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 9.1m/s, the average wind speed was 2.1m/s, and the low wind speed from 0-1.0m/s was very much, accounting for 38.9% of the whole year, the high wind speed above 6m/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 6h 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 0.09-13.73mm 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 6h 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.
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