Modelling NBSs for coastal erosion and marine flooding: the Emilia-Romagna case studies

The study was conducted in the context of the OPEn-air laboRAtories for Nature baseD solUtions to Manage environmental risks (OPERANDUM) project which is an H2020 project which aims at providing tools and methodologies for the assessment of NBS efficiency around the world. Two NBs were tested via modelling simulations on the Bellocchio Beach at Lido di Spina (Italy) located in the northern part of the Emilia-Romagna coast (northern Adriatic Sea): an artificial dune built with natural materials and a marine seagrass meadow. The artificial dune is an engineered structure that will mimic the functioning of natural dunes. Its aims are reducing both natural dune erosion and flooding in adjacent coastal lowlands. It consists of a barrier between the sea and land, in a similar way to a seawall. Unlike the latter, the NBS are ‘dynamic’, i.e. the dune/beach system interacts a great deal and is constantly undergoing small adjustments in response to changes in wind and wave climate or sea level. Its construction involves the placement of sediment from dredged sources on the beach and it will be reinforced with a structure composed of biodegradable material. Different typologies of experimental solutions are foreseen. The second NBS consists of an alongshore seagrass belt located in front of the coastal area. It was investigated as a potential mechanism for wave amplitude reduction. Among the few species that can live in the northern Adriatic Sea, Zostera Marina was chosen due to its ability to live in a marine environment influenced by freshwaters. A more detailed description can be found in (Pillai et al., 2021). The numerical model chain, specifically developed for the study, consists of an Ocean Circulation model, so-called SHYFEM (Umgiesser et al., 2004), a wave model, so-called WWIII (Alves and Ardhuin, 2016), and a morphological model, so-called XBeach (Roelvink et al., 2009). Ten years of XBeach simulations have been executed to simulate the morphological impacts on the coastal strip for the present (2010-19) and future climate (2040-49). For each 10 years period, four scenarios were simulated: the baseline scenario without NBS (baseline_run), the scenario with the dune (dune_run), the scenario with the seagrass effect (seagrass_run) and the scenario with the two NBS integration (dune_seagrass_run).XBeach was forced with sea level and wave time series predicted by the SHYFEM and WWIII models respectively. The model domain consists in a curvilinear structured grid of about 3.2 km (longshore) x 2.8 km (cross-shore) covering the coastal stretch of Bellocchio beach at Lido di Spina (Italy) and extends seaward up to about 10 m depth. The performance of the NBSs and their impact on coastal erosion and marine flooding were investigated. For both present and future scenarios (201-2019 and 2040-2049), the reduction in wave intensity obtained with the seagrass provided greater benefits in terms of erosion mitigation and flood reduction. The analysis highlighted the limited scale of the dune intervention, in particular under present conditions, highlighting that the longer the artificial dune implemented, the larger the beach and dune area protected. For the future scenarios, the results are still significant and even small projects are expected to help in mitigating coastal erosion and marine flooding. For long-period simulations, no relevant improvements in reducing beach erosion was observed when the artificial dune was combined with the seagrass meadows with respect to the seagrass effects only. Instead, a dominant increase in sea levels will probably highlight the dune functions in hindering the marine ingression into the lagoon area behind and the consequent sediment redistribution. This dataset consists of XBeach model results, mainly: Morphological evolution of the coastal bottom at Bellocchio beach (Lido di Spina, Italy) in terms of initial and final bed levels, for the current (201-2019) and the future (2040-2049) scenarios. Results are available for the four NBS scenarios described above (and detailed in the Presentation.pdf) Maximum flood depth, defined as the non-simultaneous maximum water depth on the beach domain of Bellocchio (Lido di Spina, Italy) for the current (201-2019) and the future (2040-2049) scenarios. Results are available for the four NBS scenarios described above (and detailed in the Presentation.pdf) Erosion-deposition maps for the current (201-2019) and the future (2040-2049) scenarios. Results are available for the four NBS scenarios described above (and detailed in the Presentation.pdf).本研究依托欧盟"面向基于自然的环境风险管理解决方案露天实验室（OPEn-air laboRAtories for Nature baseD solUtions to Manage environmental risks，缩写OPERANDUM）"项目开展，该项目为欧盟地平线2020（H2020）计划资助项目，旨在全球范围内提供用于评估基于自然的解决方案（Nature-based Solutions，以下简称NBS）效能的工具与方法论。 研究以意大利艾米利亚-罗马涅海岸北部（亚得里亚海北部）的利多迪斯皮纳（Lido di Spina）贝洛基奥海滩为研究区域，通过建模模拟对两类NBS开展测试：一类为采用天然材料构筑的人工沙丘，另一类为海洋海草床。 该人工沙丘为仿生自然沙丘功能的工程构筑物，核心目标为同时缓解自然沙丘侵蚀与邻近沿海低地的洪涝灾害。其作为海洋与陆地间的屏障，功能类似海堤，但与海堤不同的是，此类NBS具有"动态特性"——即沙丘-海滩系统会与周边环境发生强烈交互，并持续根据风浪气候或海平面变化进行小幅自适应调整。该构筑物通过在海滩上投放疏浚沉积物构筑而成，并将采用可降解材料结构进行加固。研究计划设置多种不同类型的实验方案。 第二类NBS为沿海岸线布设的海草带，本研究将其作为降低波浪振幅的潜在技术路径开展研究。在亚得里亚海北部可存活的少数海草物种中，研究选取了大叶藻（Zostera Marina），因其能够在受淡水影响的海洋环境中存活。更详细的研究背景可参见文献（Pillai et al., 2021）。 本研究专属开发的数值模型链包含三类模型：分别为海洋环流模型SHYFEM（Umgiesser et al., 2004）、波浪模型WWIII（Alves and Ardhuin, 2016）以及地貌演变模型XBeach（Roelvink et al., 2009）。研究开展了10年时长的XBeach模拟，以复现当前气候时段（2010-2019）与未来气候时段（2040-2049）下沿海岸带的地貌演变效应。每个10年时段设置4组模拟场景：无NBS的基准场景（baseline_run）、仅布设人工沙丘的场景（dune_run）、仅设置海草床效应的场景（seagrass_run）以及两类NBS协同作用的场景（dune_seagrass_run）。XBeach模型的强迫场分别采用SHYFEM与WWIII模型预测得到的海平面与波浪时间序列。 模型域采用曲线结构化网格，范围约为3.2 km（沿岸方向）×2.8 km（跨岸方向），覆盖意大利利多迪斯皮纳的贝洛基奥海滩沿岸区域，向海延伸至约10 m水深处。 研究分析了NBS的性能及其对海岸侵蚀与海洋洪涝的影响。结果显示，无论当前还是未来气候场景下，海草床带来的波浪强度衰减均能在缓解侵蚀与降低洪涝方面产生更显著的效益。分析同时指出，人工沙丘干预的效果规模有限，尤其在当前气候条件下；研究发现，人工沙丘的实施长度越长，受保护的海滩与沙丘区域面积越大。在未来气候场景中，人工沙丘的干预效果仍较为显著，即便小型工程也有望助力缓解海岸侵蚀与海洋洪涝。 对于长周期模拟而言，相较于仅采用海草床的场景，人工沙丘与海草床协同的场景并未在降低海滩侵蚀方面展现出显著增益。但随着海平面持续上升，人工沙丘在阻碍海水侵入后方潟湖区域以及促进沉积物重新分布方面的功能将愈发凸显。 本数据集包含XBeach模型的主要模拟结果，具体如下： 1. 意大利利多迪斯皮纳贝洛基奥海滩的海岸底床地貌演变数据，涵盖当前（2010-2019）与未来（2040-2049）场景下的初始与最终床面高程，对应上述4类NBS场景（详细内容参见Presentation.pdf）； 2. 意大利利多迪斯皮纳贝洛基奥海滩研究域内的最大淹没水深数据，定义为研究区域内的非同步最大水深，涵盖当前与未来气候场景，对应上述4类NBS场景（详细内容参见Presentation.pdf）； 3. 当前与未来气候场景下的侵蚀-沉积分布图，对应上述4类NBS场景（详细内容参见Presentation.pdf）。