Nantahala Dam InspectionsFERC Part 12 Safety Inspections
According to Federal Energy Regulatory Commission (FERC) Order 122, owners of certain licensed hydroelectric projects are required as part of their license to engage an independent consult to perform Part 12 safety inspections every five years.
ARCADIS has been provided independent consult services to Nantahala Power and Light Company for the following projects over the last 10 years:
East Fork, a 140-foot-high, 385-foot-long rockfill, sloping core dam with fuse plugs and gated spillway, saddle dam, powerhouse, and appurtenances.
Wolf Creek, a 175-foot-high, 810-foot-long rockfill dam with two fuse plugs and a gated spillway, powerhouse, and appurtenances.
Bear Creek, a 215-foot-high, 760-foot-long rockfill, sloping core dam with two fuse plugs and an automatic gate.
Cedar Cliff, a 173-foot-high, 590-foot-long rockfill, sloping core dam with fuse plug and gated concrete spillway, powerhouse, and appurtenances.
Nantahala, a 250-foot-high, 1,042-foot-long rockfill embankment and two diversion dams with 16-foot-high concrete gravity overflow sections.
Queens Creek, a 78-foot-high, 382-foot-long rockfill, sloping core dam, powerhouse, and appurtenances.
Thorpe, a 150-foot-high, 900-foot-long rockfill, sloping core dam with powerhouse and appurtenances.
Tuckasegee, a 61-foot-high, 254-foot-long arch dam.
Bryson, a 36-foot-high, 200-foot-long multiple-arch concrete dam, powerhouse, and appurtenances.
Mission, a 50-foot-high, 397-foot-long concrete Ambursen dam, powerhouse, and appurtenances.
As directed by comments from the FERC on the Part 12 inspection results, ARCADIS conducted breach analyses, prepared inundation mapping, and developed emergency action plans for all Nantahala projects in accordance with FERC guidelines. We also provided engineering design, plans, specifications, and construction observation for the following projects in response to FERC comments:
Wolf Creek - Construction of a 4-foot-high, 800-foot-long wall along the crest of the dam to increase the spillway capacity to accommodate the probable maximum flood (PMF).
Bear Creek - Construction of an 11-foot-high, 600-foot-long wall along the crest of the dam to increase the spillway capacity to accommodate the PMF.
Cedar Cliff - Detailed hydrologic and hydraulic analysis, breach studies, and modeling of the downstream reach of the dam to determine the impact of failure; feasibility studies to modify the dam to accommodate the PMF; investigation of erosion of cascade spillway in rock and recommendations to prevent erosion from affecting the dam.
East Fork - Modification of the saddle dam to serve as a fuse plug, allowing the project to pass the PMF.
Nantahala - Design plans and specifications for replacing and upgrading powerhouse pumps, switchyard runoff, and oil collection and separation.
East Fork - Plans, specifications, and consulting services during construction for remedial grouting and Gunite treatment to repair weathered and fractured rock in abutment of this dam.
Mission, Bryson, and Franklin - Flood frequency analysis and spillway rating.
Wolf Creek, East Fork, Cedar Cliff, Bear Creek, Thorpe - Slope stability analyses of all of Nantahala embankment projects. Geotechnical investigations included drilling, sampling, and testing. More than 85 triaxial consolidated-drained and consolidated-undrained shear tests were performed.
Thorpe, Tuckasegee, Nantahala, Queens Creek, Cedar Cliff, Bear Creek, Wolf Creek, East Fork - Unit hydrograph development from stream and rainfall records using the HEC-1 computer program, spillway rating, and PMF routing.
Additional Studies
ARCADIS has also completed numerous other studies and investigations and Nantahala Power and Light Company projects, including:
Multiple-arch structural stress analysis at Bryson Dam.
Arch structural stress analysis at Tuckasegee Dam.
Sliding analysis at Mission and Bryson dams.
Shear friction field and laboratory investigations at concrete/rock interface at Mission Dam.
Rock bolting at Bear Creek Dam.
Gate hoist modifications at Nantahala Dam.
Gunite repairs to Mission, Bryson, and Franklin dams.
Hydro feasibility studies for additional capacity at Franklin, Bryson, and Dillsboro dams.
Tainter gate rehabilitation for Franklin Dam.
Specifications for generator rewinding for Bear Creek powerhouse.
Power tunnel inspections for Bear Creek, Tennessee Creek, and Cedar Cliff dams.
Site design and foundation design at Saffire Valley and Webster substations.
Analysis of tainter gate capacity at Bear Creek, Bryson, Cedar Cliff, East Fork, Franklin, Mission, Nantahala, Thorpe, and Wolf Creek dams.
