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Summary Report No. 44

Capabilities and Limitations of Physically Based Hydrological Modelling on the Hillslope Scale

A. Bronstert (April 1998)

Hillslope hydrological modelling is considered to be of great importance for the understanding and quantification of hydrological processes in hilly or mountainous landscapes. In recent years a few comprehensive hydrological models have been developed at the hillslope scale which have resulted in an advanced representation of hillslope hydrological processes (including their interactions), and in some operational applications, such as in runoff and erosion studies at field scale or lateral flow simulation in environmental and geo-technical engineering.

In this paper an overview on the objectives for hillslope hydrological modelling is given, followed by a brief introduction of an exemplary comprehensive hillslope model, which simulates a series of hydrological processes such as interception, evapotranspiration, infiltration into the soil matrix and into macropores, lateral and vertical subsurface soil water flow both in the matrix and preferential flow paths, surface runoff and channel discharge. Several examples of this model are presented and discussed in order to figure out the model's capabilities and limitations. Finally, conclusions about the limitations of detailed hillslope modelling are drawn and an outlook on the future prospects of hydrological models on the hillslope scale is given.

The presented model performed reasonable calculations of Hortonian surface runoff and subsequent erosion processes, given detailed information of initial soil water content and on soil hydraulic conditions. The vertical and lateral soil moisture dynamics were also represented quite well. However, the given examples of model applications show that quite detailed climatic and soil data is required to obtain satisfactory results. The limitations of detailed hillslope hydrological modelling arise from different points: difficulties in the representations of certain processes (e.g. surface crusting, unsaturated-saturated soil moisture flow, macropore flow), problems of small scale variability, a general scarcity of detailed soil data, uncomplete process parametrization, and problems with the interdependent linkage of several hillslopes and channel-hillslope interactions.

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