Aporte de sedimentos em suspensão no baixo Rio São Francisco (SE/AL), em diferentes condições hidrológicas

Abstract

The São Francisco River estuary has since the Seventies been subject to the impact of a dam cascade constructed along its middle-lower semi-arid river course. Suspended matter and water fluxes were reduced both in their magnitude and natural seasonal pulsation. However, today´s regulated fluxes are still prone to sporadic short-term perturbations induced by extreme climatic events in the drainage basin. This study addresses suspended matter fluxes of three anomalous events, one corresponding to the drought of 2001 and the other to the floods of 2004 and 2007. The drought event extended over the whole basin leading to low suspended matter concentrations of < 5 mg/L and fluxes of 0,2 x 10^6 t/y due to low discharges and efficient material retention by the dam reservoirs. In contrast, the flood of 2004 was generated by high precipitation in the middle-lower semi-arid basin and yielded higher concentrations of suspended matter with a pulse of up to 490 mg/L and fluxes of 7,7 x 10^6 t/y. The flood of 2007 produced lower suspended matter concentrations of up to 25 mg/L and fluxes of 1,1 x 10^6 t/y, as it was induced by precipitation in the upper basin and materials were retained by the dams. The results exemplify that spatial differences of precipitation in the basin in relation to the location of the dam cascade generate different water run-off and material yields to the coast.