风浪扰动下南四湖悬浮颗粒物分布与侵蚀深度模拟

Simulation of suspended solids distribution and erosion depth under winds and waves disturbance in Nansi lake,China

风浪扰动下河湖底泥再悬浮和沉降过程中悬浮颗粒物的分布、沉积对区域水土保持与环境保育具有重要意义。以山东南四湖南阳湖区为研究对象,在风情统计的基础上,利用Y型旋浆式底泥再悬浮装置对底泥再悬浮和沉降过程进行模拟,并对底泥悬浮颗粒物的动态分布特征和物理侵蚀深度进行研究。结果表明:小风、中风和大风扰动条件下,夏季和冬季南阳湖湖心区最大悬浮物增量分别比河口区高35.8%、25.0%、47.1%和54.2%、74.1%、22.7%,大风作用下湖心区和河口区夏季比冬季最大悬浮物增量分别高62.2%和22.6%;沉降过程显示,最初沉降6 h内,不同风速下悬浮物量均下降85%以上,20 h后,水柱中悬浮物浓度与风浪前初始浓度趋于一致;南阳湖不同风浪扰动条件下表层底泥侵蚀深度在0.09~13.73 mm之间。风浪扰动下南阳湖底泥再悬浮规律在空间和季节上差异显著,这种差异主要是由表层底泥颗粒尺寸的不同和冬季湖面被菹草大面积覆盖所致;风浪扰动停止后,最初沉降6 h是水体透明度恢复的关键;常规风情下,南阳湖底泥很难出现分米级甚至厘米级的表层底泥侵蚀。

[Background]Distribution and sedimentation of suspended solids during sediment resuspension and settlement process in rivers and lakes under different winds and waves disturbance are of great significance for regional water and soil conservation and environmental protection.It is particularly important to simulate the sediment resuspension and settlement process of Nansi lake in Shandong province,the most important shipping section of the Beijing-Hangzhou Grand Canal,which is frequently disturbed by wind-waves and ships.[Methods]In order to study the dynamic distribution of suspended solids and the erosion depth of surface sediment during the process of sediment resuspension and settlement,taking Nanyang lake area of Nansi lake as research object,on the basis of local wind statistics,Y-shape apparatus was used to simulate sediment resuspension and sedimentation process under common wind conditions,and dynamic distribution of suspended solids and physical erosion depth at estuary and lake center area were studied respectively under different winds and waves in summer and winter.[Results]1)According to analyzed wind statistics from October 2012 to September 2013 of Nanyang lake,the annual maximum wind speed was 9.1 m/s,the average wind speed was 2.1 m/s,and the low wind speed from 0-1.0 m/s was very much,accounting for 38.9%of the whole year,the high wind speed above 6 m/s was relatively small,only accounting for 2.4%of the whole year.2)The maximum suspended solids increment in the lake center area was 35.8%,25.0%,47.1%and 54.2%,74.1%,22.7%higher than that of estuary in summer and winter under slight,moderate and strong winds,respectively.The maximum suspended solids increment in the lake center and estuary area in summer was 62.2%and 22.6%higher than that in winter under strong wind conditions.3)The amount of suspended solids decreased more than 85%under different wind speeds in first 6 h of settlement,and after 20 h sedimentation,the concentration of suspended solids in water column tended to be consistent with the initial concentration before the disturbance.4)The surface sediment erosion depth was 0.09-13.73 mm under different winds and waves disturbance in Nanyang lake.[Conclusions]The sediment resuspension regularities in Nanyang lake were significantly different with spatial and seasonal level,the differences were caused by different size of surface sediment particles at the estuary and lake center area and large acreages of Nanyang lake were covered by Potamogeton crispus,which reduce the amount of suspended solids.Settlement simulation process demonstrated that the first 6 h of settlement was critical for lower particulate matter in Nanyang lake.It was very difficult to erode surface sediments on the scale of decimeter or even centimeter under conventional wind conditions in Nanyang lake area of Nansi lake.