Freshwater-related risks of climate change including that of extreme weather events such as floods, will increase significantly with increasing greenhouse gas concentrations (IPCC 2014). Hydrological modelling is an effective method for quantifying the peak flood and area inundated by floods. The present study is an attempt to create an open source software system to estimate basic hydrological components from freely available topographical data, which can be used for estimating flood peak from a given rainfall event. This tool consists of two parts: Terrain processing part and Hydrological modelling part. Terrain processing part includes basic hydro processing functions such as fill sinks, flow direction, flow accumulation, stream definition and watershed delineation from given Digital Elevation Model (DEM). All the processes are automatic, only the raw DEM raster file and outlet shape file is needed as input. Output of the terrain processing is used as input of the hydrological processing section. The created GIS files can read in any open source freely available software such as QGIS or ILWIS. Hydrological modeling part consists of two parts: transformation method and flood routing. Synder’s unit hydrograph method is implemented as rainfall-runoff transformation method. Muskingum’s method is used as flood routing method. This tool is able to find the flood peak discharge for individual sub-watershed of a basin. The tool has been developed in Python scripting language, resulting this is machine independent and have more scope for further development by including more methods for runoff estimation and flow routing.
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