Land Use Management Effects in Extreme Floods

在英国(如《为水创造空间》，Defra，2005)和国际上，越来越多的人认识到，土地和水的管理是相互依存的，需要综合管理方法。洪灾有一些特别的问题，有证据表明农业土地管理会增加当地的洪灾风险，但没有对更大规模的下游影响进行循证量化。如果存在这样的影响，正如当地证据所表明的那样，显然有可能利用土地管理来减轻洪水风险。因此，这项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地方尺度(~1公顷及以下)传播到中尺度集水区(~100平方公里)，并影响极端洪水？如果能够找到答案，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。这种预测将有广泛的用途，包括在制定集水区洪水管理计划方面。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。要最大限度地利用现有数据，并概括和探讨土地利用管理的变化与洪灾之间的联系所涉及的过程，建模是必不可少的。不幸的是，我们目前的降雨/径流模型根本不能满足这项任务，因为它们不能充分反映土地利用管理对径流产生的影响或这些影响向下游传播的潜在复杂性。了解和操纵土地利用管理与洪灾之间的联系的活动程度和兴趣非常高，最近的缓解工作和对实地研究的投资使调查人员可以获得新的独特和重要的数据集：位于塞文河上游彭特布赖恩的FRMRC实地站点；对伊甸园流域的多尺度监测；以及目前在Ribble流域正在进行的SCAMP大规模土地利用管理变化。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规模径流生成模型和纽卡斯尔大学开发的网络路线建模和信息跟踪方法。这些数据和模型将结合在一起，在预测特定极端洪水重现期的一系列土地利用管理缓解和适应战略在降低塞文河、伊甸河和里伯河流域洪水风险方面可能产生的影响的实际背景下，解决上述基本科学问题。该项目将提高对极端洪水中土地使用管理的影响的科学认识，并提供参与决策的人员所要求的结果，例如顾问和政策制定者寻求对Defra在为水创造空间咨询中提出的一些一般性问题的答案。结果将包括针对当前和可能的未来气候，显示实现有效的下游过程线衰减的任何管理干预措施的应用领域的地图。该项目也是对下一代全流域连续模拟模型的重大贡献，这将有助于提高其预测土地利用管理变化对极端洪水的影响的能力和可靠性。EA/Defra已同意资助上Ribble的一个平行实验研究计划，为植树造林和封堵沼地围栏的效果提供必要的数据。

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.