The Lower Columbia Estuary Partnership, the US Forest Service, and partners completed construction of the Thousand Acres Floodplain Restoration Project, a habitat restoration project at the Sandy River Delta, in 2014. The site is part of the 1,500 acre natural area at the confluence of the Sandy and Columbia rivers known as the Sandy River Delta (SRD) in the Columbia River Gorge. The site, owned by the US Forest Service, was historically a dynamic alluvial floodplain with two distributaries of the Sandy River flowing across it and a mosaic of bottomland forests, wetlands and meadows. This area provided valuable habitat for many species, including rearing and refuge habitat for juvenile salmon. The site has been severely impacted by deforestation, draining of wetlands, and cattle grazing, leaving a system dominated by invasive weeds with degraded hydrology and water quality and lack of diverse habitat. The Estuary Partnership and partners have been working for several years with the Forest Service on reforestation efforts on a 500 acre portion of the SRD, and have now initiated a new phase of restoration on the eastern portion called “Thousand Acres” (outlined in red, photo at left). The project will restore natural hydrology and access for juvenile salmonids to the wetland system in this high priority area by removing an old tide gate and water control structure. The project will also re-establish the site’s native plant communities. These habitat enhancements will benefit many regionally important species of birds, amphibians, reptiles, and plants.
The Sandy River Delta is one of the largest and most ecologically significant undeveloped Columbia River bottomlands in the Portland Metropolitan Area. There are limited habitat restoration opportunities in the Columbia River Gorge, primarily due to geomorphology, transportation, and current land uses. Not only is the Thousand Acres project site one of the few large, contiguous tracts of intact floodplain under public ownership, but it is known to support several stocks of salmon. The site also supports a variety of other native species, including beaver, great blue heron, red-legged frogs, painted turtle, and a variety of waterfowl. Many of these native species have seen their populations decline since development of the Columbia River Gorge National Scenic Area.
The SRD has been significantly altered during the past century by human activities, primarily clearing of the forest, grazing and agriculture, addition of drainage channels and a tide gate, damming of the Sandy and the Columbia rivers, construction of the railroad and I-84, and invasive species.
Currently, the site is managed by the US Forest Service, which acquired the SRD in 1991 after it had been grazed for many years. When grazing ceased in the early 1990’s, invasive weeds spread throughout the property, primarily reed canarygrass and non-native blackberry. The Forest Service completed the Sandy River Delta Plan in 1995. The goals of the plan include restoration of the landscape with wetland, riparian forest, shrub-scrub, upland forest, and upland meadows. In 1997, the Forest Service began vegetative restoration on Sundial Island and wetland restoration on Thousand Acres, both of which are ongoing.
Historic aerial photos
This 1935 photo shows relative pre-disturbance conditions at the site, including significant forest cover, ponds, and wetlands, including the long linear “Wetland D” and “Horseshoe Wetland,” and the North and South Channels that connect them to the river.
By the time of this 1948 photo (right), significant alterations have occurred. Forestland has been cleared, and vehicle tracks are visible throughout the site. The North Channel between the wetlands and the river was deepened and widened by excavation. The South Channel was excavated to drain water away from the wetlands adjacent to the highway out to the river. Highway construction is shown along the southern boundary of the site. Vehicle crossings of the channels indicate that there may have been culverts or other structures installed to maintain vehicle access. Alterations from the highway construction are largely responsible for the current site conditions.
In this current aerial photo, invasive weeds (primarily reed canarygrass and blackberry) dominate the site, while the major hydrologic features such as Wetland D, Horseshoe Wetland, and the North and South Channels appear in essentially the same alignment.
Once Estuary Partnership restoration work is complete, the tide gate and water control structures will be removed, restoring the natural hydrology, and allowing native salmon to access the restored wetlands. The site will also be replanted with native trees and shrubs, though these will take several years to reach full growth and coverage.
The Lower Columbia Estuary Partnership managed the project, which was a collaborative effort with the landowner, the U.S. Forest Service. Additional partners include Ash Creek Forest Management, Friends of Sandy River Delta and the Sandy River Basin Watershed Council.
Funders include the U.S. Forest Service, Oregon Watershed Enhancement Board, Bonneville Power Administration, East Multnomah Soil and Water Conservation District, Oregon Community Foundation, and National Forest Foundation.
David Evans and Associates provided assistance with the Feasibility Assistance for the initial project development. ESA-Vigil Agrimis is providing design and engineering services. Aquatic Contracting, Inc. is constructing the project. Ash Creek Forest Management is providing revegetation services.