淤泥质潮流深槽最大冲刷深度的一个概念模型

Modeling maximum scour depths of tidal channels with mud substrate in shallow marine environments

以概念模式方法计算了淤泥质潮流深槽的最大深度,探讨了涨落潮流速、涨落潮历时、深槽淤泥质物质粒径、深槽顶底部原始深度、水道长度等因素对潮流深槽最大深度的影响。概念模式的假设条件是:(1)深槽形态为长方体,底部纵向坡度为0;(2)沉积物粒径无垂向变化;(3)只考虑潮流作用的影响,涨、落潮流速在时间序列上呈正弦分布;(4)不考虑细颗粒物质的粘性和絮凝作用。模拟结果显示:(1)涨、落潮历时对深槽最大深度的影响很小。(2)优势潮流流速与最大深槽深度之间存在着幂函数关系。(3)深槽的底质粒径、深槽的长度均与最大冲刷深度呈正相关关系。(4)深槽顶部水深与最大深度呈负相关关系。(5)由于潮汐水道深度与潮流流速和沉积物侵蚀强度之间具有负反馈关系,因此水道冲刷存在着一个极限,即最终可以达到均衡状态。潮流深槽的均衡态特征和达到均衡态所需的时间可运用沉积动力学方法来确定;同时,若应用深槽的真实参数,进一步减少模型的假设条件,可望使该模型具有实际的应用价值。

Maximum scour depths of tidal channels with mud substrates formed by tidal currents are controlled by many factors. In this contribution, a conceptual model is established to calculate the maximum depth. Numerical experiments were carried out to evaluate the effects of the factors such as velocities and durations of flood and ebb tidal phases, grain size of bottom sediments in the channel, bank water depth and channel lengths on the maximum scour depth. Assumptions of the modeling are： （1） the tidal velocities change sinusoidally with time; （2） the channel bottom has no slope along its axes; （3） there are no variations in grain sizes throughout the sediment column; （4） tidal currents are the only dynamic force scouring tidal channels; and （5） effects of cohesiveness and flocculation of fine-grained sediments are neglected. The results of calculation reveal that ： （1） the flood or ebb duration has little effect on the maximum depth; （2） there is a powerlaw relationship between the maximum depth and the velocity of dominant tidal current; （3） the grain size of sediment and the length of the channel is correlated positively with the maximum depth; and （4） the water depth at the bank of the channel is correlated negatively with the maximum depth. The numerical experiments show that because there is a negative feedback mechanism between tidal currents and the intensity of erosion, a limit for channel scour exists, i. e. , an equilibrium status will be eventually reached. The channel morphology at equilibrium and the length of the period of time to reach equilibrium can be determined with sediment dynamic methods. Using real parameters associated with a channel and reducing the number of assumptions adopted in this study, the model has a potential to produce realistic results.