黄河上游宁蒙河道冲淤变化分析

黄河上游来水沙地区分布不均匀，水沙异源。大型水库修库前，来沙多，宁蒙河道淤积，５０年代淤积尤为严重。青铜峡、刘家峡水库运用后，水库大量拦沙，宁蒙河道发生冲刷。龙羊峡，刘家峡水库联合运用后，汛期蓄水削峰，出库中小水流量历时加长，大流量出现机会大大减少，宁蒙河道重新调整，主要表现在；水流挟沙能力降低；河道淤积严重，水位升高，平滩流量减小；河势摆动加剧，滩岸坍塌严重；西柳沟高含沙洪水淤堵干流呈加重趋势。

Analysis of Scouring and Sedimentation in the Channel from Ningxia to Inner Mongolia in the Upper Yellow River

There are different sources for water flow and sediment in the upper Yellow River with uneven distribution of water and sediment inflows. The reach from Ningxia to Inner Mongolia was silted before large reservoirs construction because there was lots of sediment inflow, especially in 1950s. The reach was scoured after Qingtongxia and Liujiaxia reservoirs put into operation, owing to large amount of sediment storage by the reservoirs. The combination operation of the two reservoirs results in flood peak deduction through water storage in flood seasons, which leads to long duration of flows with middle and small discharges, great reduction of chances of large discharge flows, and re adjustment of the reach from Ningxia to Inner Mongolia. The re adjustment of channel is demonstrated as follows: reduction in sediment carrying capacity of the flows; high water level and decrease of bank full discharge due to heavy sedimentation in the river channel; severe bank collapse and intensified river shifting; the increasing trend of the Yellow River channel blocked by hyper concentrated flows from Xiliugou river. It is suggested to speed up the harness in the branches with high sediment concentration, to decrease water consumption in dry years and to consider the volume of water for sediment transportation in the reach.