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Photo By Richard Thornton / Shutterstock.com

By Scott Hamilton, President, Hamilton Resource Economics

The recent announcements of low water allocations for 2021 highlight the need for improved water management in California. California farmers typically see years that are wet or dry and not much in between. Understanding and embracing that phenomenon is the key to successful water management in California–turning a series of random water supply feasts and famines into a reliable water supply.

Where Delta water went 1980-2016. The crimson bars indicate the quantity of uncaptured water—water not used for other designated purposes and average 10 million acre-feet per year. The letters in parentheses indicate the water-year type: W–wet, A–above normal, B–below normal, D–dry, C–critical. (Public Policy Institute of California (2017), A New Approach to Accounting for Environmental Water: Insights from the Sacramento–San Joaquin Delta)

The vast majority of the San Joaquin Valley has good quality groundwater housed in deep aquifers. The storage capacity of those aquifers is astounding, many times the size of the largest surface reservoirs in the United States. And for decades, water managers in the San Joaquin Valley have been capturing the high flows in the years of plenty and storing it in the ground for the inevitable droughts which follow. But for too long, withdrawal from the aquifers have exceeded the recharge. In response, groundwater managers have judiciously added more groundwater recharge capacity, and that kind of intelligent resource management has been extremely effective. In Kern County for example, it was not unusual for flood water to leave the county. But in 2017, the wettest year in the last 20, all of the flows of the Kern River were captured and stored within the county. Almost certainly that trend of building more recharge will continue so that the flows of the White, Tule, Kaweah and Kings rivers are captured locally to the fullest extent possible. Unfortunately, that will not be enough.

Various organizations have advocated for local self-sufficiency—that the various regions should be independent when it comes to water supply and use. They suggest that such independence can be achieved through water conservation, water recycling, water reclamation, capturing local flood water and water marketing. As useful as these practices are, they fall far short of meeting the water needs to maintain the dynamic agricultural engine of the San Joaquin Valley. Combined, these practices may reduce deficits by 250,000 acre-feet on average when the Valley faces shortfalls in excess of 1.5 million acre-feet. And why would it make sense to allow water from northern California, that is surplus to dedicated environmental and other beneficial purposes, to flow to the ocean when the water can be put to beneficial use to help feed and clothe a growing population? The idea of water self-sufficiency appears to be at odds with the concept of the State of California—is the state not one? Does water regional self-sufficiency make any more sense than regional energy self-sufficiency or regional food self-sufficiency?

If all of the local sources of water are insufficient to meet the needs of the Valley, where can additional water be found? The Public Policy Institute of California conducted a detailed and illuminating study of water uses in the Sacramento-San Joaquin Delta (the Delta). The Delta is the hub of water conveyance in California. All of the water released from northern reservoirs like Shasta and Oroville must pass through it. Delta waters must meet many needs: in-Delta agricultural and urban uses, outflows to prevent salt water intrusion (system water), a range of environmental needs (ecosystem water), and export supplies for the state and federal water projects. As can be seen in the figure below, in some years, those uses exhaust all of the Delta water supplies. But in other years, there are substantial quantities of “uncaptured” water—the crimson bars in the figure. On average, the uncaptured water amounts to around 10 million acre-feet. Compare that to the roughly 1.5 million acre-feet needed by the Valley. But averages can be deceptive. In some years, such as the drought of 1987 to 1992, there was barely any uncaptured water. This means that in the wet years, like 1995 through 1998, more than 3 million acre-feet per year would need to be redirected to the Valley for groundwater storage. 

Why isn’t this water being diverted now? The answer is rooted in both politics and a large number of regulations designed to protect endangered species. Needless to say, before more water can be diverted from the Delta, infrastructure needs to be improved so that water can be diverted without harming endangered species. Implementing that technology will not be simple or cheap, but the strength of the Valley economy and its communities depend on getting that right (a topic for a future column in the Valley Ag Voice). 

The Public Policy Institute of California has shown that there are large quantities of uncaptured water, but only in some years. 15% of the uncaptured water might be sufficient to achieve groundwater sustainability in the Valley. However, that water can only be diverted during periods of feast, and that the Delta waters are needed elsewhere during times of famine. That concept needs to be at the heart of any project aimed at achieving groundwater sustainability.