Flood Estimation for Ungauged Catchments Using the GIUH

Traditional techniques for design flood estimation use historical rainfall-runoff data and unit hydrographs derived from them. Such procedures are questioned for their reliability due to the climatic and physical changes in the watershed and their application to ungauged areas. To overcome such difficulties, the use of physically based rainfall-runoff estimation methods such as the geomorphological instantaneous unit hydrograph (GIUH) have evolved. In this study, the GIUH is derived from watershed geomorphological characteristics and is then related to the parameters of the Nash instantaneous unit hydrograph (IUH) model for deriving its complete shape. The model parameters of the GIUH and the Nash IUH model are derived using two different approaches. In the first approach (referred to as GIUH-I) the rainfall intensity during each time interval is allowed to vary, whereas in the second approach (referred to as GIUH-II) rainfall intensity is averaged over the entire storm period. This methodology has been applied to the Jira river subcatchment in eastern India to simulate floods from 12 storm events. Results from both the GIUH approaches and those obtained by using Nash IUH are comparable with observed events.