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（公法11-5）资助的。丘陵和山区的大多数河流都有小而陡峭的河道，这些河道通常被很少移动的巨石覆盖。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，形成了局部的砾石斑块，并为鲑鱼和钢头鱼等各种生物的产卵提供了重要的栖息地。粗质泥沙也可能被河流洪水夹带，冲下斜坡，造成相当大的破坏后果。目前还没有理论或经验模型能够成功地预测河流过程中巨石运动的阈值或它们的组织。本研究项目通过理论、实验和实地研究相结合的方法来解决这一基础知识的基本差距。在加州理工学院新建的最先进的实验室水槽中，将开发和测试一种关于巨石流动性和阶梯池形成的半经验理论。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受到严重限制。实验将被设计来调查在何种条件下，巨石移动和机制负责巨石组织成台阶和池。这些实验的数据将用于测试和验证巨石移动和阶梯池形成的预测模型。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流动条件进行比较。研究结果将提供一种计算陡峭山间溪流中巨石移动动力学的可靠方法，对预测景观演变、沉积物通过陡峭河道的移动速度、临界生境条件以及在恢复项目中对巨石的有益利用具有重要意义。这项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恢复和减灾工作，在这些工作中，需要评估巨石的流动性，以恢复河流栖息地（如鲑鱼产卵）和功能，以及减轻陡峭城市地区的洪水和泥石流危害。本研究项目包括指导本科生、博士生1名、博士后1名，涉及实验科学、实地科学和理论科学。本研究的研究结果将用于为地区高中教师设计为期一天的工作坊。其目标是为教师提供必要的技能，教学生简单的方法来评估可能导致洛杉矶地区生命和财产损失的洪水和泥石流危险。

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.