Investigating the effects of sediment supply, width variation, and unsteady flow on riffle-pool dynamics

研究沉积物供应、宽度变化和不稳定流对浅滩动力学的影响

• 批准号: 1425067
• 负责人: Peter Nelson
• 金额: $ 27.9万
• 依托单位: Colorado State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1425067&HistoricalAwards=false
• 关键词: Investigating; effects; sediment; supply; width

Many gravel-bedded rivers feature quasi-regular alternations of deep and shallow zones known as riffle-pool sequences, which, in straight sections of the river, are often influenced by variations in channel width. These zones provide an important diversity of habitats, and the reestablishment of riffle-pool sequences can be a desired outcome of river restoration projects. How pool-riffle sequences persist is a century-old question in geomorphology that is still not fully resolved, and there is currently a lack of field-based, theoretical, or experimental studies that explore the relationship between unsteady flow, sediment supply, sorting, and riffle-pool morphology. This study aims to fill this gap through numerical modeling, flume experiments, and field observations. The project will train a graduate student, engage several undergraduate students in supervised independent research projects, and incorporate activities into undergraduate and graduate classes in river mechanics and sediment transport. Improvements made to the computer model will be incorporated into freely-available software package so that findings from this study can be applied to other settings for a wide range of scientific questions.A two-dimensional morphodynamic model will be used to explore how river channel width variations, hydrograph shapes, and changes in sediment supply influence equilibrium patterns of topography and bed-surface sorting. Model results will guide mobile-bed, mixed-grain-size experiments conducted in a variable-width flume. Experimental runs under constant discharge and repeat hydrographs will provide insight on the effects of unsteady flow on riffle-pool dynamics, and experimental runs with decreased and increased sediment supply will investigate how riffles and pools might be affected by dam installation or dam removal. The laboratory-scale simulations and experiments will be complemented with data collected from a riffle-pool sequence on the Elwha River, Washington, USA, where an ongoing dam removal project has created a natural experiment in which the river is subject to a greatly increased sediment supply.

许多砾石层状河流的特点是深水区和浅水区的准规则交替，即所谓的小河-池序列，在河流的直线段，这种序列经常受到河道宽度变化的影响。这些区域提供了重要的生境多样性，并且重建小池序列可能是河流恢复工程的理想结果。池-沟序列如何持续存在是地貌学中一个百年的问题，至今仍未完全解决，目前缺乏基于现场、理论或实验的研究来探索非定常流、沉积物供应、分选和池-沟形态之间的关系。本研究旨在通过数值模拟、水槽实验和实地观测来填补这一空白。该项目将培养一名研究生，让几名本科生参与监督下的独立研究项目，并将活动纳入河流力学和泥沙运输的本科生和研究生课程。对计算机模型所做的改进将被纳入免费提供的软件包中，以便本研究的结果可以应用于其他设置，以解决广泛的科学问题。一个二维形态动力学模型将用于探索河道宽度变化、水道形状和泥沙供应的变化如何影响地形和床面分选的平衡模式。模型结果将指导在变宽水槽中进行的移动床、混合粒度实验。在恒定流量和重复水文条件下进行的实验将深入了解非定常流对水塘动力学的影响，而在泥沙供应减少和增加的情况下进行的实验将研究大坝安装或拆除对水塘和水塘的影响。实验室规模的模拟和实验将辅以从美国华盛顿州埃尔瓦河上的一个小水塘序列收集的数据，在那里，一个正在进行的水坝拆除项目创造了一个自然实验，在这个实验中，河流受到沉积物供应大大增加的影响。