风暴过程中潮滩悬沙浓度和悬沙输运的变化及其动力机制——以长江三角洲南汇潮滩为例

Variations of suspended sediment concentrations and transport in response to a storm and its dynamic mechanism——A study case of Nanhui tidal flat of the Yangtze River Delta

悬沙浓度是淤泥质海岸重要的环境指标。为探讨潮滩悬沙浓度和悬沙输运对风暴事件的响应过程及其动力机制,于2014年9月"凤凰"台风过境前、中、后在长江三角洲南汇潮滩进行了现场观测,获得同步高分辨率的水深、波高、近底流速和浊度剖面时间序列(9个潮周期)。结果表明,风暴中平均和最大波高、波-流联合底床剪切应力、悬沙浓度和悬沙输运率可比平静天气高数倍;风暴期间高潮位低流速阶段悬沙沉降导致近底发育数十厘米厚的浮泥层(悬沙浓度大于10g/L)。研究认为风暴事件中淤泥质海岸悬沙浓度和悬沙输运的剧烈变化其根本动力机制是风暴把巨大能量传递给近岸水体,进而显著增大波-流联合底床剪切应力,导致细颗粒泥沙再悬浮。

Suspended sediment concentration（SSC）is an important environmental index of muddy coasts.To understand the response of the suspended sediment concentration and suspended sediment transport on tidal flat to a certain storm event,we carried out in situ measurements of water depth,wave height,near-bed velocity and SSC profiles in high resolution on an intertidal mudflat of Nanhui Spit,which is on the delta front of the Yangtze River,China.The measurements last for 9tidal cycles,covering pre-,intra-and post-＂Fung-wong＂typhoon.The results show that：（1）mean and max wave heights,bed shear stress,SSC and suspended sediment transport rate during storm condition were several times higher than those in calm weather;（2）in storm condition,a fluid mud layer（SSC10g/L）in the thickness of tens of centimeters developed during slack water at high tides,resulting from settling of suspended sediment.We conclude that the drastic variation of suspended sediment concentration in muddy coastal areas is caused by enhanced energy in the water column caused by storm,leading to increasing combined wave-current bed shear stress,which leads to bed sediment resuspension.