试验性蓄水期嘉陵江长江交汇河段的冲淤特性

Study of sediment silting-scouring in Jialing-Yangtze confluence reach during 175m experimental impoundment period

变动回水区河段的侵蚀基准面在蓄水期抬升,在消落期和汛期逐渐恢复为天然状态,其冲淤调整特点不同于自然条件.以三峡库区嘉陵江与长江交汇河段为例,分析了175m试验性蓄水期前后交汇河段冲淤特性的变化.结果发现,175m试验性蓄水以前,交汇河段由于上游来沙持续减少出现了累积性冲刷,175m试验性蓄水以后,侵蚀基准面的抬升抑制了交汇河段的冲刷发展态势;其中支流嘉陵江来沙量减少的程度高于长江干流以及2008-2012年汛期汇流比大于2003-2007年,使得嘉陵江支流河段继续冲刷,而长江干流河段转为淤积.175m试验性蓄水前后交汇河段年内汛淤枯冲的基本规律未变,但主要走沙期由汛后推迟到了次年的水位消落期,走沙量减少.

As the level of erosion base raised, general cumulative deposition occurred in reservoir area inclu- ding its river confluence reach. While concerning the fluctuating backwater area, its erosion basis rose up in impoundment period, and turned to the natural state during the period of low level or flood season, ac- cordingly the silting-scouring characteristics is different from the other area. Based on confluence between the Jialing River and the Yangtze River in Three Gorges Project fluctuating backwater area, this paper ana- lyzes silting-scouring characteristics at river confluence before and after 175 m experimental impoundment. The results show- because of incoming sediment amount reduced, the accumulated scouring appeared in the river confluence in natural state. After 175 m impoundment the scouring was restricted by raised ero- sion base level. Incoming sediment reduction degree in the Yangtze River was larger than that in the Jialing River, in addition the confluence ratio during 2008-2012 in flood season was larger than the situation in 2003-2007; so the scouring continued to develop in tributary channel while the mainstream channel started silting. The basic law almost maintained silting in flood season and scouring in dry season; however, scou- ring was delayed to low level period in following year and the scouring volume decreased.