Testing the Existence of a Threshold Discharge in Bedrock Channels

0507098 Wohl许多标准的概念模型开发的冲积河流没有充分描述基岩渠道，有一个更大的门槛的侵蚀阻力和更长的响应时间的变化驱动力。提高对基岩河流的认识很重要，因为：形成于基岩上的部分排水网络对流域的演变具有不成比例的大的控制作用，有效地建造、修改和拆除大坝需要了解基岩河道的形态和过程。拟议的研究将系统地调查基岩基底、河道几何形状、粗泥沙运动、以及沿着基岩河道段的水流水力学，以测试不同基底和几何形状的基岩河道段之间的实质性河道变化是否存在一致的临界流量。研究结果将提供洞察基岩河道动力学的关键问题，无论数据是否支持存在一个阈值discharge.Field work将进行沿着田纳西州的Ocoee河和西弗吉尼亚州的Gauley河，其中每个都包括一个基岩峡谷与下游的岩石类型和渠道几何形状的变化。沿着每个峡谷段的流量由上游的大坝严格控制，使流量降至最低，然后定期以较高的流量释放。这将使我们能够在低流量期间详细描述通道几何形状和基底，反复测量各种流量下的水力变量，并将水力变量与基底和粗泥沙运动和沉积联系起来。实地测量将包括：河道几何形状和粗泥沙分布;在节理几何形状、岩体强度、岩性和相对耐磨性方面的基底;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.