DISTRIBUTED-PARAMETER HYDROLOGY MODEL (ANSWERS) APPLIED TO A RANGE OFCATCHMENT SCALES USING RAINFALL SIMULATOR DATA - IV - EVALUATING PASTURE CATCHMENT HYDROLOGY

Measured and simulated runoff data were used to evaluate the effects o f surface conditions, particularly vegetative cover, on runoff from a 10 ha pasture catchment in the semi-arid tropics of Queensland. The An swers model, modified to include a multilayered Green and Ampt represe ntation of infiltration, was used to simulate runoff. Development, par ametrisation and testing of Answers is described in Parts I and III of this series, Measured annual runoff at the catchment outlet decreased from 30% of rainfall when the catchment was in a bare, grazed conditi on, to 5% of rainfall when vegetative cover increased to 60% after des tocking and revegetation. A thorough comparison of the effect of cover on runoff from the measured record was difficult as rainfall was vari able over the experimental period and surface conditions changed with revegetation. Answers was used to simulate runoff for the experimental duration using the measured rainfall record, but with consistent cove r and surface conditions. Two cover conditions were simulated, bare (a s in the early stages of the experiment) and covered (typical of cover conditions late in the experiment). Simulated high cover conditions i ncreased by 10 mm the amount of rainfall required for runoff to occur, relative to bare conditions. Peak discharge was reduced with increase d cover for runoff events with an average recurrence interval of up to 3 years. Several revegetation strategies were simulated. The most eff ective revegetation strategy, in terms of runoff reduction from all ra infall events, was to increase cover levels modestly across the whole catchment rather than to revegetate small areas intensively. (C) 1997 Elsevier Science B.V.