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Forecasting coastal evolution on time-scales of days to decades
Coastal Engineering ( IF 4.2 ) Pub Date : 2021-06-10 , DOI: 10.1016/j.coastaleng.2021.103928
Mark Davidson

Increasing pressures on coastal environments induced by sea level rise and coastal squeeze has meant that tracking the morphological evolution of sedimentary coasts from the last known survey, pre-empting storm impacts and forecasting potential beach recovery following extreme events is of substantial and increasing societal importance. Equilibrium models for forecasting coastal evolution have figured prominently in the literature in the past two decades and show a strong potential for fulfilling this societal need. In particular some very skilful shoreline evolution models have been proposed based on equilibrium concepts. These models are stable, simple and permit long-term (O(10) years) predictions of coastal change. However, equilibrium models are typically highly empirical and in many cases do not consider explicitly the impact of dynamic sea level, which is modulated by tides, surge and global sea level rise. Equilibrium-based models of shoreline evolution have shown particular promise, but these models generally do not consider the role of the sub- and supra-tidal morphology on coastal evolution (e.g. the importance of coastal dune systems). This contribution presents a new model for Forecasting Coastal Evolution (ForCE), which addresses these issues. The model algorithm adopts a reduced complexity but fundamentally physics-based approach, whilst maintaining equilibrium principles. Unlike, most prior models, the sub- and supra-tidal areas are represented explicitly in the model, as are sea level variations. Sediment transport is equated directly with the disequilibrium in wave energy dissipation flux, leading to a sediment transport formulation that negates the normal intermediate step of computing surfzone currents, generally required in process models. Two components of sediment transport are considered: The first is forced by the turbulent kinetic energy associated with wave breaking and the second diffusive term, is related to a sea bed-slope disequilibrium. The first component perturbs the equilibrium profile and dominates in the surfzone, whilst that latter component plays an important role in beach recovery. Equations are developed for a depth-averaged, beach profile model, assuming longshore uniformity. These computational efficient and stable equations facilitate long forecasts (>decade) and easy comparisons with a field data at cross-shore transport dominated field sites. At the test field site, the model is capable of reproducing qualitative observations of nearshore sand-bar dynamics and quantitative comparisons with measured coastal state indicators including both the shoreline displacement (r = 0.90, N.M.S.E. = 0.145) and intertidal beach volume (r = 0.87).



中文翻译:

在几天到几十年的时间尺度上预测沿海演变

海平面上升和沿海挤压对沿海环境造成的压力越来越大,这意味着跟踪最近一次已知调查中沉积海岸的形态演变、预防风暴影响和预测极端事件后潜在的海滩恢复具有重大和日益增加的社会重要性。在过去的二十年里,用于预测沿海演变的均衡模型在文献中占有突出地位,并显示出满足这一社会需求的强大潜力。特别是一些非常有技巧的海岸线演化模型已经基于平衡概念提出。这些模型稳定、简单并且允许对海岸变化进行长期(O(10) 年)预测。然而,平衡模型通常是高度经验性的,在许多情况下没有明确考虑动态海平面的影响,动态海平面受潮汐、潮汐和全球海平面上升的调节。基于平衡的海岸线演化模型显示出特别的前景,但这些模型通常没有考虑潮下和潮上形态对海岸演化的作用(例如海岸沙丘系统的重要性)。这一贡献提出了一个新的模型对于ecasting Ç oastal Ëvolution (ForCE),它解决了这些问题。模型算法采用降低复杂性但从根本上基于物理学的方法,同时保持平衡原则。与大多数先前模型不同,潮下和潮上区域在模型中明确表示,海平面变化也是如此。沉积物输送直接等同于波浪能耗散通量的不平衡,导致沉积物输送公式否定计算海浪带流的正常中间步骤,通常在过程模型中需要。考虑了沉积物运输的两个组成部分:第一个是由与波浪破碎相关的湍流动能推动的,第二个是与海床-坡度不平衡相关的扩散项。第一个分量扰乱平衡剖面并在冲浪区占主导地位,而后一个组成部分在海滩恢复中起着重要作用。方程是为深度平均的海滩剖面模型开发的,假设沿岸均匀。这些计算效率高且稳定的方程有助于长期预测(> 十年)并易于与跨岸运输主导的现场现场数据进行比较。在试验现场,该模型能够再现近岸沙洲动力学的定性观测和与测量的沿海状态指标的定量比较,包括海岸线位移(十年),并与以跨岸运输为主的现场现场的现场数据进行轻松比较。在试验现场,该模型能够再现近岸沙洲动力学的定性观测和与测量的沿海状态指标的定量比较,包括海岸线位移(十年),并与以跨岸运输为主的现场现场的现场数据进行轻松比较。在试验现场,该模型能够再现近岸沙洲动力学的定性观测和与测量的沿海状态指标的定量比较,包括海岸线位移(r  = 0.90, NMSE  = 0.145) 和潮间带海滩体积 ( r  = 0.87)。

更新日期:2021-06-17
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