Distributed parameter hydrology model (ANSWERS) applied to a range of catchment 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 tested using measured runoff from a 9.6-ha spatially variable grassland catchment in the semi-arid tropics in Central Queensland. A description of the development of the modified ANSWERS model and testing with runoff from relatively uniform, cultivated catchments is given in earlier papers in this series. Important infiltration parameter values were derived from 1-m(2) rainfall simulator plots. Functions describing change in soil infiltration capacity with increasing pasture cover were included in ANSWERS. Other parameter values describing infiltration, catchment topography and surface conditions were measured directly, estimated 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 varying areas, soil types and infiltration capacities was also well predicted. Runoff from high intensity rainfall events was more accurately predicted than from low intensity events. Using the application and parameterisation methods described in this paper, the modified ANSWERS model could be used to predict runoff from spatially complex catchments without optimisation of parameter values against measured runoff.