RIVER RECOVERY AND BEDFORM EVOLUTION IN A NEW ENGLAND STREAM POST-DAM REMOVAL

Dam removals present a unique opportunity to study channel evolution in river systems by creating an entirely new channel in place of the former reservoir. In this project I seek to determine if it is possible to predict bedform evolution as river channels recover post-dam removal. The removal of a small (4m tall, 450m³ of concrete) dam and ~6000m³ of impounded sediment during the fall of 2018 on Charles Brown Brook in Norwich, Vermont, has created an excellent natural laboratory. Through repeated spatial mapping with terrestrial LiDAR, total station surveys, UAV photography, and pebble counts of the new channel, we have quantified grain size, slope, bankfull width and depth, and sinuosity compared to an undisturbed upstream control channel. Additionally, we have placed ~100 tracer rocks tagged with RFID chips and 56 larger rocks equipped with accelerometers in addition to RFID chips. RFID chips provide information about the magnitude of clast movement while accelerometers add a temporal component to the data and allow each displacement to be matched to a hydrograph. Together, spatial and tracer data will be used to monitor the recovery of the channel in the former reservoir over the next two years. We are interested in whether it is possible to predict bedform evolution (following the reach classification system outlined by Montgomery and Buffington, 1997) by comparing the new channel to the upstream control. Further, we hope to determine whether observed channel recovery and evolution is driven by processes or events (Pizzuto, 2002). Preliminary data, collected during and after the removal of the dam between October and the end of the field season in December 2018, record significant sediment mobility within the disturbed reach compared to the upstream control, channel widening, and a spatially controlled pattern of deposition and aggradation within the former reservoir. Broadly, this work is aimed to inform our understanding of how fluvial systems respond to rapid and substantial change, of which dam removal is a prime example. Specifically, this work may help direct future river restoration projects towards appropriate and sustainable designs.