近10年来长江口水下三角洲的冲淤变化——兼论三峡工程蓄水的影响

Accretion/erosion of the Subaqueous Delta at the Yangtze Estuary in Recent 10 Years

根据对近10年来长江入海泥沙量和河口冲淤的对比分析,探讨水下三角洲冲淤对长江入海泥沙锐减以及三峡工程运行的响应。结果表明:(1)三峡水库蓄水导致长江入海泥沙减少1×108t/a量级;(2)1995-2000年、2000-2004年和2004-2005年研究区淤积(冲刷)面积分别占75.5%(24.5%)、30.5%(69.5%)和14%(86%),垂向冲淤速率(负为冲刷)分别为6.4cm/a、-3.8cm/a和-21cm/a。(3)由于地形和水动力的变化以及工程的影响,研究区内冲淤对河流来沙减少的响应存在显著空间差异。结论包括:三峡水库蓄水加剧了长江入海泥沙的减少;入海泥沙的锐减是水下三角洲从淤积为主向侵蚀为主转变的主要原因。随着水库拦沙能力的增强等流域人类活动的影响,长江入海泥沙将进一步下降,河口口门区的冲刷可能加剧,值得有关部门重视。

Based on the sediment supply from the Yangtze River and the analysis of the accretion/erosion of the subaqueous delta at the Yangtze Estuary in recent ten years, the accretion/erosion response of the subaqueous delta to the sharp decline of the sediment supply from the Yangtze River to the sea and the impoundment of the Three Gorges Reservoir was preliminarily discussed. The results show that （1） because of the impoundment of the Three Gorges Reservoir, the sediment supply from the Yangtze River to the sea decreased at an order of magnitude 1 ×10^8 t/a; （2） the proportion of accretion area to the total area is 75.5%, 30.5% and 14% in the three periods. The accretion/erosion rates of the three periods （1995-2000, 2000-2004, 2004-2005） are 6.4 cm/a, -3.8 cm/a and -21 cm/a respectively in the study area; and （3） the accretion/erosion response to the decrease of the sediment discharge from the Yangtze River in the study area has significant spacial different results in the influence of topography, the change of hydrodynamics and the engineering projects. The conclusions are that the impoundment of the Three Gorges Reservoir accelerated the decrease of the sediment from the Yangtze River which is the main cause for the change from accretion to erosion of the subaqueous delta. Attentions should be paid to the future evolution processes of the Yangtze River Delta in view of the further decrease of sediment supply of the Yangtze River, which is due to the more dam construction and land conservation in the future, and the consequent further erosion in the subaqueous delta.