UM-3/97-98 : Expert System for Unit Hydrograph Analysis

Abstract

As the unit hydrographs establish a relationship between the excess rainfall and the direct runoff hydrograph, they are of immense value in the study of the hydrology of a catchment. They are of great use in (i) the development of flood hydrographs for extreme rainfall magnitudes for use in the design of hydraulic structures, (ii) extention of flood flow records based on rainfall records and (iii) development of flood forecasting and warning systems based on rainfall.

By definition, unit hydrograph is the direct surface runoff hydrograph resulted at the catchment outlet due to unit( 1 mm/1 cm/1 inch) rainfall excess falling uniformly over the catchment in time as well as in space for the specified duration. The unit hydrograph is basically a multiplier which converts the excess rainfall to direct surface runoff. Thus it can be said that the unit hydrograph only deals with the direct surface runoff and excess rainfall. Therefore, the baseflow must be seperated from the streamflow hydrograph and losses must be accounted from the average rainfall hyetograph in order to get the direct surface runoff hydrograph and excess rainfall hyetograph respectively.