Need a dam to hold a lake

Published 4:52 pm Wednesday, February 22, 2017

The following information was presented to the Polk County Board of Commissioners on Feb. 13, 2017.

Inadequate repairs and modifications to our aging Turner Shoals Dam could ruin the plans for the Lake Adger/Green River serving as the region’s drinking water supply source. Without an intact dam, you have no reservoir. Without a reliable reservoir, we have no future.

Never, has Polk County needed to prioritize the safe and adequate rebuilding of its water infrastructure more. The ambitious TIEC project — a full time year round resort (1,500 room hotel and home to 2018 World Equestrian Games) — and the regional water customers of North and South Carolina (BRWA/ICWD/Polk County) are hanging their hats on it.

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Instead, Polk County is cutting corners to cheapen the stability construction design and dangerously ignoring recommendations issued from the last inspection report in 2014 — to survey the unknown amount of silt pushing up against the dam’s multiple arch spillway structure.

California’s Oroville Dam trouble should be a punch-you-in-the-face wake up call to Polk County, N.C. Oroville dam is a mere 48 years old; Turner Shoals Dam is 92.

The Oroville dam spillway was built inadequately to withstand today’s severe flooding load forces, and our Turner Shoals was built without even a separate principal or emergency spillway (Black & Veatch 2007 Lake Adger Technical Assessment). “Excessive storm inflows are directed over the central section of the dam” and those (left and central) sections continue to experience significant concrete deterioration” – 10 years ago and worsening to this day.

So does it seem like a good, safe idea for our today’s engineers to cut corners, reducing the predicted flood numbers from two thirds down to one half, in these times where we should expect even greater storm intensity?

Stronger storm surges against a planned cheaper, minimally modified spillway design, seems to spell disaster.

Did you know 34 percent of all US dam failures are caused by overtopping due to inadequate spillway design or debris blocking the spillway? (Living With Dams: Know Your Risks/ Are we headed for inadequate spillway design rehabilitations?

Oroville thought their dam was adequately strong enough to withstand storms until it wasn’t! Don’t let this be us!

Did you know 30 percent of US dam failures are due to structural damages from earthquakes? In 2007, Turner Shoals experienced a 3.1 Richter scale earthquake whose epicenter was just one-quarter mile away on Garrett Road. Is this significant event noted in the ongoing AECOM Comprehensive Stability Analysis and will the design drawings for construction modifications reflect this?

Finally, there are still no answers to my last speech regarding the apparent omission of the recommended Bathymetric Survey at the dam (AECOM 2014 Dam Safety Inspection: Recommendation #8). Siltation accumulation on the west side of Lake Adger is finally being addressed and it is not a good, safe idea to continue to ignore this impact on the east dam side. The silt levels at the upstream face of the arch spillway and bulkheads need to be evaluated now in the Comprehensive Stability Analysis so the next phase of structural design modifications will be adequate.

Sky Conard
Mill Spring, N.C.