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

世界各地的天然和受管理的河流显示了广泛的水文图，从华而不实和陡峭的流量到更渐进的流量变化。过程线形状(通过流量峰值和流量变化率来量化)对可供人类利用和水生生态系统使用的水量、时间和质量有重要影响。表征过程线的非恒定流如何影响推移质通量和滞后、颗粒尺寸分布和装甲层的持久性仍然存在不确定性。缺乏对过程线影响的机械性和预测性理解，也可能部分解释了为什么砾石河床河流的推移质输运方程往往不准确。研究小组建议进行免费的水槽、现场和数值模拟实验，以量化水文对泥沙运动的影响。具体地说，他们假设过程线形状影响如下：(1)推移质输移率、滞后和给定切应力下的流动颗粒尺寸；(2)床沙颗粒分布和床面护甲的持久性/程度。在水槽试验中，将测量一系列过程线形状的推移质通量、颗粒尺寸分布和装甲持久性的时间变异性。现场试验将进一步研究过程线形状对推移质输沙率、床面粒度变化以及装甲持久度、移动性和移动性的影响。综合水槽和现场测量将被用来测试和验证推移质输运的数值和分析模型。水位图表示河流中的水量如何随时间变化，并可通过流量的时间、大小和变化率来表征。人类对这些水文特征的修改对经济发展产生了积极影响，但对水生物种和航道形态产生了负面影响。这一点很重要，因为北半球大型河流总排水量的77%受到大坝和改道的中度到严重影响。水资源管理者通常寻求通过河流恢复工作、重新调节水电，以及在某些情况下拆除大坝，来评估和减轻这些影响。例如，砾石加固通常用于缓解泥沙供应不足和改善堤坝下鱼类栖息地的问题，但由于缺乏对不同水流引起的泥沙输移的预测性了解，这一方法的结果往往好坏参半。管理者可以利用这项研究的结果来确定水流过程线形状，这些形状可能会减轻水流调节对受威胁或濒危水生生物的影响。此外，这项研究将导致对水流过程、泥沙输移和河床泥沙大小随时间变化之间的相互作用有一个预测性和机械性的理解。这些知识对于正确设计河流基础设施和修复项目，以及预测长期河道切割率和景观变化是必要的。此外，该项目将为研究生和本科生提供独特的教育机会，支持女性户外科学夏令营将鼓励年轻女性进入STEM领域。

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 project will contribute towards unique educational opportunities for graduate and undergraduate students and support for a Women Outdoors with Science Camp will encourage young females to enter STEM fields.