开敞式潮滩-潮沟系统发育演变动力机制——Ⅲ.海平面上升影响

Mechanisms underlying the dynamic evolution of an open-coast tidal flat-creek system: Ⅲ: impact of sea level rise

为研究海平面上升对潮滩-潮沟系统的影响,以江苏中部粉砂淤泥质海岸为原型,建立变态物理模型,模拟研究在不同海平面潮汐过程作用下的潮沟发育和演变过程,分析了潮滩淹没历时、排水密度、潮沟断面形态等特征参数变化规律。研究表明:潮沟在发育初期伸长速率高于拓宽速率,最终趋于动态平衡;海平面上升后,潮滩淹没历时增加,露滩时间缩短,归槽水对潮沟底床的塑造作用减弱;平均归槽水流长度和Horton排水长度均随海平面上升呈现出减小趋势,潮沟的排水能力增强;潮沟断面宽深比服从对数正态分布,随着海平面上升,潮沟断面面积和宽深比均呈现出增大趋势,宽深比分布范围变广。

To explore the influence of sea level rise on the evolution of tidal flat and tidal creek system,adistorted physical model was established,taking a silt-muddy tidal flat-creek system in the central Jiangsu coastas the prototype.Based on the model,a variety of parameters were analyzed to illustrate the properties of the creek system changed with the sea level rise,such as duration of submergence,drainage density,cross section profile of the tidal channel,etc.Results indicate that the elongation increases more rapid than the elaboration at the initial stage of the creek system development,but both approach a dynamic equilibrium ultimately. Under the pressure of sea level rise,the inundation period increases hence the exposure duration of the tidal flats decreases,resulting in reduced shaping effects of the shift return flow on the creek bottom. Both mean unchannelled length and Hortonian drainage length show a decreasing trend,indicating a higher drainage ability of the creek system. In addition,the width/depth ratio follows an approximate lognormal distribution. The cross-section area and the width/depth ratio increase with sea level rise,as well as the distribution range of the width/depth ratio.