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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 eedimentation 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 es- timate the trapping efficiency(TE)of the Manwan Dam.The TE value was then compared with the es- timates using the modified Brune and Siysm models.The results Indicate that:(1)The TE of the Man- wan 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.
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 eedimentation is the key to assess its environment Impacts. Sediment load data obtained over 39 years at the gauging stations located in the upstream and downstream of the Manwan Reservoir were used to es- timate the trapping efficiency (TE) of the Manwan Dam. TE value was then compared with the es timates using the modified Brune and Siysm models. the results indicator that: (1) The TE of the Man-wan 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 were 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 Jingh ong 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 by the paper could also be used to estimate the TE in other river basins in southwestern China.