White Salmon Delta Habitat Enhancement Restoration

This project was designed to address impaired habitat conditions related to the large volumes of sediments that were deposited in and around the White Salmon Delta following the 2011 breach of Condit Dam. The objective of this project was to enhance aquatic and riparian habitat by increasing the quantity and quality of channel margin habitat for salmonid rearing and increasing the amount and diversity of native woody riparian vegetation communities. The Project involved dredging sediments from the navigation channel to restore navigation and reuse of the dredged materials to construct a riparian island complex and cobble bank habitat to the north of the navigation channel. The bank along the northern edge of the navigation channel was designed to mimic gently sloping cobble shoreline habitat that is frequently utilized by juvenile salmonids.

PCSRF funds specifically paid for construction costs to treat 0.75 miles for channel reconfiguration and connectivity and to perform the following actions:

•Dredged 15,500 cubic yards of sediments from the navigational channel to restore and dredged sediments were used to form elevated riparian islands with meanders.
•Placed 1,500 cubic yards of streambed cobbles to create cobble bank habitat for juvenile fish habitat to the north of the navigation channel.
•Placed 715 cubic yards of class B riprap. The YN Team designed the project to minimize the volume of riprap. Imported riprap was sealed with soil and heavily vegetated to the greatest extent possible. This was done to minimize large interstitial spaces that provide habitat favored by the invasive bass.
•No logs/root wads were encountered in the excavation process.

The riparian island complex was designed to mimic historical delta islands that existed in mid-Columbia River tributary confluences prior to the construction of Bonneville Dam. Constructed islands were designed to support diverse native riparian vegetation communities (Attachment A - figure 3), with low, medium and high target elevations (Zones 1-3), as well as an upland zone (Zone 4) based on a nearby reference island and hydrologic analyses of the site. Riparian plantings were paid for under a non-PCSRF funding source. The goal of these planting efforts was to reestablish a diverse, resilient, and functional floodplain gallery forest similar to what would have existed historically. Riparian upland trees were planted on the higher elevation surfaces, woody shrub species on more frequently inundated surfaces and emergent wetland vegetation on the lowest and most frequently inundated surfaces.

The islands were constructed with a top elevation set at 83.0 feet, which will typically be inundated at flows higher than the 5-year flood event. These features are expected to provide off-channel and riparian habitat for native fish species at moderate to high Columbia River stages. An added benefit of this project was that it reduced and minimized the amount of shallow impaired habitat impacted by hydro-system ramping events (stranding juvenile salmonids, desiccates lamprey marothelmea) and reduced shallow water conditions that increase water temperatures. As White Salmon river summer water temperatures are cooler than the mainstem Columbia, these newly created habitats will also provide rearing habitats for outmigration salmonids from outside the White Salmon Subbasin, and overall effectively reduced 5.7 acres of shallow warm river bar habitat.

This project addresses factors that limit productivity (Priority 1) of Middle Columbia River Steelhead (threatened), Lower Columbia River Chinook (threatened), Lower Columbia River Coho (threatened), pink salmon, bull trout (threatened), Pacific lamprey (Lower Columbia ESA Salmon Recovery Plan Appendix C: White Salmon Management Unit Plan identifies 2012). Specifically this project will rehabilitate shallow delta habitats identified as “impaired habitats” within the Recovery Plan. Project will create side channels that maintain wetted channel area and habitat complexity during low pool conditions to reduce stranding. As White Salmon river summer water temperatures are cooler than the mainstem Columbia, these newly created habitats may also provide rearing habitats for outmigration salmonids from outside the White Salmon Subbasin.