To cope with the drought, the South San Joaquin Irrigation District will reduce by 20 percent the amount of drinking water it supplies to Manteca, Lathrop and Tracy.
The cutback in surface water deliveries will last from August through September.
The cities are expected to make up the difference through increased groundwater pumping and conservation efforts.
“They have tools in their toolbox to cover this,” said Jeff Shields, the irrigation district’s general manager.
His century-old district provides irrigation water from Sierra snowmelt to 48,000 acres of farmland around Escalon, Ripon and Manteca. In 2005, it started operating the DeGroot Water Treatment Plant to provide drinking water to Manteca, Lathrop and Tracy residents.
Earlier this year, those cities were asked to voluntarily reduce their water demands by 20 percent, but Shields said they didn’t reach that goal. He said Tracy’s water usage dropped 14 percent and Lathrop’s declined 16 percent, but Manteca’s demand increased 1 percent.
It wasn’t that Manteca residents were using more water, but rather city officials decided to use a higher percentage of the irrigation district’s water in place of groundwater.
“We’ve been trying to use more surface water the last couple years to give the groundwater a break,” explained Phil Govea, Manteca’s deputy director for public works.
Now that there’s a shortage of surface water, Govea said his city will start pumping more groundwater.
Manteca – like other cities throughout California – is promoting conservation efforts. Govea said Manteca residents already have reduced their water usage, and the city’s water billing system rewards them for doing so.
“If you use more water, you pay more for it,” Govea said. “So people just naturally cut back.”
The South San Joaquin Irrigation District is getting less water than normal this year from New Melones Reservoir because there was less snowmelt and runoff from the Sierra.
Shields said his district’s farmers will continue to receive enough irrigation water to get a healthy crop with deliveries of 30 inches or more per acre.
His district also pumped 3,471 acre-feet of groundwater from January to June this year. The South San Joaquin district pumps water for reasons other than irrigating crops.
Shields said district pumps south and east of Manteca are where the depth to groundwater is just 5 feet to 10 feet.
“We need to keep water out of the root zone of crops, as well as making sure buried pipe and even swimming pools don’t experience problems,” Shields said. “I know that seems like an odd problem in the Valley, but it is unique to that area of our service territory.”
Because the district has less surface water than it needs this summer, Shields said it will “optimize” the use of its groundwater wells to the greatest extent possible.
The district will ask growers who have wells to rely on groundwater for their last irrigation after harvest.
Shields said his district expects to have enough water available in Woodward Reservoir to provide Manteca, Lathrop and Tracy their normal water allocations by October.
Woodward Reservoir, north of Oakdale, is expected to remain open for recreation purposes through Labor Day weekend.