Role of Infiltration and Saturation Excess in Rainfall-Runoff Modelling in Small Catchments

The paper presents the essential differences in small catchment model behaviour depending on the assumed runoff procedure, i.e. infiltration or saturation excess. It suggests an appropriate model structure and a way to obtain the required boundary conditions. In order to design the flood mitigation measures in small catchments, there is a need of reliable prediction of their behaviour. Long time series of data are rather rare here and the simple models are usually not capable to reflect all the necessary variables and their distribution. However, more comprehensive models are usually very demanding with respect to input data. A model of Bykovicky stream catchment (6.3 km²) was built in the physically based distributed model GSSHA. Out of two years of rainfall-runoff data several events were used for model calibration. Gradually the model was changed in order to explain observed data better. First modelling outcomes suggested a significant influence of saturation excess on flood hydrographs in most of the scenarios. In order to reflect this, the model needs to contain groundwater related processes, but the data on groundwater table position was not available. Therefore a simple method how to obtain it was proposed and tested. The paper discusses the achievements of this modelling experiment.