Impacts of extreme flooding on physical habitats and flood risk management

具有破坏性的河流洪水，如2009年底在坎布里亚发生的洪水，由于其经济和社会影响，具有重要的预测意义，但也必须从它们如何创造新的自然栖息地和河道的角度加以理解。虽然最近的报告正确地集中在极端水浸的直接破坏性影响上，但关于河道变化的长期影响的信息较少。后者之所以重要，有两个原因。首先，洪水后河道调整所需的河道维护变化往往会造成巨大的经济成本。第二，与之相反，改变自然栖息地和河道实际上可能会带来好处，这可能会降低随后的洪水风险。这在一系列立法中得到了接受，根据这些立法，欧洲(和美国)的河流管理者被要求恢复和加强河道，以满足严格的生态标准。从这个意义上说，我们目前对极端洪灾带来的好处的了解很少。因此，我们拟议研究的一部分将分析2009年底坎布里亚极端洪水造成的栖息地和航道的变化。目前的河流恢复方法空间有限且成本高昂，但我们的目标是证明极端洪水可以带来物理栖息地的重大变化，并有可能按照监管机构的要求进行河道规模的恢复。据预测，在英国和其他地方，在一系列气候和土地使用情景下，极端洪水将变得更加频繁。但人们对极端洪水的频率或回归时间缺乏了解，因为监测到的河流洪水记录往往相对较短。因此，我们的研究的第二条线索是在巴森斯韦特湖床最近积累的湖泊沉积物中发现最近的坎布里亚极端洪水的信号。如果最近的洪水信号能够被清楚地建立起来，20/21世纪早期的洪水可以在较低的沉积物中被识别出来，并被洪水记录所证实。然后可以对更深的沉积物进行分析，以提供几个世纪以来洪水频率及其大小的区域记录。从这些数据中，我们可以更多地了解几个世纪以来极端洪水的普遍程度，以及自20世纪初以来，在气候变化和人类活动的主要时期，洪水是变得更加常见还是变得不常见。我们的项目将从巴森斯韦特湖及其下游受到坎布里亚最近洪水严重影响的地点收集现场数据。这项研究将直接影响对洪泛区和河道的适当洪灾后管理的评估，以及对未来极端洪灾可能性的战略评估--这对包括当地居民和农民、环境局、DEFRA和大型国际学术界在内的许多利益攸关方都有好处。

Destructive river floods, like the ones in Cumbria in late 2009, are important to forecast because of their economic and social impacts, but are also important to understand from the viewpoint of how they create new physical habitats and river channels. Whilst recent reports rightly concentrate on the immediate damaging impacts of extreme flooding, less information is available about the long term impacts of changes in river channel. The latter is important for two reasons. First, large economic costs can often result from changes in flood channel maintenance necessitated by post-flood channel adjustments. Second, and in contrast, there may actually be benefits arising from changes to physical habitats and river channels which may lessen subsequent flood risk. This is accepted within a raft of legislation whereby European (and US) river managers are required to restore and enhance river channels to meet stringent ecological standards. In this sense, our current knowledge of the benefits resulting from extreme flooding is poor. Thus one strand of our proposed research will analyse the changes in habitat and channels that were caused by the extreme floods in Cumbria in late 2009. Current river restoration methods are both spatially limited and expensive, but we aim to demonstrate that extreme floods can provide substantial changes in physical habitats and have the potential to deliver channel-scale restoration as demanded by regulators. Extreme floods are forecast to become more frequent under a range of climate and land use scenarios in the UK and elsewhere. But there is a lack of knowledge about the frequency, or return time, of extreme floods because monitored records of river flooding are often relatively short. A second strand of our research therefore takes the opportunity to find the signal of the recent extreme Cumbrian floods in the recent lake sediments accumulating at the bed of lake Bassenthwaite. If the recent flood signal can be clearly established, earlier 20th/21st century floods can be identified in lower sediments and confirmed by flood records. Deeper sediments can then be analysed to provide a regional record of flood frequencies and their sizes over several centuries. From these data, we can then say more about how common extreme floods are when viewed over centuries and whether the floods are becoming more or less common during the major periods of climate chnage and human activitiessince the early 20th century. Our project will collect field data from sites in and downstream of lake Bassenthwaite that were seriously affected by recent flooding in Cumbria. The research will impact directly on assessing appropriate post-flood management of floodplains and channel, and on the strategic assessment of the likelihood of future extreme flooding - both to the benefit of many stakeholders including local residents and farmers, the Environment Agency, DEFRA and a large international academic community.