Geographic information systems and non‐point source water quality and quantity modelling

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Abstract
Hydrologic processes are affected by the spatial variability of soils, topography, land use and cover, climate, and human‐induced changes and management. Because contaminants are transported by runoff to surface waters and by infiltration and deep percolation to groundwater, hydrologic processes are often at the core of water quality and quantity concerns. Water quality and quantity affected by non‐point sources of contaiminants is dependent on spatially distributed attributes of a catchment or watershed.The integration or linkage of the spatial data handling capabilities of a GIS with a distributed process, hydrologic model offers the advantages associated with utilizing the full information content of the spatially distributed data to analyse the hydrologic processes. Distributed process models use computational elements smaller than the scale of the process or the system being modelled. The information content of the model output is greater than a lumped model though obtained at greater cost. A GIS is capable of manipulating both the input and output parameters required by distributed process models.This paper presents a review of water quality and quantity modelling and GIS applications in water resources. An application of the GIS, ARC/INFO and the finite element solution to the kinematic wave equations is presented. In this application, ARC/INFO is used to process the spatially variable terrain in a small watershed using a Triangular Irregular Network on TIN. The TIN facets are used to provide land surface slope in a finite element solution of overland flow which is a fundamental subprocess affecting non‐point source, water quality and quantity.