Crews work on patching a leaky levee at Tyler Island

​At Tyler Island, crews were working frantically Tuesday to patch a leaky levee in the hopes of saving around 20 homes from being inundated.
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​At Tyler Island, crews were working frantically Tuesday to patch a leaky levee in the hopes of saving around 20 homes from being inundated.
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Oroville Dam isn’t the only piece of California flood infrastructure under strain

By Ryan Sabalow, Ellen Garrison and Brad Branan

rsabalow@sacbee.com

February 14, 2017 06:23 PM

WALNUT GROVE

All eyes have been on the crisis at Oroville Dam, but weeks of wet weather have put pressure elsewhere on the network of levees and dams protecting cities and farms in California’s vast Central Valley flood plain.

Almost all of the major reservoirs that ring the Valley have filled to the point that officials have cranked up releases to catch water from a storm building up off California’s coast that’s expected to hit Wednesday night.

Most of the river flows below the dams haven’t exceeded the capacity of the levees that line their channels, and independent experts say California’s flood-control network has endured the exceptionally wet winter rather well.

But some levees, including those that protect the Sacramento region, are showing signs of the strain as prolonged heavy river flows push back.

“That groaning sound you’re hearing throughout the Central Valley isn’t the dams – it’s the levees,” said Jeffrey Mount, the former director of the UC Davis Center for Watershed Sciences. “We’re stressing them pretty well right now. And, just as you’d expect, issues are starting to crop up.”

The most obvious of those near Sacramento is in the northern Sacramento-San Joaquin Delta.

Fearing a dangerous levee-cracking “flood pulse,” workers this weekend intentionally breached a levee along the Mokelumne River in the north Delta. The breach flooded the levee-ringed McCormack-Williamson Tract of farmland near Walnut Grove in Sacramento County.

A bit farther south at Tyler Island, crews were working frantically Tuesday to patch a levee in the hopes of saving around 20 homes from being inundated from what officials described as an imminent collapse.

On Tuesday, crews used a crane to scoop huge loads of stone from a barge onto the huge crater that had formed in the levee, taking most of a gravel road with it.

“The key is we’ve got to get weight on this thing,” said Steve Mello, a Tyler Island resident and a trustee of the local reclamation district. He had no estimate when residents could return to their homes.

Mount said he expects more trouble to pop up along Delta levees in the weeks ahead from the continual rush of powerful flows from the estuary’s two primary rivers – the Sacramento and San Joaquin.

Mount said the flows from the rivers and tributaries such as the Mokelumne have fueled powerful tides from the Pacific Ocean that are pushing back in the other direction.

“The Delta is basically in a hydrological vise right now,” he said.

With potentially months left of rain and runoff from melting mountain snow, crews are already working round the clock to patrol the levees looking for breaches along the 70 levee-ringed tracts of land that make up the Delta, said Erik Vink, executive director of the Delta Protection Commission. These tracts are commonly called “islands” because they’re surrounded by canals, sloughs and channels.

“There’s certainly a lot of vigilance right now,” he said. “People are keeping a really close eye out, and they’re prepared to shift into flood-fight mode at a moment’s notice. There’s just a lot of water out there.”

Of particular concern both in and out of the Delta is the San Joaquin River, which is flowing higher than it has in years. Some buildings along its banks west of Turlock already have flooded. On Tuesday, officials issued a flood warning along the river southwest of Manteca.

Meanwhile, a key tributary of San Joaquin River – the Tuolumne River – has strained the regional flood-protection system east of Modesto to the brink.

Locals have been nervously watching the precariously full Don Pedro Reservoir. The reservoir, which has more than twice the capacity of Folsom Lake, was less than 3 feet from being completely full on Tuesday.

Operators of New Don Pedro Dam have their fingers crossed that the approaching storm follows Tuesday’s forecast: a relatively cold storm that will dump snow in the Sierra Nevada instead of the warm rain and melting snow that could prompt huge releases at the lake. That would overwhelm the small Tuolumne River channel and flood part of Modesto.

As it stood Tuesday, forecasts pointed to the lake avoiding such problems for the next 16 days, said Calvin Curtin, a spokesman for the Turlock Irrigation District, which manages the dam.

“It will be extremely close, but ... it’s not projected to spill at this point,” he said.

Closer to Sacramento, local levees were showing signs of stress, but experts weren’t worried.

“Sacramento has a lot of protection,” said Joe Countryman, a member of the Central Valley Flood Protection Board and a former engineer with the U.S. Army Corps of Engineers.

He said the region has performed substantial levee upgrades over the years. Sacramento also is protected by a robust system of outlets that spill major Sacramento and American river flows in the massive engineered Yolo Bypass flood plain west of the city.

But Countryman added, “You have levees, you have water – you’re going to have seepage.”

That was evident Monday when crews began emergency work along the Sacramento River to cork three boils that formed along a levee near the confluence of the Feather River north of Sacramento International Airport. Boils form when water seeps under the levee and eventually pushes its way to the land side, creating a small geyser. Local flood officials said they believed they had the problem under control.

Farther south, in urban Sacramento, residents were spotting likely levee seepage in some areas of the Pocket, Little Pocket and Land Park neighborhoods adjacent to the Sacramento River.

So far, nothing has raised concerns, said Russ Eckman, a California Department of Water Resources superintendent responsible for levee maintenance in several capital-area counties.

In the Little Pocket on Tuesday, water was actually trickling down the lawns in front of some homes, but residents also didn’t seem too worried.

Michael Proctor said his family has owned his home on Riverview Court since 1971, and he remembers when the seepage used to be really bad before local levees were upgraded.

“We’d have 4 or 5 inches of water in the backyard,” Proctor said. “When my family first moved here, you’d see pipes coming out of everyone’s backyard.”

The Bee’s Dale Kasler contributed to this story.

Ryan Sabalow: 916-321-1264, @ryansabalow