Abstract: In late stage diversion, more power generation benefit can be achieved by impounding water earlier. However, in flood season, this measure will increase the risk of overtopping during dam construction and add the cost for accelerating progress to meet the early impoundment goal, making diversion decision more complicated. In this study, we simulate the diversion risk rates of dam construction in different schemes of initial water impoundment, considering hydrological and hydraulic uncertainties and flood prevention during dam construction. And we calculate impoundment duration, power generation and generation benefit for different impoundment schemes and different guarantee rates. Through a comprehensive consideration of the risk rate, power generation benefit and construction cost, we develop a multi-objective decision model for seeking a satisfactory start timing of dam impoundment. A case study of an under-construction dam on the Yalong River shows this method can give a comprehensive evaluation on the economic benefit and risk of early impoundment schemes aimed at finding reasonable impoundment timing.

Key words: high dam construction, initial impoundment, early power generation, diversion risk, stochastic simulation, multi-objective decision making