Author(s): Newton De Oliveira Carvalho; Fernando Arruda Cafe; Gilson De Oliveira Mota; Helio Costa De Barros Franco; Anderson Braga
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Abstract: The Belo Monte Hydroelectric Complex (11,181 MW), in project stage, is planned to be built near the city of Altamira, on the lower course of the Xingu River, ParaState, Brazil. Its reservoir presents uncommon characteristics, mainly as regards its layout. It can be said that the complex is composed of two reservoirs linked by high flow canals. Such a characteristic triggered three independent sedimentation studies, one for each reservoir. The reservoir reach upstream the canals consists, basically, of the Xingu River channel incorporating small bordering flooded areas and islands and stone sites existent on its bed. Such a reach of the reservoir, named “reservoir of the Xingu River Channel”, though with more capacity, may present more significant silting up problems. To foresee the sedimentation phenomenon were used sediment discharge data dated since 1979. It was observed that the sediment yield is increasing in the basin at an annual rate of 2% due to problems triggered by deforestation, increase in the land use and climatic changes. Such a yield which may be increased by recent interference in the basin. Owing to the fact that the Xingu River Channel Dam is short in height, when compared with the flow through the turbines, as well as the water intake sills of the complementary power house are at very low elevation, such reservoir presents reduction of its useful life. The silting up prognostic, based on the computation of the time necessary for the deposits at the dam toe to reach the intake sills of its complementary power house, indicated the need to keep the previous upstream cofferdam (dike) separating the spillway catchment canals and the intake aiming hold back the sediments and therefore increase its useful life. The second reservoir may not present silting up problems within the economic life of the undertaking. By taking into account that the sedimentometric data used was obtained in previous periods of deforestation, it is necessary to implement total sediment discharge sampling campaigns to enable the revision of the sedimentation assessment in the reservoirs. As a result, it became evident the necessity of a program focusing on forest preservation in the basin and other sediment control measures.
Year: 2004