长江三峡水坝下游河道悬沙恢复和床沙补给机制

流域水库工程的修建,将改变坝下游原有的水沙输移过程,三峡水库蓄水作用对坝下游水沙输移的影响已初步显现。具体表现为：① 三峡水库坝下游洪水持续时间和流量被削减,下泄沙量大幅减少,沿程上输沙量虽得到一定恢复,但总量仍未超过蓄水前多年均值;② 2003-2014年d > 0.125 mm（粗）输沙量得到一定恢复,至监利站恢复程度最大,基本达到蓄水前均值,在恢复后其下游该组分泥沙冲淤特性与蓄水前一致,其中2008-2014年恢复程度弱于2003-2007年;③ 三峡水库蓄水后坝下游d < 0.125 mm（细）输沙量沿程上得到一定程度恢复,但总量仍小于蓄水前均值;④ 三峡水库蓄水后坝下游d > 0.125 mm泥沙输移量因河床补给作用,沿程上得到恢复,但补给量将不超过0.44亿t/y,主要受制于洪水持续时间及流量均值,而上游干流、河段间支流和湖泊分汇作用占次要地位,而d < 0.125 mm悬沙恢复受上游干流、区间支流和湖泊分汇及河床补给控制,因河床粗化使得床沙对细颗粒悬沙的补给作用减弱;⑤ 2003-2007年和2008-2014年两时段间宜昌至枝城、上荆江为粗细均冲,下荆江为淤粗冲细,汉口至大通河段为淤粗冲细,城陵矶至汉口河段2003-2007年为淤粗冲细,2008-2014年为粗细均冲,这一差异受控于螺山站洪水流量持续时间和量值。

Suspended sediment recovery and bedsand compensation mechanism affected by the Three Gorges Project

Construction of basin reservoir projects can change the water and sediment transport processes in the lower reaches. The effects of the Three Gorges Project (TGP) on water and sediment transport in lower reaches are emerging. Specifically: (1) The duration and volume of floods in the lower reaches of TGP declined sharply. The sediment value was of such a low concentration that the water was nearly clear. The suspended sediment discharge gradually recovered downwards but its total amount still could not outcompete the annual average of that before the impoundment of TGP. (2) The sediment with d > 0.125 mm recovered to some extent in 2003-2014 (more in 2003-2007 than in 2008-2014) and basically recovered to the average value before the impoundment at the Jianli Station. After recovery, its transport trend in the lower reaches was in line with that before the impoundment. (3) After the impoundment, sediment with d < 0.125 mm recovered to some extent but its total amount was still less than the average of before the impoundment. (4) The recovery of sediment with d > 0.125 mm was mainly from river-bed erosion but with an amount not exceeding 44 million t/y which was primarily limited by duration and average flow of floods and secondarily by the upper mainstream, tributaries between river sections and the sub-sink effects of lakes. Recovery of the suspended sediment with d < 0.125 mm was controlled by the upper mainstream, tributaries between river sections, the sub-sinks of lakes and river-bed compensation. The suspended sediment compensation from river-bed decreased due to the coarsening of bedsands. (4) In 2003-2007 and 2008-2014, both coarse and fine sands were eroded in the Yichang-Zhicheng section in the upper Jingjiang River while coarse sands deposited and fine sands eroded in the lower Jingjiang River. In the Hankou-Datong section, coarse sands deposited and fine sands eroded. From 2003 to 2007, coarse sands deposited while fine sands eroded in the Chenglingji-Hankou section. In 2008-2014, both coarse and fine sands eroded in the Chenglingji-Hankou section. The differences were caused by the duration and volume of the floods in the Luoshan Station.