Software for reservoir silting forecast based on sediment trapping efficiency methods

Abstract

Silting is one of the main problems of reservoirs formed by dams. These water bodies have stagnant velocity fields, resulting in high capacity for growth of bottom deposits. The focus of this work is the silting forecast of Bom Jardim reservoir, located in Uberlândia, Minas Gerais state, Brazil. Estimates were based on classical methods of sediment trapping efficiency. Sediment input is introduced by curves that relate solid loads with inlet flows. The affluent flow rates are based on synthetic series obtained by stream flow regionalization. In the context of this paper, the calculations were systematized in the SILTINGZ software, a computer simulator able of estimating the spatial and temporal advance of sediment deposits in reservoirs. In this model, the algorithms are coded in the Visual Basic for Applications (VBA) language. The software is able to use four classical methods in order to calculate the sediment trapping efficiency. The results revealed monthly silting rates between 916 m³/month and 1040 m³/month, including the latent possibility of forming localized sandbanks. For periods over 50 years, the simulation predicts evolution of considerable deposits between the half of the reservoir and the dam. The main sandbanks are formed immediately downstream of the confluence of Bom Jardim stream. The useful volume of the reservoir may be gradually affected after a period of 56 to 64 years. This predictive study considered stationary conditions of contributing basins to the reservoir. Actual silting rates can be amplified with deforestation or delayed by reforestation in these watersheds.