太湖沉积物的分布和动力扰动下最大侵蚀深度的确定

Sediment distribution and the maximum resuspension depth with disturbance in Lake Taihu

利用 2 0 0 2年对太湖沉积物空间分布的调查数据 ,将太湖划分成 69× 69个网格 ,利用最优插值法对整个太湖的沉积物总量进行了计算 ,得出太湖沉积物的蓄积量大约在 1 8 5 7亿m3左右 ,主要分布在西部沿岸和北部的梅梁湾 ,在湖心和东太湖 ,沉积物覆盖量很小 ,有泥区面积占整个水面积的 47 45 % ,在 60 %的有泥区中 ,沉积物厚度集中在 2 5m以下 ,小于 5 0cm和大于 3 5m的有泥区面积所占比例不大。此外 ,利用Shields方法计算了太湖沉积物上层 1m内不同深度上的临界切应力 ,采用SMB浅水波动模式 ,计算了夏季受东南风和冬季受西北风影响下的波切应力值 ,确定了不同扰动所能引起的最大侵蚀深度。计算结果说明 ,无论上述何种风向情况下 ,能产生悬浮的临界风速大约在 5 0m s左右 ,当风速大于临界风速时 ,悬浮深度随着风速的增加而增大 ,当风速达到 2 0 0m s时所能引起的最大侵蚀深度均在 3 0cm左右。

Based on a 69×69 grid net and the investigation on sediment depth in Lake Taihu in 2002, numerical calculation of total sediment volume is conducted with optimum interpolation scheme used to get all the grid values of sediment depth in the whole lake. The result suggests that the sediment volume is about 18.57×10 8 m 3 with an area percentage 47.45% of the total water surface area in Lake Taihu. Most of the sediment is located in the west shore area and Meiliang Bay and little is in the center and east region. The depth is no more than 2.5m in most of the sediment region and the area with sediment depth less than 50cm or more than 3.5m just takes a little occupancy in the whole sediment region. The critical shear stresses at different layers in the upper 100cm depth for sediment resuspension are decided by using the combination of experimental data and Shields method. With SMB shallow-water wave model, significant wave heights and periods are calculated at all the grids driven by SE or NW wind, which are used to decide the bottom wave stress for sediment suspension. The critical wind speed for the both winds ( SE in summer and NW in winter) is about 5.0m/s. However, the maximum sediment depth available for resuspension will increase with increased wind speed and the value is about 30cm with 20.0m/s wind-forcing in winter or in summer in Lake Taihu.