崇明东滩水文泥沙过程分析

Preliminary study on hydrodynamics and sediment processes in Chongming Dongtan

基于2005年9月在崇明东滩采集的现场观测数据,分析了水流和泥沙在潮滩上从光滩到植被区域的不同输运过程。研究结果表明,从光滩到植被带,涨潮和落潮流速逐渐变小,大潮时最大流速由113 cm/s(光滩)减小到8.1 cm/s(植被带);从光滩外侧(靠海)到内侧(靠岸),含沙量逐渐增加,至植被带再减小。潮周期内,流速和水体含沙量变化过程均呈现"双峰",峰值出现在涨潮初期和落潮中期,最大含沙量高达7.7kg/m3。测点各潮周期内流速最大值、平均含沙量均与潮汐强弱显著相关。流速增大引起泥沙再悬浮,瞬时含沙量响应流速变化。表层沉积物由光滩外侧(靠海)到内侧逐渐变细,得出泥沙由光滩外侧区域再悬浮,经潮流输移至潮滩内部的泥沙输运模式。分析光滩和植被水沙数据差异表明,植被具有较强的"缓流滞沙"作用。

Using the in situ observed data collected in September 2005 in Chongming Dongtan,this paper tries to demonstrate three aspects of tidal flat：processes of flow and sediment transport from bare flat to vegetational zone,main factors influencing the suspended sediment concentration（SSC） of current,and effects of vegetation on hydrodynamics and sediment transport compared with non-vegetation zone.Based on the aforesaid analysis,the following conclusions are worked out.Velocities during both flood and ebb tide decrease from the bare flat to the vegetation zone.During the spring tide,the max velocity drops from 113cm/s（bare flat） to 8.1cm/s（vegetation zone）.In spring tide period,SSC increases from sea side to land side on bare flat,and decreases in vegetation zone.During each tidal cycle,peaks of velocity and SSC occur in the initial stage of flood tide and the middle stage of ebb.The peak of SSC can reach the value of 7.7kg/m^3.Both max velocities and mean SSC are closely linearly correlated with max water depths at each site during different tidal cycles.SSC increases when current velocity increases.All these indicate that tidal current which helps sediment resuspended plays a dominant role in sediment transport during fair weather.Surficial sediments show that the size changed from coarse to fine grain along the direction toward land.In addition,the differences in magnitude of SSC and current velocity clearly illuminate the functions of vegetation in slowing current and trapping sediment.