Northwest Swale, Vanport Wetlands

Background
The Northwest Swale site is 0.1 acre of forested wetland habitat located in the northwest corner of the Vanport Wetlands mitigation site. The project stems from a Type II Environmental Review by the City of Portland for impacts to 0.03 acre of wetlands in the city's Conservation Zone during the removal of the radio tower grounding wires. The project will promote diversity of wetland habitat by removing invasive species and planting native species in riparian wetland forest habitat.

Mitigation Plan
The goal of the mitigation is to enhance 0.1 acre of the existing riparian forest habitat within the Peninsula 1 Drainage District (Pen 1) northeast drainageway. In addition to removal of the invasive species, the mitigation plan called for the installation of 12 trees (black cottonwood and Oregon ash), 15 red-osier dogwood cuttings, 140 willow stakes, slough sedge and mannagrass.

Status
Invasive weed removal and native planting was completed by February 2001. Prior to planting, invasive species such as Himalayan blackberry and reed canarygrass were cleared from the area. Existing native trees and shrubs were identified and left undisturbed. Native species that were planted included red-osier dogwood, black cottonwood, Oregon ash, several willow species, creeping spikerush, slough sedge and sawbeak sedge. Monitoring has indicated abundant natural recruitment in areas where invasive weeds were removed. Consequently, the numbers of native trees and shrubs have exceeded permit requirements. Wildlife observations are reported as part of the Vanport Wetlands results.
Once the Port met the 5 year requirement for monitoring, the City of Portland conducted a final inspection and approved the NW Swale mitigation site in the fall of 2006. The Port continues to manage and maintain the site as part of the Vanport Wetlands.

Related Link:
Mitigation Management Program 2008 Annual Report (pdf - 20 MB)