Computation of the instantaneous unit hydrograph and identifiable component flows with application to two small upland catchments

Abstract

Our approach is based upon three factors: (i) the representation of total streamflow response as a linear convolution of the instantaneous unit hydrograph with rainfall excess; (ii) approximation of this representation in discrete time by a rational transfer function relationship which involves an efficient and flexible parameterisation; (iii) use of a simple refined version of the instrumental variable method of parameter estimation as the major tool to determine the number of identifiable flow components in the representation and to estimate their dynamic contributions to the instantaneous unit hydrograph. Stream hydrograph separation is undertaken by convoluting rainfall excess with the identified components of the unit hydrograph. The procedure is applied to two small upland catchments in Wales. The results demonstrate that at sampling intervals of the order of one hour, successful separation of quick and slow flow components can be achieved with short time series of rainfall and streamflow.