Wakulla County, Florida and Incorporated Areas

WAKULLA COUNTY, FLORIDA AND INCORPORATED AREAS

COMMUNITY COMMUNITY Wakulla County NAME NUMBER

SOPCHOPPY, CITY OF 120620 ST. MARKS, CITY OF 120316 WAKULLA COUNTY (UNINCORPORATED AREAS) 120315

EFFECTIVE

September 26, 2014

Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER 12129CV000A 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.

Part or all of this FIS may be revised and republished 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 repository to obtain the most current FIS components.

Initial Countywide FIS Effective Date: September 26, 2014

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...... 3

2.1 Scope of Study ...... 3 2.2 Community Description ...... 4 2.3 Principal Flood Problems ...... 5 2.4 Flood Protection Measures ...... 7

3.0 ENGINEERING METHODS ...... 7

3.1 Hydrologic Analyses ...... 8 3.2 Hydraulic Analyses ...... 10 3.3 Coastal Hydrologic Analyses ...... 12 3.4 Coastal Hydraulic Analyses ...... 18 3.5 Vertical Datum ...... 30

4.0 FLOODPLAIN MANAGEMENT APPLICATIONS ...... 31

4.1 Floodplain Boundaries ...... 32 4.2 Floodways ...... 33

5.0 INSURANCE APPLICATION ...... 39

6.0 FLOOD INSURANCE RATE MAP ...... 40

7.0 OTHER STUDIES ...... 41

8.0 LOCATION OF DATA ...... 41

9.0 BIBLIOGRAPHY AND REFERENCES ...... 43

TABLE OF CONTENTS – continued

Page

FIGURE

Figure 1 – Transect Schematic 19

Figure 2 – Transect Location Map 23

Figure 3 – Floodway Schematic 34

TABLES

Table 1 – Scope of Revision 3

Table 2 – Summary of Discharges 10

Table 3 – Summary of Stillwater Elevations 16-18

Table 4 – Transect Descriptions 24-26

Table 5 – Transect Data 27-30

Table 6 – Floodway Data 35-38

Table 7 – Community Map History 42

TABLE OF CONTENTS – continued

EXHIBITS

Exhibit 1 – Flood Profiles

Buckhorn Creek Panel 01P Lost Creek Panels 02P-03P Sopchoppy River Panels 04P-06P St. Marks River Panel 07P West Branch Buckhorn Creek Panel 08P

Exhibit 2 (Published Separately) – Flood Insurance Rate Map Index Flood Insurance Rate Map

iii

FLOOD INSURANCE STUDY WAKULLA COUNTY, FLORIDA AND INCORPORATED AREAS

1.0 INTRODUCTION

1.1 Purpose of Study

This countywide Flood Insurance Study (FIS) investigates the existence and severity of flood hazards in, or revises and updates previous FISs/Flood Insurance Rate Maps (FIRMs) for the geographic area of Wakulla County, Florida, including the City of Sopchoppy, the City of St. Marks, and the unincorporated areas of Wakulla County (hereinafter referred to collectively as Wakulla 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 Wakulla County to update existing floodplain regulations as part of the Regular Phase of the National Flood Insurance Program (NFIP), and will also be used 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 (CFR) 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 source of authority for this Flood Insurance Study is the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973.

This FIS was prepared to include all jurisdictions within Wakulla County in a countywide FIS. Information on the authority and acknowledgments for each jurisdiction included in this countywide FIS, as compiled from their previously printed FIS reports, is shown below.

Sopchoppy, City of: The hydrologic and hydraulic analyses for the FIS report dated February 15, 1984, were prepared by the U. S. Geological Survey, for the Federal Emergency Management Agency (FEMA). That work was completed in January 1981.

St. Marks, City of: The hydrologic and hydraulic analyses for the FIS report dated September 18, 1979, were prepared by the U. S. Geological Survey (USGS), for the Federal

Emergency Management Agency (FEMA). That work was completed in February 1978.

Wakulla County (Unincorporated Areas): The hydrologic and hydraulic analyses for the FIS report dated June 17, 1986, were prepared by Gee & Jensen EAP Inc., for FEMA under Contract No. H- 4625. That work was completed in January 1981.

For the June 17, 1986 Wakulla County FIS, the coastal analyses were revised by Coastal and Offshore Engineering and Research, Inc. (COER). This revision affects the area known as Shell Point, which lies on the coast in the vicinity of Walker Creek. Transect 4 was recomputed using new information supplied by COER.

For this countywide FIS, revised coastal analyses for the Gulf of Mexico, including the entire shoreline of Wakulla County, have been prepared for FEMA by the Northwest Florida Water Management District (NWFWMD) under Contract No. EMA-2008-CA-5886. Additionally, the St. Marks River and Wakulla Gardens area was studied using detailed methods and all approximate flood hazards have been re-evaluated. All unrevised detailed studied streams have been redelineated using updated topographic data. This work was completed in 2011.

Base map information for this FIRM was developed from high resolution digital orthoimagery provided by the Florida Department of Transportation. This information was produced at a resolution of 1 foot in 2010.

The coordinate system used for the production of this FIRM is Florida State Plane North Zone 0903, referenced to the North American Datum of 1983 (NAD83) HARN. Corner coordinates shown on the FIRM are in latitude and longitude referenced to the State Plane projection, NAD 83 HARN. Differences in the datum and spheroid used in the production of FIRMs for adjacent counties may result in slight positional differences in map features at the county boundaries. These differences do not affect the accuracy of information shown on the FIRM.

1.3 Coordination

Consultation Coordination Officer’s (CCO) meetings may be held for each jurisdiction in this countywide FIS. An initial CCO meeting is held typically with representatives of 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 typically with representatives of FEMA, the community, and the study contractor to review the results of the study.

The dates of the initial and final CCO meetings held prior to the countywide FIS for Wakulla County and the incorporated communities within its boundaries are in the following tabulation:

Community Name Initial CCO Date Final CCO Date

Sopchoppy, City of N/A September 21, 1983 St. Marks, City of November 1974 February 6, 1979 Wakulla County (Unincorporated Areas) March 22, 1978 December 8, 1982

For this countywide FIS, an initial CCO (Scoping) meeting was held on January 12, 2007 and was attended by representatives of the study contractors, the communities, the NWFWMD and FEMA. A final CCO meeting was held on September 13, 2012.

2.0 AREA STUDIED

2.1 Scope of Study

This FIS covers the geographic area of Wakulla County, Florida. Flooding caused by overflow of Sopchoppy River, Lost Creek, Buckhorn Creek, West Branch Buckhorn Creek and the lower Ochlockonee River was previously studied in detail.

For this countywide FIS, all coastal flood hazards affecting the county were restudied. The entire shoreline of Wakulla County along the Gulf of Mexico was restudied with a new coastal storm surge and overland wave analysis. In addition, new or revised detailed hydrologic and hydraulic analyses were included for the flooding sources shown in Table 1 – “Scope of Revision.”

TABLE 1 - SCOPE OF REVISION

Stream Limits of New or Revised Detailed Study

St. Marks River The St. Marks River study area extends approximately 5.6 miles from Apalachee Bay to the Leon County Line.

Wakulla Gardens Wakulla Gardens Subdivision Area

Wakulla River The Wakulla River study area extends from the St. Marks River confluence to the Wakulla Spring, approximately 9.15 miles.

The areas studied by detailed methods were selected with priority given to all known flood hazards and areas of projected development and proposed construction.

All or portions of 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, the NWFWMD, and Wakulla County.

2.2 Community Description

Wakulla County is located in northwest Florida on the Gulf of Mexico, approximately 15 miles south of Tallahassee. It is bordered on the west by Liberty and Franklin Counties, on the north by Leon County, and on the east by Jefferson County. Major communities within the county are the incorporated cities of St. Marks and Sopchoppy, and the unincorporated communities of Crawfordville, Medart, Newport, Panacea, and Wakulla. Crawfordville, which lies approximately 20 miles south of Tallahassee, is the county seat. The 2012 population estimate for the county was reported to be 30,818 (U.S. Census Bureau, 2013).

The primary east-west artery serving the county is State Highway 30 (U.S. 98) which provides interconnection to most of the coastal counties in the area. State Highway 363 provides access to areas north of the county.

Other transportation services include rail service to St. Marks, bus service, and air service via the Tallahassee Municipal Airport to the north.

No primary growth centers exist in the county; however, some residential development appears to be occurring in the extreme northern sections of the county as a result of urbanization from nearby Tallahassee. Future development potential is limited, primarily because of the large land areas occupied by the Apalachicola National Forest, and the St. Marks National Wildlife Refuge. Some development has occurred along Ochlockonee Bay, and the coastline near Panacea. Any expected future development will probably occur in the northern and southwestern regions of the county.

The county's economy is primarily forestry oriented, with other economic activities including manufacturing, agriculture, and fishing. Future economic growth should follow the urban expansion from the nearby City of Tallahassee (Reference 3).

Ground elevations are generally very low throughout the county, typically ranging from sea level to 10 feet North American Vertical Datum (NAVD) near the coast to over 100 feet NAVD in the northern portions of the county.

The climate of the area is moderated by the effects of the Gulf of Mexico and temperatures are usually mild and sub-tropical, subject to wide winter variations. According to the National Oceanic and Atmospheric Administration records (Reference 4), the normal average daytime temperatures vary from about 55 degrees Fahrenheit (F) in January to 88 degrees F in August. The average annual precipitation is about 57 inches.

Thunderstorms occur in all months with about three-quarters of them occurring in the summer. The prevailing wind is from the southeast in the summer, switching to northerly and northeasterly during the winter months.

2.3 Principal Flood Problems

Wakulla County is subject to coastal flooding caused by extra tropical cyclones and hurricanes. Extra tropical cyclones can occur at any time of the year but are more prevalent in the winter. The prime hurricane season is from August to October during which time 80 percent of all hurricanes occur. September is the worst month for hurricanes; during which 32 percent of the total occur. Hurricanes are of shorter duration than northeasters and generally last through only one tidal cycle.

In meteorological terms, a hurricane is defined as a tropical cyclone which has a central barometric pressure of 29 inches or less of mercury, and wind velocities of 75 miles per hour or more. The low barometric pressures and high winds combine to produce abnormally high tides and accompanying tidal flooding. The high winds can generate large waves, provided there are no obstructions or barrier beaches to dissipate wave momentum. The winds of a hurricane in the Northern Hemisphere spiral inward in a counterclockwise direction towards the "eye" or center of low pressure. The eye of the hurricane (where winds are subdued) can vary in diameter. Normally, the "eye" can extend for 15 miles, although the eye of a mature hurricane can reach diameters of 20 to 30 miles or even greater.

A hurricane develops as a tropical storm either near the Cape Verde Islands off the African coast or in the western Caribbean Sea. Most hurricanes which reach northwestern Florida approach from a southerly direction after crossing the Florida peninsula, the island of Cuba, or the western Gulf of Mexico. These hurricanes start their journey northward with a forward speed of about 10 miles per hour.

The most destructive winds in a hurricane occur east of the eye, where the spiral wind movement and forward motion of the storm combine. Several past hurricanes have tracked over the Florida Panhandle; therefore, Wakulla County is prone to experience the full intensity of a major hurricane. In order for Wakulla County to experience the highest winds and accompanying highest tides of a hurricane, the storm would need to track west of the county.

The principal flood hazard in terms of damage to Wakulla County is the inundation of low-lying coastal areas during the passage of a severe hurricane or tropical storm. The flood plains of the Ochlockonee and St. Marks Rivers are also subject to flood damage during high river stages. Other low-lying areas throughout the county are subject to rainfall ponding flooding during periods of high rainfall. The area is particularly prone to extreme storm tides as discussed below.

Storm surge elevations within the Apalachee Bay area are generally higher than the adjacent areas to the west and south of the bay. The reason for this is twofold; first, shallow water depths extend a great distance offshore, thus increasing the effects of

bottom and wind friction which results in higher storm surge elevations; and second, storm generated winds out of the south-southeast tend to create a flow or movement of water in a northwest direction along Florida's west coast into Apalachee Bay.

Historically, the county has experienced a few damaging hurricanes. During the 1837 season a storm originated in the Gulf of Mexico or the western Caribbean, and caused flooding in Wakulla County on August 31, 1837. An account of the storm given in Reference 5 describes the Town of St. Marks being inundated to a depth of seven feet. The editor of the Tallahassee Floridian at the time found it hard to account for the depth of the tide, in view of the prevailing northeast winds at the time of high water. He reasoned that this occurrence was a result of the strong southeast currents noticed in the Gulf of Mexico before the storm made landfall.

During 1843, the county was subjected to another devastating storm. At the height of the storm the Town of Port Leon (south of St. Marks) was reported inundated to a depth of ten feet.

In recent years, both hurricanes Alma (1966) and Agnes (1972) have affected Wakulla County. Hurricane Alma proceeded on a north-northwesterly course travelling approximately parallel to Florida's west coast, making landfall near St. Marks, Florida on June 9, 1966. The tide station operated by the ACOE at St. Marks recorded a peak tide of five feet NGVD, a tide that would occur, on the average, once every 4 years.

Hurricane Agnes formed as a tropical depression on the northeast tip of the Yucatan Peninsula on June 15, 1972. The storm moved northward approximately 200 miles west of the west coast of Florida becoming of hurricane status on the 18th of June. Agnes continued north making landfall near Panama City, Florida on June 19, 1972. The U.S. Army Corps of Engineers tide station at St. Marks recorded a peak tide of 7.9 feet NGVD, a tide that could be expected to occur once every 9 years. Many low-lying areas along the coast were inundated during Hurricane Agnes.

Hurricane Elena, in 1985, made two passes offshore of Wakulla County before making landfall in Mississippi. Wind damage associated with Hurricane Elena was limited to shoreline areas of Jefferson County; however, the accompanying storm surge, of approximately 8 to 9 feet at St. Marks, resulted in damage to shorefront protection structures and buildings.

Hurricane Earl, in 1998, made landfall in Panama City Beach in Bay County. In Wakulla County, the storm surge was approximately 8 feet at St. Marks. Shorefront erosion resulted in damage to the Marsh Islands.

Hurricane Dennis, in 2005, made landfall on Santa Rosa Island, between Navarre Beach and Pensacola Beach, in Escambia County. Although well westward of Wakulla County, this hurricane produced a storm surge of 6 to 9 feet in Apalachee Bay. High waves, associated with Hurricane Dennis resulted in beach erosion to open coast areas of both Franklin County and Wakulla County.

Coastal flooding is not limited to hurricane activity; in fact, extra tropical cyclones have resulted in significant tidal flooding along the Florida panhandle. Extra tropical cyclones can develop in the Gulf of Mexico and along strong frontal boundaries and can potentially occur at any time of year, but most frequently in the winter and spring months. Typically, these storms have centers that are colder than the surrounding air, with strongest winds in the upper atmosphere, and lower wind velocities and higher central pressures than a major hurricane; however, wind velocities associated with an extra tropical cyclone can easily reach tropical storm and Category 1 hurricane levels. In addition, the high winds of an extra tropical cyclone can last for several days, causing repeated flooding and excessive coastal erosion. The long exposure of property to high water, high winds, and pounding wave action can result severe property damage.

2.4 Flood Protection Measures

Wakulla County does not have any flood protection measures designed and constructed specifically for that purpose. The Jackson Bluff Dam located on Lake Talquin (Ochlockonee River) is a hydroelectric installation operated by the Florida Power Corporation. This project was completed in 1930, and offers no appreciable flood control for properties located downstream. Although there are no coastal protective structures, some resistance to coastal storm surge flooding will result as a secondary benefit of the dikes, highways, and logging trails.

The county has enacted an ordinance which prohibits new buildings with first-floor elevations less than 4 feet National Geodetic Vertical Datum (NGVD) and less than 18 inches above any adjacent road.

3.0 ENGINEERING METHODS

For the flooding sources studied in detail in the community, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this FIS. Flood events of a magnitude that is 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 100-year flood (1 percent chance of annual exceedence) in any 50-year period is approximately 40 percent (4 in 10), and, 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 FIS. Maps and flood elevations will be amended periodically to reflect future changes.

3.1 Hydrologic Analyses

Hydrologic analyses were carried out to establish the peak discharge-frequency relationships for the flooding sources studied in detail affecting the county.

The unincorporated areas of Wakulla County have a previously printed FIS report. The hydrologic analyses described in that report are summarized below.

June 17, 1986 Analyses

Data obtained from a Flood Insurance Study previously prepared for FEMA by the USGS, Water Resources Division, Tallahassee, Florida was used for the merging of the coastal and riverine elevations in the lower reaches of the Ochlockonee and Sopchoppy Rivers, and for Buckhorn Creek.

Peak discharge-drainage area relationships for the Sopchoppy River, Lost Creek, Buckhorn Creek, West Branch Buckhorn Creek, and the Ochlockonee River are shown in Table 2 – "Summary of Discharges.”

Countywide Analyses

For this countywide FIS, the areas below were analyzed by detailed methods.

The St. Marks River study area extends approximately 5.6 miles from Apalachee Bay to the Leon County line. The Wakulla River study area extends from the St. Marks River confluence to the Wakulla Spring, approximately 9.15 miles.

Wakulla Gardens Subdivision was platted in the late 1950’s. Wakulla Gardens is located in central Wakulla County and is approximately 592 acres. In this area, the Streamline Technologies ICPR v.3 unsteady flow model was used to estimate flood discharges and elevations for a series of flood frequencies including the 10, 2, 1, and 0.2 percent annual chance events.

The rainfall amounts for the 24-hour 10, 2, 1, and 0.2 percent storm events were obtained from Appendix B of Drainage Manual published by State of Florida Department of Transportation. Synthetic (Type II Florida Modified) rainfall time distribution was used to develop the ICPR models. Watershed boundaries were delineated using Light Detection and Ranging (LiDAR) information and topographic survey of the study area. The SCS Curve Number Method was used in this study to compute the direct runoff resulting from each of the analyzed frequencies. Basin time of concentration was determined using the procedures outlined in the National Resource Conservation Service (NRCS) TR-55 publication. The SCS Unit Hydrograph method was used to generate the hydrographs resulting from the analyzed storms. A unit hydrograph peak factor of 323 was selected.

The Wakulla River study area extends from the St. Marks River confluence to the Wakulla Spring. This river has an approximately basin area 56 square miles. The St. Marks River study area extends approximately 5.6 miles from Apalachee Bay

to the Leon County line. This river has an approximate basin area of 574 square miles.

For the Wakulla River and St. Marks River detailed studies, streamflows were estimated using USGS Regional Regression Equations for a series of flood frequencies. Flood frequency methods were used to estimate streamflows at USGS gages within and adjacent to Wakulla County on streams with characteristics similar to those of the study reaches. Estimated streamflows for each of the study reaches (both methods) were compared to a log plot of discharge versus drainage area for the gage estimates, and assessed against their fit within confidence limits representing plus or minus one standard deviation for a normal distribution. The comparison was conducted for all flood frequencies determined as part of this assessment.

USGS Regional Regression Equations developed for use in this study were based on methodologies and equations presented in detail in USGS, Water Resources Investigations 82-4012, Technique for Estimating Magnitude and Frequency of Floods on Natural-Flow Streams in Florida, 1982. The National Flood Frequency (NFF) Program, Version 3, was used compute streamflow estimates for this analysis.

Drainage basin maps for the study areas were prepared using GIS. Input data required for the regression equation estimates, including Drainage Area, Channel Slope and Lake Area, were all determined using GIS based data.

Peak discharge-drainage area relationships for the 10-, 2-, 1-, and 0.2-percent annual chance floods of each flooding source studied by detailed methods in the community are shown in Table 2 – “Summary of Discharges.”

TABLE 2 – SUMMARY OF DISCHARGES

FLOODING SOURCE AND Drainage Area Peak Discharge (cfs) LOCATION (square miles) 10-YEAR 50-YEAR 100-YEAR 500-YEAR

BUCKHORN CREEK Downstream of confluence with 9.7 340 530 580 730 West Branch Buckhorn Creek Upstream of confluence with 8.5 270 420 460 580 West Branch Buckhorn Creek LOST CREEK At U.S. Highway 319 Southwest 70.2 4,200 6,900 8,000 10,600 of Crawfordville OCHLOCKONEE RIVER At mouth 2000.0 31,000 59,000 74,000 116,000 SOPCHOPPY RIVER At Forest Road North of 100.0 5,200 8,400 9,800 12,900 Sopchoppy ST. MARKS RIVER At Natural Bridge 535 3,980 6,090 7,060 9,530 WAKULLA RIVER At CR 365 40 1,880 2,730 3,130 4,130 WEST BRANCH BUCKHORN

CREEK At mouth 1.2 75 120 130 160

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 tables in the FIS report. For construction and/or floodplain management purposes, users are encouraged to use the flood elevation data presented in this FIS in conjunction with the data shown on the FIRM.

Cross sections were determined from topographic maps and field surveys. All bridges, dams, and culverts were field surveyed to obtain elevation data and structural geometry.

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). Flood profiles were drawn showing computed water-surface elevations for floods of the selected recurrence intervals.

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.

The unincorporated areas of Wakulla County have a previously printed FIS report. The hydraulic analyses described in that report are summarized below.

June 17, 1986 Analyses

The shoreline areas of Wakulla County are primarily subject to flooding from hurricane storm surges. Detailed hydraulic analysis of the shoreline and bay characteristics were carried out to provide estimates of the elevations of floods of the selected recurrence intervals. The U.S. Department of Housing and Urban Development's standard coastal storm surge model was utilized to determine these flood levels. This model is a numerical hydrodynamic computer model which calculates the coastal storm surges generated by the simulated storms.

Countywide Analyses

For this countywide FIS, the areas presented below were studied by detail methods to estimate flood elevations for the selected recurrence intervals.

For the Wakulla Gardens area, the Streamline Technologies ICPR v.3 unsteady flow model was used to estimate flood levels. The development of the model schematic was performed using ArcGIS. Various sources were utilized in developing the schematic including GIS shapefiles of the transportation network, ortho-aerial photography of Wakulla County, the Digital Elevation Model (DEM) of Wakulla County, field survey data and contours derived from the DEM. An ArcGIS automated subroutine was used to determine the stage-area relationships for each subbasin. Overtopping weirs were used in ICPR to transfer water between the storage areas. Structure information and the cross sections for the overtopping weirs were derived using the field survey data and the DEM for Wakulla County. Starting water surface elevations for each subbasin were determined from the field survey data and DEM. An ICPR model for the study area was developed based on the information described above.

The Wakulla River extends from the St. Marks River confluence to the Wakulla Spring, approximately 9.15 miles. The St. Marks River study area extends approximately 5.6 miles from Apalachee Bay to the Leon County line. This river has an overall length of 11.51 miles. Riverine analyses were performed on both the Wakulla River and St. Marks River. For the Wakulla River, the coastal surge dominated and the riverine results were not used. For the St. Marks River, the coastal surge dominated up until a small area of the river near the Leon/Wakulla border where the riverine analysis flood elevations were higher.

HEC-RAS models were developed to simulate flood elevations. Each model included details of natural channel geometry and considered all structures which potentially impact flood levels such as bridges and culverts. Channel cross-sections

were obtained from field survey and LiDAR topographic data for Wakulla County. Available bridge and culvert structure data was also obtained from FDOT.

Channel and floodplain roughness coefficients (Manning’s “n”) were estimated based upon the methodology documented in USGS Water Supply Paper 2339. A combination of field observation, photographs, and aerial photography was used to establish the parameters used in the methodology. Roughness values for the main channels ranged from 0.039 to 0.048, and overbank values ranged from 0.035 to 0.20 for the streams studied in detail in this revised analysis.

The starting water surface elevations for the HEC-RAS models were determined using a mean high tide equal to 2.10 feet, measured at the Wakulla and St. Marks River’s confluence was used as the boundary condition for both models. No floodways were determined for the streams in this study.

3.3 Coastal Hydrologic Analyses

Storm Surge Analysis and Modeling

For areas subject to tidal inundation, the 10-, 2-, 1-, and 0.2-percent-annual- chance stillwater elevations and delineations were taken directly from a detailed storm surge study documented in the Technical Support Data Notebook (TSDN) for the Northwest Florida Water Management District coastal flood hazard study for Franklin, Wakulla, and Jefferson Counties.

The Advanced Circulation model for Coastal Ocean Hydrodynamics (ADCIRC), (Luettich, 1992), developed by the (USACE) was selected to develop the stillwater elevations or storm surge for northwest Florida’s Franklin, Wakulla, and Jefferson Counties. ADCIRC uses an unstructured grid and is a finite-element long wave model. ADCIRC has the capability to simulate tidal circulation and storm surge propagation over large areas and is able to provide highly detailed resolution along the shorelines and areas of interest along the open coast and inland bays. It solves three dimensional equations of motion, including tidal potential, Coriolis, and nonlinear terms of the governing equations. The model is formulated from the depth averaged shallow water equations for conservation of mass and momentum which results in the generalized wave continuity equation. The model has the capability to simulate tidal circulation and storm surge propagation over large domains and is able to provide highly detailed resolution along the shoreline and other areas of interest.

The coastal wave model Simulating Waves Nearshore (SWAN) developed by Delft University in the Netherlands is used to calculate the nearshore wave fields required for the addition of wave setup effects. This numerical model is a third- generation (phase-averaged) wave model for the simulation of waves in waters of extreme, intermediate, and finite depths. Model characteristics include the capping of the atmospheric drag coefficient, dynamic adjustment of bathymetry for changing water levels, and specification of the required save points. Three nested grids are used to obtain sufficient nearshore resolution to represent the

radiation stress gradients required as ADCIRC inputs. Radiation stress fields output from the SWAN inner grids are used by ADCIRC to estimate the contribution of breaking waves (wave setup effects) to the total storm surge water level.

In order to model storm surge and wave fields using ADCIRC and SWAN, wind and pressure fields are required for input. A model called the Planetary Boundary Layer model (PBL) (Cardone, 1992), uses the parameters from a hurricane or storm to simulate the event and develop wind and pressure fields. The PBL model simulates hurricane induced wind and pressure fields by applying the vertically integrated equations of motion. Oceanweather Inc. provided support to run the PBL model and provide wind and pressure fields for each of the selected storms events.

The Joint Probability Method (JPM) was used to develop the stillwater frequency curves for the 10-, 2-, 1-, and 0.2-percent-annual-chance stillwater elevations. The JPM application was not originally named as such (Russell, 1968). The JPM approach is a simulation methodology that relies on the development of statistical distributions of key hurricane input variables such as central pressure, radius to maximum wind speed, maximum wind speed, translation speed, track heading, and sampling from these distributions to develop model hurricanes. The resulting simulation results in a family of modeled storms that preserve the relationships between the various input model components, but provides a means to model the effects and probabilities of storms that historically have not occurred.

An ADCIRC finite element mesh was created to determine inundation extents and depths due to hurricane storm surge in Northwest Florida’s Franklin, Wakulla, and Jefferson Counties. The offshore portion of the mesh covers the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico west of 60o West Longitude. This offshore portion is adapted from a proven existing mesh (Hagen, 2006). The inland portion of the mesh was extended to floodplain areas of Franklin, Wakulla, and Jefferson Counties and refined with node spacing ranging from 40-50 meters to 250-300 meters. The inland bathymetry portion of the ADCIRC mesh was populated with datasets taken from National Ocean Service (NOS) and USACE Surveys, HEC-RAS one-dimensional river cross-sections, NOAA nautical charts, and NWFWMD field knowledge. Bathymetry for most of the bays and northeastern Gulf of Mexico was constructed from the National Geophysical Data Center's (NGDC) Coastal Relief Model and USACE channel surveys. A portion of the northern Apalachee Bay was constructed from NOS Surveys, NOAA nautical chart data, and USACE channel surveys. Further offshore, the mesh restrains its original node elevations as detailed in Hagen, 2006.

The topographic portion of the ADCIRC mesh was populated with topographic LiDAR data along with five non-LiDAR terrain datasets. LiDAR data was available for most of the study area and all of the subject counties with the exception of small portions on the western boundary of Franklin County and the eastern boundary of Jefferson County. LiDAR data for Franklin, Wakulla, and Jefferson Counties was collected between July and December of 2007 as part of the Florida Department of Emergency Management's mapping update program.

For all other areas, non-LiDAR terrain datasets were downloaded from the USGS National Map Seamless Server, National Elevation Dataset. A shoreline was manually digitized referencing the LiDAR data and 2007 aerial photos to define the change between water and land elements.

The ADCIRC model mesh includes other features, such as rivers, roads, ridges and valleys. The final mesh includes approximately 2,250 square miles of floodplain area with 869,000 total computational nodes. The horizontal datum for the mesh is North American Datum (NAD) 1983, Geographic Coordinate System. The vertical datum is referenced to the North American Vertical Datum 1988 (NAVD 88) in units of meters. A land cover dataset assembled by the Florida Fish and Wildlife Commission (FWC) specifically to describe the diversity and distribution of vegetation within the state of Florida was used to define Manning’s n values for bottom roughness coefficients input at each node in the mesh. Model validation, which tests the model hydraulics and ability to reproduce events, was performed against Hurricanes Agnes (1972), Kate (1985), Opal (1995) and Dennis (2005). Simulated water levels for each event were compared to High Water Mark (HWM) data supplied by FEMA and historic reports and hydrograph data supplied by NWFWMD and NOAA.

The SWAN model, used to calculate the wave setup component, uses ocean bathymetry and coastal topography taken from two sources, the National Geophysical Data Center (NGDC – GEODAS data set) and the NWFWMD ADCIRC Grid, which incorporated the high resolution LiDAR survey data reported on elsewhere. The Coastal bathymetry data merged both the NGDC and ADCIRC Grid data to more accurately represent the topography over the land. The topography data was interpolated from the LiDAR data used to form the ADCIRC grid. At locations farther inland than ADCIRC grid, the NGDC dataset was used. The SWAN model was implemented on a set of nested grids, with resolutions ranging from 10 kilometers down to approximately 160 meters. The model is forced with the same wind and pressure fields from Oceanweather Inc. Hurricanes Kate (1986), Opal (1995), and Dennis (2005) were used to validate the SWAN model. Modeled wave heights were compared to available historic wave data from NOAA wave buoys.

Statistical Analyses

Due to the excessive number of simulations required for the traditional JPM method, the Joint Probability Method-Optimum Sampling (JPM-OS) was utilized to determine the stillwater elevations associated with tropical events. JPM-OS is a modification of the JPM method developed cooperatively by FEMA and the USACE for Mississippi and Louisiana coastal flood studies that were being performed simultaneously, and is intended to minimize the number of synthetic storms that are needed as input to the ADCIRC model. The methodology entails sampling from a distribution of model storm parameters (e.g., central pressure, radius to maximum wind speed, maximum wind speed, translation speed, and track heading) whose statistical properties are consistent with historical storms impacting the region, but whose detailed tracks differ.

Production runs were carried out with SWAN and ADCIRC on a set of hypothetical storm tracks and storm parameters in order to obtain the maximum water levels for input to the statistical analysis. A total of 159 individual storms with different tracks and various combinations of the storm parameters were chosen for the production run set of synthetic hurricane simulations. Each storm was run for at least 4 days of simulation and did not include tidal forcing. Wind and pressure fields obtained from the PBL model and wave radiation stress from the SWAN model were input to the ADCIRC model for each production storm. All stillwater results for this study include the effects of wave setup; to a period after setup.

Stillwater Elevations

The results of the ADCIRC model, as described above, provided stillwater elevations, including wave setup effects that are statistically analyzed to produce probability curves. The JPM-OS is applied to obtain the return periods associated with tropical storm events. The approach involves assigning statistical weights to each of the simulated storms and generating the flood hazard curves using these statistical weights. The statistical weights are chosen so that the effective probability distributions associated with the selected greater and lesser storm populations reproduce the modeled statistical distributions derived from all historical storms. All of the 869,000 ADCIRC nodes were used as JPM output points. This provided the maximum resolution and provided detailed coverage in Wakulla County. At each JPM point, the surge elevations obtained from the standard ADCIRC output files for each of the 159 storms and the annual recurrence rates for each storm were used as input of JPM-OS method. The final result was surge elevations at each JPM point for each recurrence rate. The stillwater elevations have been determined for the 10-, 2-, 1-, and 0.2-percent annual chance floods for the flooding sources studied by detailed methods and are summarized in Table 3 – “Summary of Stillwater Elevations.”

TABLE 3 – SUMMARY OF STILLWATER ELEVATIONS

ELEVATION (feet1 NAVD88*) FLOODING SOURCE AND LOCATION 10-PERCENT 2-PERCENT 1-PERCENT 0.2-PERCENT

APALACHEE BAY East shoreline from Ochlockonee Point to 7.4-7.5 13.2-13.5 15.1-15.5 18.9-19.3 Ullmore Cove East shoreline from Ullmore Cove to Whetstone Point 7.5-7.7 13.5-13.9 15.5-15.9 19.4-19.8 East shoreline from Whetstone Point to the north 7.7-8.0 13.9-14.4 15.9-16.4 19.8-20.4 end of Mashes Island South shoreline from Johns Cove to Sprague Island 7.8-7.9 14.5-14.8 16.4-16.8 20.0-20.5 East shoreline from Sprague Island to the confluence of Big West Bayou and the St. 7.8-8.0 14.5-15.1 16.5-17.1 20.1-20.9 Marks River West shoreline from Fourmile Point to the confluence of the St. Marks River and the East 7.8-8.0 14.6-15.0 16.5-17.0 20.1-20.8 River South shoreline from the East River to the inlet to Big Cove 7.6-7.8 14.2-14.6 16.1-16.5 19.6-20.1 South shoreline from the inlet to Big Cove to the mouth of 7.7-7.8 14.2-14.5 16.1-16.4 19.6-19.9 Stony Bayou South shoreline from the mouth of Stony Bayou to the 7.8 14.5-14.6 16.4-16.6 19.9-20.1 mouth of Deep Creek South shoreline from the mouth of Deep Creek to the 7.8 14.6-14.7 16.6-16.7 20.1-20.2 mouth of Little Porpoise Creek East shoreline of Piney Island 7.8-8.1 14.1-14.9 16.1-17.0 20.0-20.9 DICKERSON BAY East shoreline from Hungry Point to the Town of Panacea 8.0-8.3 14.6-15.0 16.7-17.1 20.7-21.1 West shoreline the Town of Panacea to the southwest end 8.0-8.3 14.5-15.0 16.5-17.1 20.5-21.1 of Porter Island

*North American Vertical Datum of 1988 1Includes wave setup

TABLE 3 – SUMMARY OF STILLWATER ELEVATIONS - continued

FLOODING SOURCE AND LOCATION ELEVATION (feet1 NAVD88*) 10-PERCENT 2-PERCENT 1-PERCENT 0.2-PERCENT

DICKERSON BAY South shoreline from the southwest end of Porter Island 7.9-8.0 14.3-14.5 16.3-16.5 20.2-20.5 to Fiddlers Point East shoreline from Fiddlers Point to the south end of 7.9-8.1 14.3-14.7 16.3-16.7 20.2-20.6 Hopkins Island East shoreline from the south end of Hopkins Island to the 8.1-8.2 14.7-15.0 16.7-17.0 20.6-21.0 mouth of Skipper Creek East shoreline from mouth of Skipper Creek to the mouth of 8.2-8.4 15.0-15.4 17.0-17.4 21.0-21.4 Purify Creek West shoreline of Piney Island 7.8-8.2 14.1-15.0 16.1-17.0 20.0-20.9 GOOSE CREEK BAY East shoreline from the mouth of Walker Creek to the mouth 7.8-8.2 14.4-15.2 16.4-17.2 20.1-21.1 of West Goose Creek Southwest shoreline from the mouth of West Goose Creek 7.9-8.2 14.8-15.3 16.8-17.3 20.5-21.2 to Johns Cove LEVY BAY West shoreline from the north end of Mashes Island to the 7.8-8.0 14.0-14.4 16.0-16.4 20.0-20.4 south end of Levy Bay East shoreline from the south end of Levy Bay to Hungry 7.8-8.0 14.0-14.6 16.0-16.7 20.0-20.6 Point OCHLOCKONEE BAY East shoreline of Grass Island from the Ochlockonee River 7.7 13.4-13.5 15.4-15.5 19.8-19.9 to the Sopchoppy River South shoreline from the Sopchoppy River to Tide 7.5-7.7 13.4-13.5 15.4-15.5 19.4-19.8 Creek South shoreline from Tide Creek to Ochlockonee Point 7.4-7.5 13.2-13.4 15.1-15.4 18.9-19.4

*North American Vertical Datum of 1988 1Includes wave setup

TABLE 3 – SUMMARY OF STILLWATER ELEVATIONS - continued

FLOODING SOURCE AND LOCATION ELEVATION (feet NAVD88*) 10-PERCENT 2-PERCENT 1-PERCENT 0.2-PERCENT

OYSTER BAY South shoreline from the mouth of Purify Creek to the 8.3-8.41 15.2-15.41 17.2-17.41 21.1-21.41 mouth of Old Creek South shoreline from the mouth of Old Creek to Grass 8.0-8.31 14.8-15.21 16.8-17.21 20.6-21.11 Inlet Southwest shoreline from Grass Inlet to the mouth of 7.8-8.01 14.4-14.81 16.4-16.81 20.2-20.61 Walker Creek

PONDING AREA 6 ** ** 19.2 ** PONDING AREA 6A ** ** 19.2 ** PONDING AREA 7 ** ** 22.0 ** PONDING AREA 8 ** ** 21.9 ** PONDING AREA 9 ** ** 20.4 ** PONDING AREA 11 ** ** 19.4 ** PONDING AREA 12 ** ** 13.7 ** PONDING AREA 18 ** ** 16.6 ** PONDING AREA 20 ** ** 21.5 ** PONDING AREA 23 ** ** 19.1 ** PONDING AREA 28 ** ** 15.8 ** PONDING AREA 29 ** ** 18.6 ** PONDING AREA 56 ** ** 19.6 ** PONDING AREA 57 ** ** 20.1 ** PONDING AREA 57A ** ** 20.1 ** PONDING AREA 84 ** ** 18.2 ** PONDING AREA 84C ** ** 20.2 ** PONDING AREA 92 ** ** 18.1 **

*North American Vertical Datum of 1988 **Data not available 1 Includes wave setup

3.4 Coastal Hydraulic Analyses

Areas of coastline subject to significant wave attack are referred to as coastal high hazard zones. The USACE has established the 3.0-foot breaking wave as the criterion for identifying the limit of coastal high hazard zones (USACE, 1975). The

3.0-foot wave has been determined as the minimum size wave capable of causing major damage to conventional wood frame and brick veneer structures.

Figure 1, “Transect Schematic,” illustrates a profile for a typical transect along with the effects of energy dissipation and regeneration on a wave as it moves inland. This figure shows the wave crest elevations being decreased by obstructions, such as buildings, vegetation, and rising ground elevations, and being increased by open, unobstructed wind fetches. The figure also illustrates the relationship between the local still water elevation, the ground profile and the location of the V/A boundary. This inland limit of the coastal high hazard area is delineated to ensure that adequate insurance rates apply and appropriate construction standards are imposed, should local agencies permit building in this coastal high hazard area.

TRANSECT SCHEMATIC Figure 1

For Wakulla County, the deepwater wave conditions associated with the 1-percent annual chance storm were developed using the SWAN model results. The outputs from the model production runs provided wave heights and periods to determine the wave heights associated with the 1-percent annual chance flood level. For each of the production runs, the maximum wave heights achieved at each grid point were put into files, as well as the average wave periods associated with the time when the maximum waves occurred. Then the wave heights at each of 596,000 coastal wave grid points were rank ordered. Using the probability of each storm, the 1-percent annual chance flood thresholds were determined, so the wave periods associated with the wave heights were determined afterwards. This technique gave a least squares best fit linear relationship between the flood levels from each storm and the wave heights for each storm.

FEMA guidelines for V Zone mapping define H s as the significant wave height or the average over the highest one third of waves and Ts as the significant wave period associated with the significant wave height. Mean wave conditions are described as:

H = H s × 0.626 T = Ts × 0.85

where H is the average wave height of all waves and T is the average wave period.

The transects were located with consideration given to the physical and cultural characteristics of the land so that they would closely represent conditions in their locality. Transects were spaced close together in areas of complex topography and dense development. In areas having more uniform characteristics, transects were spaced at larger intervals. It was also necessary to locate transects in areas where unique flooding existed and in areas where computed wave heights varied significantly between adjacent transects. Transects are shown on the FIRM panels.

The transect profiles were obtained using bathymetric and topographic data from various sources. The topographic dataset is comprised of LiDAR data provided by NWFWMD. LiDAR Data was collected between July 2007 in leaf-off conditions, and delivered to Dewberry in ESRI multipoint format during November 2008. Data, as delivered, was in the North American Datum (NAD) of 1983, projected to Florida HARN State Plane coordinates, North Zone, in units of feet. The vertical datum was relative to North American Vertical Datum (NAVD) of 1988 in units of feet. The LiDAR mass point dataset had a nominal point spacing of 4 feet, with a horizontal accuracy of 3.8-foot (2.2-foot RMSE), and a 0.6-foot fundamental vertical accuracy. This data fully meets and exceeds the accuracy standards of FEMA specifications, and should meet the expectations for an accurate, high quality digital terrain product.

The bathymetric dataset was processed and provided by the University of Central Florida during April 2009. Bathymetry for most of the bays and northeastern Gulf of Mexico consisted of NOAA National Ocean Service (NOS) hydrographic surveys, NOAA National Geophysical Data Center (NGDC) Coastal Relief Model, NOAA nautical chart data, and USACE navigation channel surveys. Data, as delivered, were in grid format with various grid spacing, in the NAD of 1983, projected to Florida State Plane coordinates, North Zone, in units of feet. The vertical datum was relative to NAVD of 1988 in units of meters.

The inland bathymetry in Apalachicola area, and Carabelle/Ochlockonee area consisted of NOS Surveys, USACE navigation channel surveys, HEC-RAS one- dimensional river cross-sections, NOAA nautical charts, and NWFWMD field knowledge. Data, as delivered, were in grid format with various grid spacing, in the NAD of 1983, projected to Florida State Plane coordinates, North Zone, in units of feet. The vertical datum was relative to NAVD of 1988 in units of meters. The grid files were loaded into GIS for the purpose of visualization and geoprocessing, and therefore ESRI shapefiles were created accordingly. The bathymetric dataset’s depths were converted from meters to feet using a factor of 3.2808. Data were then reprojected to the NAD83 FL HARN State Plane North zone coordinate system in units of feet, in agreement with the topographic dataset.

Where surveys overlapped, the older survey data were removed. To facilitate use of the bathymetric data to build a seamless digital elevation model, the ESRI shapefile-format point data were converted to three-dimensional feature class, and then to ASCII format dataset. Finally, the bathymetric data were ready to be merged with the topographic data-multipoint feature class.

To facilitate floodplain analysis, the provided datasets were processed into a DEM. The recently developed ESRI Terrain modeling framework is considered to be the most efficient data format to create terrain, and was utilized for this study. First, a file geodatabase was created to contain the topographic and bathymetric dataset and allow generation of the terrain model. A pre-determined coverage shapefile was loaded into the database to serve as the study area boundary. Next, a shoreline vector was also loaded as a hard line feature class with an assigned zero- elevation, in order to enforce the shoreline feature in the terrain dataset. The terrain was then created by combining the topographic and bathymetric multipoint files, zero-elevation shoreline vector and study-area boundary. The completed terrain dataset was generated with an average point spacing of 10 feet. The terrain was then converted directly to the final seamless DEM in order to support the overland wave modeling and coastal hazard mapping.

Storm-induced beach erosion is well documented along the Gulf of Mexico coastlines of Wakulla County. Review of the literature showed that the standard FEMA (2007) Guidelines and Specifications for Flood Hazard Mapping Partners methodology were applicable for the Gulf Coast of Wakulla County. Where dunes were identified and delineated, the VE Zone was mapped up to the extent of the Primary Frontal Dune.

Nearshore wave-induced processes, such as wave setup and wave run-up, constitute a greater part of the combined wave envelope than storm surge due to the coast exposure to ocean waves. For this study the wave setup was included in the storm surge modeling results. RUNUP 2.0 was used to predict wave run-up value on natural shore then adjusted to follow the FEMA (2005) “Procedure Memorandum No. 37” that recommends the use of the 2% wave run-up for determining base flood elevations. For wave run-up at the crest of a slope that transitions to a plateau or downslope, run-up values were determined using the “Methodology for wave run-up on a hypothetical slope” as described in the FEMA (2007) Guidelines and Specifications for Flood Hazard Mapping Partners.

Wave height calculation used in this study follows the methodology described in the FEMA (2003) and the FEMA (2007) Guidelines and Specifications for Flood Hazard Mapping Partners. The Wave Height Analysis for Flood Insurance Studies (WHAFIS) was used to propagate wave heights over land and to define the base flood elevations for mapping. The starting wave conditions were obtained just offshore of the shoreline from the 2D wave model SWAN as described previously. Local land use, field reconnaissance data and aerial photography were used to define the overland wave obstruction coefficients for input to WHAFIS. The 1% stillwater elevations were extract from the storm surge modeling results to define a stillwater profile along each transect.

Figure 2- “Transect Location Map,” illustrates the location of each transect. Along each transect, wave envelopes were computed considering the combined effects of changes in ground elevation, vegetation and physical features. Between transects, elevations were interpolated using topographic maps, land-use and land- cover data, and engineering judgment to determine the aerial extent of flooding. The results of the calculations are accurate until local topography, vegetation, or cultural developments within the community undergo major changes. The transect data for the county are presented in Table 4 – “Transect Descriptions,” which describes the location of each transect. In addition, Table 5 – “Transect Data,” provides the 1-percent annual chance stillwater with wave setup and the maximum wave crest elevations for each transect along coastline. In Table 5 the flood hazard zone and base flood elevations for each transect flooding source is provided, along with the 10-, 2-, 1-, and 0.2-percent annual chance stillwater elevations for the respective flooding source.

Users of the FIRM should also be aware that coastal flood elevations are provided in the Summary of Stillwater Elevations table (Table 4) in this report. If the elevation on the FIRM is higher than the elevation shown in this table, a wave height, wave run-up, and/or wave setup component likely exists, in which case, the higher elevation should be used for construction and/or floodplain management purposes. FEMA (2003) and the FEMA (2007) Guidelines and Specifications for Flood Hazard Mapping Partners, the coastal high hazard area (Zone VE) is the area where wave action and/or high velocity water can cause structural damage. It is designated on the FIRM as the most landward of the following three points:

1) The point where the 3.0 ft. or greater wave height could occur; 2) The point where the eroded ground profile is 3.0 ft. or more below the maximum run-up elevation; and 3) The primary frontal dune as defined in the NFIP regulations.

These three points are used to locate the inland limit of the coastal high hazard area to ensure that adequate insurance rates apply and appropriate construction standards are imposed, should local agencies permit building in this area.

Along each transect, wave heights and wave crest elevations were computed considering the combined effects of changes in ground elevation, vegetation, and physical features. Wave heights were calculated to the nearest 0.1 foot, and wave crest elevations were determined at whole-foot increments along the transects. The calculations were carried inland along the transect until the wave crest elevation was permanently less than 0.5 foot above the stillwater-surge elevation or the coastal flooding met another flooding source (i.e., riverine) with an equal water-surface elevation. The results of the calculations are accurate until local topography, vegetation, or cultural developments of the community undergo any major changes.

TABLE 4 – TRANSECT DESCRIPTIONS

Wakulla County

ELEVATION (ft. NAVD 88*) MAXIMUM 1-PERCENT 1-PERCENT ANNUAL CHANCE ANNUAL CHANCE TRANSECT LOCATION STILLWATER WAVE CREST

1 On the Ochlockonee Bay coastline, at the mouth of 15.41 19.3 the Ochlockonee River at the south end of Grass Island, at N 29.978347°, W 84.437211° 2 On the Ochlockonee Bay coastline, approximately 15.51 19.6 800 feet east of St. James Street and 1000 feet west of River Bend Road, at N 29.983471 °, W 84.418976° 3 On the Ochlockonee Bay coastline, approximately 15.41 19.8 800 feet south of the Wakulla County Airport, at N 29.982683°, W-84.395568° 4 On the Ochlockonee Bay coastline, approximately 15.41 19.9 300 feet east of the Coastal Highway Bridge, at N 29.977043°, W 84.382338° 5 On the Ochlockonee Bay coastline, at the end of 15.11 20.0 Blue Heron Way , at N 29.969787°, W 84.349629° 6 On the Apalachee Bay coastline, approximately 15.31 20.2 1000 feet north of Mashes Sands Road, at N 29.976211°, W 84.341138° 7 On the Dickerson Bay coastline, approximately 15.91 20.5 300 feet north of Chattahoochee Street, at N 29.992694°, W 84.362193° 8 On the Levy Bay coastline, at the end of Palmdale 16.61 20.0 Street, at N 30.015734° W 84.382474° 9 On the Dickerson Bay coastline, approximately 16.81 20.3 900 feet north of Walker Street, at N 30.023718°, W 84.385932° 10 On the Dickerson Bay coastline, approximately 17.01 20.4 1600 feet east of the intersection of Jer-Be-Lou Boulevard and State Highway 98, at N 30.032355°, W 84.385451° 11 On the Dickson Bay coastline, approximately 750 17.11 20.3 feet north of the end of Skipper Bay Road, at N 30.049724°, W 84.359724°

*North American Vertical Datum of 1988 1Includes wave setup

TABLE 4 – TRANSECT DESCRIPTIONS – continued

Wakulla County

ELEVATION (ft. NAVD 88*) MAXIMUM 1-PERCENT 1-PERCENT ANNUAL CHANCE ANNUAL CHANCE TRANSECT LOCATION STILLWATER WAVE CREST

12 On the Oyster Bay coastline, approximately 2500 17.51 20.6 feet southeast of the end of Purity Bay Road, at N 30.065370°, W 84.35809° 13 On the Oyster Bay coastline, approximately 1400 17.21 20.4 feet west of the mouth of Old Creek, at N 30.063884°, W 84.343788° 14 On the Oyster Bay coastline, at the east end of 17.11 20.3 Boggy Island approximately 700 feet west of the mouth of Spring Creek, at N 30.069512°, W 84.325089° 15 On the Oyster Bay coastline at the south end of 17.11 20.5 Cutoff Island, at N 30.074307°, W 84.315633° 16 On the Oyster Bay coastline, approximately 750 16.81 20.2 feet west of Grass Inlet, at N 30.067394°, W 84.306229° 17 On the Oyster Bay coastline, approximately 650 16.61 21.7 feet north of Cedar Island Way, at N 30.060642°, W 84.299235° 18 On the Apalachee Bay coastline, at the intersection 16.31 21.2 of Sandy Way and Beaty Taff Drive, at N 30.057534°, W 84.288281° 19 On the Apalachee Bay coastline, approximately 16.41 21.2 400 feet east of Live Oak Island Road, at N 30.061410°, W 84.275849° 20 On the Goose Creek Bay coastline, approximately 17.21 20.6 1400 feet west of the mouth of West Goose Creek, at N 30.094450°, W 84.273713° 21 On the Goose Creek Bay coastline, approximately 17.31 20.3 400 feet northeast of Wakulla Beach Road, at N 30.105614°, W 84.26006° 22 On the Apalachee Bay coastline, at the north end of 16.71 21.3 Kitchen Cove , at N 30.088858°, W 84.233571° 23 On the Apalachee Bay coastline, approximately 16.51 21.1 4100 feet west of the St. Marks River, at N 30.084154°, W 84.218478°

*North American Vertical Datum of 1988 1Includes wave setup

TABLE 4 – TRANSECT DESCRIPTIONS – continued

Wakulla County

ELEVATION (ft. NAVD 88*) MAXIMUM 1-PERCENT 1-PERCENT ANNUAL CHANCE ANNUAL CHANCE TRANSECT LOCATION STILLWATER WAVE CREST

24 On the Apalachee Bay coastline, at the confluence 16.51 20.4 of the St. Marks River and the East River, at N 30.093289°, W 84.183996° 25 On the Apalachee Bay coastline, at the inlet to Big 16.21 21.0 Cove, at N 30.155120°, W 84.155120° 26 On the Apalachee Bay coastline, at the confluence 16.51 20.4 of Cedar Creek and Sand Creek, at N 30.087419°, W 84.116713° 27 On the Apalachee Bay coastline, approximately 16.71 20.2 800 feet west of the mouth of Little Porpoise Creek, at N 30.094889°, W 84.078821° 28 On the Apalachee Bay coastline, approximately 16.21 21.0 950 feet north of the south end of Piney Island, at N 30.015837°, W 84.349665° 29 On the Apalachee Bay coastline, approximately 16.21 21.1 3900 feet northeast of the south end of Piney Island , at N 30.022543°, W 84.343989° 30 On the Apalachee Bay coastline, approximately 16.41 21.0 1500 feet southwest of Middle Point Island , at N 30.028281°, W 84.343575° 31 On the Apalachee Bay coastline, approximately 16.41 21.1 1400 feet northeast of Middle Point Island, at N 30.035129°, W 84.335850°

*North American Vertical Datum of 1988 1Includes wave setup

TABLE 5 – TRANSECT DATA

Wakulla County

BASE FLOOD FLOODING STILLWATER ELEVATION (feet1 NAVD88*) ELEVATION SOURCE TRANSECT 10-PERCENT 2-PERCENT 1-PERCENT 0.2-PERCENT ZONE (feet NAVD88*)

Ochlockonee Bay 1 7.7 13.5 15.5 19.9 VE 18-19 7.8 12.8 15.4 19.9 AE 15-18

Ochlockonee Bay 2 7.5 13.6 15.6 19.8 VE 18-20 7.3 13.6 15.7 19.9 AE 18 7.3 13.7 15.8 20.0 VE 18-19 7.5 13.2 15.6 20.1 AE 16-18 7.7 13.1 15.6 20.2 VE 18 7.8 12.6 15.2 20.1 AE 16-18

Ochlockonee Bay 3 7.6 13.5 15.5 19.6 VE 18-20 7.7 13.8 15.7 19.9 AE 18 7.7 14.1 16.1 20.2 VE 18-19

Ochlockonee Bay 4 7.7 13.8 15.8 19.8 VE 19-20

Ochlockonee Bay 5 7.4 13.3 15.2 19.1 VE 19-20

Apalachee Bay 6 7.4 13.4 15.3 19.1 VE 19-20

Apalachee 7 7.9 14.1 16.1 20.1 VE 20-21 Bay/Levy Bay 7.5 14.0 16.0 20.1 VE 18-19

Levy Bay 8 7.9 14.5 16.5 20.5 VE 18-20 7.4 13.6 16.1 20.3 AE 17-18 7.4 13.1 15.5 20.1 AE 16-18

Dickerson Bay 9 7.8 14.7 16.8 20.8 VE 19-20 7.8 13.9 16.1 20.4 AE 17-19

Dickerson Bay 10 8.2 14.9 17.0 21.0 VE 20 7.9 14.5 16.6 20.8 AE 18-19 7.8 13.3 15.6 20.2 AE 16-17

Dickerson Bay 11 8.3 15.3 17.3 21.3 VE 20-21 8.4 15.1 17.4 21.5 AE 18-20

Oyster Bay 12 8.5 15.6 17.6 21.6 VE 20-21 8.5 15.2 17.6 21.6 AE 18-20 *North American Vertical Datum of 1988 1Includes wave setup

TABLE 5 – TRANSECT DATA – continued

Wakulla County

BASE FLOOD FLOODING STILLWATER ELEVATION (feet1 NAVD88*) ELEVATION SOURCE TRANSECT 10-PERCENT 2-PERCENT 1-PERCENT 0.2-PERCENT ZONE (feet NAVD88*)

Oyster Bay 13 8.4 15.4 17.4 21.2 VE 20-21 8.3 15.2 17.5 21.5 AE 18-20 Oyster Bay 14 8.3 15.3 17.3 21.3 VE 20-21 8.2 15.2 17.5 21.5 AE 18-20

Oyster Bay 15 8.1 15.1 17.1 21.0 VE 19-21 7.8 15.1 17.1 21.1 AE 19 8.1 14.0 16.7 21.1 AE 17-18 7.9 9.4 12.8 17.8 AE 13

Oyster Bay 16 8.0 15.0 17.0 20.8 VE 19-21 8.1 15.0 17.1 21.0 AE 19

Oyster Bay 17 7.9 14.6 16.6 20.4 VE 20-21 7.8 14.6 16.6 20.4 AE 18

Oyster Bay 18 7.8 14.5 16.4 20.2 VE 20-21 7.8 14.6 16.6 20.4 AE 18 8.0 14.9 16.9 20.7 VE 19-20 8.2 14.7 16.8 21.1 AE 17-19 7.9 13.5 15.9 20.0 AE 16

Goose Creek Bay 19 7.9 14.7 16.6 20.4 VE 20-21

Goose Creek Bay 20 8.3 15.4 17.4 21.3 VE 20-21 7.9 14.8 17.1 21.2 AE 17-19

Goose Creek Bay 21 8.3 15.3 17.4 21.4 VE 19-21 7.9 14.7 17.0 21.2 AE 18-19 7.5 13.4 16.3 21.2 AE 16-17

Apalachee Bay 22 8.2 15.2 17.2 21.1 VE 19-21 7.9 14.9 16.9 21.0 AE 18-19 7.4 13.8 15.9 19.9 AE 16-17 6.7 13.3 15.2 19.1 AE 16 6.0 12.4 14.1 18.6 AE 14-15

*North American Vertical Datum of 1988 1Includes wave setup

TABLE 5 – TRANSECT DATA – continued

Wakulla County

BASE FLOOD FLOODING STILLWATER ELEVATION (feet1 NAVD88*) ELEVATION SOURCE TRANSECT 10-PERCENT 2-PERCENT 1-PERCENT 0.2-PERCENT ZONE (feet NAVD88*)

Apalachee Bay 23 8.0 14.8 16.9 20.7 VE 19-22 7.4 13.9 16.0 20.2 AE 17-18 7.2 13.5 15.2 19.6 AE 16 7.2 13.3 14.5 19.2 AE 15 7.2 12.0 13.3 18.5 AE 13-14

Apalachee Bay 24 7.9 14.9 16.8 20.5 VE 21 8.0 15.2 17.2 21.0 VE 19-20 7.7 15.1 17.0 20.9 AE 18-19 7.4 14.4 16.5 20.6 AE 17-18 7.2 13.8 15.8 20.3 AE 16-17 7.2 13.0 14.8 18.5 AE 15-16 6.6 12.4 13.8 18.0 AE 13-15

Apalachee Bay 25 7.8 14.6 16.6 20.2 VE 19-21 7.8 14.9 16.8 20.5 AE 19 8.0 15.1 17.1 20.9 VE 19-20 7.9 14.8 16.6 20.4 AE 18-19 7.9 13.2 15.8 19.7 AE 17 7.5 12.7 14.8 19.1 AE 15-16 7.2 12.4 13.7 18.3 AE 13-14

Apalachee Bay 26 8.0 14.8 16.8 20.3 VE 21-22 5.1 14.8 16.8 20.4 VE 18-20 4.8 14.2 16.2 19.9 AE 18 4.9 13.6 15.5 19.3 AE 17 5.3 12.8 14.7 18.6 AE 16 6.2 12.2 14.1 18.0 AE 15 7.2 11.5 13.7 16.0 AE 13-14

Apalachee Bay 27 7.9 14.8 16.8 20.4 VE 20-21 7.1 14.1 16.1 19.7 VE 18-19 6.9 13.2 15.0 18.7 AE 16-18 7.2 11.9 13.8 17.7 AE 15 7.3 11.2 13.1 17.2 AE 13-14

*North American Vertical Datum of 1988 1Includes wave setup

TABLE 5 – TRANSECT DATA – continued

Wakulla County

BASE FLOOD FLOODING STILLWATER ELEVATION (feet1 NAVD88*) ELEVATION SOURCE TRANSECT 10-PERCENT 2-PERCENT 1-PERCENT 0.2-PERCENT ZONE (feet NAVD88*)

Apalachee Bay 28 7.8 14.3 16.3 20.0 VE 21

Apalachee Bay 29 7.9 14.4 16.5 20.4 VE 21

Apalachee Bay 30 8.0 14.6 16.6 20.5 VE 21

Apalachee Bay 31 8.0 14.7 16.7 20.6 VE 21

*North American Vertical Datum of 1988 1Includes wave setup

It has been shown in laboratory tests and observed in field investigations that wave heights as little as 1.5 feet can cause damage to and failure of typical Zone AE construction. Therefore, for advisory purposes only, a Limit of Moderate Wave Action (LiMWA) boundary has been added in coastal areas subject to wave action. The LiMWA represents the approximate landward limit of the 1.5-foot breaking wave.

The effects of wave hazards in the Zone AE between the Zone VE (or shoreline in areas where VE Zones are not identified) and the limit of the LiMWA boundary are similar to, but less severe than, those in Zone VE where 3-foot breaking waves are projected during a 1-percent annual chance flooding event.

In areas where wave run-up elevations dominate over wave heights, such as areas with steeply sloped beaches, bluffs, and/or shore-parallel flood protection structures, there is no evidence to date of significant damage to residential structures by run-up depths less than 3 feet. However, to simplify representation, the LiMWA is continued immediately landward of the VE/AE boundary in areas where wave run-up elevations dominate. Similarly, in areas where the Zone VE designation is based on the presence of a primary frontal dune or wave overtopping, the LiMWA is also delineated immediately landward of the Zone VE/AE boundary.

3.5 Vertical Datum

All FISs 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 FISs and FIRMS was NGVD 29. With the finalization of

the NAVD 88, many FIS reports and FIRMs are being prepared using NAVD 88 as the referenced vertical datum.

All flood elevations shown in this FIS report and on the FIRM are referenced to NAVD 88. Structure and ground elevations in the community must, therefore, be referenced to NAVD 88. It is important to note that adjacent communities may be referenced to NGVD 29. This may result in differences in Base Flood Elevations (BFEs) across the corporate limits between the communities.

Prior versions of the FIS report and FIRM were referenced to NGVD 29. When a datum conversion is effected for an FIS report and FIRM, the Flood Profiles, BFEs, and Elevation Reference Marks (ERMs) reflect the new datum values. To compare structure and ground elevations to 1 percent annual chance flood elevations shown in the FIS and on the FIRM, the subject structure and ground elevations must be referenced to the new datum values.

As noted above, the elevations shown in the FIS report and on the FIRM for Wakulla County and incorporated areas are referenced to NAVD 88. Ground, structure, and flood elevations may be compared and/or referenced to NGVD 29 using a standard conversion factor. The conversion factor from NGVD 29 to NAVD 88 is -0.63 feet. The conversion between the datum’s may be expressed as an equation:

NGVD 29 = NAVD 88 + 0.63 feet

The BFEs shown on the FIRM represent whole-foot rounded values. For example a BFE of 102.4 will appear as 102 on the FIRM and 102.6 will appear as 103. Therefore, users that wish to convert the elevations in this FIS to NGVD 29 should apply the stated conversion factor(s) to elevations shown on the Flood Profiles and supporting data tables in the FIS report, which are shown at a minimum to the nearest 0.1 foot.

For more information on NAVD 88, see Converting the National Flood Insurance Program to the North American Vertical Datum of 1988, FEMA Publication FIA20/June 1992, or contact the National Geodetic Survey (NGS) Information Services, NOAA N/NGS12, National Geodetic Survey, SSMC-3, #9202, 1315 East-West Highway, Silver Spring, Maryland 20910-3282 (Internet address http://www.ngs.noaa.gov).

4.0 FLOODPLAIN MANAGEMENT APPLICATIONS

The NFIP encourages State and local governments to adopt sound floodplain management programs. To assist in this endeavor, each FIS provides 1 percent annual chance floodplain data, which may include a combination of the following: 10-, 2-, 1-, and 0.2- percent annual chance flood elevations; delineations of the 1-percent and 0.2-percent annual chance floodplains; and 1-percent annual chance floodway. This information is presented on the

FIRM and in many components of the FIS, including Flood Profiles, Floodway Data tables, and Summary of Stillwater Elevation tables. Users should reference the data presented in the FIS as well as additional information that may be available at the local community map repository before making flood elevation and/or floodplain boundary determinations.

4.1 Floodplain Boundaries

To provide a national standard without regional discrimination, the 1-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 in detail, the 1- and 0.2-percent annual chance floodplain boundaries have been delineated using the flood elevations determined at each cross section.

LiDAR data is remotely sensed high resolution elevation data collected by an airborne collection platform. The LiDAR data used to delineate floodplain boundaries for the countywide analysis was collected from two separate projects. The first project collected LiDAR data from Feb 22, 2007 to March 13, 2007 for the northern portion of the county. The average point spacing for this data is 0.7 m and vertical accuracy is 11.12 cm RMSEz. The second project collected LiDAR from July 18, 2007 to July 20, 2007 for the southern portion of the county. The average point spacing for this data is 0.7 m and vertical accuracy is 9.45 cm RMSEz.

Floodplain delineations for approximate 1% annual chance floodplains were taken from the existing FIRM for Wakulla County (FEMA, 1986).

The 1- and 0.2-percent annual chance floodplain boundaries are shown on the FIRM (Exhibit 2). On this map, the 1-percent annual chance floodplain boundary corresponds to the boundary of the areas of special flood hazards (Zones A and AE), and the 0.2-percent annual chance floodplain boundary corresponds to the boundary of areas of moderate flood hazards. In cases where the 1- and 0.2-percent annual chance floodplain boundaries are close together, only the 1-percent annual chance floodplain boundary has been shown. Small areas within the floodplain boundaries may lie above the flood elevations but cannot be shown due to limitations of the map scale and/or lack of detailed topographic data.

In areas where a wave height analysis was performed, the A and V zones were divided into whole-foot elevation zones based on the average wave crest elevation in that zone. Where the map scale did not permit delineating zones at 1 foot intervals, larger increments were used.

For the streams studied by approximate 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 the flood-carrying capacity, increases the 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 1.0 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 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 are tabulated for selected cross sections (Table 6). The computed floodways are shown on the FIRM (Exhibit 2). In cases where the floodway and 1-percent annual chance floodplain boundaries are either close together or collinear, only the floodway boundary is shown.

Portions of the floodway for the Ochlockonee River extend beyond the county boundary. The portion of the Ochlockonee River downstream of the floodway indicated is subject to coastal storm surge. A floodway is generally not appropriate for coastal areas flooded by coastal storm surge and therefore, are not included in this FIS. No floodway was computed for the St. Marks River or Wakulla River.

Encroachment into areas subject to inundation by floodwaters having hazardous velocities aggravates the risk of flood damage, and heightens potential flood hazards by further increasing velocities. A listing of stream velocities at selected cross sections is provided in Table 6 – “Floodway Data." In order to reduce the risk of property damage in areas where the stream velocities are high, the community may wish to restrict development in areas outside the floodway.

The results of these computations are tabulated at selected cross sections for each stream segment for which a floodway is computed (Table 6).

The area between the floodway and 1-percent annual chance floodplain boundaries is termed the floodway fringe. The floodway fringe encompasses the portion of the floodplain that could be completely obstructed without increasing the water-surface elevation of the 1-percent annual chance flood by more than 1.0 foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to floodplain development are shown in Figure 3.

FLOODWAY SCHEMATIC Figure 3

BASE FLOOD FLOODING SOURCE FLOODWAY WATER SURFACE ELEVATION SECTION MEAN WITHOUT WITH REGULATORY INCREASE WIDTH AREA VELOCITY FLOODWAY FLOODWAY CROSS SECTION DISTANCE (FEET) (SQUARE (FEET PER (FEET NAVD88) FEET) SECOND) Buckhorn Creek A* 1,8301 100 472 1.2 17.0 5.53 6.53 1.0 B* 3,1901 1,2004 2,500 0.4 17.0 6.33 7.33 1.0 C 8,5801 50 120 6.0 13.2 13.2 14.2 1.0 D 10,1501 50 200 2.9 20.0 20.0 21.0 1.0 E 10,1901 75 396 1.2 20.1 20.1 21.1 1.0 F 11,1601 100 350 1.3 22.1 22.1 23.1 1.0

West Branch Buckhorn Creek A 3,5902 200 400 0.3 15.0 11.03 12.03 1.0 B 4,5802 100 200 0.6 15.0 14.93 15.83 0.9 C 5,3102 15 50 2.6 16.8 16.8 17.8 1.0 D 5,3402 50 150 0.8 22.1 22.1 22.1 0.0 E 6,6202 50 130 1.0 23.6 23.6 24.4 0.8

1 Feet above State Route 372 2 Feet above confluence with Buckhorn Creek 3 Elevation computed without consideration of coastal flooding effects. 4 Width includes influence of West Branch Buckhorn Creek. * Cross section not shown on Flood Profile; coastal flooding

TABLE 6 TABLE FEDERAL EMERGENCY MANAGEMENT AGENCY FLOODWAY DATA

WAKULLA COUNTY, FL (AND INCORPORATED AREAS) BUCKHORN CREEK-WEST BRANCH BUCKHORN CREEK

1 Feet above U.S. Highway 319

TABLE 6 TABLE FEDERAL EMERGENCY MANAGEMENT AGENCY FLOODWAY DATA

WAKULLA COUNTY, FL (AND INCORPORATED AREAS) LOST CREEK

BASE FLOOD FLOODING SOURCE FLOODWAY WATER SURFACE ELEVATION MEAN WITHOUT WITH SECTION REGULATORY INCREASE VELOCITY FLOODWAY FLOODWAY WIDTH2 AREA CROSS SECTION DISTANCE1 (FEET (FEET) (SQUARE PER (FEET NAVD88) FEET) SECOND) Ochlockonee River

B -1,970 2,000/1,150 28,570 2.6 17.0 10.43 11.13 0.7 C 630 2,000/700 25,110 3.0 15.0 10.83 11.43 0.6 D 10,230 2,000/1,520 28,480 2.6 13.0 12.13 12.83 0.7 E 21,630 1,000/500 17,480 4.2 13.9 13.9 14.7 0.8

1 Feet above U.S. Highway 319 2 Total width/width within county limits. 3 Elevation computed without consideration of coastal flooding effects.

TABLE 6 TABLE FEDERAL EMERGENCY MANAGEMENT AGENCY FLOODWAY DATA

WAKULLA COUNTY, FL (AND INCORPORATED AREAS) OCHLOCKONEE RIVER

BASE FLOOD FLOODING SOURCE FLOODWAY WATER SURFACE ELEVATION SECTION MEAN WITHOUT WITH REGULATORY INCREASE WIDTH AREA VELOCITY FLOODWAY FLOODWAY CROSS SECTION DISTANCE1 (FEET) (SQUARE (FEET PER (FEET NAVD88) FEET) SECOND) Sopchoppy River A* 180 400 3,200 3.1 17.0 6.32 7.32 1.0 B* 630 400 2,870 3.4 17.0 6.32 7.32 1.0 C* 3,160 700 6,500 2.3 17.0 7.12 8.12 1.0 D* 6,800 1,000 8,000 1.1 16.0 7.62 8.62 1.0 E* 8,030 760 5,950 1.6 16.0 7.82 8.82 1.0 F* 12,920 640 5,740 1.7 15.0 9.22 10.22 1.0 G* 17,900 460 4,770 2.0 15.0 10.12 11.12 1.0 H* 22,400 590 6,940 1.4 15.0 11.02 12.02 1.0 I* 29,040 750/4003 5,750 1.7 15.0 12.42 13.22 1.0 J* 29,280 210/1003 3,220 3.0 15.0 12.52 13.52 1.0 K* 29,530 200/1003 3,110 3.2 15.0 12.52 13.52 1.0 L* 29,600 165/1003 2,460 4.0 15.0 12.52 13.52 1.0 M* 32,400 200/1003 2,600 3.8 15.0 13.82 14.82 1.0 N 37,500 625 5,580 1.8 15.7 15.7 16.7 1.0 O 42,190 570 4,890 2.0 17.0 17.0 18.0 1.0 P 45,300 575 4,750 2.1 18.9 18.9 20.0 1.0 Q 49,830 605 6,250 1.6 20.4 20.4 21.3 0.9 R 53,100 400 4,240 2.3 21.8 21.8 22.8 1.0 S 53,450 465 4,830 2.0 22.0 22.0 23.0 1.0 T 55,980 365 4,190 2.3 23.2 23.2 24.1 0.9 U 59,120 560 5,680 1.7 24.6 24.6 25.5 0.9 V 62,400 400 3,990 2.5 26.0 26.0 27.0 0.9 W 65,120 225 2,940 3.3 27.2 27.2 28.1 0.9 X 68,400 180 3,100 3.1 28.6 28.6 29.5 0.9 Y 76,950 700 5,900 1.7 33.5 33.5 34.4 0.9 1 Feet above U.S. Highway 319 2 Elevation computed without consideration of coastal flooding effects. 3 Total width/width within county limits. * Cross section not shown on Flood Profile; coastal flooding

TABLE 6 TABLE FEDERAL EMERGENCY MANAGEMENT AGENCY FLOODWAY DATA

WAKULLA COUNTY, FL (AND INCORPORATED AREAS) SOPCHOPPY RIVER

5.0 INSURANCE APPLICATION

For flood insurance rating purposes, flood insurance zone designations are assigned to a community based on the results of the engineering analyses. The zones are as follows:

Zone A

Zone A is the flood insurance rate 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 base flood elevations or depths are shown within this zone.

Zone AE

Zone AE is the flood insurance rate zone that corresponds to the 1-percent annual chance floodplains that are determined in the FIS by detailed methods. In most instances, whole-foot base flood elevations derived from the detailed hydraulic analyses are shown at selected intervals within this zone.

Zone AH

Zone AH is the flood insurance rate zone that corresponds to the areas of 1-percent annual chance shallow flooding (usually areas of ponding) where average depths are between 1 and 3 feet. Whole-foot base flood elevations derived from the detailed hydraulic analyses are shown at selected intervals within this zone.

Zone AO

Zone AO is the flood insurance rate zone that corresponds to the areas of 1-percent annual chance shallow flooding (usually sheet flow on sloping terrain) where average depths are between 1 and 3 feet. Average whole-foot depths derived from the detailed hydraulic analyses are shown within this zone.

Zone AR

Area of special flood hazard formerly protected from the 1-percent annual chance flood event by a flood control system that was subsequently decertified. Zone AR indicates that the former flood control system is being restored to provide protection from the 1-percent annual chance or greater flood event.

Zone A99

Zone A99 is the flood insurance rate zone that corresponds to areas of the 1-percent annual chance floodplain that will be protected by a Federal flood protection system where construction has reached specified statutory milestones. No base flood elevations or depths are shown within this zone.

Zone V

Zone V is the flood insurance rate zone that corresponds to the 1-percent annual chance coastal floodplains that have additional hazards associated with storm waves. Because approximate hydraulic analyses are performed for such areas, no base flood elevations are shown within this zone.

Zone VE

Zone VE is the flood insurance rate zone that corresponds to the 1-percent annual chance coastal floodplains that have additional hazards associated with storm waves. Whole-foot base flood elevations derived from the detailed hydraulic analyses are shown at selected intervals within this zone.

Zone X

Zone X is the flood insurance rate zone that corresponds to areas outside the 0.2- percent annual chance floodplain, areas within the 0.2-percent annual chance floodplain, and to 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 base flood elevations or depths are shown within this zone.

Zone D

Zone D is the flood insurance rate zone that corresponds to unstudied areas where flood hazards are undetermined, but possible.

6.0 FLOOD INSURANCE RATE MAP

The FIRM is designed for flood insurance and floodplain management applications.

For flood insurance applications, the map designated flood insurance rate 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, the floodways, and the locations of selected cross sections used in the hydraulic analyses and floodway computations.

The current FIRM presents flooding information for the entire geographic area of Wakulla County. Previously, separate Flood Hazard Boundary Maps and/or FIRMS were prepared for each identified flood prone incorporated community and the unincorporated areas of the county. This countywide FIRM 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, up to and including this countywide FIS, are presented in Table 7, “Community Map History.”

7.0 OTHER STUDIES

Information pertaining to revised and unrevised flood hazards for the unincorporated and incorporated areas of Wakulla County has been compiled into this FIS. Therefore, this FIS supersedes all previously printed FISs and FIRMs for the unincorporated and incorporated areas of Wakulla County.

8.0 LOCATION OF DATA

Information concerning the pertinent data used in the preparation of this FIS can be obtained by contacting FEMA, Federal Insurance and Mitigation Division, Koger Center – Rutgers Building, 3003 Chamblee Tucker Road, Atlanta, Georgia 30341.

FLOOD HAZARD BOUNDARY MAP REVISIONS FIRM FIRM COMMUNITY NAME INITIAL IDENTIFICATION DATE EFFECTIVE DATE REVISIONS DATE

Sopchoppy, City of August 15, 1984 None August 15, 1984 None

St. Marks, City of November 9, 1973 February 27, 1976 March 18, 1980 None

Wakulla County (Unincorporated Areas) February 14, 1975 None January 16, 1981 November 16, 1983 June 17, 1986 June 2,1992

TABLE TABLE FEDERAL EMERGENCY MANAGEMENT AGENCY

WAKULLA COUNTY, FL COMMUNITY MAP HISTORY 7 7 AND INCORPORATED AREAS

9.0 BIBLIOGRAPHY AND REFERENCES

1. American Meteorological Society, Early American Hurricanes 1492-1870, Ludlum, David M., 1963.

2. Cardone, V. J., Greenwood, C. V., and Greenwood, J. A. (1992). “Unified Program for the Specification of Hurricane Boundary Layer Winds Over Surfaces of Specified Roughness,” Contract Report CERC-92-1, U. S. Army Engineer Waterways Experiment Station, Vicksburg, MS.

3. Federal Emergency Management Agency. (February 2007). Atlantic Ocean and Gulf of Mexico Coastal Guidelines update, Final Draft. Washington, D.C.

4. Federal Emergency Management Agency. (August 2005). Procedure Memorandum #37, Protocol for Atlantic and Gulf Coast Coastal Flood Insurance Studies in FY05. Washington, D.C.

5. Federal Emergency Management Agency. (April 2003). Guidelines and Specifications for Flood Hazard Mapping Partners. Appendix D: Guidance for Coastal Flooding Analysis and Mapping. Washington, D.C.

6. Federal Emergency Management Agency. (July 16, 1991, Flood Insurance Rate Map; July 16, 1991, Flood Insurance Study report). Flood Insurance Study, Jefferson County, Florida (Unincorporated Areas). Washington, D.C.

7. Federal Emergency Management Agency. (Revised February 1981). User’s Manual for Wave Height Analysis. Washington, D.C.

8. Federal Emergency Management Agency. (Revised January 1981). Computer Model for Determining Wave Height Elevations for Flood Insurance Studies. Washington, D.C.

9. Federal Emergency Management Agency, Federal Insurance Administration, Flood Insurance Study for Wakulla County, Florida, Proof Copy, Effective date January 16, 1981.

10. Federal Emergency Management Agency, Federal Insurance Administration, Flood Insurance Study, Leon County, Florida (Unincorporated Areas), unpublished.

11. Hagen, S.C., A. Zundel, and S. Kojima (2006), “Automatic, Unstructured Mesh Generation for Tidal Calculations in a Large Domain”, International Journal of Computational Fluid Dynamics, 20 (8), 593-608.

12. Luettich, R.A., J.J. Westerink, and N.W. Scheffner. (1992). “ADCIRC: An Advanced Three-dimensional Circulation Model for Shelves, Coasts and Estuaries, Report 1: Theory and Methodology of ADCIRC-2DDI and ADCIRC- 3DL.” Tech. Rep. DRP-92-6, U.S. Army Corps of Engineers. Available at: ERDC Vicksburg (WES), U.S. Army Engineer Waterways Experiment Station

(WES), ATTN: ERDC-ITL-K, 3909 Halls Ferry Road, Vicksburg, Mississippi, 39180-6199.

13. National Oceanic and Atmospheric Administration, Environmental Data Service, National Climatic Center, Asheville, North Carolina; Climate of Florida, 1978.

14. National Oceanic and Atmospheric Administration, National Ocean Survey, Selected NOS Hyrdographic Surveys, various dates and scales.

15. Northwest Florida Water Management District. (February 2011). St. Marks River Hydrologic – Hydraulic Analysis. Havana, Florida.

16. Northwest Florida Water Management District. (June 2010). Wakulla Gardens Hydrologic – Hydraulic Analysis. Havana, Florida.

17. Russell, L. R. (1968). Probability Distribution for Texas Gulf Coast Hurricane Effects of Engineering Interest. Ph.D. Thesis, Stanford University.

18. State of Florida; Department of Environmental Regulation, Division of Environmental Programs, Bureau of Coastal Zone Planning, Florida Regional Coastal Zone Economic Analysis Region 2, July 1977.

19. U.S. Department of the Army, Corps of Engineers, Alabama District, Special Flood Hazard Information Ochlockonee River Lake Talquin to Allen Landing, Mobile, Alabama, November 1971.

20. U.S. Army Corps of Engineers, Galveston District. (June 1975). Guidelines for Identifying Coastal Hazard Areas.

21. U.S. Army Corps of Engineers, Hydrologic Engineering Center. (April 1984). HEC-2 Water Surface Profiles, Computer Program. Davis, California.

22. U.S. Department of Commerce, Bureau of the Census. (2010). 2010 Census of Population. Washington, D.C.

23. U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood Insurance Study, Town of St. Marks, Florida, February 1978.

24. U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood Hazard Boundary Map Wakulla County, Florida, Scale 1:12,000, February, 1975.

25. U.S. Department of the Interior, Geological Survey, Interagency Advisory Committee on Water Data, Office of Water Data Coordination, Hydrology Subcommittee. (September 1981). Bulletin No. 17B: Guidelines for Determining Flood Flow Frequency.

26. U.S. Department of the Interior, Geological Survey. (1967). Roughness Characteristics of Natural Channels. Washington, D.C.

27. U.S. Department of the Interior, Geological Survey. (1982). Water Resources Investigation Report 82-4012, Techniques for Estimating Magnitude and Frequency of Floods on Natural-Flow Streams in Florida. Wayne C. Bridges.

28. U.S. Department of the Interior, Geological Survey. (1993). Water Resources Investigation Report 94-4002, Nationwide Summary of U.S. Geological Survey Regional Regression Equations for Estimating Magnitude and Frequency of Floods for Ungaged Sites.

29. U.S. Department of Transportation, Highway Administration. (April, 1984). Guide for Selecting Manning’s Roughness Coefficients for Nature Channels and Flood Plains. Washington, D.C.