Reservoirs silting up by sediments transported by floods

摘要

Small reservoirs are usually subjected to undesirable and fast sedimentation. In case of an extraordinary flood, the reservoir can be silted up or, at least, the operation of the plant can be affected. Sedimentation studies for three hydroelectric sites in Brasil, which led to this conclusion, are presented, as resumed below. The Mascarenhas power plant, on the low Doce River, a 120,000 kW plant, was put into operation in 1974. Just five years later, the 42 x 10~6 m~3 of capacity reservoir was silted up after a flood of 12,000 m~3.sec~(-1) peak flow. It is estimated that the useful life of the reservoir was only 5 years and that the sediment transported by that flood was enough for its siltation up. Another study was carried out for Itiquira, which is a 180,000 kW power plant, running since 1999 on a tributary of Paraguai River. The watershed was under a strong erosion process and an annual growing of about 16% was estimated, which would lead the silting up time of the reservoir to just 2 years. Furthermore, it is shown that the sediment transported by a 50-y flood would silt up the reservoir. As sediment control measures, the dam was provided with a bottom outlet and a sedimentation basin were constructed upstream the forebay. Last, it is showed that the occurrence of floods in just a wet year would compromise almost all the reservoir capacity of Quartel 2, a 100,000 kW power plant to be constructed on a tributary of Velhas River.