Improving a High Hazard Dam's Safety with Difficult Site Access

Ethan Miller, E.I.T., Engineer, Gannett Fleming, Inc.

Clifton Forge Dam is a high‐hazard potential concrete gravity dam located in western Virginia that provides
municipal water supply to the Town of Clifton Forge and its surrounding service area. The Town has a
population of nearly 4,000 and sits directly in the path of a hypothetical floodwave should the dam fail.
Due to inadequate spillway capacity, insufficient structural stability during the design flood, and a
significant leak in a horizontal concrete lift joint, the Town of Clifton Forge was ordered by the Virginia
Department of Conservation and Recreation to rehabilitate the dam to address these dam safety
deficiencies which inherently also improve the reliability of this critical water supply resource. The design
of the project began in 2014 and, after successfully securing funding through USDA‐Rural Development in
2019, construction was undertaken and substantially completed in 2020 at a cost of approximately
$3.7 million.

The rehabilitation of Clifton Forge Dam involved a wide range of construction work, including concrete
demolition, conventional and mass concrete placement to raise the crest of the non‐overflow sections of
the dam, repair of deteriorated concrete, horizontal concrete lift joint grouting, earthwork, installation of
three post‐tension anchors within the spillway monoliths, and replacement of the existing spillway bridge
with a new single‐span structure. Construction access was limited to a steep, narrow right abutment;
forcing most of the construction activities to be performed from, or supported by, a barge‐mounted crane.
The contractor’s barge operations were subject to additional restrictions needed in order to protect the
water supply infrastructure and prevent any obstruction of the spillway area, since the work had to be
completed at a near‐normal pool level. This presentation describes the purpose and nature of the dam
safety improvements, and the design and construction techniques used to perform the work given the
difficult site access and work restrictions.

Author Bio

Ethan Miller has been employed as an Engineer with Gannett Fleming, Inc. in Camp Hill, PA since 2017. As part of the Dams and Hydraulics team at Gannett Fleming, Ethan's work experience has primarily centered around dam rehabilitation design and construction. Ethan graduated with a bachelor's degree in Civil Engineering from Penn State University in 2016. Outside of work, Ethan enjoys fly-fishing, camping, and otherwise exploring the wildernesses of Pennsylvania.