COMPACT: The role of soil management in mitigating catchment flood risk

洪水风险在英国是一个日益严峻的挑战，有240万处房产容易受到河流洪水的影响。这种类型的洪水是由于河流排放的径流量超过了河道的容量而造成的。这导致水被转移到洪泛区，可能产生严重的经济和社会影响。从景观流入河流的径流量和速度是产生洪水的主要因素。因此，管理景观的方式可能对这一进程产生重大影响。据推测，在过去50年左右的时间里，通过增加牧场牲畜数量和使用更大、更重的机械进行耕作，农业集约化对洪水的严重程度和频率产生了影响。这些土地管理做法造成土壤压实，从而降低了降雨渗透率和地下可储存的水量。这导致更多的降雨被分配到更快的地表径流路径进入河流，并可能导致下游洪水。然而，土壤压实的水平在空间和时间上是高度不均匀的。这是因为不同的动物，如牛、羊和马，对土壤施加不同的负荷，并保持不同的密度。此外，已知农场动物表现出这样的行为，即田地的某些部分比其他部分更频繁地移动。在可耕地的耕作方法中也是如此，即犁耕形成更紧凑的车辙或轮。从免耕到常规耕作等不同形式的管理做法在一年中的不同时间对土壤产生不同的压力。然而，对于不同管理措施下土壤压实程度的变化，人们知之甚少，本研究旨在利用新型探地雷达（Ground Penetrating Radar，GPR）技术量化压实程度和压实深度的变化，并评估其对土壤物理性质的影响。水如何与土壤相互作用，以及这种影响对流域洪水风险的重要性。这将通过使用多种方法结合实地实验、土壤样本实验室测试和数值水文模型来实现。首先，将使用探地雷达识别高压实度和低压实度区域，并使用传统的基于现场的方法进行验证。这些将通过关于动物和机械移动位置的全球定位系统空间数据与负载相关。然后将进行广泛的现场和实验室测试，以量化体积密度、孔隙度、饱和导水率和粒度等特性。此外，X射线CT扫描将揭示压实对土壤结构的细尺度影响。这些数据将形成一个基于物理的，降低复杂性，空间分布的水文模型，CRUM 3的输入。可行"如果？"方案将与项目合作伙伴共同制作，包括环境署、特伦特河流信托基金、可持续土地信托基金、自然英格兰和全国农民联盟通过Soar集水合作伙伴关系。这将使当地土地管理和土壤特性的变化升级到流域规模的洪水。这项研究将与一组流域管理者、土地所有者和当地居民一起进行。这将有利于研究范围和研究结果的影响。为行业、监管机构、政府机构、慈善机构和当地土地所有者和居民提供的建议和宣传将为基于证据的自然洪水管理政策提供信息。这将通过指导小组会议，英国水文学会全国会议，项目Away日，项目河边野餐结束以及使用社交媒体来实现。传播也将通过更传统的学术途径进行。

Flood risk is an increasing challenge in the UK, with 2.4 million properties being susceptible to fluvial flooding. This type of flooding is caused by the quantity of runoff being discharged by a river exceeding the capacity of the river channel. This results in water being transferred to the floodplain, which can have severe economic and social impacts. The quantity and speed of runoff from the landscape into rivers is a major factor in generating flooding. The way in which the landscape is managed therefore can have a significant impact on this process. The intensification of agriculture, through increasing the number of animals in pasture, and the use of larger, heavier machinery for arable farming, over the past 50 years or so is hypothesised to have had an impact on the severity and frequency of flooding. These land management practices cause soil compaction, which reduces the rate of rainfall infiltration and the volume of water that can be stored within the sub-surface. This results in more rainfall being partitioned into the faster surface runoff pathway into rivers and potentially causing flooding downstream.However, the level of soil compaction is highly heterogeneous over space and time. This is because different animals i.e. cattle, sheep and horses, exert different loads on the soil and are kept at different densities. Furthermore, farm animals are known to exhibit behaviour whereby certain parts of the field are moved over more frequently than others. The same is the case in arable farming practices, whereby ploughing forms tramlines or wheelings, which are more compacted. Different forms of management practice ranging from zero-tillage to conventional cultivation exert different pressures on the soil at different times of year. However, very little is known about this variability of soil compaction levels at the sub-field level and land under different management practices.This research aims to quantify this sub-field variation in compaction severity and depths through using novel Ground Penetrating Radar (GPR) technology, and assess the impact on the physical soil properties, how water interacts with the soil and ultimately how important this effect is on catchment scale flood risk. This will be achieved through using a multi-methods approach combining field experiments, laboratory tests on soil samples and numerical hydrological modelling. First areas of high and low compaction will be identified using GPR and validated using traditional field based approaches. These will be related to loadings through GPS spatial data on where animals and machinery have moved over. A wide range of field and laboratory tests will then be carried out to quantify properties such as bulk density, porosity, saturated hydraulic conductivity, and particle size. Furthermore, X-Ray CT scanning will reveal the fine scale impacts of compaction on soil structure. This data will form the input to a physically based, reduced complexity, spatially distributed hydrological model, CRUM3. Feasible "what if?" scenarios will be co-produced with the project partners, including the Environment Agency, Trent Rivers Trust, Sustainable Land Trust, Natural England, and National Farmers Union through the Soar Catchment Partnership. This will upscale local changes in land management and soil characteristics to catchment scale flooding.This research will be undertaken with a group of catchment managers, land owners and local residents. This will both benefit the research scope and impacts of the findings. Recommendations and dissemination for industry, regulators, governmental bodies, charities and local land owners and residents will inform evidence based policy on Natural Flood Management. This will be achieved through steering group meetings, a British Hydrological Society national meeting, Project Away day, end of project riverside picnic, and the use of social media. Dissemination will also occur through more traditional academic routes.