Dams
  Goldsborough Creek | Matilija Dam | Chief Joseph Dam | Piedra Liza Dam

This project was a fast-track study to address Total Dissolved Gas (TDG) supersaturation of water downstream of the Chief Joseph Dam on the Columbia River. The study identified means for reducing TDG contribution from the dam including re-operation, channel bypass, and flow deflectors. The preferred alternatives, flow deflectors, were developed at the preliminary design level and included a cofferdam design for construction. The project addresses concerns for threatened and endangered fish stocks (steelhead, spring Chinook, bull trout).

Tetra Tech provided research, plan formulation, graphics, report writing, engineering design, and economic analysis services in the development of a General Reevaluation Report (GRR) for the project. Tasks included 1) review existing information on the Chief Joseph project including existing project authorizing study documents, technical studies related to the project modification, impact assessments of project modifications, and proposed operating rules and physical model results; 2) documentation of plan formulation criteria and screening processes/results; 3) preparation of GRR; 4) attendance and participation at in-progress-review conferences (including AFB) and other project meetings; and 5) preparation of 10% design drawings for the recommended plan.