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.

摘要：大型水库调度会改变河流的全部天然河流水动力过程，因此需深入认知此类干扰的影响，以制定合理的管理策略，最大限度降低负面影响。鉴于此，本研究旨在识别皮拉西卡巴河（Piracicaba River）流域主要河流的径流情势（flow regime）变化，该变化主要由坎塔雷拉水库群（Cantareira System reservoirs）的建设运行引发。本分析以阿蒂巴亚河、雅瓜里河、皮拉西卡巴河（均受坎塔雷拉水库群影响）以及卡曼杜卡亚河（同属该流域但不受坎塔雷拉水库群影响）的4个水文站的日平均流量序列为基础，采用IHA（水文改变指标，Indicators of Hydrologic Alteration）软件开展对比研究。该软件可计算33个具有生态意义的水文参数的水文改变因子，用以表征径流变化的量级、发生时机、频率、持续时长及变化速率。针对受坎塔雷拉水库群影响的河流，研究发现：自20世纪70、80年代起，整体平均流量呈下降趋势，其中阿蒂巴亚河下降约24%，雅瓜里河下降50%，皮拉西卡巴河下降14%；流量下降主要集中于枯水季（4月至9月），同时年最小7日流量中位数分别下降25%、56%与15%。此外，低流量事件的发生频率与持续时长均有所增加，而高流量事件的持续时长则呈下降趋势。变化最显著的为雅瓜里河，其次为阿蒂巴亚河，而距离水库最远的皮拉西卡巴河变化幅度最小。对于卡曼杜卡亚河，20世纪70年代后其年最小7日流量中位数未发生变化，整体平均流量上升21%，同时最大流量事件的发生频率有所增加，但该河流的变化幅度仍不及前述三条受水库影响的河流显著。