Background The Port filled approximately 65 acres of wetland at the southwest quadrant of Portland International Airport in 1993. The majority of the fill project's required wetland mitigation occurred at the Jewett Lake site. The 427-acre Jewett Lake mitigation site, located on Government Island, was a shallow basin that had been connected to the Columbia River via a man-made channel. The channel allowed water to flow into the lake whenever river elevations exceeded 10.7 feet. However, water also flowed out of the lake when river levels dropped below this elevation, which resulted in the lake and residual wetlands drying in the summer. The mitigation plan was designed to increase water retention in the lake and enhance and restore adjacent wetlands.
Mitigation Plan The goal of the mitigation at Jewett Lake was to diversify winter waterfowl habitat because this was the primary wetland function lost upon filling the southwest quadrant. Permit conditions required compensatory wetland mitigation using a Habitat Evaluation Procedure (HEP) as the methodology for measuring success. Wildlife habitat conditions at both the southwest quadrant and Jewett Lake were documented in HEP analyses prior to filling and mitigation actions. The mitigation plan called for installing a water control and fish exclusion structure to increase the water retention time in Jewett Lake, creating approximately 30 acres of wetland at Jewett Lake, replacing 149 Average Annual Habitat Units (AAHU) that had been lost at the southwest quadrant and enhancing – through cattle management and vegetation management – the remaining wetland and upland areas within the site.
Status The final year of monitoring took place in 1999. A review of the site was conducted by re-evaluating the original "target year (TY) 5" HEP predictions with those calculated from data collected in 1999. The results demonstrated that the mitigation site had exceeded predictions with approximately 100 AAHU in excess of the TY 5 estimate. In addition, approximately 58 new wetland acres were created.
In 1999 the Port signed a ground lease with the Oregon Parks and Recreation Department (OPRD). Although the Port retains management of the mitigation site, OPRD now manages the rest of the island complex.