长江下游铁板洲洲头冲淤变化规律

长江下游是典型的分汊型河道，其江心洲的洲头正面临清水冲刷蚀退的严峻形势，如大通河段的铁板洲。基于大通水文站年均水沙数据（1956~2014年），选取铁板洲的遥感影像（1998~2016年）和实测地形数据（2004~2011年），并采用MIKE21 FM模拟铁板洲河段的水动力变化，分析近20年大通站年际及年内水沙变化、铁板洲的形态变化、洲头冲淤变化及主控因素。2003年后长江下游年均径流量变化较小，年均输沙量比2003年之前锐减67.4%。铁板洲受到低含沙水流的冲刷，洲头显著蚀退，其体积从163.57万m3（2004年）萎缩至68.84万m3（2011年），且年均蚀退率由8.88%（2004~2008年）增至11.57%（2008~2011年）。水动力模拟表明来流量增大对洲头的冲刷作用更加剧烈，即铁板洲在洪水期受到的冲刷大于枯水期。由于洲头的逆坡和阻挡作用，铁板洲洲头上游沿程流速不断减小并在洲头前缘岸边急剧降至零，最大流速出现在洲头左侧，使得其左侧成为主要蚀退区。

Erosion-deposition Processes of the Bar Head inTiebanzhou Island in the Lower Yangtze River

The Lower Yangtze River is the typical anabranching channel, where the head of mid-channel bars are facing the seriously scouring situation under the impact of the sediment-starved flow, e.g., Tiebanzhou Island in the Datong reach. Water-sediment temporal change, area of Tiebanzhou Island, sediment deposition of bar head, and hydrodynamic characteristics (MIKE 21 model) were analyzed using the hydrological data of the Datong station (1956-2014), remote sensing imagery (1998-2016), channel topography (2004-2011). From 2003 to 2014, the mean annual runoff in the Datong station did not change much, but the mean annual sediment load decreased by 67.4%. The Tiebanzhou Island was eroded by the sediment-starved flow in the long-term, i.e., the volume of the bar head eroded from 1,635,700 m3 in 2004 to 688,400 m3 in 2011, and the average erosion rate from 8.88% in 2004-2008 increased to 11.57% in 2008-2011. The hydrodynamic simulation demonstrated that the greater incoming discharge, the strong scouring effect on the bar head, i.e., the erosion in flood seasons stronger than that in non-flood seasons. Owing to the backward slope and blocking effect on the upstream of bar head, the flow velocity decreases along the upper segment of the bar head, and sharply drops to zero when the flow is approaching the front of the bar head. The maximum velocity appears on the left side of the bar head that leads to the left side as the main erosion area.