Estimation and dimulation of sheet run-off

Abstract

Sheet run-off was estimated for a Townsville stylo-annual grass pasture with 1% slope in the northern Australian monsoonal region by using neutron hydrometry supplemented by gravimetric soil sampling, both carefully timed with respect to the rainfall event. The technique is applicable to run-off and run-on situations. An empirical model was developed and incorporated into a water balance routine in an existing growth model. It relates surface sheet run-off to the soil antecedent water content (top 20 cm) and the standard daily rainfall total; the coefficients of the empirical functions are site specific. For the rainfall events studied, run-off was 37 ± 12% of the rainfall. The soil water values simulated with the run-off model included were significantly closer to the experimental values than when run-off was assumed to be zero. This improvement in simulation of soil water profiles was consistent with an improvement in subsequent dry matter simulation.