ABSTRACT OF THE DISSERTATION





A GIS-Based Water Resource



Assessment Tool



by



Brian Robert Brodeur





Dissertation Director: Professor Robert M. Hordon





Local land use decisions affect the quantity and quality of water resources. Those involved in local land use debates have limited resources to address water resource concerns. One potential form of help would be user-friendly models based on available data. This research defines and develops such a set of models.





The Water Resource Assessment Tool is programmed in "C" as a module in the Geographic Resource Analysis Support System (GRASS). It is designed for watershed areas which include a variety of land uses. The required GIS database must include a digital elevation model, land cover map and soils maps of hydrologic soil group, soil texture and erodibility (K factor). Terrain analysis routines interpret digital elevation models defining watershed areas, channel length, channel slope, drainage direction and drainage work. Algorithms were adapted from several existing models to simulate runoff, peak discharge, sediment, nitrogen, phosphorous, and chemical oxygen demand (COD) source areas. Routing routines sum contaminant contributions down all watersheds in the study area, with provisions for best management practices.





Testing indicates excellent simulating of surface hydrology. The contaminant module replicated rankings of neighboring watersheds according to simulated production of nitrogen and phosphorous and according to observed concentrations. Ranking of watersheds according to COD production strongly resembled the ranking of those



subwatersheds according to biological oxygen demand (BOD) indicators. BOD rankings change, depending on the test employed, making complete agreement impossible. Sediment and nutrient simulations are sensitive to antecedent conditions. COD simulations are based purely on annual average loading factors.





A menu driven user interface organizes work into projects and guides users. The interface keeps track of the geographic region studied in a project and the spatial resolution employed by GRASS. A project file stores user input and the names of output maps. Major assumptions may be modified through the interface. The resulting Water





Resource Assessment Tool provides fast quantitative comparison of potential nonpoint source contaminant problems between watersheds or alternate land cover scenarios.