An investigation of bed armoring process and its implications for channel bed stability

砾石河床中沉积物粒度分布和河道水流水力学对铠甲层形成的影响和相互作用尚未完全确定。叠瓦和微团簇作为装甲层的一部分发展，并有助于装甲床的整体稳定性增加。最近的研究集中在如何湍流场的影响，他们的存在，这还没有完全阐明。这项研究将连接的过程中的床装甲，微簇的形成，和床的稳定性，并提供必要的量化管理流量释放，使下游渠道表面不侵蚀和潜在的损害下游ecosystems.Flume实验将创建装甲床测试4泥沙混合物对4流速。微簇密度和床的地形将从床表面的激光轮廓扫描测量。声学多普勒测速仪（ADV）将记录点速度（u，v，w）和波动（u？，v？，w？）装甲表面和周围的微团，从湍流描述符，如湍流动能（TKE）的计算。将使用双平均纳维尔-斯托克斯（DANS）方法和象限分析来分析流量数据，该方法与详细的河床地形一起将提供对发生的动量传递和装甲床特定位置流场中存在的相干流结构的深入了解。使用ADV测量，将有可能区分由于微团簇、地形表面、粘性应力或来自多个团簇的相互作用的应力的边界应力。在所提出的研究的结论，在装甲层形成过程中的河床基质粒度分布和流速的影响将被量化，并链接到装甲层地形和河床的稳定性的结构的创建。将获得对装甲层形成和床层稳定性的控制变量的理解。这项研究将提供一种方法来预测流量，这将打破下游装甲床层作为一个功能的基板在通道和现有的床微观形貌，这两者都可以在现场测量。

The influence and interaction of sediment grain size distributions and channel flow hydraulics over the formation of armor layers in gravel bed rivers has yet to be fully defined. Imbrications and microclusters develop as part of the armor layer and contribute to the overall increased stability of armored beds. Recent research on microclusters has focused on how the turbulent flow field is affected by their presence, which has not been fully elucidated. This research will connect the processes of bed armoring, microcluster formation, and bed stability and provide the quantification necessary to manage flow releases so that the downstream channel surface does not erode and potentially harm the downstream ecosystem.Flume experiments will create armored beds testing 4 sediment mixtures against 4 flow rates. Microcluster density and bed topography will be measured from laser profile scans of the bed surface. Acoustic Doppler Velocimeters (ADVs) will record point velocities (u,v,w) and fluctuations (u?,v?,w?) over the armored surface and around microclusters, from which turbulence descriptors, such as Turbulent Kinetic Energy (TKE), are calculated. Flow data will be analyzed using the Double Averaged Navier-Stokes (DANS) approach and quadrant analysis, which together with the detailed bed topography will provide insight into the momentum transfers occurring and the coherent flow structures present in the flow field at specific locations over the armored bed. Using ADV measurements, it will be possible to differentiate the boundary stresses as due to microcluster, topographic surface, viscous stress, or stress from the interaction of multiple clusters. At the conclusion of the proposed research, the effect of bed substrate grain size distributions and flow rate during armor layer formation will be quantified and linked to the creation of structure in the armor layer topography and the stability of the channel bed. An understanding of the controlling variables over armor layer formation and bed stability will be gained. This research will provide a means of predicting the flow rate that will break the downstream armored bed layer as a function of the substrate in the channel and the existing bed microtopography, both of which can be measured in the field.