Using a fully coupled surface water - groundwater model to quantify streamflow components

Separation of streamflow components into quickflow and baseflow is usually carried out in two main ways: hydrograph recession analysis and tracer-based methods. In this paper, it is proposed to use a fully coupled surface and subsurface flow and transport model to gain a better understanding of the relationship between physical catchment characteristics (e.g. aquifer hydraulic conductivity) and hydrological response (e.g. stream salinity and flow response) to a rainfall event. This enables an evaluation of the common empirical approaches of recession analysis and baseflow separation in practice. This is achieved by conducting a range of numerical experiments on a hypothetical case study, which is based on a commonly used surface water-groundwater interaction benchmarking problem. A fully coupled, variably saturated surface-subsurface flow and transport model (HydroGeoSphere) forms the basis of the numerical experiments conducted in this investigation. The results indicate that the empirical baseflow separation algorithms failed to reproduce the simulated groundwater discharge to the stream from the theoretical catchment, although it was identified that the surface-subsurface benchmark problem needs to be further developed to produce more realistic hydrograph behaviour before a proper comparison between the two approaches can be made.