COMMON UNITGRAPHS FOR SETS OF RUNOFF EVENTS .2. COMPARISONS AND INFERENCES FOR RAINFALL LOSS MODELS

Common unitgraphs obtained from streamflow data for a set of runoff ev ents have higher peaks, shorter times to peak and generally shorter to tal durations than average unitgraphs obtained by conventional techniq ues from rainfall and streamflow data for single events. The calculate d inputs to these unitgraphs lag behind the corresponding peaks in the catchment rainfall and continue after the end of rainfall. It eventua tes that these inputs are best modelled by including a strongly non-li near storage in the rainfall loss model. For common loss and storage p arameters, runoff hydrographs from the overall model fit the observed hydrographs over a wider range of flows than predictions from applicat ion of conventional unitgraph methods. The new approach can be interpr eted physically as a non-linear process of rainfall loss and routing t o stream channels, followed by linear routing of stream flow; or funct ionally as a separation of the common linear elements in the overall r ainfall-runoff process from the loss and non-linear elements. It has t he potential to lead to improved predictions of storm runoff hydrograp hs.