RISCO and Civil Engineering Department, University of Aveiro, Portugal.
CESAM and Physics Department, University of Aveiro, Portugal.
J Environ Manage. 2024 Nov;370:122835. doi: 10.1016/j.jenvman.2024.122835. Epub 2024 Oct 11.
Nearshore nourishments are a common intervention used to mitigate sediment deficits in coastal areas experiencing erosion problems. This coastal intervention involves placing nourished sediments in the submerged zone of the beach profile to form an artificial submerged sandbar which are then distributed by natural forces occurring in the coastal zone. Coastal processes that control the morphological evolution of coastal zones operate on several spatial and temporal scales (seconds to years) and can be divided into cross-shore and longshore components. Usually, the numerical models that simulate the evolution of cross-shore profiles due to sediment transport within the profiles, are related with short to medium-term events (days to months), and shoreline evolution models, that allow for long-term analysis (years to decades), are typically only considering longshore sediment transport. Describing all the processes in a single numerical model is complex and computationally demanding, and therefore, the numerical models are typically focused on specific processes, categorized by their temporal and spatial scales. This article presents a numerical study focused on medium to long-term numerical modelling of coastal zone evolution, examining the combined effects of cross-shore and longshore sediment transport processes of sediment transport. The model incorporates two simplified numerical models: LTC - Long Term Configuration, for shoreline evolution and CS-Model, for cross-shore sediment exchanges. Applied to nine different sandbar scenarios, model results revealed that disturbances in sandbar volume tend to return to equilibrium through cross-shore sediment transport processes. In situations that considered a constant sandbar volume alongshore, the longshore effects are null, because the volume entering in the coastal domain is equal to the volume leaving, and the sediment balance is only dependent of the cross-shore processes. Variable sandbar volume alongshore leads to impacts on shoreline position due to longshore sediment transport gradients generated by the sandbar disturbance. The results demonstrate the potential of the proposed combined model for medium to long-term projections, allowing for the interpretation of how physical aspects of nearshore nourishments evolve. These aspects include sandbar volume, shoreline position, berm width, and shoreline displacements induced by cross-shore and longshore sediment transport processes. These parameters aid in understanding sandbar-beach sediment dynamics, which is valuable for supporting coastal management, particularly in the development and design of shoreface sand nourishments, enabling the optimization of sand resources.
近岸补给是一种常见的干预措施，用于缓解遭受侵蚀问题的沿海地区的泥沙短缺。这种沿海干预措施包括将补给的泥沙放置在海滩剖面的淹没区域中，形成人工淹没沙坝，然后由沿海地区发生的自然力分布。控制沿海地区形态演变的沿海过程在几个时空尺度上（秒到年）运行，可分为横向和纵向分量。通常，模拟由于剖面内泥沙输运引起的横向剖面演变的数值模型与短期到中期事件（天到月）相关，而允许长期分析（年到十年）的海岸线演变模型通常只考虑横向泥沙输运。在单个数值模型中描述所有过程是复杂且计算要求高的，因此，数值模型通常侧重于特定过程，根据其时间和空间尺度进行分类。本文提出了一项数值研究，重点是中到长期的海岸带演变数值模拟，研究了横向和纵向泥沙输运过程对泥沙输运的综合影响。该模型包含两个简化的数值模型：LTC-长期配置，用于海岸线演变，CS 模型，用于横向泥沙交换。应用于九个不同的沙坝场景，模型结果表明，沙坝体积的干扰倾向于通过横向泥沙输运过程恢复平衡。在考虑沙坝体积沿岸线恒定时，横向效应为零，因为进入沿海区域的体积等于离开的体积，并且泥沙平衡仅取决于横向过程。沙坝体积沿岸线变化会导致由于沙坝干扰产生的横向泥沙输运梯度对海岸线位置产生影响。结果表明，所提出的组合模型具有中到长期预测的潜力，允许解释近岸补给的物理方面如何演变。这些方面包括沙坝体积、海岸线位置、滩肩宽度以及横向和纵向泥沙输运过程引起的海岸线位移。这些参数有助于理解沙坝-海滩泥沙动力学，这对于支持沿海管理是有价值的，特别是在开发和设计岸滩沙补给时，可以优化沙资源。
