. The procedures outlined in U.S. Water Resources Council Bulletin No. 17B were used in applying the distributions to the observed streamflow records (Reference 27). The hydrologic analysis for Spruce Creek Tributary 1, Spruce Creek Tributary 2, Spruce Creek Tributary A, and Bulow Creek are not available. April 15, 2002, Countywide Analyses The USACE HEC-l computer program was used to estimate the discharge-frequency relationships for streams studied in detail except for the Eleventh Street Canal, Eleventh Street Canal Tributary No.2, Eleventh Street Canal Tributary No. 2A, and Shooting Range Canal (References 28, 29, 30, and 31). Those streams used SWMM 4.3. Except for the Tomoka River, the limited history of stream gage records for these streams precluded effective statistical analysis. The gage on Tomoka River, located at Eleventh Street near Holly Hill, provided 31 years of data. Although statistical analyses of these data proved useful for comparison/verification purposes, HEC-l was considered more appropriate for the basin as a whole, which includes four ungaged, detailed study streams. For the Tomoka River, USGS published discharge-frequency relationships, computed by a weighted combination of USGS regression equations and log-pearson Type III statistical analysis, were compared to the HEC-l discharges with favorable results. For all other streams, USGS regional regression equations were used for comparison purposes. These results also compared reasonably well with the HEC-l results (Reference 26). HEC-l modeling incorporated the SCS unit hydrograph and kinematic wave routing methods. Parameters supplied to the model of each stream included subbasin runoff curve numbers, lag times, stream cross sections, and Manning s n roughness factors. Curve numbers were calculated using the SCS curve number method (Reference 32) based on FDOT aerial photographs at a scale of 1:25,000 (Reference 11

17 33), GIS soils and land use coverages (Reference 34), and available, calibrated hydrologic model studies (References 13 and 17). Lag times were calculated using the empirical SCS curve number formula (Reference 35). The HEC-l models of Tomoka River and B-19 Canal were calibrated and verified using storm discharge data provided by the Tallahassee Subdistrict of the USGS and corresponding hourly rainfall data obtained from the National Weather Service. USGS gages/locations used for calibration were Tomoka River near Holly Hill (Eleventh Street), B-19 Canal at State Route 414, and B-19 Canal at Willow Run. For calibration, an observed storm was simulated with HEC-l and model parameters, including curve numbers, lag times, and initial abstractions, were adjusted until reasonable fits between observed and predicted peak flows were obtained. For verification, a second storm was simulated to establish the accuracy of the calibrated model parameters. Based on the final calibration results, model parameters in downstream, ungaged basins were adjusted similarly to the calibrated parameters for each stream. For Tomoka River, these downstream basins included the detail study stream basins for Groover Branch, Little Tomoka River, Thompson/Strickland Creek, and Misner Branch. Following successful calibration, the HEC-l models were used to estimate peak discharges for the selected recurrence intervals throughout each stream study reach except for the Eleventh Street Canal, Eleventh Street Canal Tributary No.2, Eleventh Street Canal Tributary No. 2A, and Shooting Range Canal. For those flooding sources, the SWMM 4.3 model was used to estimate 1-percent-annual peak discharge. For these storm events, total storm rainfall amounts were based on the TP-40 rainfall frequency atlas for a 24-hour storm duration (Reference 11). The temporal rainfall distribution used in the models was the SCS Type II Florida modified distribution (Reference 36). A summary of the drainage area-peak discharge relationships for all streams studied by detailed methods is shown in Table 3, Summary of Discharges. TABLE 3 SUMMARY OF DISCHARGES PEAK DISCHARGES (cfs) DRAINAGE 10-Percent- 2-Percent- 1-Percent- AREA Annual- Annual- Annual- (sq. miles) Chance Chance Chance 0.2-Percent- Annual- Chance FLOODING SOURCE AND LOCATION B-19 CANAL At mouth ,089 1,338 At Willow Run Boulevard ,102 At Pelican Bay Drive B-19 CANAL TRIBUTARY NO. 1 At Interstate B-19 CANAL TRIBUTARY NO. 2 At mouth B-19 CANAL TRIBUTARY NO. 7 At Bellville Road 0.40 * * 148 * 12

18 TABLE 3 SUMMARY OF DISCHARGES (continued) PEAK DISCHARGES (cfs) DRAINAGE 10-Percent- 2-Percent- 1-Percent- AREA Annual- Annual- Annual- (sq. miles) Chance Chance Chance 0.2-Percent- Annual- Chance FLOODING SOURCE AND LOCATION BULOW CREEK At Washington Avenue ,282 2,258 2,744 4,067 CANAL BETWEEN At mouth 0.49 * * 154 * E CANAL At mouth At Fern Palm Drive ELEVENTH STREET CANAL At mouth 4.20 * * 1,070 * ELEVENTH STREET CANAL TRIBUTARY NO. 2 At confluence with Eleventh Street Canal 0.76 * * 678 * ELEVENTH STREET CANAL TRIBUTARY NO. 2A Just upstream of Daytona 0.28 * * 678 * Beach corporate limits GROOVER BRANCH At Tymber Run Road At Airport Road At Tymber Creek LITTLE TOMOKA RIVER At Tymber Creek Road North At Breakway Trail At State Route 40 MISNER BRANCH At mouth At Main Trail Road At State Route 40 At Falls Way Boulevard ,774 1,720 1,650 3,205 2, ,483 2,409 2,316 4,417 3,907 2, ,961 2,869 2,759 5,222 4,613 2, ,744 3,618 3,482 6,552 5,776 3,046 1,177 1,071 1, SHOOTING RANGE CANAL At Interstate SOUTH CANAL At mouth SPRUCE CREEK At Interstate 95 Just upstream of Fly-In Road At unnamed road ,843 1,365 1,101 2,667 1,976 1,594 3,039 2,253 1,820 3,889 2,906 2,366 SPRUCE CREEK TRIBUTARY NO. 2 At confluence with Spruce Creek ,047 1,326 13

19 TABLE 3 SUMMARY OF DISCHARGES (continued) PEAK DISCHARGES (cfs) DRAINAGE 10-Percent- 2-Percent- 1-Percent- AREA Annual- Annual- Annual- (sq. miles) Chance Chance Chance 0.2-Percent- Annual- Chance FLOODING SOURCE AND LOCATION SPRUCE CREEK * * * 8,600 * TRIBUTARY A At confluence with Spruce Creek THOMPSON CREEK At U.S. Highway At FEC railroad At State Route At Tomoka Avenue TOMOKA RIVER ,470 7,396 8,914 At Old Dixie Highway ,489 10,380 12,366 At U.S. Highway ,393 11,622 13,784 At Interstate Route ,521 6,206 7,332 At State Route ,520 4,786 5,628 At Eleventh Street ,268 1,494 At U.S. Route 92 WALLY HOFFMEYER CANAL At mouth 2.29 * * 833 * *Data not available ,522 15,670 17,385 9,185 7,015 1,866 For Crescent Lake, lake level records for 12 lakes in Alachua, Clay, and Marion Counties, which are adjacent to Putnam County, were used to define maximum lake volume-frequency relationships for each site. Seven of these lake-level records had data for more than 20 years, and the maximum length of record is 35 years. Of the 12 records, the shortest is 14 years. The drainage areas for these lakes ranged form 0.19 square mile to 319 square miles, and the surface areas of these lakes ranged from square mile (9.6 acres) to 20.6 square miles (more than 13,000 acres). The range of change in lake level was from less than two feet to more than 30 feet. These lakes were also vastly different in outflow characteristics from completely closed (no outflow at any flood frequency) to outflow at all flood frequencies. Flood-frequency curves were defined for each of the 12 lake-level records. These curves were developed in terms of lake volume measured above a defined base. Volumes were adjusted for outflow, as applicable, and the base level was defined as the mean lake stage. After all annual data (based on year beginning on June 1 and ending on May 31) were adjusted; analyses were carried out to determine the best technique for fitting flood-frequency curves to the lake-volume data. A log-pearson Type III distribution, using the average skew coefficient as outlined in U.S. Water Resources Council Bulletin 17A, was found to be an acceptable technique for fitting flood-frequency curves to lake-volume data (Reference 37). Values of the selected recurrence intervals were obtained for each of the 12 lakes from this log-pearson Type III distribution. A regression analysis of frequency data versus drainage area for the 12 lakes was used to define a regional relationship for each recurrence interval. The analysis showed that drainage basin size explained 14

20 nearly all of the variation in the lake volumes. Regression analysis was also used to define a regional relationship between the mean lake stage and grassline elevation along the lakes shores of the 12 lakes. The analysis showed that the elevation of the grassline along the shoreline explained nearly all of the variation in mean lake stage. The Stillwater elevations for the 10-, 2-, 1-, 0.2-percent-annual-chance floods for the Atlantic Ocean coastline subject to tidal surge and Crescent Lake have been determined and are summarized in Table 4, Summary of Stillwater Elevations. The analyses reported herein reflect the Stillwater elevations of the Atlantic Ocean due to tidal and wind setup effects and include the contributions from wave action effects. TABLE 4 SUMMARY OF STILLWATER ELEVATIONS ELEVATION (feet NAVD) FLOODING SOURCE AND LOCATION 10-Percent- Annual- Chance 2-Percent- Annual- Chance 1-Percent- Annual- Chance 0.2-Percent- Annual- Chance CRESCENT LAKE Riverine 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 Flood Insurance Rate Map (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 us the flood elevation data presented in this FIS report in conjunction with the data shown on the FIRM. Except where noted, cross section were obtained form field surveys. All bridges, dams, and culverts were field surveyed to obtain elevation data and structural geometry. Cross sections were located at close intervals upstream and downstream of bridge and culverts to compute the significant backwater effects of these structures. 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). The hydraulic analyses for this FIS were based on unobstructed flow. The flood elevations shown on the profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. All elevations are referenced to the North American Vertical Datum of 1988 (NAVD88). Elevation reference marks (ERMs) used in this study, and their descriptions, are shown on the FIRM. ERMs shown on the FIRM represent those used during the preparation of this and previous FISs. The elevations associated with each ERM were obtained and/or developed during FIS production to establish vertical control for determination of flood elevations and floodplain boundaries shown on the FIRM. Users should be aware that these ERM elevations may have changed since the publication of this FIS. To obtain up-to-date elevation information on National Geodetic Survey (NGS) ERMs shown on this map, please contact the Information 15

21 Services Branch of the NGS at (301) , or visit their website at Map users should seek verification of non-ngs ERM monument elevations when using these elevations for construction or floodplain management purposes. Precountywide Analyses For the St. Johns River in the City of DeBary and unincorporated areas of Volusia County, cross sections were obtained from field surveys (Reference 38). In some cases, topographic maps were used to extend surveyed cross sections (References 39, 40, and 41). Water-surface elevations of floods of the selected recurrence intervals were computed using the USACE HEC-2 step-backwater computer program (Reference 42). For Canal Between, Eleventh Street Canal, and Wally Hoffmeyer Canal in the City of Daytona Beach, hydraulic data were obtained from the city s drainage facility inventory, survey, and field identification. The EXTRAN computer model was used to calculate water-surface profiles (Reference 24). The EXTRAN model received hydrograph input at specific nodal locations by disk file transfer from the RUNOFF hydrologic model (Reference 23). For E Canal and South Canal in the City of Edgewater, hydraulic analyses were performed based on a combination of methods using the hydraulic characteristics of the canals and accounting for storage in the upstream terrace areas. Water-surface profiles for South Canal inland from the Indian River, along the northern corporate limits of the city and for E Canal from the Indian River north to the east side of FEC railroad were developed using the USGS step-backwater computer program (Reference 43). Computations of water-surface elevations above culverts were done manually or using the USGS computer program for automatic computations of stagedischarge relations at culverts (Reference 44). It was assumed that maximum tidal elevations and maximum freshwater flood elevations will not occur simultaneously. When the tide is highest, flow in the streams will be upstream, not toward the coast. Downstream flow will occur during the freshwater flood peak. Certain culverts or series of culverts in the streams restrict flood flows in both directions, resulting in appreciably higher water-surface elevations upstream (with respect to flow direction) of the culverts than downstream. These culverts, under Magnolia Street and U.S. Highway 1 on South Canal, and under FEC railroad on E Canal, form the boundaries between areas where tidal and freshwater floods predominate under all but the most severe (SOD-year) flooding conditions. Shallow freshwater flooding, partly due to the culverts and partly due to the nature of the areas, makes storage an important consideration in the wide, flat terrace areas upstream of the control culverts. Shallow flooding in the terrace areas is created by inadequate drainage. To account for storage, stage-discharge ratings upstream of the control culverts in each of the two canals were developed from step-backwater results. These ratings, together with stage-volume curves constructed from cross section properties and input hydrographs developed from regional streamflow records, provided input to a reservoir-routing computer program developed by the USGS (Reference 45). The program simulated storage of excess rainfall in the terrace areas above the control culverts, thereby reducing peak discharge and maximum freshwater flood elevation in those areas. Thus, the stream profiles reflect the superposition of tidal flood elevations on the downstream sections of the step-backwater profiles and 16

22 the superposition of storage-adjusted freshwater flood elevations at the upstream ends of the backwater profiles. Starting water-surface elevations were taken from the analysis of the Indian River performed for the previously published City of New Smyrna Beach FIS (Reference 46). For Eleventh Street Canal Tributary Nos. 2 and 2A, and Shooting Range Canal in the City of Ormond Beach and the unincorporated areas of Volusia County, water surface elevations were developed using the WSP-2 water-surface profile computer model (Reference 47). Cross sections were obtained from field surveys (Reference 38). For Spruce Creek in the City of Port Orange, water-surface elevations were developed using the USACE HEC-2 water-surface profile computer model (Reference 48). Water-surface elevations for B-19 Canal Tributaries Nos. 1 and 2 in the City of Port Orange and the unincorporated areas of Volusia County were developed using the WSP-2 water-surface profile computer model (Reference 47). For Bulow Creek, Spruce Creek, and Spruce Creek Tributary Nos. 1 and 2 in the unincorporated areas of Volusia County, various hydraulic methods were used. Water-surface elevations for floods of the selected recurrence intervals were developed using the USACE HEC-2 water-surface profile computer model (Reference 48). Cross sections for the backwater analyses were obtained from field surveys; in some cases, topographic maps were used to extend surveyed cross sections (References 38, 39, 40, and 41). Cross sections for Bulow Creek were developed from topographic data furnished by Bellemead Corporation, the Volusia County Engineering Department, and the topographic maps (References 49 and 39). The slope/area method was used to set the HEC-2 starting water-surface elevations for Bulow Creek, and Spruce Creek and its tributaries. The 1-percent-annual-chance flooding elevation for Spruce Creek Tributary A was determined by standard stepbackwater procedures (Reference 7). The 10-percent-annual-chance flooding elevation was determined by approximate methods. Roughness factors (Manning s n ) used in the hydraulic computations were chosen on the basis of field observations and aerial photographs of the streams and floodplain areas. Roughness values for all streams are shown in Table 5, Manning s n Values. April 15, 2002, Countywide Analyses Water-surface elevations of floods of the selected recurrence intervals were computed through use of the USACE HEC-2 water-surface profile computer program (References 42 and 50). Starting water-surface elevations for the Tomoka River tributaries were specified as the mean annual Tomoka River flood elevations at the confluence of the tributaries. For the Tomoka River, Mean High Water in Tomoka Basin, provided by the FDEP, was used for the starting water-surface elevation (Reference 51). For B-19 Canal, the slope/area method was used to establish starting water-surface elevations based on stream invert elevations near the beginning of the stream study reach. Disparity in drainage basin areas precluded the use of the coincident Peak method to establish starting elevations on tributaries to main streams. For the Eleventh Street Canal, Eleventh Street Canal TributaryNo.2, Eleventh Street Canal Tributary No. 2A, and Shooting Range Canal, SWMM 4.3 was used for the 17