UBC Theses and Dissertations

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UBC Theses and Dissertations

The formation and adjustment of a pool-riffle sequence in a gravel bed flume Buckrell, Emma


Pool-riffle sequences are a dominant morphological feature found in a wide range of fluvial environments. The hydraulic and sedimentological complexity that they impart provides important aquatic habitat, resulting in their increasing implementation in river restoration projects, despite the fact that there are still many inconsistencies in the literature relating to the processes involved in their formation and maintenance. The main research objective was to study the formation, adjustment, and maintenance of pool-riffle morphology in gravel bed rivers. A variable width, mobile-bed flume was configured as a model of a pool-riffle reach in East Creek, British Columbia, and the development of a pool-riffle sequence under bankfull discharge, and subsequent adjustment to increased discharges were studied. The central pool-riffle sequence developed around a major width constriction and persisted in that location throughout the entirety of the experiment, increasing in amplitude in response to increased discharge. Bed texture was initially quite variable, but became relatively constant throughout the entire flume near equilibrium, including the pool and riffle. Hydraulic parameter reversals from low to high flow were observed between the pool and riffle, including water surface slope, section averaged velocity, and bed shear stress. Particle mobility was higher in the pool, but the virtual velocities of mobile particles were constant until the highest discharge. Evidence of secondary flow patterns was recorded in the pool, which could suggest a maintenance process in addition to velocity reversal. These results should inform future studies and design projects on pools and riffles, especially in relation to their behaviour during flood events.

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