Woody debris effects on upland river hydromorphological processes

最近在约克郡和英国更广泛的洪水事件突出了高地河流管理在减少下游洪峰流量方面的潜在作用。河流中大木材（>1米长）的自然积累通常与自然生境的变化（深度、流速、有机物保留）有关，这可能有利于减缓下游的流量峰值时间和幅度。然而，这样的特征是罕见的，因为几个世纪以来，木材已经从许多河流中移走，以帮助航行和“改善”水流输送。英国水源河流的木材管理/再引入建议可从环境署获得，但这些建议主要基于低地河流研究。在何种程度上，这些是可转移到高地地方是不清楚的，通常陡峭的梯度，粗糙的底层和flaserous流动制度的高地河流。在高地河流中引入木结构和促进自然积累，可以通过改变河道形态来延迟下游地区的流量峰值，并且考虑到这些地区人口稀少和典型的低密度农业，局部洪水风险问题较小。低地地区。然而，到目前为止，在英国很少有研究的影响，木材放置在高地河流。如果河流管理者要制定更有效的恢复和管理计划，更全面地了解高地河流对木质残体的水文形态反应是至关重要的。要回答的中心问题是，重新引入木材到高地河流导致河流形态的显着变化，减少的幅度，并推迟了时间，进一步下游的高峰流量？学生将解决的问题，如：在哪里应该放置木材和/或允许在高地河流积累，以优化效益？以及，哪种类型的结构对高地河流过程的影响最大？特别是，我们试图更好地限制达到水文形态（即考虑流深度，宽度和粗糙度相对于木材直径/长度）恢复successful.The项目将主要结合观测和实验方法的影响。其中一个组成部分将是监测英格兰北方高地河流中现有的木质残体地点。学生将受益于访问河流覆盖，约克郡山谷，其中现有的水文（流量，温度）和地貌（水深，山谷形态）数据可用。在这里，自2014年以来，已经建立了使用固定木结构的BACI风格实验，并计划进行进一步的试验，以比较其他结构与自然积累。使用结构从运动测量，再加上对象检测软件采用通过水，新的见解木材几何形状，地貌响应，分布表面粒度将监测从补丁到河流尺度，而不干扰沉积物，并与水力特性，使用速度剖面和示踪技术。这项主要的研究将广泛地通过调查恢复从业者（如河流恢复中心，EA），包括CASE合作伙伴，记录使用木质残体，恢复设计和河流特性的经验，并组装一个最新的数据库，包括木材英国河流恢复项目。将新颖的地貌测量方法与已建立的水文监测技术和广泛的上下文元分析相结合，将首次为高地河流管理中使用木材的潜力提供新的重要见解。

Recent flood events in Yorkshire and in the UK more widely have highlighted the potential role of upland river management in reducing peak flood flows downstream. Natural accumulations of large wood (>1 m length) in rivers are often associated with physical habitat changes (depth, velocity, organic matter retention) which can have benefits for moderating flow peak timing and magnitude downstream. However, such features are rare because, for centuries, wood has been removed from many rivers to aid navigation and 'improve' flow conveyance. Recommendations for wood management/reintroduction in UK headwater rivers are available from the Environment Agency but these are based largely on lowland river studies. The extent to which these are transferrable to upland localities is unclear given the typically steeper gradients, coarser substrata and flashier flow regimes of upland rivers. Introducing wood structures and promoting natural accumulations in upland rivers could have benefits for delaying flow peaks to downstream areas via modification of channel morphology, and with localised flood risk less of an issue given sparse human populations and typically low intensity farming in these areas cf. lowland areas. However, there has so far been very little research in the UK on the effects of wood placement in upland rivers. A more complete understanding of upland river hydromorphological response to woody debris is vital if river managers are to develop more effective restoration and management schemes.This studentship will address the need to develop a quantitative evidence-base of wood-morphology-hydrology interactions in upland rivers. The central question to be answered is does reintroduction of wood into upland rivers lead to significant changes in river morphology that reduce the magnitude, and delay the timing, of peak flows further downstream? The student will address questions such as: where should wood be placed and/or allowed to accumulate in upland rivers to optimise benefits? and, which types of structures have the largest influence on upland river processes? In particular, we seek to constrain better the influence of reach hydromorphology (i.e. considering stream depth, width and roughness relative to wood diameter/length) on restoration success.The project will predominantly integrate observational and experimental approaches. One component will be monitoring of existing sites with woody debris in upland rivers of northern England. The student will benefit from access to the River Cover, Yorkshire Dales, where existing hydrological (discharge, temperature) and geomorphological (bathymetry, valley morphology) data are available. Here, BACI style experiments using fixed wood structures have been established since 2014, and further trials are planned to compare other structures vs. natural accumulations. Using Structure-from-Motion surveying, coupled with object-detection software employed through-water, novel insights into wood geometry, geomorphological response, and distributed surface grain size will be monitored from patch to river-scale without disturbing sediments, and related to hydraulic characteristics using velocity profiling and tracer techniques. This primary research will be contextualised widely via surveys of restoration practitioners (e.g. River Restoration Centre, EA) including CASE partners, to document experiences of using woody debris, restoration design and river characteristics, and assemble an up to date database of UK river restoration projects that include wood. Coupling novel geomorphological surveying approaches with established hydrological monitoring techniques and broad contextual meta-analysis will, for the first-time, provide new significant insights into the potential for using wood in upland river management.