Modelling ungauged lowland basins

Does complementary groundwater data add value to topography driven conceptual modelling?

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A common practice for hydrologists to determine the performance of a hydrological model and its parameter values, is by calibrating the model parameters on observed discharge data, but this data is not always available. For this reason, other data should be used as complementary data in order to reduce the uncertainty of outflow and processes in the ungauged basins. This thesis presents a case study on an area in Baden-Württemberg, Germany, to see whether groundwaterlevel data can be used as complementary data for hydrological models of ungauged basins. It has been divided into two Hydrological Response Units (Lowland and Hillslope) with use of the surface slope and the height above the nearest drainage (HAND) algorithm. The main result is that a combined addition of groundwater level measurements and constraints did show reduced uncertainty, and thus improvement, of the internal model processes, especially the fluxes towards and out of the slow responding reservoir. Validation of these processes still remains difficult in ungauged areas, but it is believed that valid results can be made on the outflow out of the lowland areas with a combination of constraints and groundwater measurements to determine internal processes, and evaporation estimates obtained from satellite imagery to reduce the uncertainty of the total runoff out of the area.