Exploring the effect of catchment morphology on streamflow characteristics with virtual experiments

The surface flow is significantly affected by catchment geomorphological characteristics, which have been widely used in the empirical equations in hydrograph predictions. Previous studies have explored the relationship between streamflow and geomorphology however mostly based on local observations, which are site-specific and unconvincing to be used as a universal principle. Here we adopted a robust approach by creating over 2000 virtual catchments from the Brue catchment in the UK using a well-trained distributed model, SHETRAN. The virtual catchments were allocated with a range of values in slope, drainage length and different shapes with a spatially uniform rainfall. We calculated the time to peak and the peak streamflow of unit hydrographs to explore the effect of catchment geomorphology on streamflow generation. The results present a consistent agreement with hydrological principles, i.e. shorter time to peak and higher peak values are observed with larger slope while longer time to peak and lower peak are experienced with longer drainage path. It was found that the shape of catchments can affect the streamflow characteristics. We found the officially used empirical UH equation in the UK represent the catchment geomorphology poorly. In addition, we found the streamflow properties are different when receiving varied intensity and temporal pattern of the storms. This study comprehensively explores the effect of geomorphology on streamflow avoiding the issues caused by catchment limitations in previous studies and imported different types of storms. Although it is away from generating an equation that can be generally adopted, more importantly it provides a feasible approach to investigate the unit hydrograph for different catchments with the virtual catchments.