The current system based on the Hetch Hetchy reservoir provides hydro-electric power generation as well as water to San Francisco. How will removing the reservoir impact that power generation facility?
San Francisco operates three medium-sized hydro-electric power plants in the Tuolumne River watershed - Kirkwood, Moccasin, and Holm. Draining the Hetch Hetchy Reservoir will reduce power generation at these by about 20% - an average of about 280 million kWh per year. This is a small part of the output of a standard combined-cycle power plant. It would result in a loss of approximately $10 million in annual power sales, but would not impact power delivery to San Francisco.
Generation at the Kirkwood power plant would depend on the natural flow of the Tuolumne River, and would be significantly diminished during late summer and fall. Generation at Holm powerhouse below Cherry Lake would be less affected. Much of the water passing through Holm would be diverted into the Mountain Tunnel and be used to generate power a second time at the Mocassin powerhouse.
The current power produced by the SFPUC system, although not carbon-based, is not green since it requires the continued destruction of significant habitat. It does not meet the California definition of “renewable” energy.
Restore Hetch Hetchy supports a power replacement plan that is truly renewable, and will not increase emissions of any pollutants or carbon that causes global warming. Emissions must be offset by dedicated conservation programs or renewable energy generation such as wind or solar. Natural gas or pumped storage may also be part of a power replacement program, provided the need for instantaneous generation is met but overall emissions will not be increased.