Water quality assessment of the Mogi-Guaçu River in Brazil: proposal of a system-based model

Abstract

The Water Code, created in 1934, was the first attempt of governmental intervention in Water Basin Management in Brazil. It was a centralized bureaucratic system established to regulate the use of water. Since the beginning, Water Management suffered significant changes and the model currently used is an integrated participative systemic model. The distribution of water resources in Brazil is very irregular, 70% of water is located in the North region, 15% to the Central-West, 12% in the South and Southeast and 3% in the Northeast region (BNDES 1997). The state of Sao Paulo is located in the Southeast region, which has the biggest water consumption. The Water Resources Agency of Sao Paulo State (CETESB) has an advanced water management system with 20 Watershed Management Committees. Groups from different social sectors compose these committees. They constitute a new kind of organization that is responsible for the watershed planning. Actually, these committees use to obtain relevant information but they are not able to develop future scenarios, objectives, strategies and temporary goals for the water basin. The Mogi-Guacu watershed is the most important basin in Sao Paulo State from the economic point of view, but the river has problems of erosion, silting, flooding and low water quality. The water quality problems are due to nonpoint sources of pollution from agriculture and municipal and industrial point sources. In order to support the committees to improve Basin Planning this study propose to apply a system dynamic model to understand watershed dynamics to evaluate the human impact to water quality through the use of scenarios. It considers that Brazilian water quality database is in a initial stage of developing and also that only a few rivers have been studied for modeling purposes. Therefore, the use of highly complex data demanding models is not practicable. The systemic model under construction intends to provide an adequate model for a simulation considering limitations of Brazilian database and also includes new variables (turbidity and organic matter in the sediment) that are considered critical to simulate a turbid river with highly sedimentary organic matter content. The longitudinal observed data is presented here and it shows an evident relation between the urban sites and the water quality degradation and self-depuration. Hopefully it will allow the evaluation of impact under different scenarios of economic and population growth, technical changes in agriculture and environmental and social policies for watershed management.