Modeling Multi-Reservoir Hydropower Systems in the Sierra Nevada with Environmental Requirements and Climate Warming
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Modeling Multi-Reservoir Hydropower Systems in the Sierra Nevada with Environmental Requirements and Climate Warming By DAVID EMMANUEL RHEINHEIMER B.S. (University of Massachusetts, Amherst) 2001 M.S. (University of California, Berkeley) 2004 DISSERTATION Submitted in partial satisfaction of the requirements for the degree of DOCTOR OF PHILOSOPHY in Water Resources Engineering in the OFFICE OF GRADUATE STUDIES of the UNIVERSITY OF CALIFORNIA DAVIS Approved: _____________________________________ Dr. Jay R. Lund, Chair _____________________________________ Dr. Joshua H. Viers _____________________________________ Dr. S. Geoffrey Schladow Committee in Charge 2011 i Acknowledgements I first would like to thank my committee members Drs. Jay Lund, Joshua Viers, and Geoffrey Schladow for their invaluable support of my academic and professional goals at UC Davis, in particular for helping me to think about and describe resource management problems in fundamentally different, yet complementary, ways. Thanks to my major professor, Jay Lund, for his ceaseless stream of ideas, his invaluable ability to help me say more with less, and, of course, his paella parties. I worked most closely with Josh Viers, who provided constant advice and constructive criticism, and, importantly, helped me keep one foot firmly planted in global freshwater conservation efforts. Several other professors have also helped along the way: Miguel Marino, Richard Howitt, Jeffrey Mount, and Bassam Younis at UC Davis, and John Dracup at UC Berkeley. I am grateful for the friendship of colleagues near and far, past and present. In completely random order, I especially thank Rachael Hersh-Burdick, Nate Burley, Rob Lusardi, Christina Buck, Kaveh Madani, Josue Azuára-Medellín, Marcelo Olivares, David Rosenberg, Julien Harou, Patrick Ji, Rachel Ragatz, Matt Seitzler, Prudentia “Gugu” Zikalala, Gerhard Epke, Sarah Null, Scott Ligare, Sarah Yarnell, and Laleh Rastagarzadeh. I am also indebted to my former colleagues at the World Wildlife Fund for, perhaps unkowingly, shining the light for my path: Bernhard Lehner, Robin Abell, Michele Thieme, Nikolai Sindorf, Rebbecca Ng, and Carissa Wong. Other people and organizations deserving particular mention for their advice, research support, and guidance include: the Stockholm Environment Institute, including Jack Seiber, David Purkey, Charles Young, and Vishal Mehta; Mike Deas of Watercourse Engineering; Gary Reedy of the South Yuba River Citizens League; Bob Center of American Whitewater; Michael Kiparsky at the University of Idaho; and Jaime Pittock at the Australian National University. My work at UC Davis, including more than this dissertation, was funded by the Resources Legacy Fund Foundation, the California Energy Commission, and the California Department of Water Resources, to whom I am grateful. I thank above all my vast family, Lowell and Jun Rheinheimer, Edith and Philip Bragdon, and my siblings Lisa, Jason, Wendell, Francis, Zenobia, Laura, Owen, and Leyla. I am indebted to you all for your love and encouragement. Thanks also to my aunt and uncle Carol and Andy Sawyer for their warm welcome to Sacramento and the Sierra Nevada, their majestic backyard. ii Abstract Hydropower systems and other river regulation often harm instream ecosystems, partly by altering the natural flow and temperature regimes that ecosystems have historically depended on. These effects are compounded at regional scales. As hydropower and ecosystems are increasingly valued globally due to growing values for clean energy and native species as well as and new threats from climate warming, it is important to understand how climate warming might affect these systems, to identify tradeoffs between different water uses for different climate conditions, and to identify promising water management solutions. This research uses traditional simulation and optimization to explore these issues in California’s upper west slope Sierra Nevada mountains. The Sierra Nevada provides most of the water for California’s vast water supply system, supporting high-elevation hydropower generation, ecosystems, recreation, and some local municipal and agricultural water supply along the way. However, regional climate warming is expected to reduce snowmelt and shift runoff to earlier in the year, affecting all water uses. This dissertation begins by reviewing important literature related to the broader motivations of this study, including river regulation, freshwater conservation, and climate change. It then describes three substantial studies. First, a weekly time step water resources management model spanning the Feather River watershed in the north to the Kern River watershed in the south is developed. The model, which uses the Water Evaluation And Planning System (WEAP), includes reservoirs, run-of-river hydropower, variable head hydropower, water supply demand, and instream flow requirements. The model is applied with a runoff dataset that considers regional air temperature increases of 0, 2, 4 and 6 °C to represent historical, near-term, mid- term and far-term (end-of-century) warming. Most major hydropower turbine flows are simulated well. Reservoir storage is also generally well simulated, mostly limited by the accuracy of inflow hydrology. System-wide hydropower generation is reduced by 9% with 6 °C warming. Most reductions in hydropower generation occur in the highly productive watersheds in the northern Sierra Nevada. The central Sierra Nevada sees less reduction in annual runoff and can adapt better to changes in runoff timing. Generation in southern watersheds is expected to decrease. System-wide, reservoirs adapt to capture earlier runoff, but mostly decrease in mean reservoir storage with warming due to decreasing annual runoff. Second, a multi-reservoir optimization model is developed using linear programming that considers the minimum instream flows (MIFs) and weekly down ramp rates (DRRs) in the Upper Yuba River in the northern Sierra Nevada. Weekly DRR constraints are used to mimic spring snowmelt flows, which are particularly important for downstream ecosystems in the Sierra Nevada but are currently missing due to the influence of dams. Trade-offs between MIFs, DRRs and hydropower are explored with air temperature warming (+0, 2, 4 and 6 °C). Under base case operations, mean annual hydropower generation increases slightly with 2 °C warming and decreases slightly with 6 °C warming. With 6 °C warming, the most ecologically beneficial MIF and DRR reduce hydropower generation 5.5% compared to base case operations and a historical climate, which has important implications for re-licensing the hydropower project. Finally, reservoir management for downstream temperatures is explored using a linear programming model to optimally release water from a reservoir using selective withdrawal. The objective function is to minimize deviations from desired downstream temperatures, which are specified to mimic the natural temperature regime in the river. One objective of this study was to develop a method that can be readily integrated into a basin-scale multi-reservoir optimization model using a network representation of system features. The second objective was to explore the potential use of reservoirs to maintain an ideal stream iii temperature regime to ameliorate the temperature effects of climate warming of air temperature. For proof-of-concept, the model is applied to Lake Spaulding in the Upper Yuba River. With selective withdrawal, the model hedges the release of cold water to decrease summer stream temperatures, but at a cost of warmer stream temperatures in the winter. Results also show that selective withdrawal can reduce, but not eliminate, the temperature effects of climate warming. The model can be extended to include other nearby reservoirs to optimally manage releases from multiple reservoirs for multiple downstream temperature targets in a highly interconnected system. While the outcomes of these studies contribute to our understanding of reservoir management and hydropower at the intersection of energy, water management, ecosystems, and climate warming, there are many opportunities to improve this work. Promising options for improving and building on the collective utility of these studies are presented. iv Table of Contents Acknowledgements .......................................................................................................................... ii Abstract ........................................................................................................................................... iii Table of Contents ............................................................................................................................. v List of Figures ................................................................................................................................. vi List of Tables ................................................................................................................................ viii Chapter 1 : Introduction ................................................................................................................... 1 Problem statement ........................................................................................................................ 1 River regulation and freshwater conservation ............................................................................. 1 Hydropower ................................................................................................................................