Can We Replenish Groundwater to Build a Stronger Ecosystem?

June 10, 2024

We chatted with Erik Ringelberg, Regional Vice President for The Freshwater Trust’s California operations. Erik joined TFT in 2016 and brings a problem-solving approach that is rooted in science and engineering to our work on the challenging water resource issues in the Golden State. One area of focus is California’s stressed and depleted groundwater supply. Read more to learn about how TFT is helping to find ways to replenish groundwater in strategic areas, and how that action creates a positive result for people, rivers, and the connected ecosystem.

What are the primary water issues in the Sacramento Valley, specifically the Cosumnes watershed, that you are most focused on?

While there are several water issues in this valley, ranging from elevated stream temperatures to fish passage barriers, our greatest focus is on groundwater. The Cosumnes River is the dividing line between California’s Sacramento and San Joaquin valleys, and these regions are significantly agricultural-based and dependent on groundwater.

The amount of groundwater in the San Joaquin Valley has severely declined. Below ground, portions of the water table have declined a staggering 700 feet. On the surface, we can see a drop in the ground level of 36 feet in some places. The Sacramento Valley is a moderately wetter region. In the Cosumnes, the water table has declined between 30 and 100 feet.

How are the effects of a declining groundwater supply seen and felt in the region?

In this region, groundwater is connected to the surface water in rivers, streams, and wetlands. When the groundwater supply declines, stream flows also decline, and riparian (streamside) forests are cut off from their water sources. We know that when a water table declines beyond 30 feet, even large trees like cottonwoods in a groundwater-dependent ecosystem are adversely affected. Smaller trees and plants such as willows and cattails feel the effect at a 10-foot decline.

Up and down the banks of the Cosumnes River, in many places the understory of small trees and shrubs is missing and not regenerating. With low stream flows and levees, the natural floodplain process of overflow isn’t happening. This is where floodwaters flow over the banks of the river and help spread the seeds of native trees. Without this natural overflow, we’re not seeing young trees in the understory of these ecosystems. Fall-run Chinook salmon returning to the river also struggle to migrate upstream when stream flows are low.

A healthy water table is also important for domestic well owners. As groundwater declines, most people do not have hundreds of thousands of dollars to dig deeper wells.

People in a dry field

Erik Ringelberg, center, and The Freshwater Trust team work with agencies, landowners, water districts and others to tackle challenging groundwater and surface water issues in northern California.

What tools are available to slow and reverse those declines?

TFT is looking at the ecological implications of the water table decline in the Cosumnes watershed. We use geospatial tools to identify and prioritize specific sites within the basin where conservation and management actions would provide the greatest ecological benefit, and to detect where declines are the greatest.

One way to reverse the decline is to engage in “managed aquifer recharge” or MAR. MAR is a cost-effective approach for retaining stormwater on agricultural fields where there would be no risk of flood or reduced agricultural productivity.

We synthesized large amounts of data to determine infiltration rates and flow metrics and link those to the most suitable fields for MAR.

Another way to reverse the decline is to provide recycled water for agriculture as a substitute for groundwater use. We have spent the last seven years supporting the State’s largest agricultural recycled water effort, the Harvest Water Program. This innovative, multi-benefit program provides reliable water and significant improvements to several thousand acres of riparian and wetland habitats.

As a part of the Harvest Water Program, our analytics are supporting new ways to look at riparian and wetland health through remote sensing. It is much more cost effective to use these tools at scale and they offer the opportunity to detect subtle changes on the landscape that traditional methods can’t capture.

Finally, there are regulatory tools, such as the Sustainable Groundwater Management Act. SGMA requires communities to come up with plans to responsibly balance their use of groundwater for agricultural, drinking water, and habitat needs. TFT has provided user-friendly tools to several groundwater sustainability agencies that weigh and rank different land and water management practices based on a suite of desired outcomes—including benefits to groundwater quantity as well as the economic impacts of implementing the selected practices.

What is exciting about the possibility of reversing the groundwater decline in the Cosumnes?

Everyone is facing a different facet of this problem. Landowners are facing the real issue of wells running dry. Farmers have unreliable water supplies. Chinook migration is reduced as groundwater levels decline. The bottom line is that all these groups need sufficient water levels, which means we have a common goal to bring us together.

We can solve this multifaceted problem by bringing together a coordinated set of actions that creates a net social, environmental, and economic benefit to this watershed.

For example, recharging the groundwater by itself isn’t a solution. But it is part of a solution when combined with good planning, direct recharge using floodwater, and bringing in recycled water instead of pumping groundwater. Looking upstream, work to protect and thin the overstocked forested headwaters of the Cosumnes is also an essential part of the plan.

Flooded vineyard in California

Walk us through a groundwater replenishment project. When does it happen? Who is involved?

One of our partners, the Omochumne-Hartnell Water District (OHWD), secured one of the first five-year permits for groundwater recharge from the State of California. OHWD wants to address an approximately 100-foot “cone of depression” where the level of water in the aquifer has declined due to excessive demand. OHWD is unique in that it doesn’t have irrigation canals or major surface water diversions. Instead, it is capturing excess winter stormwater and directing it back into the groundwater supply.

In practice, this takes place on 1,100 acres of vineyards that have a gravelly, sandy aquifer underneath. OHWD uses a large flexible pipe to capture floodwater from the Cosumnes and shoot the water into the fields between the rows of grapevines. Because the soil is so porous, the water disappears quickly past the root zone and into the groundwater table. In a single rainy season, OHWD can apply between 200 to 2,500 acre-feet per year of water to these fields, providing a significant boost to the water table below.

What were landowner interests and concerns about managed aquifer recharge (MAR)?

This approach must be geographically specific. The soil type, crop type, and compaction need to allow the excess water to move through quickly. It works great in some places but doesn’t work at all in other places. For example, in some mature orchards, landowners do not want water to sit on the roots too long. This can cause root rot or contribute to trees falling over in the wind. So, we have to be strategic about where to implement this solution.

Flexible water pipe in vineyard

Floodwater from the Cosumnes River is transferred to nearby vineyards to replenish water levels in underground aquifers.

What does a funder such as Microsoft or Amazon help you achieve? What do they get out of it?

By getting involved in groundwater replenishment projects, Microsoft and Amazon can help meet their sustainability goals. Basically, they can help fund ecologically targeted replenishment actions that we identify through advanced analytics to offset the water used by their operations. We have identified the best places to replenish water to create quantifiable environmental benefits, and they have been very supportive. This is a helpful element of a broader plan to restore a water-stressed basin.

How could this effort be amplified or expanded?

Fortunately, multi-party projects are the norm, not the exception, in this watershed, which makes amplification and expansion more likely to occur.

So many people are also emotionally connected to this place, making them want to work harder for change. We have a solid foundation to work from, and the early successes foster more interest and engagement.

With expansion, California’s Department of Water Resources (DWR), local water agencies, and nonprofits are working together to expand the foundational work by OHWD. DWR is providing technical assistance to build state support of MAR in this region. TFT is proposing methods to the Natural Resources Conservation Service (NRCS) that make it feasible to implement MAR practices on selected ag lands at scale to help the environment, domestic wells, and agricultural sustainability. The hurdle at this point is bringing together sufficient funding and effective systems to deploy that funding when and where it is needed.

The floods here two years ago were severe, resulting in a declaration of emergency after the regrettable loss of life. MAR could help reduce the threat of flooding and potentially save lives. Downstream of OHWD, in areas that were once natural floodplains, coalitions are looking at modifications to levees and flood retention structures to allow natural recharge. This could allow floodwater to passively flow into fields during major storms, even if the power goes out, reducing the likelihood of devastating flooding scenarios.

How do we know this approach is working?

Right, it’s important to show these actions have real benefits. Everyone who is involved in these projects wants to see how groundwater levels improve and wants to know that money is spent efficiently. Independent verifications of recharge and groundwater well monitoring are tracking changes in groundwater levels and the resulting ecosystem benefits associated with more groundwater. TFT and its partners have a decade of groundwater modeling that shows that without these kinds of replenishment projects, the riparian ecosystem community would largely be lost to climate change. The projects in this integrated strategy will take time to implement, and we will continue to monitor results to verify we’re trending in the right direction to reach the positive environmental impact the modeling has predicted.

Additionally, for Harvest Water, we developed an innovative adaptive management program with annual performance milestones, five-year evaluations of program effectiveness, and an operations and maintenance fund to cover any additional program costs.

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