Risk Analysis of Dynamic Control of Flood Limiting Water Level for Danjiangkou Reservoir

The Danjiangkou Reservoir is a large-scale multi-purpose water conservancy project located in the Hanjiang River Basin of central China, which also serves as the water supply source project for the middle line of the South-to-North Water Transfer Project in China. The flood limiting water level (FLWL) of the reservoir is crucial for coordinating the relationship between flood control and water resources utilization during flood season, especially for dry years. Under the premise of ensuring the safety of the dam itself and the downstream flood control sections, the dynamic control of the FLWL based on available hydrological forecasts during flood season can effectively improve the water resource utilization of small and medium-scale floods. In this paper, the seasonal regimes and forecast skills with different lead-times of rainfall and runoff in the Hanjiang River Basin were analyzed. Based on a FLWL dynamic control model and a number of typical flood hydrographs, the lower and upper bounds of FLWLs for Danjiangkou Reservoir when encountering different kinds of small and medium-sized floods were then derived under foresight lead-times of 1-3 days. The risks of dynamic control of FLWLs for Danjiangkou Reservoir to dam safety, downstream flood control and submerged damage in the reservoir area were assessed by comparing the maximum water level and maximum discharge flow during the scheduling period with that of the designed operating rules. Also, the benefits such as increased water supply volumes and hydropower generation were estimated under different proposal FLWLs. It can be informed from the results that under most cases, the Danjiangkou Reservoir can release the conserved storage through the pre-discharge operation with reliable hydrological prediction safely, except for some unfavorable situations, resulting in flood control risk of overtopping the allowable water level of the dam. Compared to operating the reservoir strictly according to the designed rules during flood season, the dynamic control of FLWL can significantly increase the power generation and water supply provided accepted flood control risks, which is valuable for the comprehensive water resources utilization considering the multi-objective characteristics of the Danjiangkou Reservoir.