Doctoral Dissertation Research: Influence of Riparian Vegetation on Near-Bank Flow Structure and Erosion Rates on a Large Alluvial River

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

The process of bank erosion in meandering alluvial rivers occurs through the dynamic interactions between channel contours, the three dimensional structure of water flow, sediment transport, and the geotechnical characteristics of the channel banks and floodplains. Rates of bank erosion are also influenced by the type of vegetation growing on the banks - a factor that is still poorly understood and therefore commonly neglected in models of river shape evolution. The goal of this doctoral dissertation research project is to examine the influence of bank vegetation on the migration of meanders in large alluvial rivers by characterizing the geotechnical properties of channel banks as well as the near-bank water flow structure for forested and non-forested bends. Channel banks and floodplains will be characterized by obtaining data on the bulk grain size distribution, cohesion, root-tensile strength, and hydraulic conductivity for forested and non-forested river bends. Time-averaged and instantaneous velocity measurements will be taken at various water flow stages in forested and non-forested meander bends to characterize the water flow structure near the river bends and how this interacts with the channel banks under differing conditions. In addition, repeat detailed bathymetric and morphologic surveys of the channel bed and banks will be obtained using state-of-the-art technologies. Analysis will focus on interactions among flow structure, vegetation, and the geotechnical properties of floodplain sediments to evaluate differences in bank erosion in forested and non-forested bends. The results of this research will provide basic insight into the dynamics of how the shapes of channels in large meandering rivers evolve and the influence of vegetation in this process. The research will produce data that can be used to calibrate, test, and evaluate numerical models of river shape dynamics, allowing for more accurate simulations of channel change in meandering rivers. Prediction of channel change is important because meandering rivers often form political boundaries between states and countries, are used as traffic ways for goods, and provide a vast range of habitats for aquatic organisms. As a meandering river migrates across its floodplain, it can result in loss of land, damage to human infrastructure, and introduction of large amounts of sediment into the river system. Thus, an improved understanding of bank-erosion processes in meandering rivers is not only important scientifically, but has important implications for environmental and societal concerns.