Another atmospheric river closing in on California may finally push two key reservoirs over the brim on the Tuolumne and Mokelumne rivers.

Don Pedro Reservoir, southeast of Stockton, could spill by Tuesday, officials said late Friday. Don Pedro is of special concern because it feeds into the San Joaquin River, which is already at or near flood stage.

If Don Pedro spills, the release is not expected to be anywhere near what happened in 1997, said Brandon McMillan, a spokesman for the Turlock Irrigation District, which owns the dam. In 1997, nearly 60,000 cubic feet per second plunged down the Tuolumne and flooded Modesto and agricultural areas of south San Joaquin County.

“This is entirely different,” McMillan said. “The range we’re looking at is significantly smaller.”

Still, flood managers are worried based on Don Pedro’s immense size, its limited ability to release water without flooding Modesto, the huge snowpack above the reservoir, the fact that it’s only mid-February, and the potential for the amount of water flowing into the reservoir in the coming days to be larger than expected.

They have urged the U.S. Army Corps of Engineers to allow somewhat higher water releases now to prevent a potential disaster later. Indeed, the Corps on Friday agreed to allow river flows about 6 inches higher in Modesto, allowing for slightly more water to be dumped from Don Pedro. As of Friday night the reservoir was 4 feet from the top.

“We’ve got their attention and they’re looking at it. Now we cross our fingers,” said Glenn Gebhardt, Lathrop’s director of community development.

Farther north, the East Bay Municipal Utility District says Lake Camanche may also spill by Tuesday for the first time in two decades. The utility, which exports Mokelumne River water to 1.3 million people in the Bay Area, is essentially out of room at Camanche and its upstream sister reservoir, Pardee. Most of its smaller reservoirs in the Bay Area are also full.

If Camanche spills, that may be unwelcome news for farmers along the Mokelumne downstream of the dam, who have already seen substantial flooding in some areas.

Based on the forecast, however, the utility says it doesn’t expect to have to dump any additional water down the river. If the reservoir spills over, officials can release less water from the bottom of the dam. Mokelumne River flows downstream should stay near 5,000 cfs, where they’ve been for some time, utility spokeswoman Andrea Pook said.

Lodi officials warned Friday that if the Mokelumne River does rise, street flooding is possible in the Rivergate area and other neighborhoods along the river. Sandbags will be available from 7 a.m. to 7 p.m. Sunday at 1331 S. Ham Lane (bring your own shovel).

With so much attention on the recent problems at Oroville Dam, it’s important to know how Camanche and Don Pedro will process the water if they reach capacity.

At Camanche, the water will simply spill over the top. Because there is no gate at the top of the spillway, there is no need for an emergency spillway, Pook said.

It’s more complicated at Don Pedro. The lake has both a gated spillway and a concrete weir over which water can flow uncontrolled. If the lake fills, officials will open the gated spillway, McMillan said. Because the reservoir should be rising slower than it did during the more intense 1997 flood, little water if any will spill over the weir, he said.

Unlike Oroville, where the emergency spillway that nearly failed last Sunday had never been used, both Don Pedro and Camanche have dealt with past floods in this manner.

— Contact reporter Alex Breitler at (209) 546-8295 or abreitler@recordnet.com. Follow him at recordnet.com/breitlerblog and on Twitter @alexbreitler.