Abstract The high-risk nature of low-lying coastal areas means that many are characterised by protective dikes, sea walls, and earthen embankments. Across Europe, such structures are employed to limit landward sea flooding and have been used historically to reclaim wetlands, many of which have since gained international protected habitat status. Sea level rise and storms threaten the future viability of fixed flood defences which will be overtopped with increasing frequency and, in extreme cases, breached. This raises questions surrounding defence maintenance and the fate of the reclaimed wetlands they encircle and support. One approach is to design defences with the expectation that they will be overtopped during extreme events, but that catastrophic failure as a result of breaching will be prevented. Such an approach was recently implemented at Blakeney Freshes, North Norfolk Coast, UK, an embanked area of reedbeds and coastal wet grassland. Lowering and widening of the Freshes embankment was undertaken following extensive breaching during the 5 December 2013 storm surge. In this paper we develop and apply a numerical model chain, comprising storm surge water levels, waves, and overtopping, to explore inundation extent, depth, and duration resulting from storm surge induced flooding under several sea level rise scenarios. Modelling results revealed that 99.5% of the flood volume of the 2013 event resulted from embankment breaching. Simulating the same storm event after embankment reprofiling shows that flooding of the Freshes is reduced by 97%, largely because the lower, wider embankments preclude breaching. However, under future sea level rise scenarios, storm surge induced overtopping results in increased inundation depths and drainage times, raising questions regarding the resilience of vegetation communities within the Freshes. By 2100 under the lowest SLR scenario, and by 2050 under the mid SLR scenario, over half of the Freshes will be inundated for >10 days, a potentially critical threshold for current wet grassland survival. Our findings suggest that while effective defence redesign may increase the viability of reclaimed wetland habitats in the short term, as sea levels rise, lengthened inundation durations may render these habitats increasingly vulnerable to ecosystem change under extreme events.

中文翻译：

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通过洪水灾害模型评估沿海湿草地对不断变化的管理制度的生存能力

摘要 沿海低洼地区的高风险性质意味着许多地区具有防护堤、海堤和土堤。在整个欧洲，这种结构被用来限制向陆上的海洋洪水，历史上曾被用来开垦湿地，其中许多已经获得了国际保护栖息地的地位。海平面上升和风暴威胁着固定防洪设施未来的生存能力，这些防洪设施将越来越频繁地被淹没，在极端情况下甚至会被破坏。这引发了围绕防御维护以及它们包围和支持的开垦湿地的命运的问题。一种方法是设计防御措施，期望它们在极端事件期间会被超越，但会防止因突破而导致的灾难性故障。最近在英国北诺福克海岸的 Blakeney Freshes 实施了这种方法，这里是一片芦苇丛生和沿海湿草地的堤防区。在 2013 年 12 月 5 日风暴潮期间发生大面积破坏后，对 Freshes 堤防进行了降低和加宽。在本文中，我们开发并应用了一个数值模型链，包括风暴潮水位、波浪和漫溢，以探索在几种海平面上升情景下风暴潮引起的洪水造成的淹没范围、深度和持续时间。建模结果显示，2013 年事件中 99.5% 的洪水量是由堤防破坏造成的。对路堤重新剖面后的同一风暴事件进行模拟表明，Freshes 的洪水减少了 97%，主要是因为较低、较宽的路堤防止了破裂。然而，在未来的海平面上升情景下，风暴潮引起的漫顶会导致淹没深度和排水时间增加，从而引发了有关 Freshes 内植被群落恢复力的问题。到 2100 年在最低 SLR 情景下，到 2050 年在中 SLR 情景下，超过一半的新鲜植物将被淹没超过 10 天，这是当前湿草原生存的潜在临界阈值。我们的研究结果表明，虽然有效的防御重新设计可能会在短期内提高开垦湿地栖息地的生存能力，但随着海平面上升，延长淹没持续时间可能会使这些栖息地在极端事件下越来越容易受到生态系统变化的影响。提出有关 Freshes 内植被群落恢复力的问题。到 2100 年在最低 SLR 情景下，到 2050 年在中 SLR 情景下，超过一半的新鲜植物将被淹没超过 10 天，这是当前湿草原生存的潜在临界阈值。我们的研究结果表明，虽然有效的防御重新设计可能会在短期内提高开垦湿地栖息地的生存能力，但随着海平面上升，延长淹没持续时间可能会使这些栖息地在极端事件下越来越容易受到生态系统变化的影响。提出有关 Freshes 内植被群落恢复力的问题。到 2100 年在最低 SLR 情景下，到 2050 年在中 SLR 情景下，超过一半的新鲜植物将被淹没超过 10 天，这是当前湿草原生存的潜在临界阈值。我们的研究结果表明，虽然有效的防御重新设计可能会在短期内提高开垦湿地栖息地的生存能力，但随着海平面上升，延长淹没持续时间可能会使这些栖息地在极端事件下越来越容易受到生态系统变化的影响。