长江口前缘沙洲演变与流域泥沙要素关系

RELATIONSHIP BETWEEN SEDIMENT ELEMENTS OF RIVER BASIN AND FRONT SAND ISLANDS EVOLUTION IN YANGTZE ESTUARY

为了研究河口前缘沙洲演变过程与流域入海泥沙要素关系,建立了长江口前缘沙洲面积冲淤速率和流域入海泥沙要素关系曲线,并预测沙洲发展趋势。结果表明:长江河口前缘沙洲1958~1989年-5m以浅面积表现为淤涨,1989~2000年为淤涨和侵蚀交替变化,但幅度较小,自2000年起为冲刷趋势发展,这一过程伴随流域入海泥沙量和含沙量的减少而产生。同时沙洲面积的锐减过程中存在临界泥沙要素条件,并建立了相应的经验曲线,当沙洲面积冲刷和淤涨达到平衡时,临界入海沙量和含沙量临界值分别为2.83×108 t/a,0.318kg/m3。依据以往三峡水库蓄水后入海沙量预测数据,三峡水库蓄水后60a左右前缘沙洲-5m以浅面积将侵蚀到1958年水平,其后沙洲面积增加趋势,面积逐渐恢复。2003~2011年长江流域入海泥沙量小于三峡水库蓄水前的预测数值,沙洲面积的冲刷趋势将加剧,应引起有关机构和部门重视。

According to the data from 1958to 2009,the relation between rate of erosion/deposition of the front sand islands and sediment elements of river basin was established in order to study the process and the trend of front sand islands evolution in Yangtze estuary.The results show that front delta above-5m deposited from 1958to 1989and the rate slowed down from 1989to 1997.From 1997to 2000,the delta deposited because of the flood around the whole basin.But the delta kept on eroding from 2000to 2009. The relation between rate of erosion/deposition and volume of water and sediment towards sea was also established.The critical volumes of water and sediment that keep balance of erosion and deposition were 2.83×108 tons per year and 0.318kg/m3 respectively.If the volume of sediment keeps the low degree after Three Gorges operation,the sand islands will erode to the degree of 1958,and the wetlands protection, natural resources and urban safety in Yangtze estuary will be seriously threatened.