I will suggest you can use ASTER data for the purpose the 3N and 3B can be used to generate DEM. this data can also help you to generate the drainage morphometry and TRMM can provide you with a reliable long term precipitation record. Themnatic integration of these and other datasets like soil, vegetation, change detection using satellite dataset of known events will help you to mak the flood zone. In addition to this you can undertake a risk analyses.

First of all, I think modeling approach would play a key role. The second most important aspect is the availability of an accurate and very precise DEM.3rd the availability of all necessary datasets.

Thanks. We later used SRTM and Medium resolution image for the analysis. The out come were ok.