Restoration prioritization of Upper Colorado tributaries in the Kawuneeche Valley, Rocky Mountain National Park, CO

Abstract

Collapse of tall willow habitat along the Upper Colorado River, Rocky Mountain National Park, CO has led to the loss of beaver and channel morphologic change. A diverse stakeholder group is pursuing restoration on Upper Colorado tributaries to improve willow habitat and downstream water quality. Utilizing field data, remote sensing, and flow inundation modeling, I investigate the processes driving channel morphology, levels of floodplain connectivity, and the extent of historical beaver activity. I develop and apply a ranking framework of geomorphic condition for restoration based on channel, floodplain, and catchment characteristics of three study sites: Upper Baker Creek, Lower Baker Creek, and Onahu Creek. Channel assessments indicate that Onahu Creek has the steepest gradient, coarsest bed material, and exhibited the greatest in-channel beaver dam density in 1990. Bankfull cross-sectional areas differ significantly between sites (p < 0.001), a product of varying channel widths. Flow inundation modeling indicates that Upper Baker has the highest degree of floodplain connectivity with a 10.3x increase in surface water extent between observed base and peak flows, relative to a 5.2x increase at Lower Baker, and a 1.9x increase at Onahu. Based on my findings, process-based restoration is a suitable technique to reconnect the channel and floodplain and promote willow growth, but the degree of restoration effort required at each site varies. Onahu Creek has the poorest relative geomorphic condition with the greatest potential for floodplain reconnection through restoration. Upper and Lower Baker Creeks have good geomorphic conditions which may benefit from less intervention to achieve the greatest river ecosystem benefit.