COMMENTARY: In wet winters, California must do more to recharge groundwater

By Joe Mouawad, general manager of Eastern Municipal Water District, and Jim Peifer, executive director of the Regional Water Authority

Another wet winter seems likely for California, giving us another chance to recharge groundwater aquifers with captured storm runoff. But are we ready? Well, there’s a lot more we could do.

Forecasters say there’s a 95 percent chance El Niño conditions will prevail during the winter to come. In addition, they say the odds are 2-in-3 that this El Niño will be “strong,” which boosts the odds for wet conditions. This means we have a chance at two wet winters in a row, a very rare occurrence in California.

If theres anything last winter’s very wet conditions showed us, its the vast opportunity we have for groundwater recharge. By capturing abundant runoff in wet years, we have potential to make major strides toward rebuilding depleted groundwater.

Note that we say potential.”

One-third of Californias total domestic water supply comes from groundwater, and about 85 percent of all Californians depend on groundwater for some of their drinking water. California water agencies are doing everything they can to rebuild groundwater supplies. But there is enormous potential to capture more — if we had additional infrastructure and a few small changes in state policy.

Here is the reality of climate change: Only a year ago we were suffering after one of the driest winters ever. Then we were gifted with one of the wettest. Scientists predict these wild swings in weather will become more common, which means smart changes in water management are essential.

Reservoirs in the State Water Project (SWP) and federal Central Valley Project are predicted to lose 10 percent of their supply by 2040 due to warmer winters that shrink the Sierra Nevada snowpack. Thats a loss of 6 million to 9 million acre-feet annually, equivalent to losing two Shasta Reservoirs.

The good news? The groundwater aquifers under our feet can hold much more. The California Department of Water Resources (DWR) estimates California aquifers can hold an additional 850 million to 1.3 billion acre-feet of water. Thats extraordinary compared to the 50 million acre-feet held by Californias existing surface reservoirs.

Unfortunately, much of that aquifer capacity is not being used. Recently we have begun to reverse that trend, spurred in part by the Sustainable Groundwater Management Act (SGMA) of 2014.

Groundwater recharge can take many forms, according to the unique needs of local water agencies. Its also a resource we can expand gradually, as money and resources allow.

The Savory Pond Expansion project in Fresno, California. The project will capture surface water to recharge the underground aquifer which will improve the drinking water supply for domestic well owners and for residents of Shady Lake Mobile Home Park, a local disadvantage community. Photo taken August 19, 2022. Kelly M. Grow / DWR

In Riverside County, for example, Eastern Municipal Water District (EMWD) recently completed the Mountain Avenue West Groundwater Replenishment Facility. This $9 million project, in wet years, can accept State Water Project (SWP) supplies imported from Northern California, spreading the water onto porous soils to recharge the aquifer. It can recharge about 30,000 acre-feet annually, enough to serve 75,000 homes.

This facility is part of a larger $150 million effort, coordinated by the Santa Ana Watershed Project Authority, allowing EMWD and five other agencies to work together on watershed-scale groundwater management.

In the Sacramento metro area, the Regional Water Authority (RWA) has developed the Sacramento Regional Water Bank. It includes plumbing interties that link numerous local water agencies, allowing surface water and groundwater to be shared.

For example, when river flows are abundant, they are shared with groundwater-dependent agencies, allowing their wells to rest” and recharge naturally through riverbed infiltration. When rivers shrink in drought years, surface-water agencies can access the stored groundwater. The $280 million investment in this system allows them to pump and refill 60,000 acre-feet of groundwater annually, enough for 180,000 homes.

State grants helped pay for some of this work, together with local ratepayers. We need more state matching funds to expand groundwater recharge. This will help not only local water users, but the state as a whole.

For example, EMWD and RWA have plans to expand groundwater recharge worth a combined $700 million — if matching funds can be secured. These projects could reduce pressure on the Sacramento-San Joaquin Delta (source of SWP water) and its tributary rivers when they are stressed by drought.

There has been widespread support for promoting groundwater recharge, with no apparent opposition. Both Gov. Newsom and the Legislature have made efforts to further this cause, which is encouraging. However, we must do more.

These groundwater projects are a good bargain. The DWR estimates the state has 13 million acre-feet of groundwater capacity available for recharge. About 2.5 million acre-feet of that — five times larger than the recharge goal set by Gov. Newsom — is available using existing infrastructure.

Thats why we are thrilled to see Gov. Gavin Newsom sign the California Water Supply Solutions Act. The legislation (SB 659), sponsored by RWA, requires a state plan to advance groundwater recharge. It also directs state agencies to identify available resources, best locations and best practices to expand groundwater recharge.

Another important step is to streamline permits to divert stormwater out of rivers for groundwater recharge. This is especially important to expand controlled flooding of farmland, a largely untapped resource for large-scale groundwater replenishment.

Californias reality is that chronic drought will continue until we manage our aquifers better. To end Californias chronic water shortages, we need to start treating our aquifers as the water infrastructure of the climate change era. To do that, we must undertake groundwater recharge on a much bigger scale.

Joe Mouawad is general manager of Eastern Municipal Water District, which serves more than 825,000 people in Riverside County.  Jim Peifer is executive director of the Regional Water Authority, a coalition of two dozen local water agencies in the Sacramento metro area.

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