Woody debris effects on upland river hydromorphological processes

木质碎屑对高地河流水貌过程的影响

• 批准号: 1793147
• 金额: --
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1793147
• 关键词: Woody; debris; effects; upland; river

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.

最近发生在约克郡和英国更广泛地区的洪水事件凸显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（bbb10 - 1m长度）的自然积累通常与自然栖息地的变化（深度、流速、有机质滞留）有关，这对调节下游的流量峰值时间和大小有好处。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。英国环境署提供了关于在英国源头河流中管理/重新引入木材的建议，但这些建议主要是基于低地河流的研究。考虑到高地河流通常坡度更陡、底质更粗糙、水流更湍急，这些可转移到高地地区的程度尚不清楚。在高地河流中引入木结构和促进自然蓄积可能有利于通过改变河道形态来推迟流向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强度农业，例如低地地区，局部洪水风险较小。然而，到目前为止，在英国很少有关于在高地河流中放置树木的影响的研究。如果河流管理者要制定更有效的恢复和管理方案，更全面地了解高地河流对木屑的水文形态反应是至关重要的。本研究将探讨开发山地河流中木材形态-水文相互作用的定量证据基础的需要。要回答的核心问题是，在高地河流中重新引入木材是否会导致河流形态的显著变化，从而降低下游河流峰值的幅度，并推迟其时间？学生将解决以下问题：木材应该放置在哪里和/或允许在高地河流中积累以优化效益？哪些类型的结构对高地河流过程的影响最大？特别是，我们试图更好地约束河段水文形态（即考虑溪流深度、宽度和相对于木材直径/长度的粗糙度）对恢复成功的影响。该项目将主要结合观察和实验方法。其中一个组成部分将是监测英格兰北部高地河流中现有的木屑遗址。学生将受益于访问河盖，约克郡山谷，那里现有的水文（流量，温度）和地貌（测深，山谷形态）的数据是可用的。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，并计划进一步的试验来比较其他结构与自然堆积。通过运动结构测量，再加上水中物体检测软件，将在不干扰沉积物的情况下，从斑块到河流尺度监测木材几何形状、地貌响应和分布表面粒度的新见解，并使用速度剖面和示踪技术与水力特性相关。这项初步研究将通过对包括CASE合作伙伴在内的修复从业者（例如河流修复中心，EA）的调查来广泛地背景化，以记录使用木质碎片、修复设计和河流特征的经验，并收集包括木材在内的英国河流修复项目的最新数据库。将新的地貌测量方法与已建立的水文监测技术和广泛的背景元分析相结合，将首次为在高地河流管理中使用木材的潜力提供新的重要见解。