Sensitivity of post-storm surge dune recovery to geomorphological variability

风暴潮后沙丘恢复对地貌变化的敏感性

基本信息

批准号：
NE/M000052/1
负责人：
Joanna Bullard
金额：
$ 6.3万
依托单位：
Loughborough University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2014
资助国家：
英国
起止时间：
2014 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FM000052%2F1
关键词：
Sensitivity post storm surge dune

项目摘要

On 5th December 2013 the UK coastline was exposed to one of the biggest storm surges on record. In the past 60 years only two storms have been of comparable size. In 1953, water levels reached 5.6 m above Ordnance Datum (ODN), in 1974 they reached 4.7 m ODN and the 2013 storm reached 5.8 m ODN. The latter caused substantial erosion of dunes and beaches. As this is such an unusual event, there have been few opportunities for scientists to study how rapidly damaged sand dunes can recover following a storm of this magnitude. It would be interesting to know because dunes play an important role in coastal defence, forming a barrier to inland flooding and dissipating storm energy so reducing risk to lives and damage to infrastructure. Planners have to decide how best to manage the coastline not only under present conditions, but also thinking ahead to what the environment might be like in future. Future climate change scenarios for the UK suggest sea level will rise at 4 mm per year rising to over 12 mm per year after 2055. At the same time, it is predicted that the frequency and severity of coastal storm surges will increase, and that storminess will have an important impact on coastal geomorphology. This research will study how quickly, and under what conditions, coastal dunes can recover their shape, ecological and defence functions following erosion by a storm event. It is exciting because we rarely get the opportunity to study the aftermath of large storm events around the UK, and we will be able to collect data that coastal planners can use to make better decisions about coastal defences. Studies of the impacts of large storms on dunes suggest the shape of the dunes before the storm plays a key role affecting how severe the storm erosion is, and also how rapidly the dunes are rebuilt by wind-blown sediments. What has not been studied is how quickly dunes on a seaward-advancing (prograding) coast recover. This is a major gap in our knowledge given this type of coastline accounts for 30% of dune-backed beaches in England and Wales. It is also unclear how variability in the direction from which sand-transporting winds blow affects the rate of dune recovery. Although dunes are normally associated with strong onshore winds that blow sand from the beach to the dunes, research has shown that winds blowing offshore can also contribute to dune-building; the extent to which this occurs depends on the shape of the sand dune which can cause airflow to change direction. Given the above, the fieldwork for this project will focus on three sites each of which had different pre-storm dune heights (from 5 to 8 m high) and slope gradients, and each of which was severely eroded by the December 2013 storm. The sites are located on the Lincolnshire coast which is advancing seawards at about 2 m per year, and which has seasonal winds blowing onshore, offshore and alongshore. By measuring the two- and three-dimensional shape of the dunes every two weeks at each site we can see how they change following the storm. We will also use data on wind speed and direction to work out patterns of wind-blown sediment transport between each set of topographic measurements. The measurements will be taken regularly for 12 months. We visited the field sites immediately after the December 2013 storm and then again two weeks later. During this time there was a prolonged period of very strong offshore winds, however even during this short time, the dunes at one site increased in volume by 3.21 m3. The data we collect for this project will provide detail concerning post-storm dune recovery. Ideally we would also conduct continuous measurements of wind speed, wind direction and sediment transport at the site, but that is not possible given resource constraints. Instead, once we have collected the topographic data, we will seek additional support to use this data for three-dimensional modelling of airflow and sediment transport over the dunes.

2013年12月5日，英国海岸线暴露于有记录以来最大的风暴潮流之一。在过去的60年中，只有两次风暴的大小相当。 1953年，水位在军械基准数据（ODN）上方5.6 m上达到5.6 m，1974年，它们达到4.7 m ODN，2013年的风暴达到5.8 m ODN。后者造成了大幅侵蚀沙丘和海滩。由于这是一个不寻常的事件，因此，科学家几乎没有机会研究巨大的风暴后，沙丘迅速损坏的沙丘如何恢复。知道这将很有趣，因为沙丘在沿海防御中起着重要作用，构成了内陆洪水和消散风暴能源的障碍，从而降低了生命的风险和基础设施的破坏。规划人员必须决定如何最好地管理海岸线，不仅在当前条件下，而且还要考虑将来的环境。英国未来的气候变化情景表明，每年4毫米的海平面将上升到2055年后每年增加12毫米。与此同时，可以预测，沿海风暴潮流的频率和严重程度将增加，而风暴感将对沿海地间的地理编码产生重要影响。这项研究将研究在暴风雨事件侵蚀后，沿海沙丘在什么条件下以及在什么条件下恢复其形状，生态和防御功能。这是令人兴奋的，因为我们很少有机会研究英国各地的大型风暴事件的后果，我们将能够收集沿海规划者可以用来做出更好决定沿海防御的数据。关于大风暴对沙丘的影响的研究表明，在风暴之前，沙丘的形状影响了暴风雨侵蚀的严重程度，以及沙丘被风吹的沉积物重建的速度。尚未研究的是，在海上野外（前列）海岸恢复的情况下，沙丘恢复了。鉴于这种海岸线占英格兰和威尔士沙丘支持的海滩的30％，这是我们所知的主要差距。还不清楚在沙滩转风吹如何影响沙丘恢复速率的方向上的变异性。尽管沙丘通常与从海滩到沙丘吹沙的强烈陆上风相关，但研究表明，吹离海上的风也可以促进沙丘建造。发生这种情况的程度取决于沙丘的形状，这可能导致气流改变方向。鉴于上述，该项目的实地调查将集中在三个地点上，每个站点都有不同的预先策略的沙丘高度（从5到8 m高）和坡度梯度，并且每个坡度都因2013年12月的风暴而严重侵蚀。这些地点位于林肯郡海岸，每年约2 m，其季节性风在陆上，海上和沿岸吹来。通过在每个地点每两周测量每两周的沙丘的二维形状和三维形状，我们可以看到它们在暴风雨后如何变化。我们还将使用有关风速和方向的数据来确定每组地形测量组之间的风吹沉积物传输模式。测量将定期进行12个月。我们在2013年12月的风暴之后立即访问了现场站点，然后在两周后再次访问。在这段时间里，距离海上风的延长很长，但是即使在短时间内，一个地点的沙丘的体积增加了3.21 m3。我们为该项目收集的数据将提供有关成功后沙丘恢复的详细信息。理想情况下，我们还将在现场进行风速，风向和沉积物传输的连续测量，但这是不可能的。取而代之的是，一旦我们收集了地形数据，我们将寻求额外的支持，以将这些数据用于沙丘上的气流和沉积物传输的三维建模。