Taking theory to the field: streamflow generation mechanisms in an intermittent, Mediterranean catchment

Abstract. Understanding streamflow dynamics at the catchment scale remains an arduous task; this is especially true for non-perennial networks. While modelling tools offer important advantages to study streamflow dynamics, the highly nonlinear, unsaturated dynamics associated with the transitions between wetting and drying in non-perennial systems make modelling cumbersome. This has stifled previous modelling attempts and alludes to why there is still a knowledge gap. In this study, we first construct a conceptual model of the physical processes of streamflow generation in an intermittent river system in South Australia, based on the hypothesis that the vertical and longitudinal soil heterogeneity and topography in a basin control short-term (fast flows), seasonal (slow flow), and a mixture of these two. We then construct and parameterise a fully integrated surface-subsurface hydrologic model to examine patterns and mechanisms of streamflow generation within the catchment. A set of scenarios are explored to understand the influences of topography and soil heterogeneity across the catchment. The results showed distinct flow generation mechanisms develop in the three conceptualized areas with marked soil and topographic characteristics, and suggested that capturing the overall distribution of soil types across the catchment was more important than capturing the wide variability of soil hydraulic properties. This study augments our understanding of catchment scale streamflow generation processes, while also providing insight on the challenges of implementing physically-based, integrated surface-subsurface hydrological models in non-perennial stream catchments.