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Blog Post · June 2, 2020

Commentary: Competing Narratives on Delta Outflow Fuel Water Conflict

Photo of an aeriel view of the Sacramento San Joaquin River Delta

This commentary was published in CalMatters on May 28, 2020.

In a February CalMatters commentary Dan Walters noted that California’s water wars had reignited. The latest dustup revolves principally around the federal government’s efforts to increase the amount of water supplied to farms and cities by the Central Valley Project, and a breakdown in cooperation between the state and federal government. It seems like everyone is suing each other. But what are they really fighting over?

To the uninitiated, the details of this conflict are hard to follow (a good summary can be found in Western Water). This is made more confusing by an array of contradictory narratives.

At the heart of the controversy is “Delta outflow.” This is the volume of water that flows from the Sacramento-San Joaquin watershed, through the Delta and into San Francisco Bay.

Regulatory changes in required Delta outflow are a big deal because they come with potential trade-offs between supplying water for farms and cities or for the ecosystems that support endangered species, recreation and other uses of the Delta.

We conducted a study in 2017 of the destination of water once it enters the Delta. About a quarter of it is either pumped from the Delta by the state and federal projects or used within the Delta. The rest becomes fought over and misunderstood outflow into San Francisco Bay.

One common narrative is that outflow is water “wasted to the sea.” Closer examination shows that most outflow either cannot be used or is needed to maintain water quality for water supply. The portion fought over—water allocated to protect the ecosystem– is surprisingly small.

Most Delta outflow is water that can’t be captured because it’s simply too costly to store, divert, and use (capturing it would require new expensive reservoirs and aqueducts). These uncapturable flows come during winter storms or periods of very high snowmelt runoff, occurring even in dry years. And this outflow is not “wasted” since it plays a vital role in the health of San Francisco Bay.

Additionally, to keep the Delta fresh enough to use for farms and cities, a large amount of water must flow into the bay year-round. If outflow drops too low—especially when export pumps are operating—the Delta gets too salty. The amount of this outflow is large—roughly four times the amount of water exported to southern California cities.

The big fights are over the third category: the outflow allocated to protect the Delta ecosystem and fishes protected by state and federal Endangered Species Acts. This is the volume of outflow over and above that required to keep the Delta fresh enough for water supply.

Environmentalists have claimed that ecological outflow is insufficient, and that it has remained largely unchanged despite 40 years of regulation. For the former claim, the uncertainties are large, but more water for the environment–more effectively allocated and paired with habitat improvements–is likely needed to improve the health of the Delta ecosystem.  But for the latter claim, they are wrong. Since 1995 the amount of water dedicated by regulation to the ecosystem has grown significantly from virtually nothing in 1980 to about 12% of average inflow today (except during dry years when the proportion is much lower).

Water user interests, for their part, emphasize the cost to water supplies from increased ecological outflow to support fish. But again, this claim is often overstated. At times, natural runoff is sufficient to meet ecological standards with no net cost to water supply. We estimate that since 2008, when the most stringent regulations were enacted, roughly half of the ecological outflow has come at the expense of supply. That is still a lot of water—enough to support more than 400,000 acres of farmland or more than two million households—but far less than commonly claimed. And focusing solely on water supply costs ignores the broader benefits of a healthy Delta ecosystem.

These facts don’t change the roots of the disagreement. The various interests are fighting over real trade-offs between water supply for farms and cities, and Delta outflow to protect the ecosystem. But both sides tend to talk past each other and overstate their cases. The numerous lawsuits are also a high-risk, low-reward strategy for addressing this problem, because the solution involves much more than a judge changing the Delta outflow equation. Instead, the answer lies in getting back to the table and negotiating a comprehensive agreement—with more on the table than just outflow—that most parties can live with, even if they don’t like everything about it.


Freshwater Ecosystems San Joaquin Valley Water Supply Water, Land & Air