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Philpott Lake’s safety ranking changed
Age, cracks cited; no danger to public
Thursday, February 28, 2013
By PAUL COLLINS - Bulletin Staff Writer
Philpott Dam’s safety rating was lowered late last year and now more accurately reflects the dam’s 60-year age and corresponding cracks, which are monitored.
That is according to a report given to the Henry County Board of Supervisors Tuesday night by Craig “Rocky” Rockwell, operations manager at Philpott Lake, and Gregory Williams, Ph.D., P.E., chief, engineering branch, Wilmington Office, U.S. Army Corps of Engineers (USACE).
They said, among other things, that Philpott Dam’s safety rating was changed from DSAC (Dam Safety Action Class) IV to DSAC III on a scale of 1 to 5, with one being the worst and 5 being the best. No Corps of Engineers dams have a DSAC Class V rating.
According to online information for the corps, Class III dams have issues where the dam is significantly inadequate, or the combination of life, economic or environmental consequences with probability of failure is moderate to high. Class IV dams are inadequate with low risk of failure, among other things.
The rating system helps determine priority for federal funding for improvements to USACE dams.
The ratings of dams are based on risk and take into account such things as the probability of failure and potential failure consequences. For instance, potential failure consequences are greater when there is a lot of development downstream from a dam, Williams said.
Of the approximately 700 corps dams, 52 percent are Class IV, 14 percent are Class III , 31 percent are Class II and 3 percent are Class I, Williams said.
Philpott Dam got a Class IV rating in 2008. “We did not think DSAC Class IV was right,” considering Philpott Dam’s age and cracks, Williams said. Officials requested a review of the rating and it was changed to DSAC Class III.
The lower rating doesn’t mean area residents should be concerned.
“It’s nothing to be concerned about. It’s (the dam is) not in any worse shape than it was four years ago,” Rockwell said.
Williams said almost all money for corps dam safety improvements is going to dams rated Class I, a little goes to dams rated Class II, and none goes to USACE dams rated Class III. Philpott Dam now being rated Class III is a step in the right direction if Congress was to increase funds for dam safety improvements, he said.
According to a PowerPoint presentation made at the board of supervisors meeting, construction of Philpott Dam was for the most part completed in April 1952, and cracks were documented as occurring in 1966. Cracks in and of themselves are not an issue, Williams said. In 1968 new cracks were found in the spillway gallery, and in 1969 anchors were placed in the spillway to help address the problem.
In 1978-79 new cracks in the gallery were found. In 2004 the cause of the cracks was found to be alkali silica reaction (ASR). Silica in concrete reacts with water to create a gel. Swelling from gel creates small cracks. Combined swelling and cracking causes large cracks. ASR is ongoing, and it is not unique to Philpott Dam.
Various types of inspections and assessments take place at Philpott Dam: annually, every five years, every 10 years, special inspections (such as dive inspections) and other inspections (such as after an earthquake). Philpott Dam is undergoing a 10-year assessment this week and next week.
Potential interim risk reduction measures are under development. They possibly could include: increasing monitoring, installing new crack measurement tools, conducting seismic review, updating the emergency action plan, conducting dam failure exercises, periodic local communication (such as appearing at the supervisors’ meeting Tuesday night), among other things, Williams said.
Rockwell also reported that Philpott Dam provides about $12 million a year in property flood protection. About 650,000 visitors a year come to the lake and they spend about $17.5 million a year in the economy, he added.
In other business, supervisors Chairman Jim Adams, who represents the Blackberry District, recognized representatives of Boy Scout Troop 167, told some of the history of the troop and presented a letter of recognition to Andrew “Drew” Lucas Nolen on becoming an Eagle Scout.
According to an email sent to Adams about the troop’s history, Troop 167 of Bassett Church of The Brethren was started in 1937 by two men of the church, Price Bowman and Bill Smith.
The troop began as Troop 67, and then the charter lapsed for a couple of years during World War II. It was re-chartered as Troop 167 in 1947. “Since then, the charter has not lapsed. So, we’ve been going strong for 66 continuous years, which, if you add the other years to it, we’re about 76 years strong,” the email stated.
The troop has had 33 Eagle Scouts to date and has “several more coming up shortly,” the email stated. “The average is three out of every 100 Scouts make Eagle.”
Allen Alderman is the troop’s scoutmaster.
“Drew” Nolen, the son of Mark and Debra Nolen, built an 8-foot by 20-foot shelter at Bassett Community Center swimming pool for his Eagle Scout project, according to a letter the parents wrote to Adams. He also built two new lifeguard chairs.
The Court of Honor for “Drew” Nolen will be in early March, according to the letter.
In other business, David Kiser, assistant resident administrator with the Virginia Department of Transportation, gave a report on general highway matters. Among other things, he said the Henry County Public Service Authority has done some temporary repairs to a section of Colonial Drive in Collinsville where the PSA did some water line work. He said the PSA will do permanent repairs in the spring when asphalt plants open.