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Posted 8/25/2010

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By Carol Labashosky

The U.S. Army Corps of Engineers Louisville District dam safety office has ongoing subsurface investigations underway at several Louisville District dams.

The investigations assist in the characterization of soil and groundwater flow conditions beneath the dam(s), and help to identify future potential issues.

These evaluations are underway as part of a national USACE "risk informed" dam saftey intitiative. The intitial stage of the program was referred to as Screening Portfolio Risk Assessment. Through the initial stage of the program several dams in the Lousiville District were identified for further study which included field investigations; these dams are J.E. Roush, Salamonie, and Brookville lake dams in Indiana, and Rough River, Nolin, Barren and Green River dams in Kentucky.

Preliminary dam explorations began in 2008 consisting of drilling small diameter holes into the ground and retrieving soil and rock samples for lab testing. In some cases, additional instrumentation to detect water levels within the rock foundation of dams was also installed. These samples and test results are used to perform further engineering evaluations and comparisons.

Over the summer, the district presented four dam safety projects to USACE headquarters senior oversight group: Salamonie, Nolin, Brookville and Roush dams. The senior oversight group approved further additional field investigation as part of the study for J.E. Roush, Nolin, and Brookville dams.

Nolin Lake Manager Chris Boggs explained that over time, the downstream face of the dam, consisting of sandstone rock fill, had degraded breaking down to a sandier material. Last year 21,000 tons of new rip rap was laid on the face of the dam.

"He did a fantastic job," Boggs said of the contractor. On the upstream face during testing, the contractor had to build a bench, similar to a platform, to check the compaction rate of the sand and check for seepage and voids. Nolin is one example of the district’s progress on dam safety issues and how geotechnical investigation helped to diagnose issues in the karst topography upon which Nolin dam was built.

Through its dam safety program, the Louisville District annually inspects all its reservoir dams. A more intensive multi-discipline team inspection occurs every five years. These inspections and USACE’s assessments of the projects determines which candidates across the country will be selected for additional study.