Crumbling Tyler Island levee ‘looks like a meteor hit it’

THE DELTA — Crews planned to work through the night Monday to fix a serious levee problem on sparsely populated Tyler Island, consisting of thousands of acres of farmland just north of Highway 12.

Crumbling and cracking on the land side, the levee was said to be in “imminent” danger of failing early Monday afternoon. That hadn’t happened by nightfall. Still, an engineer said the danger hadn’t passed.

“We’re a long way from being in a position where we can say this levee is safe,” engineer Chris Neudeck of Stockton said.

The town of Walnut Grove, which sits near the north end of the island, is protected by another levee and was not in danger, said Neudeck, who represents the local reclamation district that maintains the levee.

The rest of the island is mostly farmland, with a small number of homes. Evacuations were in progress while levee crews rushed to place rock and sandbags on the dry side of the levee, which appeared to be crumbling under pressure from the swollen Mokelumne River.

“We’re hanging on by our fingernails,” Neudeck said.

If it floods, Tyler Island would be the first substantial Delta island to be inundated since Jones Tract in 2004.

Like many Delta islands, the land surface on Tyler Island is much lower than water in adjacent channels, making it more like a bowl that will fill with water slowly if the levee breaks. Much of the southern area of the island ranges from 5 to 10 feet below sea level; if a flood occurs, the waters may be 15 feet deep or more, Neudeck said.

But Steve Mello, whose family farms on Tyler Island, said Monday that it would take a day and a half for the flood to reach most of the homes that might be in danger. Tyler Island is massive, stretching close to eight miles from the southern end to Walnut Grove Road near the northern end.

“The only place that’s on low ground is my son’s house, and that has already been evacuated,” Mello said.

The sudden deterioration of the levee on Monday was a surprise for more reasons than one. First, according to a map produced by the state, the levee around the south side of Tyler Island is built to a relatively high standard, as Delta levees go.

Second, flows on the Mokelumne actually had gone down a couple of feet over the past few days — though, to be sure, the water remained very high.

“All I can say is that once these things get saturated, they start to lose strength. And when they lose strength, you don’t know when they’re going to go,” Neudeck said. “Why it just melted on us is anyone’s guess. It looks like a meteor hit it.”

Neudeck said it was not entirely clear whether a flood at Tyler Island might affect neighboring islands. It might help by reducing flows on the Mokelumne, but he warned that an abrupt reduction in river flows actually can destabilize the water side of other levees.

Large quantities of water still were coursing into the Delta on Monday after last week’s storms, increasing the pressure on 1,100 miles of levees. Flows at Rio Vista are expected to remain relatively high for the foreseeable future.

And in the south, the San Joaquin River near Vernalis is expected to rise above flood stage by Wednesday, for the first time since the storms began in earnest in early January.