USGS Washington Water Science Center
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WA812 - Flood-Hazard Mapping in Honduras by the USGS Washington Water Science Center - Completed FY2002
Problem - Honduras is currently (2001) rebuilding its housing and infrastructure that was destroyed by Hurricane Mitch. To plan responsibly and minimize damage during future floods, the Honduran government needs reliable maps of the areas and depth of inundation by the 50-year flood, the design flood chosen for this project. A systematic method for defining areas and depths of inundation is needed that can be easily applied to the country as a whole. A method needs to be developed and applied to compute the 50-year flood at selected locations using the available hydrologic and meteorological data.
Relevance and Benefits - This study targets the issue of hydrologic hazards, one of four Water Resources Division priority water issues for Fiscal Year 2000(WRD memo. 99.30). Specific benefits that will be provided by the proposed work are opportunities to:
Approach - Two approaches for determining the discharge of the design flood will be used. First, a simple regional regression approach with regression coefficients from a nearby or similar region will be used to estimate the 50-year discharge. The regression equation uses basin and precipitation characteristics to compute the magnitude of the design flood, and these characteristics will be obtained from available Geographic Information System (GIS) coverages. Second, a modeling approach using a continuous or event-based model will be used for selected watersheds where sufficient data are available. A continuous model can simulate a long-term record of simulated peak discharges. From the long-term record, peak-flow statistics can be used to estimate the 50-year flood. With the event-type model, the 50-year precipitation event is used to estimate the 50-year discharge. Both approaches will initially investigate the availability and quality of streamflow and precipitation data in the study area that can be used for this study. Water-surface profiles will be computed using standard step-backwater modeling techniques using the values for the design flood, channel geometry, and roughness coefficients as input. Channel geometry of the above-water portion of the floodplain will be obtained from LIDAR surveys. Field visits to the sites will be made to obtain roughness coefficients, bridge opening geometry, and a few representative under-water, cross-section surveys. After the 50-year water-surface profiles have been computed, the elevations will be combined with the Digital Elevation Models (DEMs) to delineate the areas of inundation using a GIS. GIS coverages of the areal extent and depth of inundation will be created and plotted with appropriate and available background coverages such as roads, building, streams, etc. The final digital mapping products will be compiled with other available coverages as ArcView project files for a concurrent Municiple GIS project that will provide the files to the municipalities along with training on how to use them. The GIS coverages will also be available on a USGS Hurricane Mitch web site.