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Tumbler Damages Canal
Rocks - some as large as a school bus - have cut off the main supply canal for the South San Joaquin Irrigation District. - photo by Photo Contributed

An event that geologists refer to as a “rock tumbler” sent a swath of rocks about the size of a half a football field spilling into the main canal just 1,000 feet downstream from Goodwin Dam at 10:45 p.m. on Tuesday, Jan. 15.

The SSJID board on Tuesday is expected to adopt a resolution allowing General Manager Jeff Shields to make emergency repairs to the 200-foot section of the canal.

“We should have it cleared and fixed by March 1,” Shields said in reference to the possible start of the irrigation season.

Water that flows through the main canal on the north side of the Stanislaus River is split between SSJID and Oakdale Irrigation District with 72 percent of the volume going to SSJID. A smaller canal on the south side of the river that carries OID water exclusively was not damaged. The main canal also supplies domestic surface water to the cities of Manteca, Lathrop, and Tracy.

Shields said even if an unexpected snafu is encountered, the SSJID still has water in Woodward Reservoir to make an initial irrigation run.

“We’re fortunate it happened this time of year and not in the middle of our irrigation season,” Shields said.

The rock that came off the side of the cliff is essentially river rock. The top of the cliff consists of an old riverbed that was pushed upward over dozens of centuries.

The rock tumbler may have caused some damage to a spawning area below in the river. Shields noted that the river is wider at that point so the flow wasn’t disrupted significantly.

Because it is a spawning area, the rock can’t simply be pushed further downhill. Instead it will have to be trucked out on a narrow road meaning only one truck at a time can use it.

The main canal is 15 feet wide and 15 feet deep.