Snyder Unit Hydrograph and GIS for Estimation of Flood for Un-Gauged Catchments in Lower Tapi Basin,India

In the flood prone catchments, it is needful to estimate the discharge, standard lag time, time of peak, and flood response of each watershed in the basin. The SUH method offers considerable advantage over others, and thus, has been chosen for estimation of flood response, contribution of flooding potential, percentage of flood volume for 25 sub-watersheds. The discretion of sub-watershed for estimation of peak discharge, time of peak, alternate lag time, and width of SUH at 50% and 75% of peak found to offer advantages over other methods. This paper considers Snyder Unit Hydrograph (SUH) with GIS based spatial database for calculating discharge at Lower Tapi Basin (LTB). The hydrological parameters of each sub-watershed such as river length, length of centroid, spatial area, land use, lateral slope, and terrain and soil factors have been extracted from GIS database. The geo-data has been combined with topographical maps to produce a digital elevation model (DEM) of 50 m cell size. The analysis for all 25 subwatersheds exhibit that 35.07 m3/s and 4.55 m3/s and 13.23 hours and 4.33 hours have been highest and lowest peak flow and time of peak respectively. The SUH model has been validated for peak discharge at a gauge site Amli (E73023' N21023') where discharge data were collected during 2010 and 2011 monsoon. A comparison between measured and SUH modelled discharge shows good fit within a mean variability range of 5-7%. The SUH methods ability to estimate hydrological parameters including peak flow discharge shows wider replication for un-gauged catchments.