Asheville plans to bolster North Fork reservoir dam
Preparing for rainstorm that comes every 50,000 years
On Jan. 18, the city of Asheville will submit its plans to the state to reinforce the dam at North Fork reservoir to better withstand runoff from severe storms and seismic activity such as earthquakes and tremors.
Work on the $30 million-$35 million project north of Black Mountain is scheduled to begin in June and will triple the amount of water the reservoir can release every second. Construction should take two years, according to city estimates, and will bring concrete trucks and other heavy equipment to North Fork Road. Because most of the earth that will thicken the dam is already onsite, construction traffic should be minimal, said Leslie Carreiro, Asheville water production and quality division manager.
Improvements are meant to help the dam withstand the kind of storm that happens every 50,000 years. The planned series of “fuse gates” is designed to handle the volume of rain runoff that occurred during storms Ivan and Frances in 2004 and during the flood of 1916, the high water mark of storms in Western North Carolina. The restricted 22,000-acre North Fork reservoir receives all the water than runs off the mountains that tower over Black Mountain.
Built in 1955, the dam there was meant to provide Asheville’s drinking water, not to mitigate the effects of flooding caused by significant rainfall, according to information on the city of Asheville’s website. A breach in the dam would be a “catastrophic event,” the website states, one that the planned improvements are meant to prevent. (Buncombe County emergency agencies have a plan for protecting the Valley in the event that the reservoir’s water levels rise quickly, Carreiro said.)
Plans to be submitted to the state Department of Environmental Quality Jan. 18 call for raising the height of the dam by four feet and for reinforcing the main dam and “saddle” dam. The plans also call for improving the principal spillway and building an auxiliary spillway.
Residents of North Fork Left Fork and North Fork Right Fork roads will share the road with concrete trucks and tandem dump trucks beginning sometime in the middle to latter part of this year, according to the city’s website. Homeowners near the dam will be notified about any drilling, blasting and jackhammering. Some will be able to request a “pre-blast survey,” at no cost, that will determine if blasting might cause structural damage to their homes.
The Asheville-Black Mountain region gets a “major flooding event” every 20 years, according to Asheville website. Current emergency plans call for releasing water as the reservoir fills up. The city’s plans include an auxiliary spillway that would allow relief for the kind of storm that happens every 200 years. The first of a series of “fuse gates” would be tripped by a storm than occurs every 1,000 years. The kind of storm that occurs every 50,000 years, based on the last two decades of regional weather patterns, would trip all of the fuse gates, according to the plan.
Engineers contracted by Asheville have simulated and planned for worst-case scenarios that also include movement of bedrock beneath the reservoir. “Based on the outcomes of these scenarios, the engineers have identified improvements to help protect the reservoir, the water source and nearby residents in the event that one of these unlikely but possible events were to occur,” the website states.
A casualty of the improvements will be the former Black Mountain Rod and Gun Club Cabin, situated near the primary spillway. Because the N.C. State Historic Preservation Office determined the structure isn’t historic, it will be demolished.