Tara Duggan, MAY 6, 2021
MODESTO — As California enters what could be a record-breaking drought, a just-completed nine-year floodplain restoration project at the confluence of the San Joaquin and Tuolumne rivers offers an ambitious attempt at one mitigation solution.
At a 1,600-acre former dairy ranch called Dos Rios, the conservation organization River Partners removed berms that farmers had originally constructed to protect their alfalfa and wheat crops from the river. It turned fields into seasonal pools where endangered baby salmon and migratory birds can rest, and water can trickle down to refill aquifers. Last month, it planted the last of more than 350,000 native grasses, shrubs and trees — acres of towering willows, flowering elderberry and creeping wild rye chosen to thrive in flood or drought.
“We’re trying to give the river space to do what it wants to do,” said Julie Rentner, president of River Partners, which purchased the property for $21.8 million in 2012 and plans to turn it over to the federal government within five years.
The project’s goal was to re-establish a natural floodplain with myriad water-saving and flood diversion benefits and to create habitat for threatened and endangered species like the least Bell’s vireo, fall-run chinook salmon and riparian brush rabbit. And while it is River Partners’ biggest project among a total of 16,500 acres of restored floodplains in California, it still represents only a fraction of the 500,000 to 1 million acres of irrigated farmland experts say will need to be retired in San Joaquin Valley to comply with the state’s Sustainable Groundwater Management Act, which requires that local governments create plans to make their aquifers sustainable by 2040.
“In the scheme of things, we’re working at lightning speed,” Rentner said.
While planting and landscaping work at Dos Rios finished a year ahead of schedule, the organization did suffer setbacks, mostly in getting funding and permits.
“To deliver 1,600 acres in 10 years isn’t fast enough,” she said.
The project cost more than $36 million in state, federal and private funding, but Rentner and supporters say projects like these have a good return on investment. Whereas the levee and aqueduct systems first introduced more than a century ago were good at flood control and helped turn the San Joaquin Valley into the world’s most productive farming region, they also removed vast floodplains where grizzly bears, salmon and millions of migratory birds thrived.
Restored riparian areas like Dos Rios, where the floodplain was widened both to control flooding and restore groundwater, have the added benefits of improving water quality, creating new wildlife habitat and sequestering carbon in newly planted vegetation. And even as the state becomes parched in summer, climate scientists expect it to experience 25% more frequent rain-producing atmospheric rivers in winter, and restored floodplains can help mitigate flooding.
During droughts, when farms are allotted less water from irrigation districts, they often must resort to pumping groundwater. In the drought of 2012-16, that led to aquifers in the San Joaquin Valley falling to dangerously low levels. Widened floodplains, on the other hand, help replenish aquifers because they slow down the flow of water, allowing it more time to drain into groundwater basins.
“We’ve put ourselves in a precarious position if we want to maintain high levels of agriculture and maintain ecosystems,” said Joshua Viers, a professor of civil and environmental engineering at UC Merced, who wasn’t involved in the Dos Rios project but has worked with River Partners on other projects. “If we just move the levees back, we can provide room for the river to support these dynamic processes.”
With headwaters in the Sierra Nevada, the San Joaquin River spills into the Central Valley around Fresno, where much of it is diverted into irrigation systems for agriculture or distribution systems for cities. As it flows northwest, it passes Dos Rios at the Tuolumne River, one of its tributaries, before it eventually empties out into San Francisco Bay and the Pacific Ocean.
Planted in phases, the ranch’s forests are at different levels of growth, from quarter-inch sprouts of mugwort, a flowering herb, to willows that have shot up to 40 feet. A 3-year-old forest at first appears to be a wild tumble of waist-high grasses and 10-foot Fremont’s cottonwoods with quivering leaves. But a closer look reveals that the plants are lined up in straight rows, just like the farm crops they replaced, because using modern farming techniques and equipment helps planting go more quickly.
“It’s a pretty unique thing to use modern agricultural practices to re-wild,” said Alex Karolyi, communications director at River Partners.
Biologists chose the mix of plants to try to introduce the right combination of flood- and drought-tolerance, because those conditions can change from year to year and season to season. Each plant in the grid is labeled so that if a tree thrives or dies, or maybe hosts the nest of a threatened Swainson’s hawk, biologists can track how the mix of nearby plants and other factors, such as water flow or salinity in the soil, worked together.
“We’ve created a system where you have to artificially introduce diversity,” Rentner said.
Until they are established, the younger forests are watered with the ranch’s existing irrigation system, which pumps water out of the rivers. The goal is to stop irrigation of the most recent plants by 2024, at which point the ranch will use 7,000 acre-feet less water per year compared with the previous dairy ranch — enough to supply 18,000 average-size households.
A graded floodplain is large enough for hundreds of thousands of baby salmon to rest on their migration from their river birthplace to the Pacific Ocean — something they once did when the valley flooded each spring before the modern aqueduct system was built. It gives them time to fatten up before racing toward the ocean and a better chance of survival.
The restoration also involved building several bunny mounds, 10-foot-tall raised hills where the endangered brush rabbit, which have returned to the area after restoration, can find refuge during floods. Previous experience taught the organization to plant enough herbs for the rabbits to eat until flooding subsides — and to create hiding spots on the mounds so they don’t become prey to predators.
Those predators are a sign of a healthy ecosystem and are easy to spot at the ranch. A coyote ambles by in broad daylight. Black and tan juvenile Swainson’s hawks practice hunting over an open grassy field.
River Partners will next work to restore the 500-acre Hidden Valley Dairy next to Dos Rios, which it has purchased. When it turns over both properties to the federal government, the organization hopes they will become part of the 90,000-acre San Luis National Wildlife Refuge, located across the river.
This level of re-wilding doesn’t need to be done to all the irrigated farmland the San Joaquin Valley needs to retire to meet state groundwater sustainability goals, said Viers, of UC Merced. But it can help the state deal with what he calls climate whiplash — increasingly close occurrences of flood and drought.
“There is no silver bullet in solving California water issues, but there may be silver buckshot,” he said. “These types of approaches are things we should be doing more of.”
See the original article in the San Francisco Chronicle.