Effect of the Cantareira System on the flow regime in Piracicaba River basin

ABSTRACT

The large reservoirs operation can change all the natural fluvial dynamics of a river, requiring a better understanding about the influences of these interferences to an appropriate management, minimizing negative impacts. Faced with this, the aim in this paper was to identify the alterations in the flow regime of the main rivers of Piracicaba River basin, mainly due to the implementation of Cantareira System reservoirs. The analyzes were based on the average daily flow series from four fluviometric stations in the rivers Atibaia and Jaguari and Piracicaba (influenced by Cantareira System) and Camanducaia (in the same basin but without influence from Cantareira System), for comparison, using the IHA (Indicators of Hydrologic Alteration) software, which calculates the hydrological alteration factors of the 33 hydrological parameters ecologically relevant, that characterizes the magnitude, timing, frequency, duration and rate of flow change. For the rivers influenced by Cantareira System was observed that from the 1970s and 1980s, overall, there was a decrease in the mean flow, approximately 24% in Atibaia River, 50% in Jaguari River, and 14% in Piracicaba River, where in the decrease in the flows was mainly in the dry season (April to September), besides a decrease in the median of the annual seven days minimum flows by 25% and 56% and 15%, respectively. There also an increase in the frequency and duration of the lower flows and a decrease in the duration of high flows. The most significant changes occurred in Jaguari River, followed by the Atibaia River and were less significant in the Piracicaba River, which is the farthest from the reservoirs. For the Camanducaia River, after the 1970s, there was no change in the median of the annual seven days minimum flows and it was observed, overall, an increase in the mean flow by 21%, as well as an increase in the frequency of the maximum flows. However, the changes were not as significant as in the others rivers.

Keywords:
PCJ basins; Cantareira System; Environmental flow; Method IHA