Can subsidence be fixed without sinking economy?
Many parts of California are sinking, and it’s time we did something about it.
Subsidence occurs when water is pumped from underground. As the empty space left behind compacts, the ground above sinks. Roads on the surface can crack and become uneven. Bridges, anchored to either side, can twist. Cement canals crack and leak.
In the 1920s, ’30s and ’40s, subsidence was a huge issue as farmers pumped with abandon and parts of the San Joaquin Valley sank 30 feet. When the federal Central Valley Project started delivering water from Sierra rivers to those farms, subsidence ended. We checked it off our to-do list. The drought has brought it back, with a vengeance.
As scarcity and environmental concerns forced state and federal water managers to cut irrigation supplies, farmers fired up their pumps. Now, some areas in the Southern San Joaquin Valley are sinking an inch a year, says Michelle Sneed of the U.S. Geological Survey; some are sinking an inch a month. Damage could reach the hundreds of millions of dollars, even billions.
The Central California Irrigation District, which serves customers along the west sides of Fresno, Merced and Stanislaus counties, is seeing some problems. The district sits atop the Corcoran Clay, a deposit up to 200 feet thick running from Modesto to the Tehachapis. When water is pumped from beneath the clay, it irreversibly compacts – and the ground above sinks.
A CCID canal has cracked and a bridge must be raised. The district has spent $4.5 million so far, said general manager Chris White, and more canals are in danger. “If that subsidence goes on unchecked, there’s millions of dollars to be spent,” he said.
None of the remedies for stopping subsidence will appeal to everyone.
First, the state knows where subsidence is most likely and the location of wells that could cause it. It could impose per-acre fees as a set-aside for infrastructure repairs where the dangers are greatest – such as the Tulare Basin. That could be politically difficult as drought fears melt in El Nino’s rains.
Second, farmers could pump only from aquifers above the clay. Those aquifers won’t compact, but they’ve already been mostly exhausted. To replenish them requires drilling injection wells and building capture basins – projects that could be paid for through the water bond passed in 2014. But the California Water Commission has said it won’t fund any projects from the $7.5 billion bond until 2017, possibly even 2018. The state must move faster.
Third, the state needs better monitoring. During the previous subsidence crisis, well-like structures were used to measure sinking. Today, the state could require real-time monitoring for all pumping from aquifers beneath vital infrastructure. If subsidence is detected, the pumps could be shut off. Similar measures are likely under the Sustainable Groundwater Management Act, passed last year. If basin-management teams were established now, they could work with those farming outside irrigation districts – and outside regulation – to reduce unrestrained and harmful pumping.
Another, perhaps more effective, solution might be the most difficult to achieve. As CCID’s White put it, the state needs to put some “sanity” back into its water delivery practices.
“The bigger perspective is water supply; what are we going to do about the delta, about water-supply consistency?” he asked. “Instability of water deliveries is the biggest reason for subsidence.”
Consider last year’s fiasco on the Sacramento River. In early spring, San Joaquin Valley farmers were told to expect a certain amount from Lake Shasta and planted accordingly. A few months later, authorities became convinced there wouldn’t be enough cold water for the winter salmon migration, so they halted deliveries. Farmers had a choice – pump or lose an entire season’s investment.
In times of scarcity, every choice has perils. Promising reliability to farmers means less reliability for environmental needs. As more demands are made on water supplies, farmers will again be faced with hard choices.
If they pump, the ground will subside. If they don’t, an entire region’s ag-based economy could sink.
This story was originally published January 8, 2016 at 2:40 PM with the headline "Can subsidence be fixed without sinking economy?."