Analysis and prediction of sediment trapping efficiencies of the reservoirs in the mainstream of the Lancang River

The water stored and sediment trapped by the reservoirs result in physical, chemical and ecological effects on downstream watercourse environment. Quantitative research on the reservoir sedimentation is the key to assess its environment impacts. The sediment load data obtained over 39 years at the gauging stations located in the upstream and downstream of the Manwan Reservoir were used to estimate the trapping efficiency (TE) of the Manwan Dam. The TE value was then compared with the estimates using the modified Brune and Siyam models. The results indicate that: (1) The TE of the Manwan Dam estimated by the gauging data was 60.48%, and both the TE values calculated by the modified Brune and Siyam models were 60.03%. The approximate TE values indicated that the modified Brune and Siyam models could be used to forecast the TEs of other reservoirs with similar storage capacities as the Manwan Reservoir in the mainstream of the Lancang River; (2) The TE values of Gongguoqiao, Dachaoshan and Jinghong Dams were about 30.23%, 66.05% and 63.50% estimated by the modified Brune model, and 38.81%, 63.97% and 62.30% by the modified Siyam model. The results and the methodologies adopted in the paper could also be used to estimate the TE in other river basins in southwestern China.