Modelling of pollutant distribution in surface runoff in ungauged catchments using geographical information systems
Mendes, Bulhoes Carlos Andre
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The aim of this thesis has been to develop a water quality model, suitable for Brazilian conditions and that is capable of estimating the effects of future land use scenarios on water quality. The model is designed to be consistent with the availability of data in less developed countries and one of its major advantages is that the parameters involved are easily defined in terms of physical characteristics. A methodology is presented which has been designed specifically to support the determination of water quality changes resulting from point and non-point sources in a large river basin with varied land use, taking into account both the magnitude and spatial distribution of the loads produced. The methodology is capable of implementation on land surfaces having heterogeneous distribution of water pollution sources. The model is based on a cellular configuration where information on land use, topography, soil type and rainfall is manipulated using geographical information systems (GIS). Information on land use in each cell is obtained by classifying remotely sensed satellite data. Topographic parameters for each cell are derived from digital elevation models (DEM). Rainfall values for each cell are obtained from the interpolation of point data derived from meteorological stations. Other more conventional data are acquired by digitising maps. Using this cellular structure, runoff, and chemical outputs from the individual cell, are routed through the catchment using a physically based mixing model to provide input to the drainage network. The network, derived automatically from a digital elevation model (DEM), defines the river system in the model. The link between the catchment and the river network defines a river 'buffer' zone where point and non-point sources are stored. The model enables spatial relationships between point and non-point sources to be investigated and the consequences to the river system can then be modelled using the river network topology.