CAREER: A mechanistic understanding of sediment transport in mountain streams with applications in river restoration and science education

在山地流域，陡坡河道（坡度为3-20%）占河道总长度的大部分，影响下游向城市地区和水电设施输送泥沙和水。这些河流提供的泥沙的体积和粒度也影响下游河流修复工程的成功。在恢复设计中，需要对流域尺度的输沙量进行预测，以解释输沙量对水生生境、水质和河道稳定性的影响。大多数泥沙输运方程是基于河段尺度测量数据的经验拟合，不包括颗粒运动的力学，并且是为低梯度河道开发的。假设陡流、粗流的河床输运方程需要包括：1)控制泥沙运动起始的湍流和颗粒性质的范围，2)斑块上应力和河床输运速率的空间变异性，以及3)泥沙供应时空变化的影响。水槽实验将用于验证这一假设，进一步阐明湍流和河床输运之间的相互作用，并为河段尺度上预测泥沙通量的理论和经验模型提供信息。这些模型将在当地和国际实地地点进行测试，并将通过提供陡峭溪流中沉积物通量的准确和机械估计，改变景观演变和河流恢复设计的预测。这项研究的智力价值在于对陡流中控制湍流和沉积物输运的过程有了基本的和预测性的理解。泥沙运输和河流恢复的框架将用于教育研究生，本科生和K-12学生关于水资源和功能河流生态系统的重要性。提出了四个教育目标：1)一系列培养批判性思维、科学写作和跨学科团队技能的研究生课程；2)为本科生和研究生提供国际研究经验；3)向K-12学生传授河流过程的课程；4)一个新的“科学女性营”，鼓励年轻女性进入数学、科学和工程领域。

In mountainous drainage basins, steep channels (gradients of 3-20%) occupy the majority of the total channel length and influence the downstream delivery of sediment and water to metropolitan areas and hydropower facilities. The volume and grain sizes of sediment supplied from these streams also impact the success of downstream river restoration projects. Basin-scale sediment transport predictions are needed in restoration design to account for the effect of sediment supply on aquatic habitat, water quality, and channel stability. Most sediment transport equations are based on empirical fits to data measured at the reach-scale, do not include the mechanics of grain motion, and were developed for lower-gradient channels. It is hypothesized that bedload transport equations for steep, rough streams need to include: 1) the range of turbulence and grain properties that control the initiation of grain motion, 2) the spatial variability in stresses and bedload transport rates on patches, and 3) the effect of temporal and spatial variations in sediment supply. Flume experiments will be used to test this hypothesis, further elucidate the interaction between turbulence and bedload transport, and inform theoretical and empirical models that predict sediment flux at the reach scale. Such models will be tested in local and international field locations and will transform predictions of landscape evolution and river restoration design by providing accurate and mechanistic estimates of sediment flux in steep streams. The intellectual merit of this research is a fundamental and predictive understanding of the processes that control turbulence and sediment transport in steep streams. The framework of sediment transport and river restoration will be used to educate graduate, undergraduate, and K-12 students on the importance of water resources and functioning stream ecosystems. Four education objectives are proposed: 1) a series of graduate student classes that develop critical thinking, scientific writing, and interdisciplinary team skills, 2) international research experience for undergraduate and graduate students, 3) programs to educate K-12 students on river processes, and 4) a new Women in Science Camp that encourages young women to enter careers in math, science, and engineering.