The Sustainable Use of Water Resources: A Technical Support for Planning. A Case Study

The paper presents both the structure and application of a Decision Support System (DSS) for an important river in Brazil—along with the sustainable management of its watershed. This DSS assesses both surface-water quality and riverine microhabitats in terms of future scenarios, taking into account regulation limits and appropriate quality indexes. Our future scenarios consider: (a) population and climate change trends; (b) upgrade of sewage systems and wastewater treatment plants; and (c) withdrawal management from rivers and reservoirs. We use some main types of interrelated models, which can simulate different aspects of the responses of a basin, with respect to different modes of use of the water resource. In particular, the surface-water quality models simulate total phosphorus, BOD, dissolved oxygen concentration and thermo-tolerant coliform bacteria pollution. The riverine microhabitat models apply habitat suitability indexes of autochthonous fish species considering water depth, velocity, bottom substrate and dissolved oxygen. Both models are based on hydrologic and hydraulic models results and both were calibrated using discharge and water quality measurements collected over a 1.5-year monitoring period. Our pre- and post-processing are based on common spreadsheets and the output data are spatially analyzed using GIS software. Examples are also shown of how the DSS can contribute to developing a sustainable use of the basin resources, including a reservoir used to supply drinking water to the capital city (Salvador da Bahia)