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Replenishing Groundwater in the San Joaquin Valley: Here's a 2024 update

By ONME Newswire

This research was completed by Caitlin Peterson, Ellen Hanak, and Zaira Joaquín Morales, with research support from Meagan Brown, Spencer Cole, and Kyle Greenspan. This report discusses the results of a repeat survey conducted in fall 2023. Their goal was to understand recharge activity in 2023—one of the wettest years on record in the southern valley—and identify areas of progress made since 2017, as well as remaining barriers to expanding this practice.             

Groundwater recharge is an important water supply strategy across California—and especially in the San Joaquin Valley, where many groundwater basins need to address significant overdraft to comply with the 2014 Sustainable Groundwater Management Act (SGMA). Managed groundwater recharge entails intentional actions to replenish underground aquifers, using methods such as spreading water on farmland, switching to surface water so that groundwater can remain unpumped, and building dedicated basins where water can more easily percolate into aquifers. Recharge is already a long-established practice in some parts of the valley, and with the advent of SGMA it has come into greater focus. In their first groundwater sustainability plans (GSPs), submitted in early 2020, the valley’s local groundwater sustainability agencies (GSAs) identified recharge as the single biggest solution for bringing basins into balance. In total, they anticipated expanding recharge by an average of roughly 1 million acre-feet per year—across both wet and dry years—or about half of the region’s groundwater deficit (Hanak et al. 2020).

However, numerous technical and institutional constraints could prevent GSAs and their members from accomplishing this goal. Rechargers need the physical capacity to divert and capture additional water during wet periods, authorizations from regulatory agencies, and the right incentives and accounting systems to track and credit those who invest in recharge. And because dozens of GSAs and other water management agencies in the San Joaquin Valley operate in a largely decentralized manner, it can be difficult to track progress on recharge and understand where the key challenges lie.

In the fall of 2017, 202 urban and agricultural water management agencies in the San Joaquin Valley were surveyed to understand their recharge activities during 2017, the first wet year following SGMA’s passage and one of the wettest on record in the northern part of the valley. The team's report Replenishing Groundwater in the San Joaquin Valley (Hanak et al. 2018) found strong interest in the practice, along with a number of issues limiting its expansion, including the availability of regional conveyance and diversion equipment to get water to recharge sites, low uptake of the relatively new technique of spreading water on farmland, regulatory barriers, and weak or nonexistent groundwater accounting systems.

Since 2017, the GSAs have begun to operate and implement their GSPs, and two further wet winters and springs (2019 and 2023) have offered additional opportunities to put groundwater recharge into practice. The state has also increased its attention to recharge.

The Newsom administration identified recharge as a priority for adapting to drought and the changing climate in its 2022 California’s Water Supply Strategy (Office of Governor Newsom 2022), and state agencies have sought to support local recharge efforts with measures including temporary permitting of high-flow diversions, over $120 million in grants for recharge projects, and emergency funding in early 2023 to support the diversion and recharge of floodwaters.

How Recharge Works in the Valley

Groundwater recharge spans a spectrum of approaches, from passive to active (see text box). On the passive end of the spectrum, some surface water seeps into the ground every year—even during droughts—as a natural by-product of irrigating fields and urban landscapes and as water moves through rivers and unlined canals. On the active end, some local agencies have invested in dedicated infrastructure, such as recharge basins on lands with good permeability. Many agencies operate somewhere in the middle of the spectrum, taking advantage of opportunities to recharge extra water in unlined canals and riverbeds and on irrigated lands when it is available. Historically, such relatively informal methods were most common, and often encouraged by water agencies through price incentives that made surface water cheaper than groundwater pumping (Hanak et al. 2011). Starting in the 1990s, agencies in some areas began adopting more formal programs and accounting systems. Some of these programs are set up as groundwater banks that offer recharge services for off-site parties who have more limited opportunities on their own lands. Over time, investments in canal lining and more efficient drip irrigation systems have also restricted the use of the more traditional, passive recharge approaches in some areas.

Much of the San Joaquin Valley has characteristics that are especially suitable for recharge. For one, soils in many areas—especially on the valley’s eastern side—tend to be highly permeable. For another, intensive groundwater use and overdraft have created room to store water underground in many basins. And with SGMA’s mandate to attain groundwater sustainability, agencies in overdrafted basins now have strong incentives to recharge to bring their basins into balance. As Figure 1 shows, basins on the valley’s eastern side, including Kern, have some of the most suitable soils for recharge, as well as the largest levels of overdraft. These are also the areas where we are seeing much of the region’s recharge activity.

Recharge Practices Are Evolving

Beyond the question of how much recharge occurred, the survey sheds light on how recharge practices are evolving in the SGMA era. Here we review recharge methods, sources of water used, and how local agencies are tracking and accounting for recharge and providing incentives to landowners.

Agencies Are Using a Similar Portfolio of Recharge Methods as in 2017

We might expect some changes in the landscape of recharge practices since 2017 given GSAs’ plans to expand recharge capacity as part of their groundwater sustainability plans. The recharge projects in those plans emphasized recharge basins and in-lieu recharge activities (Jezdimirovic et al. 2020). There have also been considerable efforts in recent years to disseminate information about the relatively new method of recharging by spreading water on active or fallowed cropland, floodplains, and other open space.(14)

On balance, while over half of all survey respondents said they expanded their recharge capacity since 2017, there was little change in the overall prevalence of various recharge methods. Four of these were used by about half of all respondents in both years: in-lieu recharge, recharge basins, unlined canals and streambeds, and spreading water on farmland (Figure 3). Several agencies also reported using two methods that we first asked about in the 2023 survey. Stormwater basins, which can be used for recharge, are especially popular with urban agencies that operate these as part of their flood control systems. And some agricultural agencies are experimenting with recharging using perforated pipes under active cropland—a technique that has higher up-front costs but offers more control to the grower than spreading water on farmland.

As in 2017, agencies were less likely to track and report volumes recharged by spreading water on farmland or by using the more traditional or passive methods—in-lieu, unlined canals, and stormwater basins.(15) In the case of recharge on farmland, agencies can either apply water to the land on their own behalf (for example, by leasing land from growers to use for recharge), or deliver water to landowners with the assumption that it is being spread for recharge. The latter practice is more difficult to track and monitor, which may partly account for the lower volumes reported for this method. In contrast, volumes stored in recharge basins or as part of off-site banking partnerships were much more likely to be tracked (Figure 3).

Some Methods Are Capturing Much More Water than Others

Even allowing for differences in reporting, it’s clear that the four widely practiced recharge methods are playing quite different roles. As in 2017, dedicated basins accounted for more than half the volumes recharged (Figure 4). In-lieu recharge volumes grew, but came in a distant second, with nearly a quarter of the total. Spreading water on farmland also grew, though tracked volumes remain small (9%).(16) Finally, recharging water in unlined canals and streambeds (11%) was the only one of the four most widespread methods that saw a dip—perhaps reflecting less tracking of this method in 2023.

In comparison, the three other on-site recharge methods—via stormwater basins, running water through tile drains under cropland, and injecting water into wells—barely register. Whereas the latter two methods are closely monitored, the small numbers for stormwater basins could partly reflect challenges in tracking volumes stored.

Finally, off-site recharge, which generally involves formal banking of water by one party on behalf of another, saw similar volumes in both years, despite the overall growth in on-site recharge. A total of seven respondents (12%) reported banking 536,000 acre-feet for their customers in off-site projects; most of this (88%) occurred through recharge partnerships among parties in the Kern subregion. It is possible that some respondents did not report other local partnerships—particularly when they occur within GSAs that responded as a group. Nevertheless, the apparent lack of growth in groundwater banking partnerships could represent a missed opportunity for agencies that do not have suitable or adequate recharge capacity on their own lands.

Rechargers Tapped More Water Sources in 2023

The main sources of water for recharge remained largely similar to those reported in 2017, with agencies drawing on water from local rivers and streams, imported water—including both regular deliveries and flood flows—from the Central Valley Project (CVP) and State Water Project (SWP),(17) and both local and imported water purchased from other parties (Figure 5). But as water agencies increased their recharge activity, they leaned more heavily on some of these sources and started tapping some new types of supplies.

  • Local rivers and streams—including floodwaters—remained a major source. Local rivers and streams on the valley’s east side—shown in Figure 1 above—supply many agricultural water agencies with irrigation water, and during wet years they serve as a major source for recharge. In 2023, flooding conditions increased both the challenges and opportunities provided by these local waters. A full 90 percent of respondents reported using local water for recharge, up from 84 percent in 2017. Several agencies received a significant influx of recharge water from flooding, and the Newsom administration’s executive orders (EOs) in the spring of 2023 (Executive Order N-4-23 and Executive Order N-7-23) granted local agencies and landowners permission to divert floodwater onto their land for recharge without water right permits. More than a quarter of respondents indicated that the EOs enabled more recharge in 2023; one GSA reported that 90 percent of recharge water applied by their members was diverted via EO N-4-23.

  • A market for recharge water is developing. Even in a very wet year, not everyone has ready access to water for recharge; one solution is to buy it from others. In 2023, a much larger share of respondents (40%) purchased recharge water than in 2017 (18%). Managers told us that the market for recharge water has been growing in recent years—in addition to the regular irrigation season market, there is now a market for recharge water in winter/early spring, and even in the fall in some years. While these trends may create opportunities for some parties to expand recharge, they also raise the price of recharge water for those who were accustomed to getting this water with less competition in the past.

  • Urban recharge sources are on the map. Both urban stormwater and recycled water now appear as recharge sources for some urban and agricultural agencies—a change since 2017, when few if any agencies reported them. While still not widespread, the growth in these sources reflects interest in tapping a variety of local sources for recharge—even in wet years—and a rise of urban–agricultural partnerships.

As PPIC has shown in earlier work, groundwater recharge is the primary supply-side option for cost-effectively reducing groundwater overdraft in the San Joaquin Valley (Escriva-Bou 2019; Hanak et al. 2019). Recharge will also become increasingly important for this region in our changing climate, as droughts become more intense (Albano et al. 2022; Moyers et al 2024), rising temperatures reduce seasonal storage of water in mountain snowpack (Shulgina et al. 2023), and larger storms increase flood risk (Swain et al. 2018). Strong progress on recharge is key, both to minimize reductions in water use and irrigated acreage as the valley implements SGMA, and to mitigate growing risks from both droughts and floods.

In many regards, 2023 was a banner year for recharge in the valley, reflecting momentum since the wet winter of 2017 from both the implementation and policy standpoints. Volumes are up, interest in recharge remains high, some of the technical difficulties have been ironed out, and both local and state policies are evolving to reflect accumulating on-the-ground experience. But more work is needed to realize the promise of this tool. Two major efforts require the robust involvement of state agencies and local stakeholders: conducting broad, watershed-scale assessments of the conditions under which water can be made available for recharge, and evaluating where improvements in regional conveyance infrastructure would be good investments.

Making continued, incremental progress in several other key areas—including groundwater accounting, recharge on farmland, regulatory flexibility, and recharge partnerships—will help the valley secure a sustainable future for its people, economy, and environment.


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