Collaborative Research: A mechanistic understanding of hydrograph shape influence on temporal variations in bedload transport, grain size distributions, and armor persistence

合作研究：从机械角度理解水文形状对河床输送、粒度分布和装甲持久性随时间变化的影响

• 批准号: 1251785
• 负责人: Elowyn Yager
• 金额: $ 22.11万
• 依托单位: Regents of the University of Idaho
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1251785&HistoricalAwards=false
• 关键词: Collaborative; Research; mechanistic; understanding; hydrograph

Natural and managed rivers throughout the world display a wide range of hydrographs, from flashy and abrupt to more gradual changes in flow. Hydrograph shape (quantified by peak magnitude and rate of discharge change) significantly influences the volume, timing, and quality of water available for anthropogenic use and aquatic ecosystems. Uncertainties remain as to how unsteady flows that characterize hydrographs impact bedload fluxes and hysteresis, grain size distributions, and the persistence of armor layers. The lack of a mechanistic and predictive understanding of hydrograph influences may also partially explain why bedload transport equations in gravel-bed rivers are often inaccurate. The research team proposes complimentary flume, field, and numerical modeling experiments to quantify the impact of hydrographs on sediment movement. Specifically, they hypothesize that hydrograph shape influences the following: (1) bed load transport rates, hysteresis, and mobile grain sizes for a given shear stress, and (2) bed grain size distributions and the persistence/degree of bed armoring. In flume experiments, temporal variability in bedload fluxes, grain size distributions, and armor persistence will be measured for a range of hydrograph shapes. Field experiments will further investigate the influence of hydrograph shape on bedload transport rates, bed grain size changes, and armor persistence, mobility and removal. The combined flume and field measurements will be used to test and validate numerical and analytical models for bedload transport. Hydrographs represent how water quantities in rivers vary over time and can be characterized by the timing, magnitude and rates of change of flow. Human modifications of these hydrograph characteristics have positively influenced economic development but negatively impacted aquatic species and channel morphology. This is important because 77% of total water discharge from large northern hemisphere rivers is moderately to severely impacted by dams and diversions. Water resource managers commonly seek to assess and mitigate these impacts through river restoration efforts, hydropower re-regulation, and in some cases dam removal. For example, gravel augmentation is commonly used to mitigate for low sediment supplies and improve fish habitat below dams but this often has mixed results because of a lack of a predictive understanding of sediment transport caused by variable flows. Managers could use the results of this research to determine flow hydrograph shapes that potentially mitigate for flow regulation influence on threatened or endangered aquatic organisms. Further, this research will result in a predictive and mechanistic understanding of the interactions between flow hydrographs, sediment transport, and temporal variations in the size of sediment on the channel bed. Such knowledge is necessary to properly design river infrastructure and restoration projects, and predict long-term channel incision rates and landscape changes. Additionally, the proposed project will contribute towards unique STEM educational opportunities for graduate and undergraduate students. Support for a Women Outdoors with Science Camp will be used to encourage young females to enter science, engineering and math fields.

全世界的自然和托管河流都展现出广泛的水文图，从浮华，突然到流动的逐渐变化。 水文形状（通过峰值幅度和放电速率量化）显着影响可用于人为使用和水生生态系统的水的体积，时机和质量。 关于水文图表的不稳定流动如何影响床负载通量和磁滞，晶粒尺寸分布以及装甲层的持久性，不确定性仍然存在。缺乏对水文影响的机械性和预测性理解也可以部分解释为什么碎石河中的床负载方程通常不准确。研究团队提出了免费的水槽，田间和数值建模实验，以量化水文图对沉积物运动的影响。 具体而言，他们假设水文形状会影响以下内容：（1）给定的剪切应力的床负荷运输速率，磁滞和移动纹理尺寸，以及（2）床晶粒尺寸分布以及持久/床装甲的持久性/程度。 在Flume实验中，将在一系列水文形状中测量床负载通量，晶粒尺寸分布和装甲持久性的时间变化。 现场实验将进一步研究水文形状对床载传输速率，床晶尺寸变化以及装甲持久性，活动性和去除的影响。 合并后的水槽和现场测量将用于测试和验证用于床负荷运输的数值和分析模型。水文图表示河流中的水量随时间变化，并且可以以流量变化的时间，幅度和变化速率来表征。 这些水文特征的人类修饰对经济发展产生了积极影响，但对水生物物种和通道形态产生了负面影响。这很重要，因为从北半球大河中的总水排出的77％受到大坝和转移的严重影响。 水资源经理通常寻求通过河流恢复工作，水力发电的重新调节以及在某些情况下消除大坝来评估和减轻这些影响。 例如，砾石增大通常用于减轻低沉积物供应并改善水坝以下的鱼类栖息地，但由于缺乏对可变流量引起的沉积物传输的预测性理解，这通常会产生不同的结果。 经理可以使用这项研究的结果来确定流量水文形状，从而有可能减轻对受威胁或濒危水上生物的影响的流量调节。 此外，这项研究将导致对流水文，沉积物传输以及通道床上沉积物大小的时间变化之间相互作用的预测和机械理解。这样的知识对于正确设计河流基础设施和恢复项目是必要的，并预测了长期的渠道切口率和景观变化。 此外，拟议的项目将为研究生和本科生提供独特的STEM教育机会。在科学训练营中对户外妇女的支持将用于鼓励年轻的女性进入科学，工程和数学领域。