Influence of Sediment Cohesion on Lateral Mobility of Deltaic Distributary Channels

Abstract

The speed at which rivers sweep across their floodplains has important socioeconomic consequences, both for predicting future land surface change and for understanding the shape and extent of sand bodies, which ultimately may evolve to serve as groundwater or hydrocarbon reservoirs. Lateral migration rates of rivers are largely controlled by sediment supply, with higher sediment load corresponding to higher rates of lateral migration. Lateral migration rates of distributary channels are therefore expected to slow down with net deposition or speed up if downstream sediment transport increases. This thesis explores that hypothesis and provides an in-depth analysis of spatial and temporal trends of distributary channel lateral migration rates under two different sediment mixtures. This research started with the design and development of the QDB-22 experimental delta, which is the first physical delta experiment conducted at Queen's University. The delta development and evolution were conducted over 80 runtime hours, which mostly matched the progradation stage of a deltaic system as the delta achieved equilibrium. To better understand lateral migration rates of rivers, this study centered on the analysis of a delta dataset that was archived on the SEAD repository of the TBD-13-1 delta experiment. The TBD-13-1 dataset was used in this research and focused on recent approaches for tracking channel bank movement using particle image velocimetry, which offered the opportunity to explore various fundamental questions surrounding river morphodynamics. The main highlights of this research are that lateral migration rates over the delta surface are radially spread over the delta surface, which may correspond to meandering-anastomosing systems. Also, sediment cohesion and channel migration rates are closely linked, with weakly and moderately cohesion displaying a progressive decrease in channel mobility. This result matches previous studies that assert that increased cohesion has a direct influence on creating very low channel mobility rates but also gives a unique approach because it isolates lateral channel mobility from channel avulsion processes. Results from this work are expected to be broadly applicable to field studies in both ancient and modern systems such as the Mississippi and Amazon rivers.