How do SGMA’s “sustainable yield” and the long-established legal concept of “safe yield” align—or differ—in practice? In a January webinar presented by the Groundwater Resources Association, panelists Stephanie Hastings of Brownstein Hyatt Shrek, Eric Garner of Best Best and Krieger, Anthony Brown, a hydrologist with Aquilogic, and Derrik Williams, a hydrogeologist with Montgomery and Associates, explored the nuances of these two terms.
While similar in definition, sustainable yield and safe yield serve distinct purposes in groundwater management. The panelists discussed how, although they often yield similar numerical estimates, the two concepts differ significantly in their underlying purposes and the processes used to determine them, highlighting key contrasts between SGMA’s forward-looking sustainability framework and the court-driven adjudication process for allocating water rights.
Sustainable yield and safe yield, defined
Sustainable yield, as defined by the Sustainable Groundwater Management Act (SGMA), refers to the maximum amount of water that can be withdrawn annually from a groundwater basin without causing undesirable results. SGMA mandates that local agencies, known as groundwater sustainability agencies (GSAs), manage groundwater basins within their jurisdictions to ensure long-term sustainability. These agencies are tasked with developing plans, implementing measures, and sometimes executing projects to operate their basins within the sustainable yield, as outlined by the statute. Specifically, SGMA defines sustainable yield as the maximum quantity of water, calculated over a representative base period of long-term conditions, including any temporary surplus, that can be withdrawn without leading to undesirable outcomes.
In contrast, the term “safe yield” has its roots in decades of groundwater adjudication and is best defined in the California Supreme Court case Los Angeles v. San Fernando. Safe yield is the maximum amount of water that can be withdrawn annually from a groundwater supply under specific conditions without causing undesirable effects, such as the gradual depletion of groundwater levels. The concept of “undesirable results” in this context typically refers to a steady decline in groundwater levels, eventually leading to groundwater depletion.
While the definitions of sustainable yield and safe yield appear similar—both aiming to avoid undesirable results—the two terms serve distinct purposes. GSAs calculate sustainable yield as a forward-looking planning tool to achieve future sustainability, whereas courts use safe yield as a backward-looking measure to determine water rights. Eric Garner highlighted this distinction, noting that in ongoing adjudications in Ventura County’s Oxnard and Pleasant Valley basins, as well as the Cuyama Basin, courts have adopted safe yields that closely align with the sustainable yields established by GSAs in their Groundwater Sustainability Plans (GSPs).
However, the purposes of these terms diverge significantly. “Safe yield is backward-looking, and its purpose is to determine water rights,” explained Eric Garner. “Sustainable yield’s purpose can’t be to determine water rights, because that’s not what the GSA can do. It’s a forward-looking planning number, an attempt to achieve sustainability in the future. So those are two different things.”
Derrik Williams further emphasized this distinction, referencing Dr. Ruth Langridge’s 2015 paper to the State Water Resources Control Board, An Evaluation of California’s Adjudicated Groundwater Basins, in which Dr. Langridge pointed out that adjudications primarily focus on establishing legal water rights, whereas SGMA is centered on the management and sustainability of groundwater resources rather than on determining water rights.
How sustainable yield and safe yield are calculated
The approach to determining sustainable yield and safe yield has remained largely consistent over the years.
“We’re still predominantly determining both safe yield and, in most cases, sustainable yield through some type of water balance; either we’re using analytical water budgets, or we’re using a groundwater model, or we’re using storage loss methods or Hill regression methods,” said Anthony Brown. “Essentially, we’re still trying to determine what the point is at which we don’t see significant and unreasonable declines in groundwater levels, and therefore significant and unreasonable declines in groundwater storage, and then we assume that most other undesirable results are then going to be tied to those groundwater levels.”
Mr. Brown also pointed out a key difference in the processes: under SGMA, there is a defined framework for determining sustainable yield, while in adjudication, the process unfolds in court under the guidance of an independent trier of fact, typically a judge.
The traditional process for determining safe yield begins by establishing the yield number, dividing it to allocate water rights, and then working through a “physical solution” comparable to the projects and management actions outlined in SGMA. “So that’s the process. Start with the safe yield. Go to water rights, go to the physical solution,” Derrik Williams said.
In contrast, SGMA flips this process. The physical solutions—projects and management actions—are decided first, and sustainable yield is determined based on those solutions. “The safe yield breaks up a factual basis of what the historical water budget was, and the sustainable yield says this is what we have to pump in order to get to sustainability,” explained Mr. Williams.
Safe yield vs. Sustainable yield: Key differences in process and equity
The panelists highlighted several key differences between the SGMA process and groundwater adjudication.
Anthony Brown noted that many overdrafted basins will likely need to reduce pumping. While a court can reduce pumping through water rights allocations, it must consider equity and cannot act arbitrarily. “The court cannot just say, party X has to stop pumping. Now the GSA can specifically say that,” he explained.
He shared an example: “I have been involved in one SGMA process, which is now an adjudication, where essentially the GSA said parties at x, y, and z have to stop pumping. So there was no consideration of water rights. It was simply a decision made by a government agency.”
Stephanie Hastings acknowledged that SGMA includes mechanisms for public participation but emphasized that it lacks the same legal obligation to consider equity as a court does. “A GSA does not have the same obligation to treat property owners who are the stakeholders in adjudication equitably. Those words are not specifically mandates of the groundwater sustainability agency. In fact, the groundwater sustainability agency’s responsibilities are to ensure sustainability,” she said.
Derrik Williams agreed but noted that GSAs must still strive to incorporate equity to avoid backlash. “Equity is going to be in the eyes of the beholder,” he said. “Equity is not the purpose of the GSA; it is getting to sustainability. Equity is something that you would like to incorporate into it, if at all possible. Just so there isn’t a small revolution.”
Anthony Brown added that while SGMA encourages public participation, it can sometimes be unevenly applied. “In some cases, in my experience, the GSA unfairly weights some of that participation. In an adjudication, a judge has an obligation to listen to all parties. Everyone gets their day in court, so to speak,” he said.
Eric Garner emphasized the importance of due process, particularly when property rights are at stake. “When you’re having a property right determined, you really need due process protections that do not exist in SGMA,” he explained. “With SGMA, when the sustainable yield is adopted, an engineer or an engineering firm has prepared a report, the GSA adopts it, and there are abilities to challenge it, but there’s no opportunity to conduct discovery and cross-examine witnesses, as you have in court. So when you’re going to determine a property right, it’s essential to have those due process protections.”
Lastly, Anthony Brown pointed out another significant difference: the limited options for challenging sustainable yield determinations under SGMA. “If you don’t think the sustainable yield determination is correct, your options are limited. You can try to challenge the GSA, but the GSA is also the judge, jury, and executioner,” he said. In contrast, in a courtroom, you can challenge decisions before an independent judge, and the court retains jurisdiction, allowing parties to revisit and reargue issues.
“Unfortunately, what we’re seeing with some of the adjudications is the parties feel they had no venue to challenge the sustainable yield, so they filed an adjudication,” Brown concluded.
Safe yield vs. sustainable yield: could they differ?
Derrik Williams explained that, to his knowledge, there hasn’t been a significant numerical difference between court estimates of safe yield and GSA estimates of sustainable yield. However, the potential for divergence exists, particularly in basins where GSAs are addressing existing undesirable results, such as seawater intrusion or impacts on interconnected surface water.
“You couldn’t just simply divide up the net inflow among pumpers and balance the water budget,” Williams said. “Because if you simply balance the water budget, you could stop the groundwater levels from dropping, but the ocean water is still higher, so you’re still going to be getting seawater intrusion, even if you stabilize groundwater levels. So under SGMA, you still have an undesirable result. It’s just not good enough.”
He emphasized that sustainable yield under SGMA is forward-looking, focusing on future conditions rather than historical ones. In cases like seawater intrusion, GSAs must first implement projects and management actions to address the issue. “You have to implement a lot of projects and management actions to stop seawater intrusion first, and then figure out, now that I’ve stopped it, how much pumping can I still maintain? And that’s your sustainable yield, and it has nothing to do with the water rights,” Williams explained.
Williams also noted that differences between safe yield and sustainable yield wouldn’t necessarily be problematic, as the two terms serve distinct purposes. “You could have a safe yield that is different, and says, based on the safe yield, this is everybody’s water right. And you could have a different sustainable yield that says this is the way we need to manage the basin in the future, and we need to match those up,” he said.
Is SGMA working?
Eric Garner noted there has not been an explosion of adjudications since SGMA was adopted over a decade ago. There have been about 4 adjudications out of about 90 medium- and high-priority basins, indicating that, in most places, SGMA is working. SGMA was intended as an alternative to adjudications, not as a replacement. It was to give a local agency all the tools that a court has in an adjudication. “I think overall, it is working pretty well. Because if you look prior to that, the only way most areas got groundwater management was through an adjudication, and now we’re seeing management in all the medium- and high-priority basins. That’s a huge step forward.”
Stephanie Hastings said the pace of adjudications is much quicker and will remain so. “We’ve really created a process through the comprehensive adjudication statute, and then figuring out what those key issues are that truly need to get resolved so that we can more quickly get to the physical solutions that the courts are required to implement, and then figure out how to marry those with the SGMA process and the GSP. So I do think the historical 30 years of groundwater adjudications we are unlikely to see again.”
“As a whole, when you look at all of California groundwater, SGMA has been a success,” said Mr. Brown. “Yes, there are a few outstanding issues in certain basins. I wouldn’t let those few bad apples sour the entire barrel of how groundwater is being managed in California under SGMA.”
Panelists share their final thoughts
“It’s important to remember that safe yield and sustainable yield are used for different purposes, so we shouldn’t try to conflate them,” said Derrik Williams. “We go through different processes to come up with them. I think what’s going to be more interesting is what we do when we have an adjudication: how do we go forward given that the courts have continuing jurisdiction and the GSA has the authority to reduce pumping as necessary to meet sustainability. Those sorts of questions are going to be interesting going forward.”
“Sometimes there’s a perception that an adjudication of the SGMA process is almost mutually exclusive, that if you’re going through the SGMA process, and then you turn to an adjudication, everything you’ve done in the SGMA gets thrown away, and now we have this new process that’s going to take over,” said Anthony Brown. “The reality of the adjudications that have occurred demonstrates that’s not the fact. In reality, what’s happened is that there may be slight differences between the safe yield and the sustainable yield numbers. But in many cases, the physical solution that’s ultimately been established by the court usually adopts the GSP as a component of the physical solution. And also they’ve, in many cases, made the GSA the watermaster. So, if you’re a GSA, it might be a painful process to go through an adjudication after you’ve had gone through the SGMA process, but what we’ve seen in the in the cases have gone so far, the outcome is it gives you additional power, gives you now, as a watermaster, the powers of the court, and it also gives you the benefit of those water rights have now being determined, and you can make decisions knowing they’ve been determined which is usually beneficial.”
“I think the SGMA process is working well, and they’re going to be some basins where courts have to get involved in determining water rights,” said Eric Garner. “But overall, it’s surprising how well it is working. But at the end of the day, you’re dealing with property rights, and so you have to give people the ability to go to court and have people review the yield number and have the court determine water rights.”
“I doubt that minor discrepancies or disputes over the GSA’s sustainability yield number are going to trigger lawsuits or groundwater adjudications,” said Stephanie Hastings. “It’s only when the actions that occur in the SGMA process have material impacts on what users’ property rights are that you’re going to find that motivation to get a second opinion from the court. The court is going to be the final arbiter, and they’re going to have to do that additional, separate process that’s not included in SGMA, which is to start by figuring out what’s the safe yield and what are those water rights and priorities, so that we can figure out whether the allocations that maybe were developed for a GSP are, in fact, consistent and equitable as compared to those water right determinations.”
