在河道上修建水工建筑物,常会改变天然水流的特性。挡水建筑物抬高了上游水位,从而致使从溢洪道、隧洞、坝身底孔等泄水建筑物泄出的水流具有较高的流速,故动能很大,这样,一会严重冲刷河岸河床,二会危及建筑物自身安全;另一方面,由于枢纽布置的要求和节省造价,建筑物的溢流前缘总是小于原有河道宽度,使泄流量集 The construction of hydraulic structures on the river often changes the nature of the natural water flow. Water retaining structures raise the upstream water level, resulting in high flow velocity of the water flowing out from the spillway such as spillways, tunnels, bottom of the dam, etc. Therefore, the kinetic energy is very large, Second, endangering the building’s own safety; the other hand, due to hub layout requirements and cost savings, the building’s overflow front is always less than the original width of the river, so that the discharge set