江苏大丰潮滩悬沙级配特征及其动力响应
Characteristics of grain-size distributions of suspended sediment and its response to dynamics over the Dafeng tidalflat, Jiangsu coast in China
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摘要: 根据2002和2003年夏季在江苏大丰潮滩的现场观测资料,详细分析了悬沙级配的时空分布特征、影响因素及其对再悬浮、沉降和流速的响应.研究结果表明,悬沙颗粒较细,以粉砂为主,悬沙级配在潮周期内的变化模式有两种类型:一是稳定型,悬沙级配的时空(垂向和平面)变化很小;二是双峰型,悬沙级配的时空变化显著,粗细峰高度不断变化.再悬浮、沉降、涨潮时输入潮滩的悬沙和底质级配是影响悬沙级配的重要因子.再悬浮使粗颗粒悬沙的含量增加,悬沙与底质级配不断接近,沉降对悬沙级配的影响与再悬浮相反.再悬浮发生时悬沙级配对流速有明显响应.在没有再悬浮和沉降影响的情况下,潮滩不同部位、不同时间的悬沙级配趋于稳定和相同,对这种状态下的悬沙级配可称为背景悬沙级配,大丰潮滩背景悬沙级配的平均粒径为7μm.Abstract: On the basis of the measurement of suspended sediment at several sites over the Dafeng tidalflat in the summer of 2002 and 2003, the northern Jiangsu coast, the spatio-temporal characteristics of grainsize distributions of suspended sediment and its response to resuspension, settling process and tidal current velocity are analyzed.The results show that the suspended sediment is mainly composed of fine and very fine silt, and the mean grain-size is 7~13 m.On the basis of the in-situ measurement data, the spatiotemporal variation models of the grain-size distributions of the suspended sediment during the tidal cycle can be summarized into two types, one is the stability type when the variation is insignificant and the other is the double-peak type when the variation is remarkable.The main factors that influence the grain-size distributions of the suspended sediment are resuspension, settling process suspended sediment imported into tidal flats during the flood phase and the grain-size distributions of seabed sediment.The resuspension can increase the coarse particles content and the mean grain-size of the suspended sediment and cause the grain-size distributions of the suspended sediment close to the seabed sediment; the effects of settling process on the suspended sediment are opposite to those of the resuspension.When the resuspension occurs, the variation of the gain-size distributions of the suspended sediment in the lower part of water column can reflect the process clearly, the mean grain-size of the suspended sediment has good linear relationships with the current velocity.Without the effects of resuspension and settling process.the grain-size distributions of the suspended sediment is inclined to be stable and invariable during the measurement period over different parts of tidal flats, the mean grain-size of the background suspended sediment over the Dafeng tidalflat is 7 μm.
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