RESERVOIR SEDIMENTATION .2. RESERVOIR DESILTATION AND LONG-TERM STORAGE CAPACITY

During the past 30 years, China has implemented structural and operational procedures to maximize sediment discharge from the impounded reaches of rivers, thereby reducing, arresting, or reversing reservoir sedimentation at many sites. Hydraulic methods used in China to preserve capacity are outlined in this paper, including sediment routing during floods, sediment flushing during floods, emptying and flushing, and density current venting. A method to compute retrogressive erosion during the drawdown of a reservoir is developed, and an approximate method for estimating the amount of sediment that can be vented from a reservoir as a density current is proposed. The computed values are compared with field data. Field data on the floodplain slope formed during flood season and the bottom slope of the main channel formed during nonflood season are analyzed. Empirical formulas for both slopes are presented for estimating long-term storage capacity.