Thought Leadership

What the Near-Term Shift in Water Storage in California Means and How you Can Adapt Quickly Now

February 8, 2023

Shasta Lake, California
When full, Shasta Lake, California’s largest reservoir, has a storage capacity over four million acre-feet.

By Chris Petersen – Senior Hydrologist

California is going “all in” on groundwater. This is clear because of new groundwater regulation in California and the states’ recently updated Water Supply Strategy. California began regulating surface water rights in 1914 and,100 years later with the passage of the Sustainable Groundwater Management Act (SGMA) in 2014, water managers are required to achieve groundwater sustainability in all developed groundwater basins within 20 years. This new regulation will have profound impacts on how water is stored, moved, and used throughout the state. This blog covers the topic of the changing landscape of water storage in California, and this first article addresses conditions as they stand in Winter 2022-2023.

The Shift in California

Developed over the past century, the storage and distribution of surface water is accomplished through an incredible tapestry of federal, state, and local projects developed to quench California’s growing thirst. Given the lack of well-suited sites and concerns for environmental impacts, new surface storage alone is no longer a feasible solution to supply the state’s growing demand for water. Notably, a few dams are now being slated for removal to restore habitat. On the other hand, the storage potential in California’s underground aquifers is enormous by comparison, and largely untapped. Total combined aquifer storage capacity within our 515 groundwater basins has been estimated by the California Department of Water Resources at between 850 million and 1.3 billion acre-feet. In comparison, surface storage from all the major reservoirs in California amounts to less than 50 million acre-feet.

Implementation (“What This Means for You”)

As of winter 2022-2023, we are near the beginning of the 20-year SGMA implementation period. Unfortunately, California and the entire Western United States are experiencing the driest 22-year period since 800 AD, challenging local and state water resource managers now tasked with implementing SGMA. On the bright side, California and the federal government have allocated vast financial resources to improve infrastructure including water system improvements. In short, these are the worst of times and the best of times to implement the new storage needed to meet the requirements of SGMA, mitigate an uncertain climate future, and meet the growing demand for water in California.

The Groundwater Sustainability Plans (GSP) – developed by local Groundwater Sustainability Agencies (GSAs), as required by SGMA – have identified many projects and management actions to avoid undesirable results and reach their sustainability goals within 20 years. However, most GSPs lack detailed implementation plans for connecting existing or expanded surface storage with groundwater storage. Connecting the two requires changes in how surface storage facilities are operated, and new infrastructure is needed to move the surface water into the groundwater aquifers when available. It’s imperative that GSAs move quickly to build these facilities to achieve the sustainability goals within the 20 years required by SGMA.

Climate Change and Population Growth are Prime Motivators

In August 2022, the Office of the Governor released California’s Water Supply Strategy which outlines actions needed now to invest in new sources and transform water management. Without action, state officials believe extreme weather could diminish California’s water supply by up to 10% by 2040.

Cover of California's Water Supply Strategy

This important strategy outlines critical actions for water management needs throughout California.

The largest component of this strategy is to increase surface and groundwater storage by at least four million acre-feet by 2040. California is prepared to continue making large investments to assist locals in the development of this needed storage. The challenge is the integration of surface and groundwater storage, so that when the big gulps of water are available, we can move quickly to capture them in surface storage facilities, then slowly release at the capacity which the aquifers can absorb.

This is the time to act. Grant money is on the table now, and the potential for groundwater storage increase is enormous…but GSAs need to adapt quickly. Our experts believe that a careful and well-thought-out Recharge Master Plan is needed for each basin complying with SGMA. The GSPs have provided few details on frequency and volumes of water available for replenishment in their groundwater basins. Most have not described needed actions to integrate surface and groundwater storage. Addressing these issues in a Recharge Master Plan will help your community to design and build sustainable projects that yield multiple benefits. Multi-benefit projects with broad stakeholder support are the ones most likely to garner state and federal funding assistance.


Integrated operation of existing surface storage with new groundwater storage is getting lots of traction in California now due to SGMA, climate change, and continuing population growth. Our team at GEI can help you adapt quickly and stay ahead of the curve. Watch for us at ACWA, GRA, AWWA, FMA, and USCID where we are presenting on the topics of groundwater recharge, groundwater storage, and banking. Also check back for regular updates on this blog and contact me to learn how we are assisting our clients with their groundwater storage needs.