Flood-Hazard Mapping in Honduras in Response to Hurricane Mitch
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Prepared in cooperation with the U.S Agency for International Development Flood-Hazard Mapping in Honduras in Response to Hurricane Mitch Water-Resources Investigations Report 01-4277 U.S. Department of the Interior U.S. Geological Survey Flood-Hazard Mapping in Honduras in Response to Hurricane Mitch By Mark C. Mastin U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 01-4277 Prepared in cooperation with U.S. AGENCY FOR INTERNATIONAL DEVELOPMENT Tacoma, Washington 2002 U.S. DEPARTMENT OF THE INTERIOR GALE A. NORTON, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. For additional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Information Services 1201 Pacific Avenue – Suite 600 Building 810 Tacoma, Washington 98402 Box 25286, Federal Center http://wa.water.usgs.gov http://wa.water.usgs.gov Denver, CO 80225-0286 CONTENTS Abstract ................................................................................................................................................................ 1 Introduction .......................................................................................................................................................... 1 Purpose and Scope ...................................................................................................................................... 3 Description of the Study Area..................................................................................................................... 3 Methods....................................................................................................................................................... 5 Acknowledgments....................................................................................................................................... 7 Regional Hydrology of Honduras ........................................................................................................................ 7 River Discharge........................................................................................................................................... 7 Precipitation ................................................................................................................................................ 9 Data Sources......................................................................................................................................................... 10 Annual Peak Discharge............................................................................................................................... 10 Precipitation ................................................................................................................................................ 12 Topography ................................................................................................................................................. 12 Frequency Analysis of Precipitation and Peak Flows.......................................................................................... 17 Precipitation Frequency .............................................................................................................................. 18 Peak-Flow Frequency at Gaged Sites ......................................................................................................... 18 Peak-Flow Frequency at Ungaged Sites ..................................................................................................... 23 A GIS to Estimate 50-Year Flood Discharges................................................................................... 31 Estimated 50-Year Flood Discharges at Selected Municipalities............................................................... 31 50-Year Flood Discharges Reported by Others .......................................................................................... 31 Flood-Hazard Mapping Method........................................................................................................................... 33 Pre- and Post-Processing GIS Data With HEC-GeoRAS........................................................................... 33 Hydraulic Modeling With HEC-RAS ......................................................................................................... 34 Summary .............................................................................................................................................................. 37 References Cited .................................................................................................................................................. 38 Contents iii FIGURES Figure 1. Map showing location of the study area, the general topography, and the three geographic regions............................................................................................................................. 4 Figure 2. Map showing flood-hazard areas that were mapped by airborne topographic surveys in this study, and extents of drainage basins that contribute streamflow discharge to the flood-hazard areas.............................................................................................................................. 6 Figure 3. Map showing the extent of the airborne topographic survey at Santa Rosa de Aguán, Honduras, and the area of inundation for the 25-year flood.............................................................. 7 Figure 4. Graphs showing mean monthly streamflow discharge at three streamgaging stations in Honduras for their periods of record.................................................................................................. 8 Figure 5. Graph showing average monthly distribution of annual maximum instantaneous streamflow discharges (peak flows) for 424 peak flows at 27 streamgaging stations in Honduras........................................................................................................................... 9 Figure 6. Map showing locations of streamflow gaging stations with 10 years or more of annual peak-flow records, lengths of records, locations of flood-hazard areas that were mapped by airborne topographic surveys, and extents of drainage basins that contribute streamflow discharge to the flood-hazard areas.................................................................................................... 11 Figure 7. Diagram showing comparison of river cross sections 55 meters downstream of the Highway Bridge on Río Humuya in Comayagua, Honduras, using elevations from a ground survey and an airborne LIDAR survey.................................................................................. 15 Figure 8. Shaded-relief images of LIDAR-derived digital elevation models with cross-section locations for the Tocoa hydraulic model (A) with vegetation, and (B) with vegetation removed through filtering .................................................................................................................. 16 Figure 9. Graph showing original and edited cross sections of Río Tocoa at station 2.098.72 of the Tocoa hydraulic model, Tocoa, Honduras......................................................................................... 17 Figure 10. Map showing lines of equal 50-year, daily precipitation totals and the locations of precipitation stations at which 50-year, daily precipitation totals were estimated ............................ 22 Figure 11. Graph showing comparison of annual peak-flow discharge and annual exceedance probability for Choluteca en Puente Choluteca, Honduras, using exceedance probabilities based on the recorded (unadjusted) record and based on local, historical information (adjusted)........................................................................................................................ 28 Figure 12. Graph showing comparison of predicted and observed 50-year peak flows at 34 streamgaging stations in Honduras .................................................................................................... 30 Figure 13. Map showing shaded-relief image of the Río Tocoa, Honduras, study site based on the LIDAR-derived digital elevation model, and the locations of the stream thalweg, river banks, approximate centerlines of overbank areas, and cross-sectional lines............................................... 35 iv Contents TABLES Table 1. Characteristics of 15 municipalities selected to demonstrate the flood-hazards mapping methodology developed for Honduras .............................................................................................. 2 Table 2. Maximum 3-day precipitation totals for selected precipitation stations in Honduras for several tropical cyclones in recent history .................................................................................. 10 Table 3. Multipliers for the 3-day daily discharge method used to estimate annual maximum instantaneous discharge (peak flow) ................................................................................................. 12 Table 4. Comparison of root mean square errors for predicting the annual maximum instantaneous discharge (peak flow) at three test sites using the peak-day daily discharge linear regression and the 3-day daily discharge methods ................................................. 13