Characterizing the physical drivers of vegetation-forced bar evolution in gravel-bed streams

河岸植被斑块迅速占领砾石河床中暴露的沙洲，在洪水事件中影响附近的水流水力学和随后的侵蚀沉积过程。这种植被对沙砾坝的侵蚀和沉积很重要，因为它改变了河床沉积物的大小和组成，影响了水生和河岸栖息地的质量，驱动了地下水力学和相关水质的变化，并影响了水流输送和社区洪水风险。该项目旨在了解水力学和输沙能力如何通过植被斑块发生变化，以解释观测到的河床沉积物的空间格局和最终形成的砾石坝形状。预计变化幅度取决于一个斑块内的植被密度。研究结果可以帮助水务部门决定在河流恢复活动中需要什么样的植被种植密度，以达到预期的进化结果。此外，研究结果有望帮助洪水管理者根据现有植被密度预测沙砾坝的尺寸，并确定为了公共安全，是否需要对植被进行减薄或移除。预测植被坝的演变是困难的，因为当地的水力学和泥沙运动（泥沙运动的起始）在空间上通过植被斑块是可变的。目前，还没有单一的参数可以预测开阔和植被河道中的粗沙流动。在这里，将结合实地调查和植被模拟的大规模水槽实验来开发一种适用于植被和非植被条件下的粗泥沙流动的机械驱动程序。在计划的实验中，将改变植被密度，以确定一个密度阈值，该密度阈值启动砾石河床的粒度变化、空间分选和坝演化。进一步，将建立植被密度与平衡坝尺寸之间的预测关系。该项目由地貌学和土地利用动力学（GLD）和促进竞争研究的既定计划（EPSCoR）共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Riparian vegetation patches rapidly colonize exposed bars in gravel-bed rivers, impacting the nearby flow hydraulics and subsequent erosional-depositional processes during flood events. This vegetation-forced erosion and deposition on gravel bars is important as it alters the size and composition of the bed sediments that affects aquatic and riparian habitat quality, drives changes in subsurface hydraulics and associated water quality, as well as impacts flow conveyance and community flood risk. This project seeks to understand how the hydraulics and sediment transport capacity change through vegetation patches to explain the spatial patterns of observed bed sediments and resultant shape of gravel bars. The magnitude of changes is expected to depend on the vegetation density within a patch. Results can help guide water agencies in deciding what vegetation planting densities are necessary during river restoration activities to achieve the desired evolutionary outcomes. Additionally, results are expected to help flood managers predict gravel bar dimensions from existing vegetation densities and determine if vegetation thinning or removal is necessary for public safety.Predicting vegetated bar evolution is difficult because the local hydraulics and sediment mobility (initiation of sediment motion) are spatially variable through a vegetation patch. Currently, no single parameter is available to predict coarse-sediment mobility in both open and vegetated channels. Here, a combination of fieldwork and large-scale flume experiments with vegetation simulants will be used to develop a mechanistic driver of coarse-sediment mobility that is applicable in both vegetated and unvegetated conditions. In the planned experiments, vegetation density will be varied to identify a density threshold that initiates grain-size changes, spatial sorting, and bar evolution in gravel-bed rivers. Further, a predictive relation between vegetation density and equilibrium bar dimensions will be developed.This project is jointly funded by Geomorphology and Land-use Dynamics (GLD) and by the Established Program to Stimulate Competitive Research (EPSCoR).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.