Distributed models

Distributed models subdivide the catchment in a regular grid of cells. For each cell they solve the equations of motion to get the runoff pattern of overland and subsurface storm flow. At the beginning these models have been restricted to one-dimensional vertical simulations. Later they were extended to 2- and even 3-dimensional approaches to give the spatial pattern of overland flow, interflow and groundwater flow. The most sophisticated and applied distributed models are the SHE-model(*1) and the Hillflow-3d model(*2). All of them use a one-dimensional approach to simulate the flow in the unsaturated soil layer. While the SHE-model and Hillflow-3d models solve the one-dimensional Richards equation the Topmodel(*3) applies a simple exponential function of water content in the saturated zone.

The latest version of the SHE-model, MIKE SHE(*4) provides a three dimensional groundwater model and calculates the overland flow on the basis of a 2-dimensional implicit finite difference model based on the kinematic wave theory. The channel flow is described by using MIKE 11(*4) or MIKE 21(*4), river modelling systems which solves the full 1- dimensional Saint-Venant equations or the 2-dimensional shallow water wave equations (dynamic wave). This system of models has reached the highest grade of hydraulic components to simulate the rainfall-runoff process. It comes closest to the target to describe fully the flow path of precipitation from the moment it reaches the earth surface to the outlet of the catchment at the end of the river.

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Hydrological modelling



*1 Abbot et al (1986)

*2 Bronstert/Plate (1996)

*3 Beven (2001a)

*4 DHI (1998)



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