Operação de reservatórios no semiárido considerando critérios de qualidade de água.

Abstract

In the Brazilian semiarid region, during drought periods, the water quality in reservoirs is highly influenced by their low storage levels. Water treatment for urban supply may not be feasible if water quality becomes very low. This dissertation presents a system for the integrated management of water quantity and quality in water supply reservoirs in this region. This system considers, particularly, the regional characteristics of the water quality monitoring network and the seasonal climate forecasting information. Boqueirao reservoir was selected for development and application of the methodology. It supplies the city of Campina Grande and its surroundings, with a population of over 400 thousand inhabitants. To elaborate the integrated management system it was necessary to investigate the possibility of modeling the qualitative behavior of the reservoir and its relationship with a quantitative parameter. For that, quality data monitored by the water supply company (CAGEPA), data from limnology studies in the reservoir and quantitative data supplied by the State water resources department (LMRS/PB) were analyzed. Both the qualitative and the quantitative parameters to be used in the modeling process were selected (respectively, Total Dissolved Solids — TDS — and the monthly reservoir storage level variation). Then a conceptual model and an operational model were conceived and, finally, an integrated management system was proposed. The main conclusions are: (a) it is possible to build such a management system, simple and functional, that considers both water quality and quantity criteria, able to simulate in the medium-term the future water quality in the reservoir intake using the climate forecasts and the present water quality indices in the reservoir, serving as base for operational decision making, since the necessary information will be available for the major reservoirs in the region; (b) in the absence of information from an appropriate water quality monitoring network, it is feasible to use, for the sake of preliminary assessments, the data from the monitoring performed by the water supply companies, as required by the Brazilian Ministry of Health 518/04 Act.; (c) TDS concentration data, measured during monthly and diurnal cycles along the depth in Boqueirao reservoir, supplied relevant and decisive information for the elaboration of the conceptual reservoir operation model proposed in this work, such as, for instance, the definition of the ideal season for accomplishment of the bottom discharges in order to make possible the reduction of the concentrations of TDS.