Risk of lake overtopping is high priority

Though the risk of seismic and seepage failure of Success Dam is not as great as previously thought, the risk of the lake overtopping has just moved up the Army Corps of Engineers’ priority list.

Darren Suen, manager of the Success Dam Remediation Project, said overtopping has become the highest risk driver, but minor relative to seismic and seepage risks.

“It’s such an infrequent event — once every 10,000 years on any given year — that means there’s a 1 percent chance. Nonetheless, it’s a risk we have to consider because it is out there,” he said.

Officials with the Corps say that one of the potential options to address overtopping is widening of the dam’s spillway, a passage for surplus water to travel from the upstream side to the downstream side of the dam.

The Corps discovered the aforementioned risks as it began looking into the possibility of raising the spillway in 1999.

“It started out as a minor remediation project but...with the policies in place back then it morphed into a greater risk of liquefaction,” Suen said. “We thought we built this dam on a bunch of sand and if an earthquake happened that would just collapse so that concern moved us into a more comprehensive analysis of the dam.”

Additional studies determined the risk of seismic or seepage failure was not as significant, “though the risk is still there, I want to underscore that, but it just so happens it’s not as great,” Suen said.

Suen added that to the public, it may appear the Corps has come full circle, but said that is not the case.

“The economic climate we’re in, the policies that have been adopted since that time frame have all changed,” he said. “We’re trying to digest this outcome and look at where things sit today and figure out what’s the most prudent step moving forward.”

The Corps is in the final stages of updating the technical appendices studies that back up the final conclusion of its Baseline Risk Assessment Report, which looks at potential project risks and evaluates them. Alternatives to fix the dam’s issues, including potentially widening of the dam’s spillway, will come after the report is confirmed and approved, Suen said.

Suen said that after evaluating the project, he foresees the operating pool restriction as not being less than what it was last year, which was at 645 feet of water depth, an increase the lake had not seen in nearly 10 years.

“The pool would not be restricted less than 645, that’s my personal belief,” Suen said. “It could be better, we’ll just have to wait, it’s too early to tell.”

Suen said he hopes to have the final conclusion on the studies by the end of 2013 at the latest.

Contact Denise Madrid at 784-5000, Ext. 1047. Follow her on Twitter @DeniseMadrid_.