FRESNO — In the spring seven years ago, the San Joaquin River filled with snowmelt after a big winter and threatened destruction across western Madera and Merced counties.
Miles of levees kept the river from ripping through millions of dollars worth of farmland, crops, barns and roads.
But since that perilous spring, some of those earthen walls have sunk along with a swath of the west San Joaquin Valley landscape, because of farm water pumping. The levees probably wouldn't stop a big flow of water now.
What if this winter suddenly turns wet and the river rises again?
"We would probably use a lot of sandbags in trouble spots, as we did before, and hope we can keep up with it," said Reggie Hill, manager of the Lower San Joaquin Levee District. "But we may need to talk about raising levees at some point."
Hill and others say state and federal agencies are going to discuss the problem in the district, which spans 191 miles of levees in Fresno, Madera and Merced counties. Levees in Madera and Merced counties have been affected.
If the levees cannot hold as much water as before, authorities may have to consider slowly releasing reservoir water earlier in the spring runoff season to prevent a dangerous surge later.
Adding to the worry: In big spring runoff events, excess Kings River floodwater is shunted into the San Joaquin because the Kings has no outlet to the Pacific Ocean. In 2006, the combined runoff of the two rivers damaged levees and briefly threatened the city of Firebaugh.
The key agency in such big runoff years is the Army Corps of Engineers, which oversees the flow of water from all the rivers in the area during flooding.
"We are aware of the land subsidence," said corps spokesman Chris Gray, who is based in Sacramento. "We are going to meet with the agencies involved in the coming weeks."
This is not a new story. Deep sediments that fill the valley have been naturally sinking for thousands of years, but very slowly.
During the past few years, however, engineers recorded an unnatural, 2-foot drop over many square miles invisible to passing drivers but a real problem for water systems.
The sinking landscape has been accelerated by farmers who are supporting crop expansions, water leaders say. The farmers, who are east of the river in Ma-dera County, have no other source of water. They did not realize their deep-water pumping was creating a problem.
Area water districts noticed the changes when they couldn't capture as much water as usual at nearby Sack Dam on the river.
Federal engineers became involved because they're designing a replacement for Sack Dam as part of the San Joaquin River restoration. The sinking ground has delayed the project.