INVESTIGATING UPSTREAM CHANNEL RESPONSE TO DAM REMOVAL, BLACKFOOT RIVER, MT

As dam removal becomes more accepted as an effective approach to river restoration, understanding the upstream channel geomorphic response is vital. This study is being conducted to examine upstream channel evolution of the Blackfoot River (BFR) in response to an 8-meter drop in base level that was caused by the 2008 removal of the Milltown Dam. This research tests the hypothesis that the first 4 km of the BFR channel has reached a new equilibrium, where change to topography and sediment profile no longer reflect the 2008 removal of the Milltown dam. Cross section elevation and grain size data from 8 BFR sites were collected: 5 sites within the area influenced by Milltown Reservoir and 3 sites upstream. To quantify the geomorphic response, I compare the change in grain size and cross section elevation for each site from data collected in 2009, 2010 and 2012. Results from 2010 indicate the main drivers of channel response are channel confinement and spring run-off magnitude. Long-term studies of upstream channel response to dam removals are rare. Results from this study will help increase the temporal understanding of dam removals and can be applied to future dam remediation projects.