Polk County Commissioners heard last week that the county likely needs to spend between $10,000 and $20,000 over the next few years on repairs to the Turner Shoals Dam at Lake Adger.
It has also been recommended for the county a plan for future repairs, which could cost millions.
Commissioners met April 22 and heard from Geoff Kruger, of AECOM, which performed an inspection on the dam that included an underwater survey. Kruger said every portion of the dam was observed during the inspection, which was done on Oct. 8, 2013.
Kruger presented photographs of the inspection beginning with the spillway on arch number one showing examples of vegetation growing with the suggestion to remove the vegetation to stop corrosion. Other photographs showed bulkheads, with number three showing seepage. Kruger said seepage is sometimes a concern but all old dams have seepage. He said dam owners want bulkheads to seep some so as not to hold all the pressure of the water.
Kruger also showed pictures of penstocks and a seepage collection ditch.
Another short-term recommendation is to repair the culvert outfall in the collection ditch so erosion doesn’t continue to progress, according to Kruger.
Turner Shoals dam has been in operation since 1925 and is owned by Polk County and regulated by the N.C. Department of Environment and Natural Resources (NCDENR). Kruger said the existing spillway capacity is 45,000 cfs (cubic feet per second).
Kruger also said the largest flood in the last five years was 4,000 cfs with Hurricane Frances in 2004 producing a flood peak of 15,200 cfs, which was a 50-year flood event.
In 2009 Polk County did a remedial options study on future repairs the dam will need. There were six options considered for the dam to meet stability requirements, ranging from estimated costs of $1.6 million to $2.8 million. Option five of the study was the least expensive at $1.6 million.
Kruger said short-term recommendations include that the county design and repair sloughing at the ditch outfall, remove vegetation on the downstream side of the arches and to install additional survey movement monitoring monuments.
Long-term recommendations include doing a structural evaluation of steel penstocks and designing dam modifications for increased spillway capacity.
Kruger said the dam is well maintained and is in good condition for its age and there are no immediate safety concerns.
“The dam is well maintained and is in good condition,” said Kruger.
The next routine dam inspection should be performed in 2018, according to Kruger.
The county hired AECOM Technical Services Inc. in September 2013 for $32,290 to perform the required inspection of the dam.