This paper presents the development and characteristics of a site-specific physically based, spatially distributed model. The Grote Nete catchment model was built to simulate the various processes of the hydrological cycle, and their interactions with each other. It highlights the various stages of model development from conceptualisation and the underlying mathematical representation of hydrological processes, through the model set-up phase, and finally to the calibration and validation. MIKE SHE was chosen for its ability to generate a spatially distributed representation of the hydrological processes within a catchment, which was necessary for future scenario analysis. The equations coupled within the system include a three-dimensional Darcy equation in the saturated zone, the Richards equation for the unsaturated zone, the diffusion wave equation for areal overland flow and the fully dynamic Saint Venant equations for flow in channels. Evapotranspiration from the surface and subsurface are modelled using land cover and climatic factors to define the complete water budget using a physically based formulation. The paper presents the results of a multi-criteria evaluation protocol that included graphical and statistical testing, which involved the use of seven data comparison plots. Results of model calibration and validation against pre-established criteria are presented and discussed.

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