平原地区的拦河闸,汛期敞开泄洪,由于闸孔净宽小于河道宽度(闸坎有时也略高出河底),存在着闸孔的束流影响.这种束流影响使上游水位壅高,过闸缓流收缩集中,落差尽管很小,但因实际流速及单宽流量均大于天然河道的数值,仍有相当巨大的剩余能量有待消散.大中型工程因设计单宽流量远较蓄水时期 In the plain area, the sluices are open to flood during the flood season, and the effect of the beam current is high due to the net width of the gate hole being less than the width of the river channel (sometimes slightly higher than the river bottom) Sluggish slump shrinkage concentration, although the drop is small, but due to the actual flow rate and single-wide flow are greater than the value of natural rivers, there is still considerable residual energy to be dissipated.Major and medium-sized projects due to the design of single-wide flow far more than the storage period