The hydrological function of organo-mineral soils in downstream flood risk

该项目将设法了解旱地有机矿物土壤中的水文过程及其管理和植被复盖如何影响河流流量高峰。这一新颖的场地、实验室和模型项目将扩大我们对具有很高保护价值的旱地土壤的功能和水文学的认识。该项目将直接为自然英格兰提供急需的旱地土壤管理方面的管理决策证据，以减少洪峰。有机矿物土壤覆盖了英国约20%的地区，在高地地区尤其常见，主要类型是停滞腐殖质潜育土和酸性棕壤。与泥炭地不同，有机矿物土壤的功能和水文学在全球范围内知之甚少，文献中存在很大空白。这些土壤通常位于具有很高保护价值的地区的高地、石南地和草原之下。目前尚不清楚这些土壤在不同的地形和降雨事件中是以贯流(及其典型的渗透范围)、渗透-过量地表径流还是饱和-过剩地表径流为主。目前还不清楚有机矿物质土壤的管理如何影响它们在径流产生中的作用。迫切需要证据证明基于自然的洪水管理解决方案，特别是在英国高地-英国主要河流的源头地区。美国利兹大学最近对泥炭地进行的模拟工作表明，通过改变集水区关键空间可识别部分的地表覆盖条件来控制地表水流速度，可以在减少洪峰方面发挥重要作用(对于某些降雨事件，最高可减少20%)。然而，我们没有来自有机矿物土壤的数据，有机矿物土壤的作用可能与泥炭完全不同，因此从业者对旱地管理决策的基础有限，这可能使下游面临洪水风险的人受益。研究设计：上述问题将通过提供PHD技能好处的综合监测、实验和建模方法来解决，包括：1)通过监测通过和在停滞腐殖质潜育层和酸性棕壤(利用地形指数控制坡位)、水分含量和地下水位深度来测量和确定主要的水文路径(例如，地表径流和地下径流)；2)渗透性测试，以测量水力传导性(加州大学利兹分校有一种新的渗透仪系统，允许同时测试25个土壤样本，允许高吞吐量)；3)通过向地块供水并测量不同坡度、水流深度和植被条件下的流速，进行试验性的陆上水流速度测量。上述三种方法将在坎布里亚的山坡地区使用，以测试与土壤条件和地表覆盖有关的水文功能的差异。该设计将包括自然英格兰评估为处于不同退化状态的土壤，包括高质量的大西洋荒漠(密集的矮灌木和苔藓下)、较差的大西洋荒漠、良好的酸性草原和重度放牧的酸性草原。上述三个野外和实验室步骤将使学生能够：4)修改由利兹大学最近开发的新的空间分布版本的TopModel；5)使用该模型测试不同的空间有机-矿物土地覆盖场景，以测试减少下游流量峰值的最佳解决方案。

This project will seek to understand hydrological processes operating in upland organo-mineral soils and how their management and vegetation cover influences river flow peaks. This novel field, lab and modelling project will expand our knowledge on the function and hydrology of upland soils which are of high conservation value. The project will directly provide Natural England with urgently needed management decision-making evidence on upland soil management for flood peak reduction. Organo-mineral soils cover around 20 % of the UK, and are particularly common in upland areas with the main types being stagnohumic gleys and acid brown earths. Unlike peatlands, the function and hydrology of organo-mineral soils is globally very poorly understood with major gaps in the literature. These soils typically underlie upland heathland and grasslands in areas with high conservation value. It is unclear whether these soils are dominated by throughflow (and what their typical permeability range is), infiltration-excess overland flow or saturation-excess overland flow in different topographic contexts and rainfall events. It is also unclear how management of organo-mineral soils impacts their role in runoff generation.There is an urgent need for evidence on 'nature-based' flood management solutions, particularly in UK uplands - source areas for the UK's major rivers. Recent modelling work on peatlands by U. Leeds has shown that controlling overland flow velocities by changing the surface cover conditions in key spatially identifiable parts of the catchment can play an important role in reducing flood peaks (by up to 20 % for some rainfall events). However, we do not have data from organo-mineral soils, which are likely to function quite differently to peat, to inform such modelling and so practitioners have limited basis for upland management decisions which may benefit those downstream at risk of flooding.Study design: The above issues will be tackled through a combined monitoring, experimental and modelling approach providing PhD skills benefits involving: 1) Measure and determine the dominant hydrological pathways (e.g. overland flow, subsurface flow) through monitoring of flow volumes / rates though and over stagnohumic gleys and acid brown earths (controlling for slope position using the topographic index), moisture content & water-table depths; 2) permeability tests to measure the hydraulic conductivity (U. Leeds have a novel permeameter system allowing 25 soil samples to be tested simultaneously, allowing high throughput); 3) experimental overland flow velocity measurements by supplying water to plots and measuring the velocities for different slope angles, flow depths and vegetation conditions. The above three approaches will be used on areas of hillslope in Cumbria to test for differences in hydrological function related to soil condition and surface cover. The design will incorporate soils that have been assessed by Natural England to be in different states of degradation including high quality Atlantic Heath (dense dwarf shrubs with an understory of mosses), poor Atlantic heath, good acid grassland and acid grassland that has heavy grazing.The three field and laboratory steps above will then enable the student to: 4) modify a new spatially-distributed version of TOPMODEL recently developed by U. Leeds; 5) use the model to test different spatial organo-mineral land-cover scenarios to test optimal solutions to reduce downstream flow peaks.