Green Island Restoration Project (NEW)
River, Stream and Wetland Restoration
Client / Agency
McKenzie River Trust
Bonneville Power Administration, Oregon Department of Fish and Wildlife, The Nature Conservancy
2011 - 2013
The McKenzie River Trust (MRT), with funding provided by, Bonneville Power Administration (BPA), the Oregon Department of Fish and Wildlife (Willamette Wildlife Mitigation Program), and The Nature Conservancy (Pacific Gas and Electric Habitat Support Program) retained River Design Group, Inc. and Tetra Tech, Inc. to prepare an existing condition analysis and restoration design for Green Island near Coburg, Oregon. Project goals included improving the function and connectivity of the historical McKenzie River channel (HMRC) and floodplain with the Willamette River, to benefit native fish species particularly Upper Willamette River spring Chinook salmon. Three project sites on Green Island include the Coburg Aggregate Reclamation Project (CARP), a low water crossing on the HMRC, and reconnecting a side channel (Neck channel) that historically linked the Willamette River with the historical McKenzie River channel.
Primary project components included field data collection, hydrologic analysis and hydraulic modeling, project design, and permitting. Each project component provided information for subsequent project elements. Field data collection was completed to prepare an updated LiDAR-based topographic surface model of the three project areas. The integrated LiDAR surface model was then used as the basis for the hydraulic model geometry. Two hydraulic models were prepared for base flood conditions (flood model) and for smaller scale site conditions (restoration model). Reach hydrology was based on the U.S. Geological Survey Harrisburg gage located downstream from Green Island. Multiple observed high water marks from 2011 and 2012 were surveyed. High water elevations were used to calibrate the restoration hydraulic model and to predict flow splits through the project areas. Stage-discharge relationships were established for three MRT staff plates located in the CARP site (South Pond), downstream from the low water crossing in the HMRC, in the Neck channel upstream from an existing access road, and in a side channel to the Willamette River at the inlet to the Neck channel. The stage-discharge relationships related observed water surface stage to time of travel-corrected discharge at the USGS gage. This information assisted with evaluating waterbody elevations within Green Island relative to estimated Willamette River discharge. Staff plate data and surveyed high water marks were also used to calibrate the restoration hydraulic model.
Engineered designs were prepared for the three project areas. Overriding project goals included improving hydraulic connectivity, fish passage and fish access between the Willamette River and HMRC, as well as within the HMRC. Restoration project elements include stream channel and CARP pond grading, aquatic and riparian habitat enhancement, road crossing design, and site revegetation. Design preparation was an iterative process that included engineering and hydraulic analysis. The proposed condition restoration hydraulic model incorporated the final design components for the three project areas. The final designs and hydraulic output were used to prepare the county, state, and federal permit applications. Project implementation is scheduled for the 2013.