Evaluating Partial Areas of Watershed Runoff

Abstract

Variations in surface storage capacity over a watershed produce partial areas of saturation overland flow, which vary from storm to storm. A method is described by which the proportions of a watershed that contributes overland flow in different storms and at different times during the same storm can be determined by analysis of rainfall and runoff records. The method is demonstrated on two catchments in Queensland, Australia, with different hydrological characteristics. One watershed is 16.8 ha in area with only two to three events per year of overland flow (no baseflow) averaging 35 mm per annum runoff; the other is 7 km in area with substantial baseflow and an average of 920 mm per annum runoff. The calculated amounts and proportions of surface storage capacity are incorporated into water balance models of watershed runoff to show the accuracy of runoff estimation.