开敞式潮滩-潮沟系统发育演变动力机制——Ⅱ.潮汐作用

Mechanisms underlying the dynamic evolution of an open-coast tidal flat-creek system:Ⅱ:influence of tidal range

为研究潮汐作用下潮沟网络形成、演变规律,结合江苏沿海粉砂淤泥质潮滩实际情况,建立试验室物理模型,模拟具有一定坡度的潮滩在潮汐作用下的地形演变,分析了潮沟发育演变中的水沙运动规律,研究了潮差对于潮沟发育的影响。研究表明,潮沟发育过程受到床面坡度变化的影响,坡度均一的潮滩上,潮沟系统通过相邻小潮沟相互连接而形成,没有明显的潮沟头部溯源侵蚀现象;在潮汐作用下,涨潮初期和落潮后期水流流速较快,泥沙运动主要出现在这一阶段,在潮滩中部泥沙运动最为剧烈;潮差对于潮沟系统形态和结构的影响较小,潮滩排水路径长度与子流域面积呈幂函数分布,潮差越大则潮沟系统越早达到动态平衡,且具有更大的拓宽潮沟的作用。

To explore the initiation and development of tidal creek network driven by tidal currents, an experimental physical model was established based on the prototype of a silt-muddy tidal fiat-creek system on the Jiangsu coast. The evolutional process was simulated with an initially gentle bed slope of about 1%. The movement of flow and sediment, as well as the influence of tidal range on tidal creek development, was analyzed. The results indicated that tidal creek development was influenced by the bed slope variation. For the cases of uniform bed slope, the connection of neighboring tidal creeks, rather than headward erosion as shown by previous studies, resulted in the development of tidal networks. A strong flow and sediment movement occurred at the early flood and the late ebb stages, and sediment movement was most active in the mid-intertidal flat. Tidal range had little influence on the overall pattern formation and the structure of tidal networks. The relationship between the mean drainage path length and the sub-basin area generally followed a power-law function. Tidal networks approached a dynamic equilibrium state earlier under larger tidal ranges which contributed more to the development of the tidal creek widths.