VALUES FOR THE EXPONENT OF THE STORAGE DISCHARGE EQUATION IN RUNOFF-ROUTING MODELS

A storage-discharge equation: S = kQ(m) is often used in runoff-routin g models. The prediction by the models is highly sensitive to the valu e of exponent m used. A discharge-depth equation: q = Ky(alpha)S(e)1/2 can be used to simulate overland and channel flows and the two equati ons considered here are shown to be similar and their parameters inter related. Although the species of vegetative covers encountered in fiel d data considered in the present study are probably not typical of tho se generally encountered on the catchments, their characteristics whic h influence overland and channel flows particularly on small catchment s are of relevance here. The values of alpha obtained from shallow ove rland flow and channel flow studies suggest that the exponent m in the storage-discharge equation should be varied between 0.33 and 1.00 dep ending upon the regime of flow and degree of turbulence in the flow. W hile the study provides a further understanding of the variation of ex ponent m, more research is needed particularly in quantifying the degr ee of turbulence in the flow and developing a practical method of vary ing m in the runoff-routing model to account for flow conditions prese nt over the catchment.