近50a来杭州湾冲淤变化规律与机制研究

Decadal variations in the erosion/deposition pattern of the Hangzhou Bay and their mechanism in recent 50a

使用杭州湾1959-2010年的水下地形图,结合过去数十年来长江入海水沙量和钱塘江河口段冲淤变化状况,分析了近50a来杭州湾在长江入海泥沙量锐减和治江围涂等人类活动作用下的冲淤变化规律及其物理机理。结果表明,乍浦以上区域近50a来处于较显著的淤积状态,且有自上向下发展的趋势,这种淤积主要是由于钱塘江河口治江缩窄工程所引起的;湾内地形发生了局部调整,部分小型潮流槽脊系统趋于消亡,地形趋于平坦化,湾口北部2003年以后有转淤为冲的趋势,这与长江入海泥沙量锐减和该区域围垦工程等因素有关;1959-2003和2003-2010年两个时段,湾内泥沙淤积的年平均值分别为0.91×108和1.66×108 m3。对于整个钱塘江河口系统而言,即自杭州湾湾口至钱塘江河口段的闸口断面,长江入海泥沙量减少所产生的影响尚不明显,2003年以后泥沙淤积速率甚至有所上升。杭州湾近50a的冲淤变化是人为强烈干预下的大流域-河口系统响应与中小流域-河口系统响应的调整结果。

Decadal variations in the erosion/deposition pattern of the Hangzhou Bay and their physical mechanism in recent years have been studied based on the bathymetrical data in 1959, 2003 and 2010, and historical changes of sediment supply from the Changjiang River and erosion/deposition in Qiantang estuary. The results show that （1） the upstream of Hangzhou Bay have been obviously deposited since 1959, and the deposition is featured by a devel- oping trend toward downstream; （2） local bathymetry have been adjusted in the last half century, some small-scale shoal-channel systems have disappeared and the northern bank of the bay mouth have been been eroded since 2003 while it was deposited before 2003; （3） during 1959--2003 and 2003--2010, the annually-averaged sediments de- posited in Hangzhou Bay are 0.91 ×10^8 and 1.66 ×10^8 m3 , respectively, and the corresponding deposition rates are0.2 and 9.3 mm/a; （4） the effects of the dramatic reduction of sediment supply from Changjiang River have been not obvious for the whole Qiantang Estuary, i.e. from the Hangzhou Bay mouth to Zakou section, further- more, the annually-averaged deposition rate after 2003 is a little more than that before 2003. This is probably caused by the land reclamation of the Qiantang Estuary in the past. The erosion/deposition pattern of the Hang- zhou Bay in recent 50 a is a result of morphological response of both large and small river basin-estuary systems to human activities.