Re-assembling Hetch Hetchy: Water supply without O’Shaughnessy Dam

The Hetch Hetchy System provides San Francisco with most of its water supply. O\u27Shaughnessy Dam is one component of this system, providing approximately 25 percent of water storage for the Hetch Hetchy System and none of its conveyance. Removing O\u27Shaughnessy Dam has gained interest for restoring Hetch Hetchy Valley. The water supply feasibility of removing O\u27Shaughnessy Dam is analyzed by examining alternative water storage and delivery operations for San Francisco using an economic engineering optimization model. This model ignores institutional and political constraints and has perfect hydrologic foresight to explore water supply possibilities through reoperation of other existing reservoirs. The economic benefits of O\u27Shaughnessy Dam and its alternatives are measured in terms of the quantity of water supplied to San Francisco and agricultural water users, water treatment costs, and hydropower generation. Results suggest there could be little water scarcity if O\u27Shaughnessy Dam were to be removed, although removal would be costly due to additional water treatment costs and lost hydropower generation