DISTRIBUTED-PARAMETER HYDROLOGY MODEL (ANSWERS) APPLIED TO A RANGE OFCATCHMENT SCALES USING RAINFALL SIMULATOR DATA .3. APPLICATION TO A SPATIALLY COMPLEX CATCHMENT

The areal non-point source watershed environment response simulation ( ANSWERS) model, modified to include Green and Ampt infiltration, was t ested using measured runoff from a 9.6-ha spatially variable grassland catchment in the semi-arid tropics in Central Queensland. A descripti on of the development of the modified ANSWERS model and testing with r unoff from relatively uniform, cultivated catchments is given in earli er papers in this series. Important infiltration parameter values were derived from 1-m(2) rainfall simulator plots. Functions describing ch ange in soil infiltration capacity with increasing pasture cover were included in ANSWERS. Other parameter values describing infiltration, c atchment topography and surface conditions were measured directly, est imated from tabulated sources or modelled with the Grasp model. Runoff at the catchment outlet was well predicted for cover conditions that varied from bare to heavy cover. Runoff from subcatchments with varyin g areas, soil types and infiltration capacities was also well predicte d. Runoff from high intensity rainfall events was more accurately pred icted than from low intensity events. Using the application and parame terisation methods described in this paper, the modified ANSWERS model could be used to predict runoff from spatially complex catchments wit hout optimisation of parameter values against measured runoff.