Formulação de um modelo de previsão da qualidade de água para gestão de reservatórios de abastecimento urbano no semiárido.

Abstract

The development of the semi-arid region of Northeast Brazil is considered a serious challenge because i t suffers long periods of drought resulting in grave economic and social impacts. Furthermore, other unfavorable environmental conditions also exist such as thin soils, high evaporations rates, intermittent rivers and reduced self-purification capacity. The reservoirs constructed in this area provide subsistence for local population and regional development. Therefore, the existence of integrated management support tools is important for the preservation of water quality and supply. In this context, the goal of this work was the development of an integrated model, both quantitative and qualitative, for the prediction of water quality in reservoirs that are located in the semi-arid region, based on hydrometeorological forecasts, current data of the watershed conservation and water quality data of the reservoir. Data collected through surveys were the original basis for the database describing the qualitative behavior of the hydrological systems. This model was tested in Epitacio Pessoa Reservoir (in Paraiba State) which is the main reservoir in Paraiba river basin, supplying water to over 600,000 people. The selected data corresponds to hydrological series and water quality data for the period from May 1998 to August 2005. The water quality parameters selected were: total dissolved solids, total alkalinity, calcium, magnesium, hardness and chloride. The main conclusions were: (a) the development of this model was possible even with short data series and showed useful results for the management of water supply reservoirs located in the semi-arid; (b) surveys allowed the development of a database with useful information for the modeling and management of the reservoirs, (c) i t was possible to verify three different climatic periods that occurred in Epitacio Pessoa Reservoir - an extremely drought period (1997 to 1999), a period of flood (2004 to 2005) and a normal period (2000 to 2003); (d) there was no water quality degradation in the reservoir during drought periods, even during the water supply crisis (occurred between the years 1997 and 1999); (e) there was a reduction o f up to 50% in the concentration of water quality parameters in periods of high flow (in relation to the amount o f stored water); (£) the parameters that were best represented were total dissolved solids and chloride, respectively with 0.916 and 0.939 correlation between the observed and the predicted series.