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

河道沙洲和其他类型的沉积地貌的形成是许多因素的作用，特别是河流携带的泥沙的数量和性质以及溪水的流量和速度。在沉积动力学分析中，一个经常被忽视的因素是水流的波动。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年代初在峡谷上方修建格伦峡谷大坝之前，科罗拉多州的流量往往遵循年度循环，春季出现大洪水，随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，通常为了发电和防洪而定期排放的水现在会产生潮汐般的每日水流。较低的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。该项目将研究大峡谷沙洲在当前泄水制度下的稳定性，重点关注主要急流下方波浪的侵蚀效应。本项目使用的研究方法将包括一些方法和测量技术，这些方法和测量技术通常用于沿海研究，但很少用于研究河流系统。测量水压、水流速度和方向的灵敏仪器将收集数据，以测试海滩平衡模型，该模型将泥沙侵蚀和吸积与波浪参数相关联。NSF的资金将补充美国地质调查局为该项目提供的支持。该项目将为大峡谷沙洲开发的动态提供有价值的数据和新的见解，这一主题具有重要的现实意义，因为沙洲作为野生动物栖息地和人们沿科罗拉多州漂流旅行的娱乐场所的关键作用。在这个项目中收集的数据和改进的模型也将具有广泛的科学意义。它们将扩大对不同流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.