江苏东台潮滩沙纹形态特征及其演变过程的数值模拟研究

Characteristics and evolution process and their modeling of sand ripples on Dongtai tidal flats,Jiangsu province China

主要研究了江苏东台潮滩下部沙纹形态特征及其主要影响因素。基于潮滩下部水深、流速、沙纹形态的观测及表层沉积物的粒度数据,分析了研究区沙纹形态特征及其与潮汐水动力条件、沉积物粒度间的关系。并建立了地貌动力学模型,模拟了不同沉积物粒度和不同水深变化条件下沙纹尺度(波长、波高)的变化和沙纹的演化过程。研究结果表明:潮滩表面主要形成尺度较小的不对称沙纹,其形态的主要影响因素是流速和沉积物粒度,在一定范围内,流速越大,沉积物颗粒越细,沙纹尺度越大。在一个潮周期内沙纹形态经历以下过程:平底→不对称性指示涨潮方向的沙纹→平底→不对称性指示落潮流方向的沙纹。

This paper is mainly about the morphological features of sand ripples, which are in the lower part of the Dongtai tidal flat, as well as the key influencing factors. Based on the measurements of water depth, tidal current, sand ripples morphology and grain size analysis of surficial sediments of the lower part of the tidal flat in the study area, the relationship among sand ripple pattern, tidal dynamics and sediment grain size are ob- tained. In addition, a morphodynamic model is built to simulate the evolution processes associated with the sand ripples under variable tidal currents and sediment grain size. Research results demonstrate： （ 1 ） Sand ripples observed on the tidal flat are small in the dimensions with the wave length of 5-12cm and the wave height of 0. 3-4cm. （2）Three stages are undergone during a tidal period： a,during the initial period of a flood tide, the tidal flat records a transition from a smooth topography, with no bed forms, to the formation of asym- metrical ripples indicating the flooding tide direction ; b,from the late stage of a flooding tide to the initial stage of ebb tide, the height of the sand ripples gradually reduces and the surface of the tidal flat resumes smooth a- gain; c,during the late stage of the ebb tide, asymmetrical sand ripples indicating the ebb tide direction are present; （3） The key factors influencing the sand ripple sizes are tidal currents and the sediment grain size. Within limits, large tidal currents correspond to large sand ripples. Further, coarse sand corresponds to small sand ripples.