APPLICATION OF UNIT-HYDROGRAPH TECHNIQUES TO SOLUTE TRANSPORT IN CATCHMENTS

Current models of solute movement in catchments are based on rainfall- runoff models and are consequently biased towards processes which dete rmine the magnitude and timing of water flux. It is shown here that th e instantaneous unit hydrograph (IUH), or runoff response function, ob tained from a hydrograph is fundamentally different from the residence time distribution which governs the response to solutes/tracers. Usin g hydrometric and tracer data obtained from a small (25 ha) catchment in the humid tropics a modification of the IUH technique is demonstrat ed which also allows approximate modelling of the tracer data. New fea tures of the modified conceptual model are identified with known hills lope processes.