FLOOD ESTIMATION FOR UNGAUGED CATCHMENTS USING THE GIUH

Traditional techniques for design flood estimation use historical rain fall-runoff data and unit hydrographs derived from them, Such procedur es are questioned for their reliability due to the climatic and physic al changes in the watershed and their application to ungauged areas. T o overcome such difficulties, the use of physically based rainfall-run off estimation methods such as the geomorphological instantaneous unit hydrograph (GIUH) have evolved. In this study, the GIUH is derived fr om watershed geomorphological characteristics and is then related to t he parameters of the Nash instantaneous unit hydrograph (IUH) model fo r deriving its complete shape. The model parameters of the GIUH and th e Nash IUH model are derived using two different approaches. In the fi rst approach (referred to as GIUH-I) the rainfall intensity during eac h time interval is allowed to vary, whereas in the second approach (re ferred to as GIUH-II) rainfall intensity is averaged over the entire s torm period. This methodology has been applied to the Jira rivet subca tchment in eastern India to simulate floods from 12 storm events. Resu lts from both the GIUH approaches and those obtained by using Nash IUH are comparable with observed events.