Land Use Management Effects in Extreme Floods

在英国（例如，Defra, 2005）和国际上，越来越多的人认识到，土地和水的管理是高度相互依存的，需要综合管理方法。洪水有一些特殊的问题，有证据表明农业用地管理会增加当地的洪水风险，但没有证据表明下游影响在更大范围内的量化。如果像当地证据显示的那样存在这样的影响，那么显然有可能利用土地管理来减轻洪水风险。因此，本研究要解决的基本科学问题是：土地利用管理的影响如何从局部尺度（~ 1公顷及以下）传播到中尺度流域（~ 100平方公里），并影响极端洪水？如果能找到答案，就有可能对未来土地利用管理变化对极端洪水的影响做出有用的预测。这样的预测将有广泛的用途，包括准备集水区洪水管理计划。像这样的研究需要高质量的长期数据集，但可用的数据集相对较少。建模对于最好地利用现有数据以及概括和探索对土地利用管理变化与洪水之间的联系所涉及的过程的理解至关重要。不幸的是，我们目前的降雨/径流模型根本不足以完成这项任务，因为它们不能充分代表与土地利用管理对径流产生的影响相关的潜在复杂性，或者这些影响在下游的传播。在理解和操纵土地利用管理与洪水之间的联系方面的活动水平和兴趣非常高，最近的缓解工程和对实地研究的投资使调查人员能够获得新的独特和重要的数据集：位于塞文河上游集水区Pontbren的FRMRC实地站点；Eden流域CHASM多尺度监测；以及目前正在里布尔流域进行的SCAMP大规模土地使用管理变革。在建模方面也有新的相关发展，包括帝国理工学院开发的局部尺度径流生成模型和纽卡斯尔大学开发的网络路由模型和信息跟踪方法。这些数据和建模将结合在一起，以解决上述基本科学问题，在实际背景下，预测给定的土地利用管理缓解和适应战略在减少塞文、伊甸和里布尔流域在一系列特定的极端洪水复发期的洪水风险方面可能产生的影响。该项目将提高对极端洪水中土地利用管理影响的科学理解，并为参与决策的人员提供所需的结果，例如顾问和政策制定者，他们正在寻找Defra“为水创造空间”咨询中提出的一些一般性问题的答案。结果将包括地图，显示任何管理干预措施的应用领域，以实现有效的下游水文衰减，针对当前和可能的未来气候。该项目还对下一代全流域连续模拟模型做出了重大贡献，这将有助于提高其预测土地利用管理变化对极端洪水影响的能力和可靠性。英国环境局和英国环境与环境事务部已经同意在里布尔上游资助一个平行的实验研究项目，为植树造林和阻塞沼地的影响提供必要的数据。

It is increasingly recognised in the UK (eg Making Space for Water, Defra, 2005), and internationally, that the management of land and water is strongly interdependent, and that integrated management approaches are needed. There are particular issues for floods, where there is evidence that agricultural land management can increase local flood risk, but no evidence-based quantification of downstream impacts at larger scales. If such effects exist, as the local evidence suggests, clearly there is potential for use of land management to mitigate flood risk. The basic scientific question to be addressed in this research is therefore: how do the effects of land use management propagate from the local scale (~ 1 ha, and below) to that of mesoscale catchments (~ 100 km2) and affect extreme floods? If an answer can be found, it will be possible to make useful predictions for the effects of future land use management changes on extreme floods. Such predictions would have wide use, including in preparing catchment flood management plans. Research like this demands high-quality long-term data sets, but there are relatively few data sets available. Modelling is essential to make the best use of the available data and to encapsulate and explore the understanding of the processes involved in the link between changes in land use management and flooding. Unfortunately, our current rainfall/runoff models are simply inadequate for this task, because they cannot adequately represent the underlying complexity associated with the effects of land use management on runoff generation, or the propagation of these effects downstream. The level of activity and interest in understanding and manipulating the link between land use management and flooding is very high, and recent mitigation works and investments in field research have resulted in new unique and important data sets being available to the Investigators: the FRMRC field sites at Pontbren in the upper Severn catchment; the CHASM multi-scale monitoring for the Eden catchment; and the SCAMP large-scale land use management changes currently underway in the Ribble catchment. There are also new relevant developments in modelling, including local-scale runoff generation modelling developed at Imperial College and network routing modelling and information tracking methods developed at Newcastle University. This data and modelling will be brought together to tackle the basic scientific question above, within the practical context of predicting the likely effects that given land use management mitigation and adaptation strategies would have in reducing flood risk in the Severn, Eden, and Ribble catchments, for a range of specified extreme flood return periods. This project will provide improved scientific understanding of the effects of land use management in extreme floods, and also provide results of the type required by those involved in decision-making, such as consultants and policy makers looking for answers to some of the general questions raised in Defra's Making Space for Water consultation. The results will include maps showing the application areas for any management interventions achieving effective downstream hydrograph attenuation, for the present and possible future climates. The project also represents a major contribution to the next generation of whole-catchment continuous simulation modelling, which will help improve its capability and reliability for predicting the effect of land use management change on extreme flooding. The EA/Defra have agreed to fund a parallel programme of experimental research in the upper Ribble, to provide the necessary data for the effects of afforestation and blocking of moorland grips.