Koivusalo, H.; Kokkonen, T.; Karvonen, T.; Croke, B. F. W.; Jakeman, A. J. 2001. Accounting for response differences in runoff events of different magnitudes. In: Ghassemi, Fereidoun; Post, David; Sivapalan, Murugesu; Vertessy, Robert, eds. Proceedings, MODSIM 2001: International Congress on Modelling and Simulation--integrating models for natural resources management across disciplines, issues and scales; Canberra, Australia. [Place of publication unknown]: Modelling and Simulation Society of Australia and New Zealand Inc.: 89-94.
Models that pass a series of estimated rainfall excess through a routing procedure of constant delay function neglect the fact that the magnitude of the flow event may have an impact on the catchment response. In this paper we demonstrate using flow data from two catchments that flow events of greater magnitude have a flashier response than smaller ones. The analysis of varying response according to event size is accomplished by utilising a two-parameter gamma function as a unit hydrograph and allowing the rainfall excess series to take any value less than or equal to the measured rainfall. Results indicate that the shape of the gamma function is event-dependent in the sense that larger events exhibit a flashier behaviour. In otherwords, a constant unit hydrograph will have problems in reproducing streamflow dynamics although the rainfall excess may adopt any reasonable values. Analysis of streamflow events reveals that the gamma distribution parameters could be related to the intensity of flow or rainfall excess.
Keywords: Rainfall; Streamflow; Unit hydrograph; Modelling