Field Investigation on Point Bar Dynamics and Planform Evolution in Meandering Rivers

Abstract

Point bars are prominent features in meandering rivers, yet our understanding of the complex interactions among channel morphology, three-dimensional flow structure, and depositional processes associated with modern and active point bars remains incomplete. Thus, the goal of this research is to characterize the morphology, three-dimensional flow structure, and depositional packages associated with point bars along a series of bends with different curvature and channel planform through detailed field measurements and relate to previous literature and current conceptual models. Chapter 3 investigates the morphology of point bars by comparing estimates of channel curvature to channel and point bar characteristics including width, migration rate, longitudinal and transverse slope, and a shape factor. Results show the Pearl River reach has abundant and a systematic distribution of bilinear transverse bar profiles relative to the Wabash River. Additionally, field data are compared to synthetic data generated from a centerline bed evolution model, where the two datasets are in general agreement, yet the model is incapable of capturing local variations in bar morphology that arise as a result of changes in channel width and curvature. Chapter 4 analyzes patterns of three-dimensional flow structure within each series of bends along the Pearl and Wabash rivers using ADCP cross-sections. Analysis of cross-sections indicate differences in flow structure associated with linear versus bilinear profiles. Furthermore, areas of flow associated with bilinear profiles occur on the Wabash River only. Chapter 5 investigates the internal structure of modern point bars relying on interpreted sedimentary facies mapped along select GPR lines on three point bars along the Wabash River and two along the Pearl River. An elevation profile of the 2011 point bar extent was extracted and overlain onto the GPR to determine how sediments have been reworked since 2011. Expansion of the channel is associated with lateral accretion packages, whereas translation is associated with more laterally continuous, near-horizontal packages. Furthermore, the 2011 profile did not align with reflectors in accretion packages associated with expansion, but did align more often with accretion packages associated with translation.