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Dry season means less water for irrigation

POSTED February 29, 2012 11:29 a.m.

A critically dry year – possibly the driest on record – led Turlock Irrigation District directors to issue the lowest initial irrigation water allocation and cap in the district's history on Tuesday.

The 2012 TID irrigation season will run from March 8 through Oct. 10, with a 24-inch per acre allotment and a 30-inch cap. That's half of the 48-inch allotment in 2011, a season in which use was not capped due to a good rain year.

“That kind of gives you an idea of the type of conditions we're in today,” said Debbie Liebersbach, water planning department manager.

To supply even that limited water allotment, the district expects to pump 120,000 acre-feet of groundwater – twice what it would pump in a normal year. TID also expects to conserve water by limiting canal spills – where excess water passes through canals to the river – to 5 percent, down from 8 percent in a normal year.

The district will begin accepting water orders on March 7. That's not a minute too soon for water-starved farmers, who already lobbied TID to conduct a rare 10-day early irrigation season in January to save row crops which would normally have been fed by rain.

As of Tuesday, the 2012 water year had totaled only 11.79 inches of precipitation in the TID watershed. That's roughly on-par with 1977, currently the driest year on record.

Under their driest of pre-season estimates, Department of Water Resources projected the watershed would see four more inches of rain this year. Even if the district sees unseasonably heavy rain for the rest of the water year, the watershed would still remain at least 4 inches below an average water year.

The lack of rain is made worse for irrigators, as natural vegetation absorbs a larger percentage of rainfall in drier years. Where an inch of rainfall might generate 80,000 acre-feet of water for the district in a normal year, that same inch of rainfall could result in only 40,000 acre-feet this year.

“What does another inch do for us? It really doesn't do a lot,” said Wes Monier, TID strategic issues and planning department manager.

In total, the district expects to have about 890,000 acre-feet of water available for irrigation. That tallies out to about 47 inches per grower, if growers generally use the same amount of water they have used in past years.

But district policy usually calls for TID to allocate as little irrigation water as possible, to carry over more water in case of a potential extended drought.

Standard TID planning practices call for an 18-inch cap for 2012, based on current figures. But the absolute dearth of rainfall has farmers’ crops dying a slow death, and 18 inches of water wouldn't save their investments.

“You're basically killing crops to have carryover water, and that's not too logical,” Monier said. “This isn't a standard drought. It could be a one in a 100 year event.”

Even if a further 4 inches of rain falls, the district would end the 2012 water year with enough carryover storage in Don Pedro to allow for only 20 inches of irrigation in 2013. Should no rain fall, or natural vegetation consume additional precipitation, TID could enter the winter with as little as 13 inches of carryover storage.

That leaves the district facing a 2 percent probability that Don Pedro will be entirely drained next year, allowing for only minimal deliveries. An 8 percent chance would see minimal deliveries, and some carryover storage following 2013 – but less than the recommended minimum carryover. There's only a one-in-three chance that the district will have both full deliveries and full carryovers in 2013.

Despite the dire picture, there's still a 10 percent probability that TID could fill the reservoir and offer a full irrigation allocation – but that depends on an extremely wet April. Should excessive rain fall this spring, TID directors could change the allocation at that time.

“It's just not likely,” Monier said.

TID will hold a series of preseason grower meetings to discuss irrigation water allotments.

Meetings will be held at: 7 p.m. today at Chatom School, 7201 Clayton Rd.; 7 p.m. Thursday in the Hughson Community Center, 2307 4th St.; 7 p.m. March 5 in the TID Boardroom, 333 E. Canal Dr.; and, 7 p.m. March 7 at the Westport Fire Station, 5160 S. Carpenter Rd.

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