Southwest Hydrology: The Resource of Semi-Arid Hydrology Volume 4 Number 2

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POINT / Hetch Hetchy Valley Restoration In 1923, the completion of the O'Shaughnessy Dam on the Tuolumne River in California flooded Hetch Hetchy Valley in Yosemite National Park, creating a reservoir for San Francisco's drinking water and a hydroelectric power supply. Now, the system requires expensive upgrades, and many feel it is time instead to remove the dam and restore the valley, considered by many to rival Yosemite's beauty, and find alternate power and water supplies to meet the growing demand. In November, the California Department of Water Resources and the Department of Parks and Recreation agreed to review existing data and write an assessment within a year Compelling arguments can be made both for and against the dam removal, as presented in these articles. POINT Restore a National Treasure Spreck Rosekrans, Senior Analyst — Environmental Defense Hetch Hetchy Valley, carved by glaciers descending the Tuc River, was described by naturalist John Muir as a "grand la. garden" and "Yosemite's wonderfully exact counterpart." C preserved Hetch Hetchy in 1890 as part of Yosemite Nation, Park. Just two decades later, however, despite a nationwide c Congress allowed the valley to be dammed to supply water b Francisco and other Bay Area cities. As San Francisco undertakes a major program to repair and e, its water system, Environmental Defense decided to consider how the system could provide reliable water and power withot a reservoir in Yosemite National Park. We developed a plannin. model, TREWSSIM (Tuolumne River Equivalent Water Supply Simulation), which incorporates features of both San Francisco' own planning model and the state- federal CALSIM model. We also retained three distinguished consulting firms to assist with engineering, water quality, and legal issues. Our report, "Paradise Regained: Solutions for Restoring Yosemite's Hetch Hetchy Valley," presents a planning -level analysis of how to replace the benefits provided by the current reservoir. Water Supply Hetch Hetchy Reservoir holds 360,000 acre -feet of water, 23 percent of San Francisco's system total and less than 13 percent of the total in the storage -rich Tuolumne watershed. Under the current system configuration, 85 percent of the water delivered to San Francisco and other Bay Area customers is diverted from Hetch Hetchy Reservoir. Under our proposal, the SFPUC would construct diversion facilities from other system reservoirs to replace the diversions from storage that are currently made during summer and fall months when the river's natural flow is insufficient. TREWSSIM results show that 96 percent of the total supply could be delivered without using Hetch Hetchy Reservoir whi' preserving significant carryover storage, in case future drouf due to global warming or other causes, are worse than those occurred in the 20th century. Even if demand increases significantly, additional supply woula only be needed in the driest of five years. The San Francisco Public Utilities Commission (SFPUC) could meet dry-year needs with the same strategies that other California water agencies have recently employed: increased local (offstream) storage, groundwater exchange programs, or dry-year purchases from irrigation districts. Continued next page 14 • March /April 2005 • Southwest Hydrology COUNTERPOINT Hetch Hetchy Reservoir Is a Vital Part of Bay Area, California Water System Michael Carlin — San Francisco Public Utilities Commission Director of Planning The Hetch Hetchy Reservoir in Yosemite National Park stores Tuolumne River water and is the primary source of drinking water for more than 2.4 million people in San Francisco, San Mateo, Santa Clara, and Alameda counties in California. Hetch Hetchy is part of a larger water system that provides irrigation water to the Modesto and Turlock irrigation districts and an average 1,700 gigawatt hours of clean power to Central Valley farmers and cities as well as to the city and county of San Francisco, or about 20 percent of San Francisco's overall power consumption. The San Francisco Public Utilities Commission (SFPUC) is California's third largest municipal water agency, after Metropolitan Water District of Southern California and the San Diego County Water Agency. Current proposals to remove O'Shaughnessy Dam do not take into account the larger context of water in California or those issues associated with draining Hetch Hetchy Reservoir. While the SFPUC appreciates the intentions of individuals and groups seeking the restoration of Hetch Hetchy Valley, we maintain that it is not effective to analyze the Hetch Hetchy system without considering the bigger picture. The Hetch Hetchy system is a critical piece in a larger and complex water and energy system including the western states, California as a whole, and the San Francisco Bay Area. We must acknowledge that changes we make with water and power affect us all, whether those changes impact access to potable, industrial, or irrigation water supplies, the quality of that water as it affects our health and safety, or the monetary and quality-of -life costs that accompany changes to the system. As national studies show, dam removal can provide environmental, economic, and social benefits in some cases. But many dams are too economically and socially valuable to be considered for removal. Any removal proposal should consider the "ripple" effects. The following primary questions and issues are not adequately addressed by proposals to drain Hetch Hetchy Reservoir: 1. Eighty-five percent of the water served to San Francisco's 2.4 million customers flows through the Hetch Hetchy Reservoir. Continued next page