珠江磨刀门河口洪季泥沙絮凝机理研究

Study on sediment flocculation mechanism at Modaomen in the Pearl River Estuary in flood season

基于珠江磨刀门河口2013年7月现场观测的悬浮物资料,综合同步测验的盐度、流速、悬沙浓度、水温,以及室内泥沙粒度分析数据,探讨了该区域泥沙絮凝特征及其主要影响因素,结果发现:磨刀门悬沙现场粒径平均达91.7μm,而平均分散粒径仅29.3μm;小潮泥沙絮凝较大潮明显,潮周期内憩流时刻絮团最大,可达200μm;絮凝效应垂向差异显著,表现为中层最大而表、底层较小;功率谱分析得到现场粒径具有3h、8h和24h的变化周期,其中8h与平均落潮周期相近,24h则与全潮周期相近。研究表明,控制磨刀门悬沙絮凝的因素主要为流速,絮凝临界流速约45cm/s;盐度则在弱动力条件下(流速<50cm/s)控制着河口泥沙絮凝,最佳絮凝盐度为21‰;悬沙浓度和温度对絮凝影响不显著;垂向水动力及盐度差异是导致絮凝效应垂向差异的主要原因。

Characteristics and mechanism of sediment flocculation in the Pearl River Estuary(Modaomen)have been studied,based on the in-situ particle size spectra data from LISST-100C,simultaneous observed data of suspended sediment concentration(SSC),current velocity,salinity and temperature.Results have obtained as following:average flocs size is 91.7μm,whereas the dispersed particle size is 29.3μm;flocculation in neap tide is more obvious than that in spring tide,and flocs get its maximum up to 200μm around the slack;flocs develop and breakup with cycles of 3h,8h,and 24 h,and 8h is close to the duration of ebb tide,whereas 24 h approach to the diurnal tide cycle.Analysis indicates that the tidal current controls the flocculation with a threshold of 45cm/s;the salinity plays an important role on flocculation when the velocity approach to the threshold,and 26.2‰ is the optimum flocculating salinity.Furthermore,the distributions of hydrodynamic condition and salinity control the vertical distribution of flocs which are biggest in the middle layer.