A Natural Channel Design to Restore the Greenwater River, Washington

Channelization of the Greenwater River has resulted in a loss of habitat for Chinook salmon, a species listed as threatened under the Endangered Species Act. In order to restore habitat for fish and other aquatic organisms, a design was developed to restore meanders to the original floodplain. The channel design process began at the watershed scale, and progressed down to the scale of the stream channel. A twelve-step design process was followed that considered the influence of watershed disturbances on channel forming processes. Trends in sediment yield were assessed using an existing landslide inventory, and changes in channel pattern were identified using historic air photos. The direction of adjustment in the channelized reach was assessed from five years of measured cross-sections. The channel pattern was established using the natural range of variability of meanders in the original channel. Air photos of the original channel were used to develop relations between bankfull channel width and meander wavelength, radius of curvature, and belt width. The dimensions of the channel cross section were designed from the hydraulic geometry of reference streams. Channel capacity was designed to pass the bank full flow determined from a survey of bank full indicators at a USGS stream gauge. Shear stress calculations were used to estimate the channel depth required to move the largest particle supplied to the project reach during bankfull flow. Restoration of the amount, size, location, and position of large woody debris was determined from the Literature, and surveys of reference streams. A revegetation plan was proposed to restore future recruitment of large woody debris, and provide channel roughness and bank cohesion during overbank flows. Finally, some objectives are suggested for a future monitoring plan