三峡工程上引航道低水位冲沙方案研究——水库不恒定流分析

Scouring of Upper Lock Approach of TGP by Reducing Depth of Flow

本文利用一维不平衡输沙及不恒定流数学模型，针对三峡水库１～１３０年的各种淤积状态，研究了坝前水位降低２ｍ冲沙所引起的水库泄水和充水的不恒定流。文中首先给出了三峡水库１～１３０年淤积的计算结果。淤积成果与前人的研究成果基本一致。在此基础上分别给出了不同淤积年份中，坝前水位降低２ｍ冲沙和恢复正常水位需要的时间、排水量、下泄洪水过程、水库沿岸水位变幅以及对三峡发电水头的影响。研究表明三峡采取降低水位冲沙的方案是可行的。由于小幅度降低水位冲沙可以缩小冲沙设施的规模及减少工程投资和技术上的困难，该方案具有明显的优点。

As the annual deposition in the upper lock approach of TGP may ultimately come close to 2 million tons, dredging alone could not remove sediment fast enough without interfering with shipping in a relative narrow lock approach channel. Flushing of sediment from the approach channel is therefore considered necessarily. As TGP has a high dam, sluicing structures would have to pass high-velocity flows that call for costly energy dissipation and expensive material for conduit lining. In order to save on expenses, it is highly desirable to reduce the discharge for flushing. Noting that the copacity of a flow to scour varies roughly as the cube of the velocity and inversely as the depth of flow, for the same discharge, the flushing capacity of the flow would be greatly enhanced by reducing the depth of flow. For this reason, the writer proposes to reduce the mean depth of flow in the approach channel from its initial value of 6m to 4m by temporarily drawing down the reservoir.This article gives a brief account of the investigations on time needed to draw down as well as to refill the reservoir both in early and advanced stages of reservoir deposition. According to the computations, the time needed to lower the reservoir from El.145m to 143m is 12hr in the early stage and only 3hr in the advanced stage. Thus, allowing 15hr for channel flushing and assuming that it takes the same time to refill as to draw down the reservoir, one could complete a cycle of channel flushing in 27hr in the early stage and 18hr in the advanced stage, respectively. The discharge adopted is 3,000 m 3/s. Since the designed capacity of sediment sluice being planned is already 2,500m 3/s, only a small flushing tunnel needs to be added. Dredging is then needed only for deposits in not accessible to the flushing flow.