HINTON — Construction is scheduled to begin in May to address the final structural issue remaining in the U.S. Army Corps of Engineers’ effort to bring 70-year-old Bluestone Dam up to modern safety standards.
While there is now light at the end of the tunnel after the two decades of upgrades and retrofits called for in the Corps’ Safety Assurance plan for the dam, the tunnel remains long and costly.
The project has already cost $300 million and spanned 20 years. The final contract in the fifth and last phase of Safety Assurance work, awarded to Brayman Construction, of Pittsburgh, late last month, will take nine years to complete and cost an additional $319 million.
Brayman is tasked with virtually rebuilding the dam’s stilling basin — an artificial pool designed to allow energy from water released from the dam to dissipate before continuing downstream.
The contractor will armor the floor of the basin with a thick layer of concrete anchored to bedrock, and replace the original baffle blocks in the basin with 42 new and larger supercavitating baffles.
A coffer dam installed last year by Brayman under a $22 million contract bisects the stilling basin, allowing half of it to continue handling outflow from the dam while the other half is drained to accommodate construction.
An estimated 60,000 cubic yards of rock and 65,000 cubic yards of earth will be excavated during the course of the contract, and more than 100,000 cubic yards of material will be used for bank stabilization. A batch plant operated onsite will produce the 90,000 cubic yards of concrete to be installed in the settling basin.
Brayman’s contract also calls for the restoration of a section of Belle Point Park now used as a staging area for construction materials and equipment once work on the stilling basin is done.
New restrooms and a second baseball field will be added and playgrounds and day use areas will be improved. A fishing pier on the opposite side of the dam, removed to accommodate construction, will be replaced.
Bluestone Dam, built at a cost of $30 million and operational since 1949, was designed to withstand the most severe 24-hour rainfall on record for its watershed, which at the time was a 1916 hurricane that dumped 13 inches of rain in the New River drainage area upstream of the dam.
In the 1990s, the Corps of Engineers adopted a new safety standard calling for its dams to be able to control a “probable maximum precipitation” model developed by the National Weather Service.
The new standard for Bluestone’s Connecticut-sized watershed was a 20-inch rainfall within a 24-hour span.
In order to process the inflow such a storm would produce and maintain the structural integrity of the dam, Bluestone would have to more than double the outflow capacity for which it was designed, according to a Dam Safety Assurance Study conducted in the mid-1990s.
The study also determined that runoff from a 20-inch rainfall would exert enough pressure on the dam’s concrete superstructure that it could potentially slide off the shale-bearing quartzite bedrock underlying it, eventually causing the dam to fail.
To make certain such a catastrophe won’t happen, a Dam Safety Assurance action plan was developed and adopted, calling for five phases of work to correct the dam’s deficiencies. The first phase of construction got underway in 2000 with the installation of large concrete thrust blocks to add support to the downstream face of the dam. Six existing penstocks initially planned for use in a hydroelectric project were converted into into an auxiliary spillway.
Later work included adding a giant concrete gravity monolith to the east abutment of the dam, and connecting the dam to nearly 500 high-capacity directionally drilled anchors secured in up to 175 feet of bedrock.
Work began last year on the installation of electronics and machinery needed to make the dam’s crest gates — opened at times of extremely high water — operable by a remote control system.
Although remaining work planned for the dam is expected to take nine years to complete, the completion date is significantly earlier than previously projected, thanks to an emergency supplemental allocation for lake and river infrastructure needs attached to the Bipartisan Budget Act of 2018.
The allocation included more than $500 million to complete all remaining work called for under Bluestone’s Safety Assurance plan. Brayman’s $319 million contract from the Corps of Engineers accounted for the largest single contract issued through the 2018 allocation.
According the Army Corps of Engineers’ Huntington District, the ability to award a single contract to complete all safety assurance work on the dam accelerated completion of the project by six years.
While the project has been costly, Bluestone Dam is credited with preventing more than $5 billion in flood damage to Hinton, Montgomery, Charleston, and other Kanawha Valley cities.
More than half of the water in the Kanawha River flowing through Charleston first passes through Bluestone, making the dam the most significant of the three flood control dams protecting the city.
Since the dam’s routine outflow capacity will be reduced while the stilling basin work is underway, with only half of its sluice gates operating, the water level in Bluestone Lake will rise more frequently and take longer to return to normal pool levels.
Whenever the volume of water flowing into Bluestone Lake exceeds 10,000 cubic feet per second, the lake will begin to rise.
“Boat ramps, parking lots, campgrounds and other features at Bluestone Lake State Park and Bluestone Wildlife Management Area will flood more often at higher levels and for longer times,” according to a Corps fact sheet on changes recreationists can expect during the final construction period.
Once the work is complete, lake conditions will return to normal.
To compensate for the closure of a fishing pier adjacent to the W.Va. 20 side of the dam to accommodate the final construction project, the Corps of Engineers installed a new fishing pier at Bluestone State Park. Immediately below the stilling basin, a 300-foot stretch of the New River will be off limits to anglers and boaters for the duration of construction work.