Separation of Stormflow Hydrographs in Surface and Subsurface Flow by Perceptual Based Modelling of Channel Inflow Components

The aim of this case study was to determine the origin of stormflow runoff in a 31 ha headwater basin in Western Germany. Therefore, the contribution of infiltration excess and saturation overland flow as well as matrix and preferential flow has been assessed along a deeply incised channel of 300 m length. Measurable parameters and simple algorithms were used to assess the flow rate of the different runoff components. Only the scaling parameter cf that represents converging flow processes and controls the actual height of the saturated zone along the channel incision has been calibrated. The results showed that during wet conditions the subsurface flow rates exceed the surface flow rates tremendously. In contrast, for the short but intense summer storm the hydrograph consists solely of surface runoff components. Obviously, the parameter cf accounts for the pre-event condition of the catchment. This leads to the conclusion, that the extension of the contributing subsurface space mainly governs stormflow processes. Further investigations shall focus on the relationship between subsurface flow processes and the lateral and vertical extension of the saturated zone.