Rate of Growth and Other Features of the Temporal Development of Pool-Bar Complexes in Meandering Streams

Abstract

Despite substantial research on various aspects of bed deformation in meandering streams, no systematic effort has yet been made to establish the timescales of the process. Additionally, in past experiments, as a rule, the bed was not monitored throughout the development, which has left undocumented essential features of the growth of meandering pool-bar complexes. In this paper, an effort is made to penetrate some of these aspects. More specifically, the five laboratory runs presented by the writers in their 2009 paper in this journal are revisited with the following two objectives: (1) to reveal the rate of growth of the resulting meandering pool-bar complexes; and (2) to document the extent, if any, of upstream or downstream migration of developing pool-bar complexes in examples of sufficiently wide streams in which the bed deformation is primarily because of the convective behavior of flow. The runs were conducted in a 70° sine-generated channel having rigid banks. In each run, the bed was allowed to deform from an initially flat bed to the equilibrium state, the deformation monitored throughout the runs. It was found that the bed development was very rapid at the early stages of the runs, with approximately 70% and 90% of the development accomplished when only one-quarter and one-half, respectively, of the total bed development time had been reached. An equation describing the growth rate of the pool–bar complexes is proposed. The plan location of these complexes remained invariant throughout each run. However, the location of maximum erosion within the pools noticeably shifted upstream during the development.