1 1 2 3 RE-ASSEMBLING HETCH HETCHY 4 Water Supply Implications and Costs of Removing O'Shaughnessy Dam 5 6 7 8 Sarah Null and Jay R. Lund2 9 10 11 ABSTRACT: The Hetch Hetchy System provides San Francisco with most of its water supply. 12 O’Shaughnessy Dam is one component of this system, providing approximately 25% of water 13 storage for the Hetch Hetchy System and none of its conveyance. Removing O’Shaughnessy 14 Dam has gained interest to restore Hetch Hetchy Valley. The water supply feasibility of 15 removing O’Shaughnessy Dam is analyzed by examining alternative water storage and delivery 16 operations for San Francisco using an economic-engineering optimization model. This model 17 ignores institutional and political constraints and has perfect hydrologic foresight to explore 18 water supply possibilities through re-operation of other existing reservoirs. The economic 19 benefits of O’Shaughnessy Dam and its alternatives are measured in terms of the quantity of 20 water supplied to San Francisco and agricultural water users, water treatment costs, and 21 hydropower generation. Results suggest there would be little water scarcity if O’Shaughnessy 22 Dam were to be removed, although removal would be costly due to additional water treatment 23 costs and lost hydropower generation. 24 (KEY TERMS: water supply, dam removal, Hetch Hetchy, optimization, filtration avoidance, 25 restoration.) 2 Respectively, Doctoral Student, Geography Graduate Group, University of California, Davis; Professor, Department of Civil and Environmental Engineering, University of California, Davis, 3109 Engineering Unit III, Davis, California 95616 2 1 INTRODUCTION 2 O’Shaughnessy Dam, located in the Hetch Hetchy Valley of Yosemite National Park, 3 was built by the city of San Francisco in 1923, as a component of the Hetch Hetchy water 4 system. The Hetch Hetchy System has ten other reservoirs, numerous water conveyance 5 pipelines, and water treatment facilities. This system provides water to 2.4 million people in the 6 San Francisco Bay Area, including the city and county of San Francisco and 29 wholesale water 7 agencies in San Mateo, Alameda, and Santa Clara Counties (USBR, 1987). 8 O’Shaughnessy Dam was controversial when proposed and built in the early 1900s. 9 Throughout the past century, the idea of removing O’Shaughnessy Dam to restore Hetch Hetchy 10 Valley has never entirely gone away, although today California is much different. Yosemite 11 National Park is now one of the most loved and visited parks in the United States. California’s 12 Bay Area is a major urban region, with millions of residents requiring water delivery, and the 13 Tuolumne River now has several times more storage capacity with the construction of New Don 14 Pedro Reservoir. For Hetch Hetchy Valley restoration to be considered, the remainder of the 15 Hetch Hetchy System or feasible alternative sources must be able to supply water without 16 O’Shaughnessy Dam. The importance of O’Shaughnessy Dam must be evaluated in the context 17 of the greater Hetch Hetchy System and other water supply alternatives. 18 This study provides quantitative estimates for the water supply feasibility of removing 19 O’Shaughnessy Dam using a spatially refined economic-engineering optimization model. Much 20 has been written and discussed about removing O’Shaughnessy Dam, but quantitative estimates 21 have not been released publicly. This project identifies cost minimizing alternatives for San 22 Francisco’s water supply and highlights how removing O’Shaughnessy Dam could change 23 current operations, water supply, deliveries, hydropower generation, water treatment, and 24 economic water supply costs. Removing O’Shaughnessy Dam could raise many additional 3 1 institutional, political, and economic questions. However, this study ignores most institutional 2 and political implications to focus on optimization of water supply and economic factors. It is 3 helpful to ignore political and institutional constraints to understand the physical limitations of a 4 water supply system. It then becomes clear whether human constraints or physical constraints 5 are limiting factors. Modeling can provide quantitative support for future discussion or actions. 6 This analysis indicates whether water scarcity would increase substantially without 7 O’Shaughnessy Dam assuming no additional water storage (Null, 2003). Such information also 8 might be useful as part of a more comprehensive benefit-cost analysis, not undertaken here. 9 This paper begins with a brief overview of Hetch Hetchy Valley, O’Shaughnessy Dam, 10 the Hetch Hetchy System, and potential O’Shaughnessy Dam removal decisions. CALVIN, the 11 computer model used to evaluate alternatives to O’Shaughnessy Dam, is explained. A summary 12 of model parameters, infrastructure modifications, benefits and limitations of CALVIN follow. 13 Model runs are described, with important assumptions noted, and results are discussed in terms 14 of operational and economic performance. The paper concludes with a short discussion on the 15 implications and water supply costs of removing O’Shaughnessy Dam, and some larger 16 institutional and economic factors affecting the feasibility of removing O’Shaughnessy Dam. 17 Background 18 Prior to construction of O’Shaughnessy Dam, Hetch Hetchy Valley was similar to 19 neighboring Yosemite Valley. Both valleys were formed from jointed granite bedrock. The 20 valleys were initially cut by the Tuolumne and Merced Rivers respectively; then glaciers scoured 21 them, widening and polishing the surrounding granite. Both valleys once had natural lakes that 22 filled with sediment, forming flat meadows (Huber, 2002). 23 In 1906, following the San Francisco earthquake, the shortcomings of San Francisco’s 24 water supply became obvious. City water planners targeted Hetch Hetchy as a site for a large 4 1 dam to ensure San Francisco’s water supply (Hundley, 1992). San Francisco’s voters approved 2 the construction of a dam in Hetch Hetchy Valley by an 86% majority vote in 1908 (Sierra Club, 3 2002). In 1913, the Raker Act was passed in Congress, enabling a large reservoir to be built in a 4 national park (Hundley, 1992). O’Shaughnessy Dam was completed in 1923, raised in 1938, and 5 has been in use for the past eighty years. 6 O’Shaughnessy Dam has a storage capacity of 360,360 acre-feet (af). Its current uses 7 include water storage, hydropower generation, and some flood reduction (USBR, 1987). The 8 reservoir behind O’Shaughnessy Dam is not used for recreation. In terms of total water storage 9 in the Hetch Hetchy System, O’Shaughnessy Dam is not exceptionally large. It’s 360 thousand 10 acre-feet (taf) of surface water storage are approximately 25% of the surface storage in the Hetch 11 Hetchy System and 14% of storage on the Tuolumne River. For this study, removal of 12 O’Shaughnessy Dam applies only to the dam and its reservoir. No pipelines, diversion capacity, 13 or conveyance facilities would be removed from the Hetch Hetchy System. 14 As illustrated in Figure 1, the Hetch Hetchy System consists of several reservoirs, power 15 plants, and conveyance facilities. Downstream of O’Shaughnessy Dam, the Kirkwood Power 16 Plant and Moccasin Power Plant generate hydropower. Nearby, Cherry Reservoir and Eleanor 17 Reservoir are currently operated primarily for hydropower at Holm Powerhouse. Adequate 18 water supply storage is usually provided by O’Shaughnessy Dam. Another much larger dam, 19 New Don Pedro Reservoir, is downstream of O’Shaughnessy Dam, Cherry, and Eleanor 20 Reservoirs (SFPUC, 2002). 21 These four reservoirs, together with numerous Bay Area reservoirs and the connecting 22 pipelines make up the Hetch Hetchy System, operated by the San Francisco Public Utilities 23 Commission (SFPUC). Total surface storage in the Hetch Hetchy System is approximately 24 1,500 taf (Table 1). Of this quantity, 570 taf of storage is located in New Don Pedro Reservoir, 5 1 downstream of current Hetch Hetchy Aqueduct intakes. In addition to the Hetch Hetchy System 2 total, another 1,460 taf of storage is owned by Modesto Irrigation District and Turlock Irrigation 3 District in the 2,030 taf New Don Pedro Reservoir. The Hetch Hetchy System supplies water to 4 77% of the urban and industrial uses of the city and county of San Francisco, as well as parts of 5 San Mateo, Santa Clara, and Alameda Counties; supplying over 2 million water users (DOE, 6 1988). Three powerhouses on the upper Tuolumne River together provide approximately 2 7 billion KW hrs/yr of hydropower (USBR, 1987). This is a clean source of energy and an 8 important source of revenue for the SFPUC. 9 Although water storage is a priority for SFPUC and the Hetch Hetchy System, it is not 10 the 360 taf of water storage that makes O’Shaughnessy Dam valuable; rather water from 11 O’Shaughnessy Dam has filtration avoidance status (SFPUC, 2002). Typically, filtration of 12 urban surface water supplies is required by federal law. Filtration avoidance means 13 O’Shaughnessy Dam impounds extremely high quality water that meets water quality standards 14 under the federal Surface Water Treatment Rule. Only minimal water treatment is currently 15 necessary, such as addition of lime for corrosion control and chlorine or chloramine as a 16 disinfectant (Redwood City PWSD, 2003, SFPUC, 2003). The watershed above O’Shaughnessy 17 Dam is pristine; it lies within Yosemite National Park. O’Shaughnessy Dam is the only reservoir 18 in the Hetch Hetchy System that has filtration avoidance (and one of only about a half dozen 19 sources nationally). Even Cherry and Eleanor Lakes, less than ten miles from O’Shaughnessy 20 Dam do not qualify for filtration avoidance. 21 Recently the SFPUC approved seismic retrofits for the Hetch Hetchy System as part of its 22 Capital Improvement Program (SFPUC, 2002). Increased local San Francisco water storage 23 would be valuable in case of an earthquake, terrorist act, or other emergency repair.