South San Joaquin Irrigation District is warning the cities of Manteca, Lathrop, and Tracy to brace for a possible 10 percent reduction in water deliveries for 2012.

That projection is based on existing water supply conditions and a “reasonable amount” of rain and snow between now and mid-March.

Actually that projection assumes ultimately a 33 percent shortfall in terms of highest water use in a typical year but what the cities may actually get reduced is based on several different circumstances.

The three cities are contracted for 31,500 acre feet of water annually. A reduction of a third would cap their use at 20,750 acre feet. They used around 17,000 acre feet last year. While the one-third reduction would come to 18,000 acre feet, the 2011 water use numbers are skewed by the unusually wet spring. That avoided the need for a lot of water use for landscaping which ranks as the top domestic use of water. The highest use the three cities have had for a typical spring is 22,000 acre feet.

The 33 percent cutback on their contracted 31,500 acre feet would come to 20,750 acre feet or just under a 10 percent reduction.

SSJID General Manager Jeff Shields emphasized if rain and snow over the next four weeks is significantly better than average it could improve the situation to the point urban water cutbacks may not be needed. However, the 15-day weather outlook calls for only two chances of slight rainfall and minimal snow.

Manteca City Manager Karen McLaughlin has indicated the city is closely monitoring the next 45 days in terms of snow and rain. And while the city’s annual conservation rules go into effect at the start of Daylight Savings Time on March 11, city staff will examine additional strategies that they may ask the council to implement if the outlook doesn’t improve. Currently Manteca’s reliance on surface water is at a minimum. Use starts spiking when the weather warms up.

The SSJID board used the latest snow survey information and took into consideration there would likely be some more rain and snow to come up with the 33 percent reduction. As things stood before the current storm, there was only 34 percent of needed water and snow on hand.

The decision to prepare for the reduction was made to help farmers make critical planting decisions in the next few weeks. Both domestic and farm water are subject to the same percentage of cutbacks in water shortage years under the agreement the three cities have with the SSJID.

Letters are going out this week to farmers to inform them the irrigation season will not start until April 1. Typically it starts in mid-March.

Also, the board instructed Shields to lower the maximum surface at Woodward Reservoir from 210 feet down to 205 feet. That will still allow for recreational usage. The lower elevation though will reduce surface area and therefore cut down on the rate of water that is evaporated. The strategy is expected to save about 2,000 acre feet over the course of the year. Farmers under the current planning will get about 147,000 acre feet of water as opposed to the 220,000 acre feet they would normally receive.

Plans also call for possible call for changes in the frequency of irrigation cycles, limiting the time that fields can be flood irrigated, and capping the amount of water that can be used for drip irrigation and sprinklers.

The SSJID will also work with Escalon and Ripon to possibly access two shuttered industrial sized wells in those two cities that have high nitrates. While high nitrate water can’t be used for domestic purposes, it can be safely used on crops with the added bonus of reducing the need to add as much fertilizer. If the wells can be used and if they are close enough to district facilities, the water pumped would be used to supplement what allocations the district will receive off the Stanislaus River watershed from the Sierra snowmelt.