The Sacramento-San Joaquin

The Sacramento and San Joaquin River basins extend nearly 500 miles north to south in what resembles a delicate array of arteries. The network acts like a major organ in the body of California. Trillions of gallons of freshwater move through it and are delivered to the rest of the state. Underneath, stores of groundwater continue their rise and fall, influenced by human usage and long-term climate effects.

The diagnosis on the health of these basins is disquieting. Drinking water wells running dry, winter snowpack disappearing, catastrophic flood risk imperiling water infrastructure, and Delta fish populations plummeting towards extinction. Additionally, the stressed basins are struggling to provide critical irrigation water for seven of the top 10 agricultural counties in the nationʼs leading farm state. Pretty soon, the system will need life support.

“The ongoing depletion of the groundwater actually disconnects rivers and streams from their flows,” said Ben Wallace, Senior Conservation Project Manager. “The looming challenges are invisible, until the rivers disappear, abruptly drying up.”

In 2021, TFTʼs California team continued its work to protect this vital resource. Notably, a new groundwater replenishment program was established in the Cosumnes. A major water district with excess surface water during the winter will apply it to dormant agricultural fields and sell credits to TFT in support of Microsoft and Amazon Web Servicesʼ “net zero” water sustainability goals.

A flock of greater white-fronted geese congregate at the Sacramento National Wildlife Refuge in Willows, Calif. Florence Low / California Department of Water Resources

“We are helping set California on the path to sound implementation of its landmark Sustainable Groundwater Management Act,” said Wallace. “We have to keep gathering diverse interest groups around the same table.”

Other projects continued. Aquifer recharge projects were adopted into a Groundwater Sustainability Plan in the Northern Delta, in both the South American and Solano subbasins. Work with Sacramento Regional County Sanitation District took steps forward to providing local farmers a safe and reliable water supply while also replenishing groundwater resources. First, letters of intent were signed with more than 50 landowners to receive recycled water delivery in late 2024. Second, the EcoPlan began implementation planning and priority analysis in 2021.

“The EcoPlan provides a critical opportunity to support biological diversity in the region for generations to come, while building capacity for sustainable agriculture,” said Wallace.

After the years of careful planning and coordination, what are the expected outcomes? Turning invisible impacts into visible solutions, such as sustainable irrigation for farmers using recycled water rather than pumping a dwindling supply of groundwater; protected drinking water for domestic wells in underserved communities; preserved natural habitat for wildlife and fish; and a regional groundwater supply in balance with multiple uses.


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In 2015 California passed Senate Bill 88, which made it mandatory for those diverting more than 10 acre-feet of surface water per year to accurately measure the amount of water used. In most cases, SB 88 requires meters for surface water diversions. However, in the Northern Delta, it is technically and logistically challenging to meter the diversions. Instead, most people use gravity-fed siphons, which are unpowered pipes that bring water from the rivers that are at higher elevations to the farms on the Delta islands. TFT is a partner in a scientific consortium to find more accurate and cost-effective methods of measuring water use.

In many locations, groundwater mixes with water in a river channel through the porous sediment surrounding a river. This is a natural process called hyporheic exchange. Rivers recharge the groundwater and, in some cases, rivers are depleted by declining groundwater. While many streams can naturally "lose" water, it is particularly the over-pumping of groundwater in much of California that has led to stream flows being significantly depleted.

For example, in south Sacramento County, a drop in the groundwater table of 30 feet in one area has jeopardized multiple other surrounding water resources – from irrigation wells to wetlands and forests to rivers that support migrating salmon.

TFT is working on several initiatives related to groundwater sustainability in northern California. It is working with the Northern Delta Groundwater Sustainability Agency (NDGSA) and its 17 member agencies to provide administrative support, analytical services, and grant-writing assistance as the NDGSA prepares their Groundwater Sustainability Plans (GSPs).

On a broader scale, TFT is developing user-friendly tools that provide information about water savings, the costs to implement savings, and, most importantly, how to add more water through conservation practices such as cover cropping and winter recharge with surface and stormwater.

In lieu recharge is where surface water is used as a substitute for pumping from a groundwater source. The substituted water is a renewable supply, such as excess surface water or treated wastewater. In lieu recharge allows for "conjunctive use," where surface water is used by persons that could otherwise extract groundwater in order to leave groundwater in the basin. This practice can help improve water reliability in California.

Groundwater is important to everyone, from farmers growing crops to local communities that rely on groundwater as their source of drinking water. Therefore, regional Groundwater Sustainability Plans (GSPs) need to consider the needs and concerns of all water users. In eastern Solano County, TFT is working with local partners to reach out to disadvantaged communities (where incomes are less than 80% of the state’s median household income) to actively engage them in the decision-making process about the future of the resource.