Hurricane Katrina Flood Recovery (Mississippi)

Mapping Methods and Data Sources

The Hurricane Katrina Surge Inundation and Advisory Base Flood Elevation Maps (or “Katrina Recovery Maps”) show a variety of information concerning the hurricane’s impact – information that was developed through numerous post-storm surveys and data analyses. The Katrina Recovery Maps also show Advisory Base Flood Elevations (ABFEs), which are the best 1%-annual-chance (100-year) coastal flood elevations currently available to guide redevelopment along the Mississippi Gulf Coast.

For comparison purposes, the Katrina Recovery Maps also list current FEMA flood map elevations, which are used by local communities to regulate development in mapped floodplains. The technical studies that developed the existing flood map elevations were conducted more than 25 years ago. The updated ABFEs incorporate water levels from tides and storm events that have occurred over the last 25 years, including (but not limited to) Hurricane Katrina.

The data sources and analysis methods used to develop the Katrina Recovery Maps are described in the sections that follow. A more detailed discussion of the data and methods is provided in a summary report, “Hurricane Katrina Surge Inundation and Advisory Base Flood Maps- Summary of Methods”, dated November 15, 2005 (PDF file, 2 KB).

Base Maps

The base map for the Katrina Recovery Maps in Mississippi is pre-storm, digital orthophotography that was provided by U.S. Department of Agriculture’s National Agriculture Imagery Program. Additional details concerning the origin of this imagery is provided below.

Location: Hancock County, MS

Data Source:
United States Department of Agriculture National Agriculture Imagery Program, dated August 13, 2004, 1 meter resolution, DOQQ mosaics in Mr. Sid format, Compression ratio 1:50

Location: Harrison County, MS

Data Source:
United States Department of Agriculture National Agriculture Imagery Program, dated October 16, 2004, 1 meter resolution, DOQQ mosaics in Mr. Sid format, Compression ratio 1:50

Location: Jackson County, MS

Data Source:
United States Department of Agriculture National Agriculture Imagery Program, dated August 15, 2004, 1 meter resolution, DOQQ mosaics in Mr. Sid format, Compression ratio 1:50

Hurricane Katrina Preliminary High Water Marks:

Sample High Water Mark (Mud Line on Building)Within days of the storm, field observers and survey crews were deployed by FEMA and various state, county, and local governments to interview residents, find evidence of coastal high water levels, take digital photographs, and survey coastal high water marks (HWMs) from Hurricane Katrina. These field crews collected detailed information about each HWM, including physical basis of the mark, such as a mud line inside the building, a mud line on the outside of the building, or debris. Wherever possible, crews also noted the coastal flooding characteristics captured by the coastal HWM, including storm surge, wave runup, and wave height. These designations were based on a combination of physical flood evidence and interviews with witnesses at the time of collection.

The survey crews used static Global Positioning System (GPS) methods to determine an accurate elevation for each coastal HWM. Coastal HWM locations were surveyed horizontally in North American Datum of 1983 (NAD 83), State Plane feet, and vertically in North American Vertical Datum of 1988 (NAVD 88), U.S. survey feet. Coastal HWM locations have been surveyed to within accuracies of 0.25 foot vertically and 10 feet horizontally, with a 95% confidence level. Results from FEMA’s HWM surveys will be published and made available to the public and local officials.

Hurricane Katrina Surge Inundation Limits

Flood inundation limits were created for the Mississippi coastal counties by mapping the coastal HWM elevations onto digital, pre-storm, topographic contour data developed from recent Light Detecting and Ranging (LIDAR) surveys. These inundation limits represent an estimate of the inland extent of flooding caused by Hurricane Katrina’s storm surge. In areas where the coastal HWMs were close together but elevations differed significantly (more than 2-3 feet), engineering judgment was used to interpolate the inundation limit between coastal HWMs. At the time of this project, post-hurricane topography was not available for the study area.

Advisory Base Flood Elevations (ABFEs)

Sample ABFE (Yellow Lines). Red Line is estimated inland limit of wave actionABFEs were developed to provide communities with recommended building elevations for use in the reconstruction process until more detailed data become available. ABFEs are based on a new flood frequency analysis that takes into account Hurricane Katrina, as well as additional tide and storm data from other events that have occurred during the 25 years since the existing Flood Insurance Rate Maps (FIRMs) were developed. The ABFEs are calculated using an updated 1%-annual-chance (100-year) stillwater level, plus estimated wave effects. ABFE values vary for each county, with elevations increasing to the west. For more information on how the ABFEs are calculated, see the "Notes to Users" (PDF, 31 KB)

Also provided with the ABFEs are the estimated limits of damaging 1.5-foot breaking waves (marked with the red ABFE contour) and 3.0-foot breaking waves (marked with the orange ABFE contour). Wave and erosion forces in these areas may warrant special design and construction considerations. For more information, please see FEMA's "Reconstruction Guidance Using Hurricane Katrina Surge Inundation and Advisory Base Flood Elevation Maps" (PDF 417 KB)and other documents located on the Recovery and Mitigation Resources page for this website.

FEMA Flood Map Data

In addition to data pertaining to Hurricane Katrina, the range of Base Flood Elevations (BFEs) and flood zones (A and V Zones) from each community’s effective Flood Insurance Rate Map (FIRM) are provided in the title blocks of the Katrina Recovery Maps. FIRMs depict flood elevations and velocity conditions that have a 1% chance of being equaled or exceeded in any given year, also referred to as the 100-year flood. In coastal areas, these FIRM flood elevations include additional effects due to wave height and/or wave runup.

Recovery map users should note: The Katrina surge inundation limits (shown on the 228 detailed map panels) and the Katrina surge elevation contours [shown on the regional overview map (PDF 0.9MB)] do not include wave effects, and therefore are not directly comparable to the FIRM flood elevations.  Advisory Base Flood Elevations (ABFEs), which were described in the previous section, do include these local wave effects and can be compared to FIRM flood elevations.

Please note: To facilitate comparison to FEMA’s effective FIRMs, all elevation data for Hancock, Harrison, and Jackson Counties, Mississippi, are referenced to the North American Vertical Datum of 1988 (NAVD 88).

Hurricane Katrina Surge Elevation Contours

Regional Overview MapTo show regional trends in Hurricane Katrina’s coastal surge as the storm came onshore, surge elevation contours were mapped at 1-foot intervals across the three Gulf Coast counties of Mississippi. These contours are shown on a regional overview map (PDF 0.9 MB) of the project area.

The Hurricane Katrina surge elevation contours are based upon the surveyed coastal HWM elevations, which were used to find patterns in the coastal storm surge as it pushed against the open coast and into the inland bays. The known path and landfall location of Hurricane Katrina, together with the knowledge of how storm surge propagates inland, allowed surge contours to be drawn across the areas where the coastal HWMs indicate a change in storm surge elevation.

Assumptions are made in some locations to allow the surge elevation contours to “step” up or down at 1-foot intervals. Because of the inherent uncertainty in and the random and irregular spacing of coastal HWMs, the surge contours represent a generalized maximum storm surge elevation, and required professional judgment in their creation. Within certain surge contours, coastal HWMs may be higher or lower than the contours if they did not fit the overall pattern.

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Last Modified: Friday, 26-May-2006 11:39:21 EDT