When do boulders move in steep mountain streams?

该奖项是根据2009年《美国复苏和再投资法案》(Public Law 11-5)资助的。丘陵和山区的大多数河流都有狭窄陡峭的河道，河道通常被几乎不动的巨石覆盖。在这些河道中，巨石减缓了河流切割的速度，使水流变得粗糙，形成了当地成片的砾石，并为鲑鱼和钢头产卵等各种生物提供了重要的栖息地。粗沙也可能被河流洪水卷走，洪水冲下斜坡，造成相当大的破坏性后果。目前还没有理论或经验模型能够成功地预测巨石移动的门槛或河流过程对其组织的影响。这一研究项目通过理论、实验和实地相结合的方法解决了基础知识方面的这一根本差距。一个关于巨石流动性和阶梯水池形成的半经验理论将被开发出来，并使用加州理工学院新建造的最先进的实验室水槽进行测试。水槽实验将允许探索河道坡度(高达30%)和颗粒尺寸(高达10厘米)，这些在过去的研究中一直受到严格限制。将设计实验来调查巨石移动的条件和负责将巨石组织成台阶和水池的机制。这些实验的数据将被用来测试和验证巨石运输和阶跃水池形成的预测模型。实验和理论结果将与加州大学安吉洛海岸保护区南福克鳗鱼河支流中观察到的巨石运动事件中的水流状况进行比较。其结果将是一种计算陡峭山溪中巨石运移动力学的可靠方法，对预测地形演变、泥沙在陡峭河道中的移动速度、关键生境条件以及在修复项目中有益地利用巨石具有重要意义。这一研究项目的结果将对基础科学和一些与社会相关的实际问题产生重大影响。该项目的成果将有助于在需要评估巨石流动性的地方开展恢复和减灾工作，以恢复溪流栖息地(例如鲑鱼产卵)和功能，并减轻陡峭城市地区的洪水和泥石流危险。这项研究项目包括指导本科生，一名博士生，以及一名博士后研究员在实验，现场和理论科学。这项研究将被用来为地区高中教师设计一个为期一天的研讨会。目标将是让教师掌握必要的技能，教会他们的学生简单地评估洪水和泥石流的危险，这些危险可能会导致洛杉矶地区的生命和财产损失。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 11-5).Most of the rivers in hilly and mountainous landscapes have small, steep channels, which are typically mantled by boulders that rarely move. In these channels, boulders moderate the rate of river incision, roughen the flow creating local patches of gravel , and provide crucial habitat for a variety of organisms such as salmon and steelhead spawning. Coarse sediment can also become entrained by river floods, which rush down slope with considerable destructive consequences. No current theory or empirical model exists that successfully predicts the threshold of movement of boulders or their organization by river processes. This research project addresses this fundamental gap in basic knowledge through a combined theoretical, experimental and field-based approach. A semi-empirical theory for boulder mobility and step-pool formation will be developed and tested using a newly constructed state-of-the-art laboratory flume at the California Institute of Technology. The flume experiments will allow exploration of channel slopes (up to 30%) and grain sizes (up to 10 cm) that have been severely limited in past studies. Experiments will be designed to investigate the conditions under which boulders move and the mechanisms responsible for boulder organization into steps and pools. Data from these experiments will be used to test and validate predictive models for boulder transport and step-pool formation. The experimental and theoretical findings will be compared to observed flow conditions during boulder movement events in tributaries of the South Fork Eel River in the University of California Angelo Coast Range Reserve. The result will be a robust method for calculating boulder transport dynamics in steep mountain streams, with implications for predicting landscape evolution, the rate of movement of sediment through steep channels, critical habitat conditions, and the beneficial use of boulders in restoration projects. The results from this research project will have significant implications for basic science and a number of practical concerns of societal relevance. Results from this project will aid in restoration and hazard mitigation efforts where assessing boulder mobility is needed for restoring stream habitat (e.g., salmon spawning) and functionality, as well as mitigating flood and debris flow hazards in steep urban areas. This research project includes mentoring undergraduates, a PhD student, and a post-doctoral researcher in experimental, field and theoretical science. Research from this study will be uswd to design a 1-day workshop for area high-school teachers. The goal will be to give teachers the necessary skills to teach their students simple ways to assess flood and debris flow hazards that can result in loss of life and property in the Los Angeles area.