Newsletter - Fall 2009

Current Research - Environmental Quality

California’s Water Storage Problem, the Underworld, and the Body

Professor Graham Fogg’s research group with graduate students Jeannette Sager and Casey Meirovitz focuses on groundwater and surface water interaction and subsurface storage as a means of mitigating effects of climate change on California water resources. Although their work focuses on the Cosumnes River-aquifer system, the climate change aspect of the research has broader implications for California and other Mediterranean-type regions. The work is being funded by ’The Nature Conservancy and Department of Water Resources’.

California relies on snow storage and historically well-timed snowmelt to drive its 7th-ranked world economy and to produce about half of the nation’s fruits and vegetables with irrigation. Climate model projections suggest the Sierra snowpack could dwindle to a mere 20 to 40 percent of its historical volume during this century. Basically, the total precipitation has not declined, but winter is bringing less snow and more rain. Climate change is expected to decrease spring runoff, but increase winter runoff and flooding events. Consequently, less water will be available when it is most needed in the summer, because surface reservoirs will have to release more water in the winter. The new timing of the runoff will require different storage mechanisms for storing water.

There exists a need for additional water storage in CA. One approach is to build more dams and raise the heights of existing dams, but there is a consensus that the problem cannot be solved solely by augmenting surface storage. Subsurface storage is a tantalizing alternative and could be vastly increased if certain technical hurdles and limitations in our knowledge of the ‘underworld’ could be addressed.

The tantalizing part: Currently there is space for storage of an additional 10 million to 50 million acre-feet of water in the Central Valley aquifer, one of the largest groundwater systems in North America. For perspective, consider that the combined capacity of our four largest reservoirs (Shasta, Oroville, Trinity and New Melones) is 13 million acre-feet. Some subsurface storage and recovery of water already occurs in the Central Valley, but the time has come to adopt a grander vision on how to better use this vast below-ground reservoir on a regional scale.

Water percolates slowly into most aquifer systems. To capture more winter runoff and move it underground will either require new reservoirs to hold the water while it is doled out to spreading basins or a way of optimizing how water soaks into the earth. The latter has not been seriously considered but, I would argue, becomes plausible with greater knowledge of the subsurface "anatomy."

The limited knowledge part: Most aquifer systems are mostly not aquifer. For example, in the aquifer systems underlying the Central Valley, only about 20-50 percent of the volume is made up of geologic materials (sands and gravels) capable of supplying significant amounts of water to wells, while the remainder is composed of non-aquifer material (silts and clays).These aquifer structures constitute an extensively connected network that is embedded in the non-aquifer materials. The way that water moves through such a system is not unlike how liquid moves through the human body. You have a 3D network of "avenues" (aquifers, analogous to veins and arteries) that support a relatively fast flow of liquids; the intervening regions consist of materials (in the body, tissues) that support much slower rates of movement. Liquid in the fast zones moves hundreds to thousands of times faster than in the slow zones, and there is a tremendous amount of liquid and chemical exchange occurring between the two. Unlike the human body, however, the locations of the fast-flowing avenues and where they approach the land surface are generally not known. Fortunately, this knowledge is obtainable, and it would create a new world of possibilities. For example, by knowing the small percentage of the landscape where the aquifers intersect the surface, one could design aquifer recharge enhancement projects to efficiently move large volumes of winter runoff into the subsurface. One possible strategy in less-developed parts of the valley is to let the river floodplains flood, thereby maximizing the chances that floodwaters soak into the "sweet spots" in the system.

The bottom line is that the subsurface storage potential in the Central Valley aquifer system is exciting, and the technical hurdles are not insurmountable. The first task is to better define the subsurface anatomy. Our Cosumnes River-aquifer system research is doing just that through advanced geologic characterization. Additionally, integrated modeling of not only the surface water and groundwater, but also the vadose zone, is providing basic insights into how the floodplains and integrated hydrologic systems could be managed to maximize subsurface storage under

For additional information, regarding CA water situation see: http://sierratosea.ucdavis.edu/