Geomorphological instantaneous unit hydrograph model and its use in hydrological practice

Practical problems concerning the adoption of the geomorphological unit hydrograph (GIUH) as a component of the rainfall-runoff modeling applied to the determination of design hydrographs in ungaged basins were considered. In particular, the reliability of basin lag estimates through lag-area relationships and the detail required in representing the basin geomorphologic features were examined. Real basins located in Central Italy and ranging in area from 12 km2 to 4147 km2 were employed, together with a variety of observed rainfall-runoff events and with an actual depth-duration curve for a 100-yr return period. It was found that usually the basin lag, which is the crucial parameter in determining the peak hydrograph, may be correctly estimated. Further, basins which may involve unappropriate estimates are specified. The minimum detail required in representing the channel network structure is pointed out.