Andy Tranmer Earns NSF Grant

Andy Tranmer, Assistant Research Professor at the Center for Ecohydraulics Research in Boise, has been awarded $443,525.00 from the National Science Foundation for his proposal “Characterizing the physical drivers of vegetation-forced bar evolution in gravel-bed streams.” One PhD and numerous UG students will be hired for this work. Funding will be spread over 3 years.

Pioneer riparian vegetation, like willows and cottonwood trees, are ubiquitous in the riverine landscape, growing on many gravel bars in the Northern Hemisphere. These play a passive habitat role in supporting aquatic and avian species over the course of the year but become powerful geomorphic agents during flood conditions. Riparian vegetation interacts with the flow during high-water events to alter the instream hydraulics, sediment transport capacity, and overall flood risk in the river. The research project is designed to investigate how the hydraulics and sediment transport capacity change through patches of riparian vegetation to explain the spatial patterns of observed bed sediments, aquatic habitat, and resultant shape of gravel bars after floods. Results can help guide water agencies in deciding what vegetation planting densities are necessary during river restoration activities to achieve the desired evolutionary outcomes. Additionally, results are expected to help flood managers predict gravel bar dimensions from existing vegetation densities and determine if vegetation thinning or removal is necessary for public safety. From a river engineering standpoint, predicting vegetated bar evolution is difficult because there is currently no single parameter available to consistently predict coarse-sediment mobility in vegetated river channels. We will use a suite of field experiments, physical modeling in the Boise flume, and large-scale physical modeling in South Korea to understand and predict vegetated gravel bar evolution.