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

过量的细小沉积物(直径2毫米，如淤泥和沙子)损害了美国超过40,000英里的溪流，降低了许多水生物种的栖息地质量，每年造成数百亿美元的损失。当细小的泥沙沉积在河床上时，它可以堆积在较粗的河床颗粒(直径2毫米，如砾石)之间的空隙中。这个过程降低了河床栖息地的质量。到目前为止，评估河床中细颗粒泥沙数量的唯一方法是通过直接的现场测量。根据洪水条件是河床细泥沙数量的主要控制因素这一初步发现，本项目重新设想了细泥沙评价。此外，该项目还试图从广泛可用的河流数据中预测整个河网的细沙堆积，这将为研究河网分支结构对河床栖息地质量的影响开辟新的途径。最终，这将导致我们对水生生态系统和盆地尺度地貌的理解和管理发生变化。项目活动还将有助于其他几个更广泛的影响：1)增加妇女和代表不足的少数民族对科学、技术、工程和数学(STEM)的参与，2)改善STEM教育，3)提高公众的科学素养和公众对STEM的参与，4)发展一支多样化的、具有全球竞争力的STEM劳动力队伍。推动这项工作的首要研究问题是：水流条件如何控制河床中存在的细颗粒泥沙的数量？初步研究结果表明，水流条件对河床中细粒泥沙的数量具有一级控制作用，与泥沙供应无关。要测试的主要假设是，这种结果背后的物理过程与沿河床移动的沙量有关，而不是当砾石河床完全停止动员且任何靠近河床的沙子锁定在砾石基质中时，沙子在流动的水中悬浮得更高。这项工作将证明这一初步发现在美国广泛适用，并阐明这些预测背后的潜在过程。这将通过以下目标来实现：1)通过分析美国环保局的数据集，证明细颗粒泥沙淤积可以从整个广泛的地形范围内的水流条件进行预测，2)通过现场测量测量细颗粒泥沙淤积的时间变异性，以及3)通过实验室实验量化不同泥沙粒度和供应情景下水流条件与细颗粒泥沙积累之间的基本过程。更广泛的影响将包括创建和评估实践学习体验，在弗吉尼亚理工科学节上吸引公众参与，并在Hokie期间吸引来自第一标题学校的五年级学生参加一天的活动，同时讨论河床栖息地并培养来自不同背景的科学家的意识。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.