Influence of Waves and Other Fluid Oscillations on the Stability of Grand Canyon Sand Bars

沿河道形成沙坝和其他类型的沉积地貌是多种因素的作用，特别是河流携带的沉积物的数量和性质以及河流水量和流速。在沉积动力学分析中经常忽略的一个因素是水流的波动。流经亚利桑那州大峡谷的科罗拉多河为分析由河流流量变化引起的沉积动力学变化提供了独特的环境。在20世纪60年代早期建造峡谷上的格伦峡谷大坝之前，科罗拉多的流量往往遵循年循环，春季大洪水之后是长时间的最小流量。然而，大坝现在拦截了所有上游的沉积物，而通常用于发电和防洪的定期排放，现在每天产生潮汐般的水脉冲。较低水平但更频繁的波动对峡谷底部沙洲的数量和大小产生了不利影响。该项目将考察大峡谷沙洲在当前排水制度下的稳定性，特别关注主要急流下方波浪的侵蚀作用。本项目使用的研究方法将包括一些通常用于海岸研究但很少用于研究河流系统的方法和测量技术。测量水压、水流速度和方向的灵敏仪器将收集数据，以测试将沉积物侵蚀和增加与波浪参数联系起来的海滩平衡模型。美国国家科学基金会的资金将补充美国地质调查局对该项目的支持。该项目将为大峡谷沙洲发展的动态提供有价值的数据和新的见解，这是一个具有重要实际意义的话题，因为沙洲作为野生动物栖息地和科罗拉多漂流者的娱乐场所至关重要。该项目收集的数据和改进的模型也将具有广泛的科学意义。他们将扩大对不同水流状态下河道沉积特征的复杂动力学的理解，并将首次详细研究反冲波对主要河流中沙洲的影响。

The formation of sand bars and other types of depositional landforms along stream channels is a function of many factors, especially the amount and nature of sediments carried by the stream and the volume and velocity of stream water. A factor often overlooked in the analysis of depositional dynamics is the fluctuation of water flows. The Colorado River flowing through the Grand Canyon of Arizona offers a unique setting for the analysis of changes in depositional dynamics resulting from changing fluctuations in stream flows. Prior to construction of the Glen Canyon Dam above the canyon in the early 1960s, the Colorado's flow tended to follow annual cycles, with large floods in spring followed by long periods of minimal flow. The dam now intercepts all upstream sediments, however, and discharges usually made on a regular basis for power generation and flood control now produce tidal-like daily pulses of water. The lower-level but more frequent fluctuations have had an adverse impact on the number and size of sand bars along the canyon floor. This project will examine the stability of sand bars in the Grand Canyon under the current water discharge regime, focusing special attention on the erosive effects of waves below major rapids. Research methods used in this project will include a number of approaches and measurement techniques commonly employed in coastal studies but rarely used to study fluvial systems. Sensitive instruments that measure water pressures and current speeds and directions will gather data to test beach equilibrium models that relate sediment erosion and accretion to wave parameters. NSF funding will complement support for this project provided by the U.S. Geological Survey. This project will provide valuable data and new insights into the dynamics of sand bar development in the Grand Canyon, a topic of great practical importance because of the critical role of sand bars as wildlife habitat and as recreational sites for people on float trips down the Colorado. The data collected in this project and the refined models will have broad scientific significance, too. They will expand understandings of the complex dynamics of depositional features in stream channels under different flow regimes and will provide the first detailed examination of backwash wave impacts on sand bars in major streams.