Editor’s note: This is part of an occasional series on rivers, lakes, reservoirs, the Delta, innovations and the weather that play a key role in supplying Manteca, Ripon and Lathrop with water.
South San Joaquin Irrigation District and its partner Oakland Irrigation District hold three aces that have allowed the farmers and cities they serve to weather droughts during the past 60 years.
Donnells and Beardsley reservoirs in the steep terrain of the Sierra on the Stanislaus River provide the two districts with 134,000 acre feet of storage. A third component of the Tri-Dam Project completed in 1957 and financed without any state or federal help is Lake Tulloch above Knights Ferry and Goodwin Dam provides an additional 58,803 acre feet of storage.
Without the three dams the current drought would have devastated 117,500 acres of farmland served by OID and SSJID and would have forced greater water cutbacks in Manteca, Tracy, and Lathrop.
When coupled with storage of 600,000 acre feet of water the two districts were guaranteed in exchange for allowing the Bureau of Reclamation to inundate the original Melones Dam SSJID and OID built on their own in 1925 and replace it with the 2.4 million acre feet capacity of New Melones Reservoir, it has provided the two districts with arguably the best independent irrigation reservoir system in California.
SSJID has a fourth ace that OID doesn’t possess — the in-district Woodward Reservoir that provides another 36,000 acre feet of water storage.
Those four dams along with New Melones has allowed Manteca, Ripon, and Escalon farmers to avoid sharing the fate of many other California farmers during severe dry spells that left land fallow or sacrificed permanent crops such as orchards and vineyards.
That wasn’t always the case. Before Melones Reservoir was built in 1925 farmers in the OID and SSJID were nearly ruined when water stopped flowing in mid-summer in 1924 even though the two districts had secured and adjudicated superior water rights in the Stanislaus River basin.
Melones Dam was credited with saving farmers in the SSJID several times over the next 20 years when drought periods devastated farm production in other parts of California.
In the late 1930s, SSJID directors – in conjunction with OID – made plans for three dams – Donnels, Beardsley, and Tulloch – along with three power houses and a seven-mile tunnel carved through solid rock.
Nothing happened until after World War II when the Tri-Dam Project actually started taking shape. Financing for the $52 million project was secured when Pacific Gas & Electric signed a contract with the two districts to buy electricity from the three dams through 2005. Power sales at a rate established in 1955 essential gave the two districts the ability to pay for the dam with additional money to operate the system and help assist with improvements in their respective districts. Since the project was paid off and the PG&E contract ended, the districts in some years have split almost as much as $12 million to fund upgrades to water delivery systems as well as enhance power generation capabilities.
The Tri-Dam Project financial benefits are being used by SSJID to provide a secure foundation in its bid to lower power rates by 15 percent across the board by acquiring the PG&E distribution system in Manteca, Ripon, and Escalon.
The project was dedicated on June 15, 1957 at Beardsley Dam. It was hailed as a remarkable project since it was completely financed by the SSJID and OID without any aid from either the state or federal governments.
At the time it was completed, it was the largest irrigation project ever undertaken by a local district in the western United States.
The Tri-Dam Project gave the districts three times the amount of water the original dams supplied and added 120 megawatts of power production.