影响界牌河段江心洲洲头低滩演变的因素分析

An Analysis of Factors Affecting the Evolution of Shoals at the Head of the Central Bar of Jiepai Reach in the Middle Yangtze River

处于自然演变状态的分汊型河道江心洲洲头一般会有洲头低滩的存在,洲头低滩通常是航道边界的重要组成部分。当洲头低滩形态完整时,航道状况往往较好;当低滩低矮分散时,航道条件变差甚至会出现碍航状况。选取界牌河段新淤洲洲头低滩为例,并结合其他河段的资料,分析了洲头低滩的演变特点,影响因素以及决定低滩不同部位冲刷强度的水动力条件指标。结果表明,与江心洲相比,洲头低滩演变更加剧烈,生成到消失的周期更短;来水来沙条件和河道地形条件是影响低滩冲淤演变的首要因素;低滩不同部位的稳定取决于当地水流动力条件与床面泥沙抵抗起动能力之间的对比,当地流速U与床沙起动流速Uc比值的大小决定了冲刷强度的大小。

At the head of central bar in braided river exist shoals which are usually important components of the navigation channel boundaries .When the shoals maintain its integrity ,the fairway is always in a good condition ,while when low and dispersed ,they may worsen the channel conditions and even impede navigation .Combined with an analysis of the field data of other braided reaches , this paper uses the Xinyuzhou in Jiepai Reach as an example to analyze the evolutionary characteristics of shoals at the head of central bar ,as well as its influencing factors and hydrodynamic conditions that determine the erosion intensity of different parts of shoals at the head .The result shows that compared to central bars ,the shoals experience more drastic evolutions and the cycle period from e‐mergence to vanishing is also shorter .The primary factors contributing to the erosion of shoals include the incoming water and sedi‐ment and the channel topography .A comparison between local hydrodynamic condition and resistances of bed surface sediment deter‐mines the stability of different parts of a shoal .Ratio of flow velocity U to the threshold velocity Uc determines erosion intensity .