Analysis of process controls on streamflow response in an Australian tropical catchment

This study investigates the dominant processes that may be responsible for the observed streamflow response in the Seventeen Mile Creek, a tropical catchment of Northern Territory, Australia. To achieve this, the available rainfall and runoff data from this catchment are analysed through the systematic development of rainfall-runoff models of appropriate complexity, by means of the "downward or top-down approach". We start with simple model constructs, and progressively increase model complexity and improved process representation, and at each step of the way, the predictions of the models are evaluated against signatures of observed runoff variability, using standard measures of goodness of fit. This systematic examination of observed streamflow variability leads to considerable physical insights into the dominant process controls, and can be extremely valuable towards the choice and development of models of appropriate complexity. The results obtained from this modelling study show that the soils within the catchment have a high storage capacity, which contributes to a significant fraction of delayed runoff, whereas saturation excess overland flow occurs only after heavy rainfall events during the wet season. Sensitivity analyses have been conducted to determine the effects of interactions between soil depth and temporal rainfall variability on the runoff regime. They show that on the one hand the catchment total runoff is more sensitive to rainfall variations than to soil variations, while on the other hand the runoff components appear more influenced by soil depth changes.