South San Joaquin Irrigation District will end the irrigation season Oct. 6.

The ability to do so at near the normal time which is mid-October in what is shaping up to be the fifth driest year in 120 years of recorded hydrology on the Stanislaus River basin is attributable to four factors:

*The effectiveness of SSJID in-field water managers to reduce water waste throughout the system by making deliveries to farmers as efficient as possible.

*Unimpaired runoff for this water year in the Stanislaus River projected by the Department of Water Resources at 360,000 acre feet is a bit better than the dismal 315,000 acre feet estimated in June. That’s thanks to a series of late summer snow storms.

*The SSJID’s New Melones conservation account at New Melones is full at 100,000 acre feet. It is projected to be at 80,000 acre feet after the district taps into it to meet this year’s needs allowing the amount to be carried over into 2022.

*Despite the heat agricultural customers as well as urban users in Manteca, Lathrop, and Tracy have been careful with water use.

The district is ending diversions into Woodward Reservoir on Sept. 30 to preserve as much water supply as possible for 2022 if drought conditions persist.

SSJID General Manger Peter Rietkerk noted historically droughts have multiple dry years.

As such wise water use this year could be crucial to meeting needs in 2022.

The outlook for 2022 is heavily dependent on hydrology. A year that is a repeat of 2021 in terms of snow could set the stage for tight supplies and the possibility of some curtailment or deliveries.

If they occur, they will be spread proportionately to growers that farm roughly 50,000 acres and 200,000 urban users in Manteca, Tracy, and Lathrop.

The three cities also rely on groundwater with Tracy having a third source — the Central Valley Project.

Even with three sources Tracy is in the most perilous position. That’s because the CVP has reduced the city’s 2021 water deliveries by 10,000 acre feet. It is why Tracy has imposed a 25 percent cutback on water use by its residents.

Compared to many irrigation districts in the state, the SSJID is in a relatively more comfortable position when it comes to water supplies.

That is due to three decisions.

*The acquisition and adjudication of pre-1915 water rights in the Stanislaus River basin.

*The building of the Melones Dam in 1925 that set the stage to further strengthen the water rights of SSJID and the Oakdale Irrigation District to 600,000 acre feet of water when the Bureau of Reclamation inundated the original dam to construct New Melones.

*The partnership with OID to build the Tri-Dam Project in the mid-1950s.

The storage between Donnells and Beardsley will go a long way toward countering a third straight dry year if it materializes in 2022.

Releases from the Tri-Dam Project was reduced to minimal flows earlier this year when it became apparent to the SSJID and OID the Sierra snowpack was shaping up to be anemic.

That is why Donnells with 64,320 acre feet is at 80 percent capacity or 116 percent of the average historic storage on Aug. 24.

Beardsley’s 97,800 acre foot reservoir is at 35 percent capacity and 73 percent of the historic average on Aug. 24.

New Melones is at 38 percent capacity with 931,000 acre feet of water in the 2.4 million acre foot reservoir. That is at 60 percent of normal this time of year.

Outflow is at 1,539 cubic feet per second while inflow has dropped to 54 cfs.

Of California’s six largest reservoirs, New Melones has the second most water left in terms of percentage of capacity. It is topped only by Don Pedro that supplies Modesto Irrigation District and Turlock Irrigation District at 54 percent of its 2 million acre feet.

The other four largest reservoirs and their current storage and overall capacity are Shasta at 28 percent (4.5 million), Oroville at 23 percent (3.5 million), Trinity Lake at 36 percent (2.49 million), and San Luis at 15 percent (2.04 million).

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com