Application of Geomorphic Process Information to River Restoration Design for Salmon Habitat

Developing river restoration concepts based on analog or historical information is problematic because of the long history of development, mining, logging and agricultural land use practices in the western United States. We applied an analysis of geomorphic characteristics and sediment transport processes to channel realignment designs for approximately 1.6 km of the South Fork Walla Walla River, Oregon.  Since the mid-1800s this river reach had been straightened and artificially confined against the valley wall. The expected planform pattern that should exist for the project reach was estimated using several methods based on discharge, slope, width, depth, Froude number, bed material size, and unit stream power.  The channel geometry and longitudinal profiles in the restored channel were subsequently designed based on estimates of sediment transport capacity in the existing channel, with the intent to encourage bed material storage and channel complexity within the restored channel.  The restored channel has a reduced slope of approximately 1.1%, and a significant increase in side channel length from 48 m in the existing channel to 1067 m in the restored channel.  Reach-averaged sediment transport capacity at bankfull discharge in the restored channel is approximately 37% of the sediment transport capacity in the existing channel.