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

世界各地的自然和管理河流显示出各种各样的水文过程，从流量的突然变化到逐渐变化。 水文线的形状（由峰值大小和流量变化率量化）显著影响可供人类使用和水生生态系统的水量、时间和水质。 不确定性仍然是如何不稳定流的特征水文影响推移质通量和滞后，粒度分布，和持久性的装甲层。缺乏对过程线影响的机械和预测性理解也可以部分解释为什么砾石河床中的推移质输运方程往往是不准确的。研究小组提出了免费的水槽，现场和数值模拟实验，以量化水文对泥沙运动的影响。 具体而言，他们假设过程线形状影响以下内容：（1）给定剪切应力下的推移质输沙率、滞后和移动的粒径，以及（2）河床粒径分布和河床粗化的持续性/程度。 在水槽实验中，推移质通量，粒度分布和装甲持久性的时间变化将测量一系列的水文曲线形状。 野外试验将进一步研究过程线形状对推移质输沙率、河床粒度变化、以及装甲持久性、流动性和清除的影响。 结合水槽和现场测量将用于测试和验证推移质输运的数值和分析模型。水文线表示河流中的水量如何随时间变化，可以通过流量的时间、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，但对水生物种和通道形态产生了负面影响。这一点很重要，因为北方大型河流总排水量的77%受到水坝和改道的中度至严重影响。 水资源管理人员通常通过河流恢复工作、水电再调节以及在某些情况下拆除大坝来评估和减轻这些影响。 例如，砾石增加通常用于减少沉积物供应量和改善大坝下的鱼类栖息地，但由于缺乏对可变流量引起的沉积物迁移的预测性理解，这往往会产生好坏参半的结果。 管理人员可以利用这项研究的结果，以确定流量过程线的形状，可能减轻流量调节对受威胁或濒危水生生物的影响。 此外，这项研究将导致一个预测性和机械的理解之间的相互作用的流量过程，泥沙输运，并在河道河床上的沉积物的大小的时间变化。这些知识对于正确设计河流基础设施和恢复项目，以及预测长期的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，并支持妇女户外科学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.