台风期间长江口南槽近底部沉积动力过程

Near-bottom sediment dynamical processes in the South Passage of the Yangtze Estuary during typhoon season

2017年10月在超强台风"兰恩"发生期间,使用三脚架坐底观测系统在长江口南槽进行了15个潮周期的大潮-小潮的连续观测,获得高精度的盐度、波浪和近底部沉积动力数据。分析表明:台风期间的浪流联合作用控制着南槽的沉积动力过程,实测最大波高为2.1 m,波浪对提高底床切应力有显著贡献;波浪存在明显的涨落潮变化,涨潮阶段有效波高是落潮的1.5~2.7倍,导致涨潮时波浪切应力显著大于落潮;台风对南槽的潮流过程和盐淡水混合程度有明显影响,西北风会抑制涨潮流速并增强水体层化;台风使南槽悬沙浓度显著提高,台风后期近底悬沙浓度高达10 kg/m^(3),底床上出现厚度超过1.15 m的浮泥层。

Field observation was carried by the bottom tripod system in October 2017 in the South Passage of the Yangtze Estuary during the occurrence of the super typhoon Lan.The high-precision salinity,wave and sediment dynamical data were collected for 15 sustained tidal cycles.Data analysis showed that the combined action of wave and current controlled the sediment dynamical processes of the South Passage during typhoon season.The observed maximum wave height reached 2.1 m and the wave had significant influence to the total bed shear stress.Wave height displayed remarkable flood-ebb variation.Average effective wave heights in floods were 1.5-2.7 times that in ebbs,leading to the wave induced larger shear stress in floods than in ebbs.Typhoon caused important influence on the current velocity and the mixing intensity of salt and fresh water.Northwestern wind restrained the flood currents and enhanced the density stratification.Typhoon increased the suspended sediment concentration(SSC)near the bottom which exceeded 10 kg/m^(3) in the late stage of the typhoon,and the thickness of fluid mud more than 1.15 m.