U.S. Army Corps of Engineers implementing new dam safety classification system

A new dam safety classification system is being used to screen 14 Army Corps of Engineers dams in the Omaha and Lincoln areas.

They are being screened using a new risk-informed process to establish priorities for investigations and remediation work on a national basis.

The Corps of Engineers released an engineering circular on May 31, 2007, titled “Interim Risk Reduction Measures for Dam Safety,” which defines the new Dam Safety Action Classification (DSAC) system. It places dams into five classes: DSAC I dams have the highest priority for action, and DSAC V dams the lowest.

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DSAC V dams are considered safe and in compliance with all current criteria. Interim risk reduction measure plans must be developed for all DSAC I, II and III dams to reduce risks while long-term solutions are investigated and implemented. These interim measures include updating the Emergency Action Plans and conducting training exercises with emergency management agencies. At some projects, interim risk reduction measures may also include performing repairs and installing additional instrumentation to better monitor the project.

There are four Corps-owned dams on the Papillion Creek system in the Omaha area. They are Glen Cunningham, Standing Bear, Zorinsky, and Wehrspann. Three of them received a DSAC IV rating and require no interim risk reduction measures.

Cunningham received a DSAC III rating, primarily due to concerns with settlement that occurred during and shortly after construction and may have resulted in damage to the embankment of the dam. Investigations are planned to verify if the embankment has actually been damaged as a result of settlement.

There are ten Corps-owned dams on the Salt Creek system in the Lincoln area. They are Olive Creek, Blue Stem, Wagon Train, Stage Coach, Yankee Hill, Conestoga, Twin Lakes, Pawnee, Holmes Lake, and Branched Oak. Five of them received a DSAC IV rating and require no interim risk reduction measures. They are Blue Stem, Yankee Hill, Conestoga, Twin Lakes and Pawnee.

Olive Creek, Wagon Train, Stage Coach, Holmes Lake, and Branched Oak received a DSAC III rating, primarily due to potential seepage issues along the outlet conduits. The conduit issues will be assessed and appropriate repairs made. Studies will also be performed to determine if other seepage issues exist at any of these projects.

A re-evaluation to determine the amount of available freeboard resulting from an extreme precipitation event is planned at all 10 of the Salt Creek dams. Such a weather event is called the “Probable Maximum Precipitation,” and the probability of this event occurring is extraordinarily low. There is no evidence to suggest an emergency situation exists, or is about to occur at any of the Nebraska dams with a DSAC III rating. Studies and appropriate repairs will be made at each of these dams to correct any confirmed dam safety problems.

The Omaha District has a comprehensive dam safety program in place at all of its dams to ensure public safety.

Dam safety engineers and project personnel routinely inspect these dams and evaluate instrumentation data throughout the year. Comprehensive Periodic Inspections are performed every five years.

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