Low angle dune response to variable flow, dune translation, and crestline dynamics in Fraser Estuary, British Columbia, Canada

Dune geometry and crestline dynamics in river environments are functions of the interaction between fluid flow and the channel bed, however, little is known about how they respond to variable flow conditions in tidal environments. This study examines the evolution of a dune field in Fraser Estuary, Canada using data collected during the largest tidal flux of the neap-spring cycle on the rising limb of the annual hydrograph. Chapter One examines changes in mean geometric properties. Height and lee slope angle respond directly to changes in flow, and are linked to suspended sediment concentration flux. Height and length also show a net increase, likely responding to larger scale changes in the annual hydrograph. Chapter Two addresses crestline dynamics in response to variable flow, examining planimetric morphology, translation rates, and changes in bifurcations. Mean translation increases toward low tide with increasing mean velocity, and decreases toward high tide. Highly bifurcated areas translate farther before low tide, while areas of lower bifurcation move farther after low tide. Bifurcation ‘deaths’ outweigh ‘births’ toward low tide, indicating a shift toward a more two-dimensional planimetric morphology, while births dominate post low tide, suggesting the bed is reorganizing toward a more three-dimensional morphology.