现代废黄河三角洲叶瓣侵蚀过程的季节性变化

The seasonal variations of erosion processes off the modern abandoned Yellow River delta lobe

基于2017年夏季以及2018年冬季在废黄河三角洲叶瓣海域关键站位的连续观测及坐底三脚架观测数据,研究了废黄河三角洲叶瓣侵蚀过程的季节性变化特征。研究结果表明:黄河废弃三角洲叶瓣侵蚀具有显著的季节性特征。夏季平静海况下,三角洲斜坡水体整体强烈混合,三角洲前缘层化显著。三角洲斜坡平均含沙量约为25~55 mg/L,是三角洲前缘的1.5~3倍,侵蚀通量是其2倍左右,悬沙单宽通量三角洲斜坡区为前缘区的2倍左右。近岸三角洲斜坡区水体含沙量和浊度均受潮流控制,具有显著的周期性变化。冬季平静海况悬沙浓度是夏季的5~7倍,三角洲斜坡平均含沙量可达175~280 mg/L。风暴期间悬浮泥沙浓度显著上升,据浊度估算其可高出夏季1~2个数量级。同时,冬季风暴期间可能发生显著的沉积物液化并跨斜坡流动。沉积物捕获器记录表明,风暴海况下近底层沉积通量远高于平静海况下,最高达20 kg/m^(2)/d以上,约为平静海况下的30~50倍,而侵蚀通量要高于沉积通量,据此推算,一次风暴过程会使得海底沉积物发生厘米级变化。潮流的持续作用是研究区三角洲叶瓣快速侵蚀的重要原因,而极端天气下短时间尺度的波浪作用亦相当可观。

Based on the continuous observation and tripod observation data of key stations in the abandoned Diaokou(DK)and Shanxiangou(SXG)delta lobe in August 2017 and in March 2018,the seasonal variations of erosion processes off the modern abandoned yellow river delta lobe were studied.The erosion process in the abandoned delta lobe of the Yellow River had significant seasonal characteristics.Under calm sea conditions in summer,the delta slope was strongly mixed and the delta front was stratified significantly.The average suspended sediment concentration(SSC)of the delta slope was about 25-55 mg/L,which was 1.5-3 times of SSC of the delta front.The erosion flux of the delta slope was about 2 times of that of the delta front.The suspended sediments were mainly transported to Bohai bay,the suspended sediment flux of the delta slope was about twice of that of the front area.The SSC in winter was 5-7 times of that in summer,and the average sediment concentration in the delta slope could reach 175-280 mg/L.The SSC increased significantly during storms and it could be 1-2 orders of magnitude higher than that in summer.Meanwhile,remarkable sediment liquefaction and cross-slope transport might occur during winter storm.Sediment trap records showed that the near bottom deposition flux under storm conditions was much higher than that under calm conditions,up to more than 20 kg/m^(2)/d,which was about 30-50 times of that under calm sea conditions.A storm process could make the seabed sediments change in centimeter scale.The continuous action of tidal current was an important reason for the rapid erosion of the delta lobe in the study area,and the short time scale wave action under extreme weather was also considerable.