Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Dr. Andrew D. Binns

Abstract

Changes in riverine discharge, such as those due to reservoir flushing, seasonal variation or extreme precipitation events, can alter sediment transport rates and morphology of the stream bed. Experimental research investigated the effect of unsteady flow event hydrographs on stream bed morphological response. Laboratory experiments were conducted in a 5.0 m-long sediment transport flume with a bed comprised of a medium sand. Experimental hydrographs were composed of antecedent (base-flow), unsteady event (flood) and post- flood (return to base-flow) stages. Three distinct series of experimental laboratory runs were conducted to systematically investigate the effect of three characteristics of unsteady flow event hydrographs: the magnitude, duration and hydrograph shape (i.e., time-to-peak flow) of the unsteady flow event. Bed morphological adjustments, sediment transport rates and the composition of the sediment in transport were measured throughout all stages of the experimental runs. Measured values were compared to predicted values calculated using traditional sediment transport and bed form geometry equations assuming steady flow conditions. In general, predicted values greatly underestimated both measured values of sediment transport and bed form geometry. Results show that systematic changes in the magnitude, duration and time-to-peak flow of the hydrograph cause varying types of hysteresis (clockwise or counter-clockwise) of the sediment transport rates which has a considerable effect on subsequent bed morphological adjustments. Shorter duration and symmetrical hydrographs exhibit counter-clockwise hysteresis while longer duration and asymmetrical hydrographs exhibit clockwise hysteresis. Results from this thesis contribute towards more accurate numerical modelling capabilities, and improved river management, engineering and restoration efforts.

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