Flood Hazard Mapping by Satellite Images and Srtm Dem in the Vu Gia – Thu Bon Alluvial Plain, Central Vietnam

The objective of this study is to generate a flood hazard map based on geomorphologic approach employing Shuttle Radar Topographic Mission (SRTM) DEM and satellite image data (ASTER and LANDSAT). Supervised classification of satellite images is implemented to characterize land cover types. Moreover, the Modified Normalized Difference Water Index (MNDWI) is undertaken to identify moist surface or saturated areas to separate flood and non-flooded areas. SRTM DEM categorization of height range is incorporated with the results of surface analysis from unsupervised classification and MNDWI to delineate the flood affected areas in relation with geomorphologic features. The results are compared with landform classification map and flood hazard map generated by image visual interpretation, field survey, topographic maps and past flood inundation maps. A case study is conducted in the alluvial plain of the Vu Gia – Thu Bon River system, central Vietnam. The extraction of moist soil by MNDWI can help to detect flooded sites and this result is compared with the landform classification map, SRTM DEM elevation ranges and land cover classification. The comparison reveals close relationship between water saturated areas, elevation ranges, and flood condition that the areas with elevation lower than 4m and classified as flood basin and deltaic lowland are inundated deeply and for rather long duration. Higher areas such as terraces and sand dunes are not flooded and natural levees are less flood-affected. Moreover, this study proves the significance of MNDWI for separating moist soil for flood prediction.