Buckhorn Dam and Reservoir Expansion
Client: City of Wilson
Location: Wilson, NC
Hazen and Sawyer provided comprehensive engineering services to the City of Wilson for the expansion of Buckhorn Reservoir, the city’s primary water source, increasing impounding capacity from 0.7 to 6.7 billion gallons and safe yield to 29 mgd. Services included planning studies, environmental and regulatory permitting preliminary design, final design, construction and post-construction services.
Project Outcomes and Benefits
- Comprehensive engineering services from project planning through construction completion.
- Selection of RCC instead of conventional earthfill saved $3 million in construction costs and reduced construction time by more than a year.
- Innovative RCC monolith design provided stable construction on a weathered rock foundation and major saving in intake construction.
- During the initial impounding sequence in September 1999, Buckhorn Dam came through with flying colors the ultimate test of passing a flood equal to almost ½ the of the probable maximum flood resulting from the one-two punch of Hurricanes Dennis and Floyd.
- Ongoing services include regular inspections and regulatory compliance services.
Following a detailed construction alternatives analysis, Hazen and Sawyer recommended roller-compacted concrete (RCC) as the most economic and overall favorable alternative for the new Buckhorn Dam. Completed in May 1999, the new dam is the first all-RCC dam constructed in North Carolina and one of the first in the U.S. constructed on a weathered rock foundation. It has a structural height of 44 feet and a total length of approximately 2,560 feet. Total project cost was approximately $45 million (2000 dollars), including design, land acquisition, environmental mitigation, and construction.
Keys to constructing a stable dam on weathered rock foundation: (1) broaden the dam base to bring foundation compressive and dam overturning forces to within national safety standards, and (2) design the dam as a series of monoliths to allow for differential settlement along its almost half-mile length. Water tightness is provided by a continuous impermeable membrane along the dam face integral with precast concrete facing panels, which served as stay-in-place forms. The intake structure is constructed as a separate conventional concrete monolith, in-line with the RCC monoliths. This innovative approach avoided the cost of a conventional stand-alone tower without interfering with RCC placement. It further reduced project costs by integrating stream diversion with phasing of the intake monolith construction.
For more information on this project, or to discuss a similar project in your area, contact Jeffery Powers at firstname.lastname@example.org