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Wednesday, June 28, 2017

CROSSVILLE FLASHBACK: Council works on Holiday Lake Dam problem

(Editor's note: This project came out of a state dam inspection that required work on the dam.  As the work moved forward the city ran into problems with the additional water in the lake and if that was a "taking" of land.  It was discovered that different deeds described the lake water line boundary in different ways and eventually the city left the dam at the level it was but with better control of the water levels. The project was finally completed in 2009)

Council works on its dam problem (July 2002)

The Crossville city council looked at options last Thursday for work required to bring the Holiday Hills Lake dam up to standards required by the Safe Dams Act while also improving the city’s control of the lake’s water level.
Council approved the option recommended by engineer Scott Christian of ECE Services at an estimated cost of $350,000 for work on the dam plus an additional cost for work on the bridge that crosses the dam’s spillway. Based on the council’s action, ECE will have a final report to present to the council at their regular meeting on August 13 with more detailed cost estimates on the project.
Once the final proposed plan is approved by the council in August it will be submitted to the state for their initial approval. When the full plans are prepared, the state must again approve the plan before the project can be put out for bids.
Engineer Scot Christian with ECE explains the plan
to the city council.
The plan chosen would widen the spillway over the dam from the current 32 feet to 150 feet and armor the dam using heavy riprap and rocks. The armor is to maintain the integrity of the dam should water ever flow over the top of it in the event of a super rain event. The spillway includes an upgraded weir system to control the actual water level in the lake. A weir is a gate like device that can be raised or lowered from the bottom.
One side benefit of the proposed dam improvement project is that it will raise the level of the lake by some 9 inches. This means the lake will hold more water increasing the capacity of the lake.
Just over a year ago the city received a notification from the state that the Holiday Lake dam was in apparent violation of the Safe Dams Act. At the time, the city was looking at making improvements to the Holiday Lake dam spillway and weir to better control the level of the lake for the city’s water plant intake.
That 2001 letter indicated that the Holiday Hills dam appeared to violate the Safe Dams Act based on a very unlikely Probable Maximum Precipitation (PMP) rainfall event of 29.85 inches of rain in a six-hour period. Based on calculations prepared by the state, such a PMP rain event would cause the water behind the Holiday Lake dam to rise more than two feet above the top of the dam and should the dam fail, it would threaten several houses and bridges below the dam.
During the council’s meeting in June of 2001, council approved amending ECE Services contract to include a study and report on improvements to bring the dam into compliance. ECE was already working on the spillway and weir project at the time.
At last week’s meeting, Christian explained to the council the reason for the state’s 2001 classification. He said that because the dam could be topped and potentially fail in such a PMP rain event that the ensuing flood would threaten 4 houses along with several bridges and roads downstream from the dam. Because loss of human life could result from such a dam failure is the reason for the states classification change in 2001.
The bridge across the spillway portion of the dam is currently is classified as one of the worst bridges in Cumberland County and is at the top of the list for state funds to improve it according to Christian. If the city receives funding form the Tennessee Department of Transportation (TDOT) 70 percent of the replacement bridge’s cost would be covered by state funds. The cost of a new longer bridge is estimated at $225,000. The city’s 30 percent share would be $67,500.
Crossville Mayor J. H. Graham III commented, “We have to look at both the dam and the bridge situation at the same time.”

Other potential options studied by ECE Services including substantially lowering the current spillway that would have had detrimental effects on the water plant intake. Also, an expensive series of smaller lakes above the dam could have held more water in the event of a large rainfall. Also studied was purchasing the downstream houses and demolishing them. Because of the bridge and roads involved though, human life could have still been threatened and the problem would not have been solved.

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