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

该项目将试图了解在高地有机-矿物土壤中运作的水文过程，以及它们的管理和植被覆盖如何影响河流流量峰值。这个新颖的领域、实验室和模型项目将扩展我们对具有高保护价值的高地土壤功能和水文的认识。该项目将直接为自然英格兰提供急需的陆地土壤管理的管理决策证据，以减少洪峰。有机矿质土壤覆盖了英国约20%的土地，在高地地区尤为常见，主要类型为停滞腐殖质土壤和酸性棕土。与泥炭地不同，有机矿质土壤的功能和水文在全球范围内的了解非常少，文献中存在重大空白。这些土壤通常在具有高保护价值的地区的高地石楠地和草地下面。目前还不清楚这些土壤在不同的地形背景和降雨事件中是由通流（以及它们的典型渗透性范围是什么）、渗透-过量地表流还是饱和-过量地表流主导。目前还不清楚有机矿质土壤的管理如何影响它们在产流中的作用。迫切需要“基于自然”的洪水管理解决方案的证据，特别是在英国高地——英国主要河流的源头地区。利兹大学最近对泥炭地进行的建模工作表明，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陆地上的水流速度，可以在减少洪峰方面发挥重要作用（在某些降雨事件中可减少20%）。然而，我们没有有机矿物土壤的数据，这些土壤的功能可能与泥炭完全不同，因此，从业者在高地管理决策方面的基础有限，而这些决策可能有利于面临洪水风险的下游地区。研究设计：上述问题将通过监测、实验和建模相结合的方法来解决，为博士技能提供以下好处：1)通过监测通过和通过停滞腐殖沟和酸性棕土的流量/速率（使用地形指数控制斜坡位置）、水分含量和地下水位深度来测量和确定主要的水文途径（例如地上流、地下流）；2)渗透性测试，以测量水力导电性（U.利兹有一个新颖的渗透性测量系统，允许同时测试25个土壤样品，允许高通量）；3)通过对样地供水，测量不同坡角、不同流深、不同植被条件下的坡面流速实验测量。以上三种方法将在坎布里亚郡的山坡地区使用，以测试与土壤条件和地表覆盖有关的水文功能差异。该设计将结合由自然英格兰评估的不同退化状态的土壤，包括高质量的大西洋荒原（浓密的矮灌木和苔藓的下层），差的大西洋荒原，良好的酸性草地和有大量放牧的酸性草地。上述三个实地和实验室步骤将使学生能够：4)修改最近由U. Leeds开发的新的空间分布版本的TOPMODEL；5)利用该模型对不同空间有机-矿物土地覆盖情景进行测试，找出降低下游流量峰值的最优方案。

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.