长江口拦门沙航道(北槽)回淤分析

北槽是长江四个出口之一.在拦门沙有8公里长的航道水深不足,1984年进行了疏浚.资料表明:挖槽航道内,大潮冲刷,小潮淤积.在洪季小潮时,滞流点移向挖槽段下游.由于絮凝和扩散作用,河流带下的泥沙沉积在滞流点向陆一侧的挖槽段内.在枯季小潮时,滞流点移到挖槽段上游,但密度水流把横沙东滩串沟和九段沙下泄的泥沙推到上游,那里的切力小于临界冲刷切力,淤积的泥沙不能再一次悬浮.这样,淤积的位置与每一潮的涨潮水流搬运泥沙之距离有关,因此实际的回淤地点一般与洪季小潮时回淤相同,均发生在相对较短的挖槽段内.

On Deposition Causes of Dredged Channel Segment of North Passage in Yangtze Estuary

The North Channel is one of the four entrances in the Yangtze estuary.There was a section of 8 km whose water depth could not satisfy navigation.It was dredged in 1984. The hydrographic aad geomorphologic data show that in the dredged channel erosion occurs during the spring tide and deposition during the neap tide.In the high water season,during the neap tide the null point moves downstream.Owing to the action of flocculation and diffusion, the suspended sediment carried by the river deposits on the landward side of the null point in the dredged channel.In the low water season,during the neap tide the null point moves upstream,however,the density flow will push the sediment from the East Hengsha Shoal and Jiuduan Sand Bank upstream to a location favoring deposition.At that location,the shear stress is lower than the critical shear stress of erosion,and the deposited material can not be resuspended,so that the deposition location is only related to the distance of sediment transport during each tide.As a result actual deposition is happened in the relatively short channel.