江苏大丰潮滩潮流边界层特征研究

Characteristics of tide-induced bottom boundary layers over the Dafeng intertidal flats,Jiangsu Province,China

2003年7月中小潮期间使用MIDAS-400用户化数据采集系统在江苏大丰潮滩上进行了垂向多层位同步的流速和悬沙浓度观测。根据观测资料研究了潮流作用下的潮滩底部边界层过程，结果表明，观测地点的潮汐不对称现象十分明显，落潮流速、历时和输水输沙量皆明显大于涨潮；在潮周期内的多数时间里流速剖面符合对数分布，但在风力较强、水流快速增加和流速缓慢的情况下，流速剖面常偏离对数分布；悬沙颗粒垂向混合均匀，悬沙浓度剖面符合Rouse公式；落潮时的底部切应力和摩阻流速明显大于涨潮，摩阻流速与各水层流速通常有较好的线性关系；滩面糙度主要与沙纹形态和推移质运动强度有关，它与摩阻流速存在密切关系；悬沙浓度具有明显的减阻效应，受其影响，摩阻流速和底部切应力分别减小了28％-41％和40％-62％。

A MIDAS-400 customized data acquisition system was used to measure the high-resolution current velocities and suspended sediment concentrations of different layers above the seabed over the Dafeng intertidal flats of northern Jiangsu during intermediate and neap tides from July 4 to July 10, 2003. The characteristics of tide-induced bottom boundary layers are analyzed. At the station of measurement, time-velocity asymmetry is significant. During the ebb phase, the current speed, water and sediment discharges and ebb duration are larger than those during the flood phase. 23% - 95% of the velocity profiles are logarithmic in a tidal cycle. Strong wind, current velocity acceleration and slack water are the main factors that cause the current profile to deviate from the logarithmic distribution. Suspended particles are mixed well within the water column, and the suspended sediment concentration profile can be fitted with the Rouse equation. The shear velocities have significant linear relationships with the current velocities of different layers, the roughness length is affected mainly by the ripple shape and the intensity of bedload transport, and there is a significant relationship between the roughness length and shear velocity. Remarked drag reduction is present due to the high suspended sediment concentrations; and the shear stresses and shear velocities calculated using Adams and Li models are 28 % - 41% and 40% - 62% lower, respectively, than those calculated by using the Von Kármán-Prandtl model.