River Resilience Requires Sufficient Floodplains: Experimental Insights from a Novel Flume Study Investigating Meander Constriction

Abstract

Globally, riparian zones are in poor condition. Numerous anthropogenic watershed modifications negatively affect water quality, resiliency, and habitat diversity of river systems. Research on the effects of constricting meandering rivers is limited. This has led to few methods that optimize riparian zone widths in ways that maintain adequate corridors or floodplains to support natural river processes and protect public safety. The goal of our research was to determine the effects of constraining the floodplain of a meandering river. Specifically, we studied the effects of constraining the Bow River in Calgary where the floodplain corridor is currently facing extensive development pressures. To achieve these goals a mobile bed laboratory experiment was completed. The experiment involved developing and then constricting a gravel bed meandering river from an initially straight channel. Alfalfa was grown alongside the river and within the floodplains to provide necessary bank strength. During the experiment, sediment leaving the flume was collected and aerial images were captured to allow topographic and sediment transport analysis. Results showed that as alfalfa grew, bank strength increased, limiting meander evolution. Despite the relatively fixed meanders, findings suggest that floodplain constraints significantly reduce river-floodplain connectivity, alter a channels flow regime by increasing velocity and flow depth, increase sediment transport, and narrow channel widths. The results of this study will impact river management practices, emphasize creating room for rivers as a nature-based solution, and improve laboratory methods for investigations of meandering rivers.