A Framework for Modelling Shoreline Response to Clustered Storm Events: Case Studies from Southeast Australia

Coastal communities in Australia are particularly exposed to coincident natural hazards, whereby tropical cyclones and extra-tropical storms cause damage to infrastructure and shorelines from severe wind, flood and storm surge. Because the climatic drivers of severe storms are stronger under certain conditions (e.g. during La Ni±a periods for tropical cyclones), these events can repeatedly impact the coast over periods of weeks to months. Historically, major episodes of beach erosion along southeast Australia have occurred during every decade over the last century, with the most severe in 1974 resulting from two extra-tropical storms in two months.
While the process of beach erosion is well understood in general terms, the response of a specific sector of coast to clustered storms may not be. For effective coastal management, this site specific knowledge becomes essential. Here we present a framework for integrating coastal geomorphology and coastal engineering approaches to model shoreline response to clustered storms at a spatial scale that can directly inform management agencies. We focus on two case study areas in southeast Australia, the beaches of the Adelaide metropolitan coast (South Australia) and Old Bar beach (central New South Wales) where erosion is a management priority.
For each site we adopt the coastal sediment compartment as the functional management unit, mapped for the Australian continent at multiple spatial scales, and use sub-surface information (boreholes, ground penetrating radar profiles) to estimate sediment volumes in the upper beach to foredune. These data are then used to inform shoreline response modelling linked to an event time series (observed and hind cast) as a separate project component. Future work includes assessment of `at-risk infrastructure at each site. This paper is a contribution to the Bushfire and Natural Hazard Cooperative Research Centre project Storm surge: Resilience to clustered disaster events on the coast.

澳大利亚沿海社区尤其易遭受并发自然灾害的冲击，热带气旋与温带风暴可通过强风、洪涝及风暴潮对基础设施与海岸线造成损毁。由于极端风暴的气候驱动因子在特定条件下更为活跃（例如热带气旋频发的拉尼娜（La Niña）时期），此类灾害事件可在数周至数月的周期内反复侵袭沿海区域。历史记录显示，过去一个世纪内，澳大利亚东南部每十年便会出现严重的海滩侵蚀事件，其中1974年的侵蚀最为剧烈，彼时两个月内接连两场温带风暴引发了大规模侵蚀。
尽管海滩侵蚀的整体机理已得到较为充分的认知，但特定岸段对集群风暴的响应机制仍有待明确。对于高效的海岸管理工作而言，这类针对特定场地的专业认知至关重要。本研究提出一套整合海岸地貌学（coastal geomorphology）与海岸工程学方法的分析框架，可在能够直接为管理机构提供决策参考的空间尺度上，模拟海岸线对集群风暴的响应过程。研究聚焦澳大利亚东南部的两个案例区域：阿德莱德都会沿海海滩（南澳大利亚州）与旧巴尔海滩（新南威尔士州中部），上述区域的海滩侵蚀均为海岸管理的优先事项。
针对每个研究场地，本研究采用海岸沉积物单元（coastal sediment compartment）作为功能管理单元——该单元已在澳大利亚大陆范围内按多空间尺度完成测绘——并利用地下探测数据（钻孔、探地雷达剖面）估算上层海滩至前沙丘区域的沉积物体积。随后，这些数据将用于支撑与事件时间序列（观测数据与后报（hindcast）模拟数据）相关的海岸线响应建模工作，该建模工作为本项目的独立组成部分。后续研究将包括评估各场地的风险基础设施。本论文是丛林火灾与自然灾害合作研究中心（Bushfire and Natural Hazard Cooperative Research Centre）项目"风暴潮：沿海集群灾害事件韧性"的研究成果之一。