Flood Estimation by GIUH-Based Clark and Nash Models

With the recent and drastic decline of hydrological in situ networks, flood estimation from ungauged basins is an imperative research area in scientific hydrology. In this regard, geomorphologic instantaneous unit hydrograph (GIUH) based on models by Clark in 1945 and Nash in 1957 are developed and applied to the Ajay River Basin at Jamtara in northern India. The geomorphologic parameters of the basin were estimated using ERDAS Imagine 8.5 image processing and geographic information system (GIS) software. The direct surface runoff (DSRO) hydrographs derived by the GIUH-based models without using historical runoff data, the conventional Clark IUH model option of the HEC-1 package, and the Nash IUH model, were compared with observed DSRO hydrographs employing four performance criteria. The DSRO hydrographs are computed with reasonable accuracy by the GIUH-based Clark and Nash models, when compared to the Clark IUH model option of the HEC-1 package and the Nash IUH model. It is observed that the GIS supported GIUH-based models hold great potential of estimating floods from ungauged basins, or basins with scant data availability. Further, the effect of the basin map scale on the performance of the GIUH-based models was evaluated for the same basin. The DSRO hydrographs computed using the GIUH-based Clark and Nash models, were estimated with reasonable accuracy at the two map scales (viz. 1:50,000 and 1:250,000).