Designing for Ecological Disturbance in River Restoration to Promote Native Species Regeneration: A Look at the River Bluffs Project on the Poudre River
Johannes Beeby1*, Travis Stroth1, and Sharon Bywater-Reyes2
1Stillwater Sciences, Boulder, CO, USA; jbeeby@stillwatersci.com, Tstroth@stillwatersci.com
2University of Northern Colorado, Greeley, CO, USA; sharon.bywaterreyes@unco.edu
Disturbance is a natural process in rivers and many riparian species actually require disturbance to regenerate. Nevertheless, disturbance is often seen as a negative by communities and practitioners alike. The 2013 Floods along the Front Range of Northern Colorado provided this necessary disturbance in many instances but also resulted in many restoration projects in river corridors to “fix” the disturbance. Many restoration designs continue to build static river corridors where constructed channels are expected to stay put, and project success is evaluated based on whether the channel is “stable”, i.e., sediment in equals sediment out, there is no bank erosion, no future channel migration, and no wood that may cause disturbance. At the River Bluffs Project on the Poudre River, we used a process-based approach to design a dynamic channel with disturbance built-in. As a metric of project success, our team is monitoring project outcomes with an eye on disturbance as a key metric of restoring system processes in hopes of returning a once frozen river corridor to a more dynamic system that can continue to move and adjust as needed through time. Our monitoring efforts include 1) grain size analysis to monitor sediment transport including riffle flushing and floodplain deposition, 2) topographic analysis via cross-section surveying and structure from motion point clouds, and 3) vegetation surveys to monitor planted and naturally recruited vegetation. Preliminary results indicate 1) mixed grain-size trends, 2) building of mid-channel bars and off-channel erosion, and 3) natural recruitment of Plains Cottonwood after one peak flow event equal to the Q2. By removing berms, reconnecting floodplain, narrowing the channel, and utilizing large wood structures, the river is now set up to create the disturbance needed to help promote new Plains Cottonwood gallery forests now and into the future.