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The city of San Diego worries some of its dams “may be nearing the end of their useful service life” and is spending up to $5 million to see how they’re doing.
Last year, city officials hired an engineering firm to do detailed checkups on each of the city’s nine dams. Carlsbad-based GEI Consultants has been working quietly ever since on a study that could take up to five years.
Most city dams are 80 years or older.
Brent Eidson, a spokesman for the city water department, said the study may ultimately find that no significant work is needed on the dams.
Officials already have a few concerns, though. In fall 2014, for instance, the city limited the amount of water it can store in the lake formed by the El Capitan Dam near Alpine, which is the city’s second-largest reservoir.
That’s because officials spotted water seeping out from underneath the dam. Some seepage is normal, but it could also be a sign of problems.
So far, there hasn’t been enough rain to raise the dam above that limit, so the city hasn’t been forced to spill any water to keep the lake low, said Isam Hireish, the deputy director of water system operations.
“We are below the level of restriction – barely there, but we are there,” he said.
But if there were ever enough downpours, the city is only allowed to keep the dam full temporarily. That means El Capitan, which has the capacity to store as much water as 900,000 people use in a year, can only store about half that much water for any extended period.
Nobody knows for sure if El Capitan is a safety issue yet. Engineers plan to do several different tests to determine the condition of the 83-year-old dam and the soil and rock on which it sits.
It’s unlikely the recommendation would be so drastic as to call for the dam to be taken out of service, said Rania Amen, an assistant director of the water department.
“They’re not going to tell us the dam is no good,” she said. “Those dams are built to last forever – kind of.”
Other issues at other dams are not serious enough to require operational limits, which in dam safety parlance are known as “fill restrictions.”
Yet, that doesn’t mean there may not be expensive dam retrofits in coming years.
The state Division of Dam Safety has “identified dam safety deficiencies that could potentially require costly modifications to city dams,” the city’s engineering consultant said in a report. “The dam safety concerns that have the greatest potential for costly modifications are related to: stability of concrete, rockfill and hydraulic fill earth dams; stability and capacity of outlet towers; and potential for overtopping of dams during the design flood.”
A dam’s outlet tower houses the controls that allow water to be released from the reservoir.
Officials also found a deficiency with the dam’s spillway, the flood control channel that famously fell apart at the Oroville Dam in Northern California earlier this year, but Morena is in no real danger of spilling water: It’s 91 percent empty right now.
The outlet tower at Savage Dam, which holds back the Lower Otay Reservior, is also a problem. The tower is seismically unstable, according to the city’s engineering consultant.
Some of the potential upgrades are in anticipation of problems – things like pipes, ladders, hatches and instruments are old, so they need to be fixed up before they become safety issues. Other issues have already been identified either by the city, which does regular inspections of its dams, or by state regulators, who do yearly inspections.
The city’s largest dam, the San Vicente Dam near Lakeside, is newly remodeled. The city of San Diego and the San Diego County Water Authority worked together to raise the dam in 2014 so that the lake it forms could hold more water to get the region through dry spells and emergencies for years to come.