入海泥沙减少对黄河三角洲潮滩粒度特征的影响——物理模型实验

Influence of reduced sediment supply on the particle size distribution on tidal flats of the Yellow River Delta:a physical experimental study

为探究不同悬沙浓度下潮滩粒度特征的变化,对黄河三角洲潮滩进行了物理模拟实验。使用采自研究区的潮滩表层沉积物,设定与实际潮滩尺寸按比例缩小的室内水槽以及波浪潮汐动力模拟,对不同悬沙浓度条件(0~14.9 kg/m^(3))下的模拟“潮滩”进行粒度分析。结果表明,随着悬沙浓度的减少,潮滩粒度特征发生了明显变化。随着含沙量的减少,整个潮滩的细颗粒沉积物分布范围减小,总体上沉积物呈现粗化特征,但颗粒较大的极粗粉砂的分布同样减少;在不同含沙量条件下,分选系数、偏度和峰度均值总体呈现出潮下带上部高、潮间带和潮下带下部低的特征,反映了模拟的潮间带上部和潮下带前缘的分选较潮滩中部更好的特征。含沙量的变化同样影响了模拟潮滩的微地貌形态,随着含沙量的降低,潮滩微地貌逐渐侵蚀破碎。潮滩物理模型实验有助于快速再现潮滩冲淤形态和变化特征,使特定条件下潮滩的变化具备可预见性,从而为人类有针对性地进行生产活动提供参考。

To explore the variation of grain size distribution in tidal flat under different suspended sediment concentrations,physical simulation experiments in flume were conducted for tidal flat of the Yellow River Delta.With the sediments(15 t)collected from the tidal flat surface in the field,an indoor flume was designed in a scaled-down size proportional to the real case,in which wave/tidal dynamic parameters were set,and the grain size distributions under different suspended sediment concentrations(0~14.9 kg/m^(3))were measured and analyzed.Results show that the characteristics of grain size distribution of tidal flat changed obviously with the decrease of suspended sediment concentration.With the decrease of sediment concentration,the distribution range of fine-grained sediments in the whole“tidal flat”decreased in a general coarsening trend;however,that of very coarse particles also decreased.Under different sediment concentrations,the average sorting coefficient,skewness,and kurtosis were generally greater in the upper intertidal zone than those in the intertidal zone and the lower subtidal zone,reflecting better sorting in the upper intertidal zone and the frontal subtidal zone than in the middle tidal flat.In addition,with the decrease in sediment concentration,the micro-topography of the“tidal flat”was gradually eroded and broken.This physical model experiment of tidal flat is able to reproduce quickly the variation in topography of erosion and deposition under different sand supplies and parameters,with which any changes of tidal flat under specific conditions can be simulated for better prediction in real cases as a reference for safe operation of human activities in similar tidal flat areas.