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Irrigation season ends on dry note

POSTED August 21, 2012 10:11 p.m.

The Turlock Irrigation District’s 2012 irrigation season is unlikely to be extended beyond its scheduled Oct. 10 end date, directors learned Tuesday, due to much lower-than-anticipated water levels in Don Pedro Reservoir.

The earliest a TID irrigation season ever ended was Sept. 30, in 1988. Normally, the irrigation season stretches to Oct. 14 or 15, even in drought years.

But low rainfall over the past year, plus the cancellation of a planned 80,000 acre-foot delivery of water, means the District will enter this winter with far less carryover water than anticipated. If the season was to be extended, even less water would be held in reserve for 2013.

“From my perspective, it would be very difficult to extend the irrigation season,” TID Water Distribution Department Manager Mike Kavarian.

Current projections indicate the District may enter this winter with 90,000 fewer acre-feet of carryover water than anticipated. That translates into between 19 and 20 inches per acre of carryover water – far below the expected carryover of 24 inches per acre.

Should TID extend the irrigation season for two weeks, the minimum extension needed to make a difference for most growers, an additional 20,000 and 25,000 acre-feet of water would be used. That would reduce carryover storage by about 3 acre-inches of water for next year’s allotment, per parcel, to as low as 16 inches of carryover storage.

The low carryover stems from an April 17 decision to increase the 2012 irrigation allotment from 24 inches to 30 inches, and to increase the cap from 30 inches to 40 inches.

At the time, the increased allotment was deemed possible due to an expected 80,000 acre-foot release of water to Don Pedro Reservoir from the City and County of San Francisco’s Cherry Reservoir, as San Francisco was expected to drain the reservoir to perform needed maintenance. But CCSF later changed its mind, delaying the maintenance indefinitely and holding the water in storage.

Groundwater pumping was expected to aid in irrigation as well, but the district will likely end up pumping only 100,000 acre-feet of water – below the 120,000 acre-feet planned. The decrease comes due to declining pumping capacity, as some wells are in need of maintenance.

Even though TID was nearly 1,000 acre-feet below irrigation water use projections as of Tuesday, the lower than expected pumping and missing 80,000 acre-feet from CCSF have led to an anticipated 90,000 acre-foot shortfall.

The low carryover means it could take as much as three years of average rainfall to fully refill Don Pedro. If dry conditions continue, it could take more than six years to refill Don Pedro –potentially with irrigation allotments of 30 acre-inches or less each year.

“This is the right time to be discussing this,” TID Director Charles Fernandes said. “If you and your staff know and relay to the growers that we have no intention of extending the season because of the shortage of water, they don’t have the excuse that they need time to get their last irrigation in.”

Kavarian said the system will likely be drained as slowly as possible following the Oct. 10 end date, allowing some late deliveries to growers near the system’s end points.

There still remains a slim chance the irrigation season may be extended, should torrential rains fall in September. But TID directors warned that growers should expect a firm, Oct. 10 end date for this irrigation season, and could see small allotments next year should dry conditions continue.

“Let’s be proactive and be upfront and clear, and tell them we need to be conservative,” TID Board Chairman Michael Frantz said. “The water we have up there isn’t that plentiful.”

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