长江梯级水库下游重点滩段河势及航道条件变化

长江上游特大型梯级水库运行后坝下游水沙条件将显著变化,对下游河势和航道条件产生影响。本文建立了向家坝下游水富至泸州(水泸段)二维水沙数学模型,在验证的基础上,计算分析了向家坝、溪洛渡水库运行后向家坝下游河段泥沙冲淤时空变化规律,研究了重点滩段河势变化及对航道的影响。研究表明,上游梯级枢纽运行后,向家坝下游河道总体呈冲刷态势,弯曲河段水流趋直但仍保持弯曲河型,分汉河段支汉水浩萎缩,主槽冲深,这对增加过渡段浅滩航深有利,但局部产生淤积,造成新的浅段;边滩淤积,滩槽高差加大,加剧局部不良流态,急流浅滩的航行条件有恶化趋势。

Changes in river regime and navigation channels downstream of Xiangjiaba reservoir after impoundment of cascade reservoirs on the upper Yangtze River

Cascade reservoirs on the upper Yangtze, after operation, will significantly change their downstream conditions, e.g. water and sediment conditions, river regime, and navigation conditions. This paper develops a 2D water-sediment mathematical model for the reach from Shuifu to Luzhou (or Shuilu reach in short) downstream of the Xiangjiaba dam. On the basis of verification, this model has been applied to calculation and analysis of riverbed scour and silting in this reach after impoundment of the Xiangjiaba and Xiluodu reservoirs, focusing on the changes in river regime and navigation conditions in some typical shoals. The results show that after the impoundment the downstream channel takes an overall scour trend, which can be demonstrated with three general changes. First, in curved reaches the flows tend to take a straightforward path though the river pattern remains curved; second, in braided reaches the branches tend to decay while the main channel to be scoured deeper, favorable to navigation, but local deposition will happen in some reaches, creating new shoals; last, the difference in elevations of floodplain and channel will be increased as a result of silting on point bars and scour in main channel, which aggravates local adverse flow patterns and deteriorates the navigation conditions in torrential shoals.