Understanding the physical processes controlling the amount of fine sediment and gravel embeddedness in streambeds

过量的细沉积物（直径2毫米，如淤泥和沙子）损害了美国超过40,000英里的河流，许多水生物种的栖息地质量下降，每年造成数百亿美元的损失。当细泥沙沉积在河床上时，它可以积聚在河床粗颗粒（直径2毫米，如砾石）之间的孔隙中。这一过程降低了河床生境质量。到目前为止，评估河床中细泥沙量的唯一方法是通过直接实地测量。本项目根据初步发现洪水条件是河床中细泥沙量的主要控制因素，重新设想细泥沙评估。此外，该项目旨在使人们有可能预测细泥沙积累整个河流网络从广泛可用的流数据，这将开辟新的途径的研究河流网络的分支结构对河床生境质量的影响。最终，这将导致我们对水生生态系统和流域尺度地貌学的理解和管理发生转变。项目活动还将有助于产生其他几个更广泛的影响：1）增加妇女和代表性不足的少数群体在科学、技术、工程和数学（STEM）领域的参与; 2）改善STEM教育; 3）提高公众科学素养和公众对STEM的参与; 4）发展多元化、具有全球竞争力的STEM劳动力。水流条件如何控制河床中细泥沙的数量？初步结果表明，流的流动条件，填补了它的银行的顶部施加一阶控制上的量的细泥沙在河床独立的泥沙供应。待检验的主要假设是，该结果背后的物理过程与当砾石河床停止充分流动且任何近床砂被锁定在砾石基质中时，沿河床沿着移动的砂量与悬浮在流动水中较高位置的砂量有关。这项工作将证明，这一初步发现广泛适用于整个美国，并阐明这些预测背后的基本过程。这将通过以下目标实现：1）通过分析美国环保署的数据集，证明细颗粒沉积物积累是可预测的，从整个广泛的自然地理范围内的流动条件，2）测量细颗粒沉积物积累的时间变化，从现场测量，和3）量化不同沉积物粒度和供应情景下水流条件与细颗粒沉积物积累之间的基本过程通过实验室实验。更广泛的影响将涉及创造和评估一个动手学习的经验，参与公众在弗吉尼亚理工大学科学节和参与五年级学生从标题一学校在霍基一天的活动，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准。

Excess fine sediment (2mm in diameter, such as silt and sand) impairs over 40,000 miles of streams in the U.S., degrading habitat quality for many aquatic species and costing tens of billions of dollars annually. When fine sediment deposits on a streambed, it can accumulate within pore spaces between coarser streambed particles (2mm in diameter, such as gravel). This process degrades streambed habitat quality. To date, the only way to assess the amount of fine sediment in streambeds is through direct field measurements. This project re-envisions fine sediment assessment based on the preliminary finding that flood flow conditions are the primary control on the amount of fine sediment in streambeds. Furthermore, this project seeks to make it possible to predict fine sediment accumulation across entire stream networks from widely available stream data, which will open up new avenues of research on the influence of river network branching structure on streambed habitat quality. Ultimately, this will lead to a transformation in our understanding and management of aquatic ecosystems and basin-scale geomorphology. Project activities will also contribute to several additional broader impacts: 1) increasing participation of women and underrepresented minorities in science, technology, engineering, and mathematics (STEM), 2) improving STEM education, 3) increasing public scientific literacy and public engagement with STEM, and 4) developing a diverse, globally competitive STEM workforce.The overarching research question driving this work is: How do flow conditions control the amount of fine sediment present in the streambed? Preliminary results show that the flow conditions that fill a stream to the top of its banks exert a first-order control on the amount of fine sediment in streambeds independent of sediment supply. The main hypothesis to be tested is that the physical process underlying this outcome is related to the amount of sand traveling along the streambed versus suspended higher up in the flowing water when full mobilization of the gravel streambed ceases and any near-bed sand becomes locked into the gravel substrate. This work will demonstrate that this preliminary finding applies broadly across the U.S. and elucidate the underlying processes behind these predictions. This will be accomplished through the following aims: 1) Demonstrate that fine sediment accumulation is predictable from flow conditions throughout a wide physiographic extent by analyzing a U.S. EPA dataset, 2) Measure the temporal variability in fine sediment accumulation from field measurements, and 3) Quantify the fundamental processes relating flow conditions to fine sediment accumulation under different sediment grain size and supply scenarios through laboratory experiments. Broader impacts will involve the creation and evaluation of a hands-on learning experience engaging the public at the Virginia Tech Science Festival and engaging fifth graders from Title I schools during the Hokie for a Day activity, while discussing streambed habitats and developing awareness of scientists from diverse backgrounds.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.