REMOTE SENSING DATA INTEGRATION AND RUNOFF MODELING TO ESTIMATE FLASH FLOODS IN EL-ARISH, SINAI, EGYPT

Flash floods are a major hazard to populations in arid regions. Wadi El-Arish in northern Sinai, Egypt, collects over 60% of Sinai's precipitation. On January 18^th­­, 2010 Wadi El-Arish experienced a heavy rainstorm caused flashfloods in El-Arish city (outlet), 780 houses were destroyed, while 1,076 were submerged; the material losses were estimated at US$25.3 million. The objective of this study is to correlate remote sensing data (TRMM, SRTM, Radarsat-1, Landsat TM, ASTER), with the spatial and temporal distribution of this rainstorm. A watershed and land-cover maps were extracted using SRTM and ASTER imagery respectively. Slope analysis and morphometric parameters show that El-Arish basin has higher potential for groundwater recharge than flood risk. Based on stream network analysis, the watershed was subdivided into 14 sub-basins representing flooding and feeding potentialities. Texture roughness classification was employed, using the Radarsat-1 data. Most coarse deposits are in the upstream and within sub-basins with high potential for flood risk. In contrast, alluvial fine-grained deposits settle downstream and in sub-basins with superior recharge potentiality. In order to detect specific locations with high probability for flash-floods risk, several GIS layers were created. Integrated analysis of the generated GIS layers was applied using a weight factor for each layer. The resulting map was compared with the spatial distribution of rainfall from TRMM data. This revealed that most precipitation concentrated on basins of high flooding probability. Due to insufficient data on surface flow, Runoff modeling adopting Soil Conservation Service method was conducted to predict the hydrological responses in ungauged sub-basins. Downstream runoff, initial upstream loss, and transmission channel loss were estimated. The results of the runoff models were validated against the DEM derived model. El-Arish watershed remains basin with high potential for groundwater recharge more than flood risk, but the presence of three narrow corridors (120-200 m wide) near the outlet, enhances the surface flow speed, in rough areas, which should be dammed. The spread of the urban areas of El-Arish city was delineated by change detection based on 1984-2003 TM data. Such growth to 380,000 inhabitants should be ameliorated.