Unsteady flow in natural compound channel: Experiment and simulation

Phragmites Australis, or common reed, is an invasive plant species that has spread along channels of the Platte River (Nebraska, USA), adversely altering the biogeomorphology of the system. Of particular interest have been the impacts on riparian habitat, specifically the reduction of suitable areas for crane roosting and shorebird nesting. A program for managing and removing these and other invasive plant species has been in place to mitigate these effects. Spraying and mechanical removal of phragmites has been the established practice, but there is interest in evaluating other potential forms of maintenance, in particular the potential of uprooting seedlings using high velocity/high shear flows. For that purpose, in 2010 a high flow experiment was conducted on a return channel to the Platte River that feeds from the Thirty Mile Canal near Brady, Nebraska. As part of the experiment, a 250-meter long reach of the channel was monitored and data were collected for the set-up, testing, and evaluation of numerical models. This article presents a description of the experimental conditions, data-collection program, and application of an unsteady, depth-averaged numerical model to reproduce the event.