Morphodynamic modeling of tidal channel evolution in comparison to empirical PA relationship
Morphodynamic modeling of tidal channel evolution in comparison to empirical PA relationship
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DOI：
10.1016/j.coastaleng.2010.04.003
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发表时间：
2010-09
影响因子：
4.4
通讯作者：
M. Wegen;A. Dastgheib;J. Roelvink
中科院分区：
文献类型：
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作者：
M. Wegen;A. Dastgheib;J. Roelvink
冲积环境中的潮汐水道和进水口是相互关联的动力系统，它们对不断变化的物理条件(如海平面上升)以及人为影响(如疏浚和护岸工程)做出反应。过去的研究得出了潮汐棱柱(P)和潮汐海湾横截面积(A)之间的进水口经验平衡关系。在几个潮汐盆地中发现了恒定的PA关系。对PA关系的物理解释是基于沿岸漂移和潮汐输运能力(对于进水口)之间的平衡，基于泥沙输送的临界剪应力的概念，或者基于与空间均匀剪应力有关的恒定的空间含沙量的出现。目前的研究旨在通过研究数千年来潮汐海湾的地貌动力学演变来阐明PA之间的关系。利用了一个基于二维过程的数值模型，该模型能够描述盆地长期的地貌动力演化和模式发展。波浪影响(即沿岸漂移)被忽略，因此焦点仅限于潮汐运动。模型结果与Jarrett(1976)的经验PA关系非常吻合，即使在没有波浪的情况下。这表明，潮汐强迫本身在PA关系的发展中起着重要作用。结果还表明，类似的潮汐棱柱的截面积从长期来看是增加的。可以通过潮汐残留沉积物输运中的小梯度来解释，这些梯度允许随着时间的推移(非常缓慢)的发展。因此，Jarrett(1976)在经验PA关系周围发现的散布可以部分地用潮汐盆地的年龄来解释。一个连接着深海的浅盆口和一个深盆地不断加深。当它附着在输出沉积物的浅水盆地上时，盆口演化变得强烈受阻。PA关系沿浅水盆地是恒定的，这归因于沿盆地恒定的潮汐条件。进一步的分析表明，受限进水口比自由进水口需要更小的横截面面积才能输送相同的潮汐棱柱。这归因于它们的横截面积相对较深，因此摩擦力起到的作用较小。这与Jarrett(1976)经验PA关系中发现的射流口和自由口的不同系数是一致的。
Tidal channels and inlets in alluvial environments are interconnected dynamic systems that react to changing physical conditions (such as sea level rise) as well as to anthropogenic impact (such as dredging and bank protection works). Past research resulted in an empirical equilibrium relationship for inlets between the tidal prism (P) and the cross-sectional area in a tidal inlet (A). Constant PA relationships were found along several tidal basins. Physical explanations of the PA relationship are based on a balance between littoral drift and tidal transport capacity (for inlets), on the concept of critical shear stress for sediment transport or on the appearance of constant spatial sediment concentrations, which is related to spatially uniform shear stresses. The current research aims to clarify the PA relationship by addressing the morphodynamic evolution of a tidal embayment over millennia. Use is made of a 2D process-based, numerical model that is capable of describing long-term morphodynamic basin evolution and pattern development. Wave impact (i.e. littoral drift) is neglected so that focus is on tidal motion only. Model results closely obey the empirical PA relationship by Jarrett (1976) even in the absence of waves. This suggests that tidal forcing alone plays a major role in the development of the PA relationship. Results also show that cross sections increase for similar tidal prisms on the long term. Explanation is found by small gradients in tide residual sediment transports that allow for (very slow) development over time. The scatter found around the empirical PA relationship by Jarrett (1976) may thus be partly explained by the age of the tidal basin. A shallow basin mouth attached to a deep ocean and a deep basin continuously deepens. The basin mouth evolution becomes strongly damped when it is attached to a shallow basin that exports sediment. The PA relationship is constant along the shallow basin which is attributed to constant tidal conditions along the basin. Further analysis shows that confined inlets require smaller cross-sectional areas than free inlets to convey the same tidal prism. This is attributed to their relatively deep cross-sectional area so that friction plays a smaller role. This is in line with different coefficients found for jettied inlets and free inlets in the empirical PA relationship of Jarrett (1976).