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Sierra snowpack supplying SSJID now at 51%; Northern SJ Valley slips into moderate drought

The two wettest months of the year — January and February — have been abnormally dry in both the Northern San Joaquin Valley and the Central Sierra.

While there is a possibility for some showers on Feb. 29, there is a good chance the first two months will end up as one of the driest on record for Manteca, Ripon, and Lathrop.

Worst yet the Sierra that is effectively the state’s largest reservoir as the snowpack provides 30 percent of California’s water needs, is at 60 percent of normal statewide for Feb. 15. The Central Sierra that feeds Tri-Dam Project reservoirs South San Joaquin Irrigation District uses to supply 52,000 acres of farmland between Manteca, Ripon, and Escalon as well as municipal water to the cities of Manteca, Lathrop, and Tracy is now at 51 percent of normal. The Central Sierra is at 41 percent of the historic average for April 1. That date is critical as it marks the end of the typical snow year. Figures on that date are used to determine water supplies for the spring, summer, and fall.

“It is dry,” noted SSJID General Manager Peter Rietkerk.

As it stands now modeling shows the inflow to New Melones that SSJID along with Tri-Dam partner Oakdale District has a contractual and historical right to the first 600,000 acre feet of runoff indicates the two districts will have adequate supplies for cities and farms they serve for the current year.

The SSJID uses a conservative model that puts the odds of a 630,000 acre foot runoff at 90 percent. A more conservative model of the runoff in the Central Sierra that feeds the Stanislaus, Tuolumne and Merced watersheds estimated runoff into New Melones as being closer to 420,000 acre feet.

The 2.4 million acre foot capacity New Melones is at 135 percent of average for this time of year with 1.048 million acre feet. OID and SSJID share 200,000 acre foot “conservation storage” at New Melones. However, the storage is eaten into when winter releases are more robust.

As things stand now, Rietkerk said releases have likely depleted that account.

The SSJID tentatively plan to start the 2020 irrigation season March 4.

Rietkerk said the district should be able to get through the water year without any restrictions.

That said if the dry conditions persist throughout March due to a high pressure ridge sending rain clouds to the Pacific Northwest there could be some concerns.

“We need a March miracle or an awesome April to get us back to normal,’ Rietkerk said.

While the SSJID is monitoring the situation daily Rietkerk indicated as things stand there should be any issues.

Having said that he noted “it is always a good time to use water wisely,” Rietkerk noted.


To contact Dennis Wyatt, email