The Challenge of Replacing Existing Infrastructure

With aging infrastructure in the United States, the need for replacement projects is becoming more commonplace. In Seattle, for example, an existing, aging elevated freeway along the city's waterfront-the Alaskan Way Viaduct-needs replacing. Adjacent to it, the Elliott Bay Seawall, with portions dating from early in the 20th century, is decaying as a result of wind-driven storm waves, erosive tidal forces, and seismic activity and is in need of replacement. This paper examines the issues involved with replacing the seawall while keeping existing uses operational during construction in the context of the environmental review process undertaken for the project. An emphasis will be placed on mitigation of adverse construction effects through design, as well as other creative measures. The design team worked closely with the City of Seattle on the environmental review process for the project, and the author led the environmental documentation process.