Changing States: Using State-and-Transition Models to Evaluate Channel Evolution Following Dam Removal Along the Clark Fork River, Montana

• Main Author: Van Dyke, Christopher
• Format: Others
• Published: UKnowledge 2015
• Subjects: Clark Fork River; channel evolution; state-and-transition model; critical physical geography; river restoration; Nature and Society Relations; Physical and Environmental Geography
• Online Access: http://uknowledge.uky.edu/geography_etds/31; http://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1037&context=geography_etds

Located just east of Missoula, Montana, Milltown Dam stood from 1908 to 2008 immediately downstream of the Clark Fork River’s confluence with the Blackfoot River. After the discovery of arsenic-contaminated groundwater in the nearby community of Milltown, as well as extensive deposits of contaminated sediment in the dam’s upstream reservoir, in 1981, the area was designated a Superfund site – along with much of the Upper Clark Fork Watershed. This motivated the eventual decision to remove the dam, perform environmental remediation, and reconstruct approximately five kilometers of the Clark Fork River and its floodplain. This study is part conceptual and part empirical. It describes a state-and-transition framework equipped to investigate channel evolution as well as the adjustment trajectories of other socio-biophysical landscapes. This framework is then applied to understand the post-restoration channel evolution of the Clark Fork River’s mainstem, secondary channels, and floodplain. Adopting a state-and-transition framework to conceptualize landscape evolution lets environmental managers more effectively anticipate river response under multiple disturbence scenarios and therefore use more improvisational and adaptive management techniques that do not attempt to guide the landscape toward a single and permanent end state. State-and-transition models can also be used to highlight the spatially explicit patterns of complex biophysical response. The state-and-transition models developed for the Clark Fork River demonstrate the possibility of multiple evolutionary trajectories. Neither the secondary channels nor the main channel have responded in a linear, monotonic fashion, and future responses will be contingent upon hydrogeomorphic and climatic variability and chance disturbances. The biogeomorphic adjustments observed so far suggest divergent evolutionary trajectories and that in some instances the long-term fates of the mainstem, floodplain, and secondary channels are inescapably enmeshed with one another.