By Jay Lund, Maurice Hall and Anthony Saracino
With the continuation of California’s historic drought and the recent passage of Proposition 1, the potential value of additional water storage in the state is an area of vigorous discussion.
In a new study released today, we look at the different roles of storage in California’s integrated water system and evaluate storage capacity expansion from what we call a “system analysis approach.” This approach emphasizes how new storage projects, both above and below ground, can work in combination with one another and in concert with the broader water management system.
Surface water reservoirs provide benefits by capturing water when it is more abundant and storing it for times of greater water scarcity (most commonly storing water from California’s wet winter for its dry spring and summer, but also providing some ability to save water for short droughts). Groundwater in California provides larger capacity storage for the longer term, such as for multi-year droughts, and is a substantial source of water and seasonal storage in places where surface water is limited.
In California’s vast and interconnected water system, storage projects should not be evaluated in isolation. Instead, storage should be considered and analyzed as part of larger portfolios of infrastructure and management actions, including: various water sources; various types and locations of surface and groundwater storage; various conveyance alternatives; and managing all forms of water demands. Such an integrated, multi-benefit perspective and analysis would be more valuable and would be a fundamental departure from most ongoing policy discussions and recent storage project analyses.
Our study and earlier work shows that the ability to utilize additional water storage in California is finite and varies greatly with its location, the availability of water conveyance capacity, and how the system is operated to integrate surface and groundwater storage, conveyance and water demands.
At most, California’s large-scale water system could potentially utilize between 5 and 6 million acre-feet of additional surface and groundwater storage capacity, and probably no more. The limitation stems primarily from a lack of streamflow to reliably fill larger amounts of storage space.
Major water storage expansion proposals
In the long term, this limitation is likely to tighten with a drier climate, though it can loosen somewhat with wetter and more variable streamflows.
The most promising new storage projects would provide annual water deliveries of 5-15 percent of the new storage capacity. Said another way, a storage project with 1 million acre-feet of storage capacity would likely provide an average of only 50,000 to 150,000 acre-feet of new supply a year.
Our study also demonstrates that the water supply and environmental performance of additional storage capacity are greatest when surface and groundwater storage operations are integrated and coordinated. The benefits and likely cost-effectiveness of coordinating surface and groundwater storage and conveyance operations greatly surpass the benefits of expanding storage capacity alone. Integrated operation can expand annual water delivery to as much as 20 percent of the increase in storage capacity.
This does not necessarily mean that the benefits of expanding surface or groundwater storage capacity exceed their substantial costs; we did not delve into benefit and cost calculations. But there is enough water and water demand to take advantage of up to about 5 or 6 million acre-feet of additional surface and groundwater storage within the Central Valley, were this capacity available and in the right places.
This new storage volume would increase California’s total water supply by at most 5 percent and, if targeted appropriately, could provide more reliable supplies for farms and cities as well as more flows at the right time and place for fish and wildlife.
However, expanding water storage is no panacea by itself; it must be combined with other system improvements and actions in an integrated portfolio approach to California’s water system.
Integrated water management and Delta water deliveries
More integrated water management greatly increases Delta water deliveries. This graph shows average water delivery increases for various Delta conveyance assumptions and combinations of four surface and groundwater storage capacity expansions in the Sacramento and San Joaquin valleys. Sources: Historical climate data and the CalLite water model described in appendix of storage study
Water infrastructure programs purposely designed and implemented to work with other parts of the water system and other water management actions can significantly outperform individual projects in achieving objectives for water supply, healthy ecosystems and flood protection — under a variety of climate conditions (Harou et al. 2010; Connell-Buck et al. 2011; Ragatz 2013).
Studies examining water storage and water management generally should explicitly consider the potential for integrating surface and groundwater storage, as well as conveyance and water demand management for water supply, ecosystems and flood protection. Recent state groundwater legislation could be instrumental in supporting such coordination regionally and locally.
The benefits of integrated management are clear. A transformation is needed in how agencies and stakeholders think about conducting water infrastructure studies if California is going to squeeze the most benefit from our water infrastructure investments, including the Prop. 1 funds.
Jay Lund is director of the UC Davis Center for Watershed Sciences. Maurice Hall is California water science and engineering lead for The Nature Conservancy and Anthony Saracino is a water resources consultant in Sacramento.
Jay Lund talks about water storage study
Connell-Buck, C.R., J. Medellín-Azuara, J.R. Lund, and K. Madani, “Adapting California’s water system to warm vs. warm-dry climates,” Climatic Change, Vol. 109 (Suppl 1), pp. S133–S149, 2011
Hanak, E., J. Lund, A. Dinar, B. Gray, R. Howitt, J. Mount, P. Moyle and B. Thompson, Managing California’s Water: From Conflict to Reconciliation, Public Policy Institute of California, San Francisco, CA, 500 pp., February 2011
Harou, J.J., J. Medellin-Azuara, T. Zhu, S.K. Tanaka, J.R. Lund, S. Stine, M.A. Olivares and M.W. Jenkins, “Economic consequences of optimized water management for a prolonged, severe drought in California,” Water Resources Research, doi:10.1029/2008WR007681, Vol. 46, 2010
Krieger, J.H. and H.O. Banks (1962), “Ground water basin management,” Cal. Law Review. V. 50:56
Lund, J., A. Munévar, A. Taghavi, M. Hall and A. Saracino, “Integrating storage in California’s changing water system,” Center for Watershed Sciences, UC Davis, November 2014
Lund, J.R. and T. Harter (2013), “California’s groundwater problems and prospects”, CaliforniaWaterBlog, Jan. 30, 2013
Lund, J.R. (2012), “Expanding Water Storage Capacity in California,” CaliforniaWaterBlog, Feb. 22, 2012
Lund, J.R. (2011), “Water Storage in California,” CaliforniaWaterBlog, Sept. 13, 2011
Ragatz, R.E. (2013), “California’s water futures: How water conservation and varying Delta exports affect water supply in the face of climate change,” Master’s thesis, Department of Civil and Environmental Engineering, UC Davis