Testing the Existence of a Threshold Discharge in Bedrock Channels

0507098 Wohl许多为冲积河流开发的标准概念模型不能充分描述基岩河道，因为基岩河道具有更大的侵蚀阻力门槛和对驱动力变化的较长反应时间。提高对基岩河流的认识是重要的，因为：基岩上形成的部分排水网络对流域演变施加了不成比例的巨大控制，有效地建造、改造和拆除大坝需要了解基岩渠道形态和过程。拟议的研究将系统地调查基岩底质、渠道几何形状、粗泥沙运动和基岩渠道段水流水力学之间的关系，以测试不同基岩和几何形状的基岩渠道段之间是否存在一致的河道变化阈值流量。无论数据是否支持阈值流量的存在，研究结果都将为基岩河道动力学的关键问题提供洞察力。田纳西州的奥科伊河和西弗吉尼亚州的高利河将进行实地工作，每条河段都包括一个基岩峡谷，其岩石类型和河道几何形状都有下游变化。每个峡谷段的流量都受到上游大坝的严密控制，这样流量就会减少到最小，然后按常规计划在更高的流量下释放。这将使我们能够在枯水期间详细描述河道几何形状和底质，重复测量各种流量下的水力变量，并将水力变量与底质和粗泥沙运动和沉积联系起来。现场测量将包括：河道几何形状和粗泥沙分布；节理几何形状、岩石强度、岩性和相对耐磨性方面的底质；以及不同流量下的水力变量(水面地形、平均流速、水流分离程度)。

0507098 Wohl Many of the standard conceptual models developed for alluvial rivers do not adequately describe bedrock channels, which have a greater threshold of erosional resistance and longer response time to a change in driving forces. Improved understanding of bedrock rivers is important because: portions of the drainage network formed on bedrock exert a disproportionately large control on drainage basin evolution, and effective construction, modification, and removal of dams requires knowledge of bedrock channel form and process.The proposed research will systematically investigate relations among bedrock substrate, channel geometry, movement of coarse sediment, and flow hydraulics along bedrock channel segments in order to test the existence of a consistent threshold discharge for substantial channel change among bedrock channel segments of differing substrate and geometry. Results from the research will provide insight into key questions of bedrock channel dynamics regardless of whether the data support the existence of a threshold discharge.Field work will be conducted along the Ocoee River of Tennessee and the Gauley River of West Virginia, each of which includes a bedrock canyon with downstream variations in rock type and channel geometry. Flow along each canyon segment is closely controlled by a dam upstream so that flow is reduced to a minimum and then released at higher discharges on a regular schedule. This will allow us to characterize channel geometry and substrate in detail during low flows, repeatedly measure hydraulic variables under various discharges, and relate hydraulic variables to substrate and to coarse sediment movement and deposition. Field measurements will include: channel geometry and coarse-sediment distribution; substrate in terms of joint geometry, rock-mass strength, lithology, and relative resistance to abrasion; and hydraulic variables (water-surface topography, mean velocity, degree of flow separation) at varying discharges.