Zoning of the magnitude and temporal variability of runoff as indicator of the potential for flow regularization from surface reservoirs

Abstract

The Brazilian semiarid region is characterized by low rainfall rates and high intra- and interannual rainfall variability, with even higher temporal variability of surface runoff. The most used way to overcome the water shortage in the region has been the construction of dams. In this context, this study sought to identify the causes of this great temporal variability in the surface runoff and how much this can impact on the flow regularization from surface reservoirs in the Federal State of Ceará, Brazil. Correlations between the depths and the coefficients of variation of the annual runoff of 37 fluviometric sections were tested
against hydro-environmental variables, such as: precipitation, drainage area, geological basement. Using the correlations obtained to estimate the average annual runoff and its respective coefficient of variation, the Triangular Regularization Diagram (DTR) was applied to calculate the flows regularized by surface reservoirs in the Banabuiú River Basin (BHB). The results were compared with regularized flow estimates of hydrological studies contracted by the State Government, based on calculation of the water balance in the reservoirs, with an overestimation of 23% of the flow regularized by strategic reservoirs in the basin. Individually, the differences were below 50% in 77% of the analyzed reservoirs.