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Lake Scranton Dam Rehabilitation

Spillway, stability, and embankment improvements ensure the peak performance of a historic dam.
  • Aerial view of five-cycle labyrinth weir at Lake Scranton - Gannett Fleming.

    A new labyrinth weir increases conveyance capacity at the Lake Scranton Dam.

  • View of historic masonry dam retaining water at Lake Scranton - Gannett Fleming.

    Masonry repointing reduced seepage and strengthened the main dam structure.

  • View of work atop masonry dam to install vertical anchors into the structure - Gannett Fleming.

    Installing 23 post-tensioned anchors enhanced the integrity of the masonry dam.

  • Construction equipment installing seepage collection system on a dam embankment - Gannett Fleming.

    Slope flattening and a new seepage collection system improved embankment stability.

Client
Pennsylvania American Water

Partner(s)
KC Construction Company

Location
Lackawanna County, Pennsylvania

Our Role
Design, Geotechnical Investigation, Construction Management.

Data
Construction Cost
$10.2 million
Completed
In progress
Type
Rehabilitation
Outcomes
  • Spillway capacity exceeds probable maximum flood without overtopping the dam
  • Enhanced stability and integrity for historic masonry gravity dam structure
  • Design refinements improve spillway constructability, saving $500,000 in costs

Optimization of the labyrinth spillway at the Lake Scranton Dam eliminated the need for auxiliary spillway improvements, saving Pennsylvania American Water (PAW) $500,000 in construction costs. A new five-cycle labyrinth weir at the dam meets current state dam safety requirements to handle the maximum amount of rain that could fall in a given time period for the area without overtopping the dam embankments. Our firm’s design modifications included repositioning the spillway and altering its geometry to enhance constructability and optimize performance.

Lake Scranton holds approximately 2.5 billion gallons of water, helping PAW serve 160,000 customers in Lackawanna County. The water is retained by two structures: a spillway dam with a 200-foot-long combination ogee and labyrinth spillway structure with an earthen embankment and a main dam consisting of a 320-foot-long masonry gravity dam with an earthen embankment. The rehabilitation project improved performance, seepage collection, and structural integrity for the dam structures.

What We Did

Gannett Fleming provided geotechnical investigation and materials testing, civil design services, and construction management for the project. The team conducted a stability analysis of the masonry gravity dam, portions of which date to 1898, when Lake Scranton was created. Its recommendations included the installation of 23 post-tensioned vertical rock anchors to enhance the structure’s stability. Masonry repointing improved its structural integrity.

Advanced hydraulic analyses and 3D computational fluid dynamics (CFD) modeling enabled the team to optimize the geometry of the labyrinth spillway for peak performance. As a result of labyrinth spillway improvements, the emergency spillway at the main dam was no longer needed. Inconspicuous infill of the masonry structure’s arches, which had previously functioned as an emergency spillway, maintains the dam’s distinctive appearance while protecting critical downstream water supply components during high reservoir levels. Embankment slope flattening and a new seepage collection system improve embankment stability. A popular hiking trail along the crest of both dams was retained to provide recreational opportunities for local residents.

Key Features

  • Five-cycle labyrinth weir increased spillway capacity to meet state requirements.
  • 3D CFD modeling and hydraulic analyses optimized spillway geometry and performance.
  • Post-tensioned vertical rock anchors, each with a design load of 546 kips, strengthened the structural integrity of the masonry dam.
  • Archway infill prevents spillway flows that could cause erosion, structural instability, and damage to the downstream water supply system.
  • Repointing improves structural integrity of masonry dam and portions of the upstream face.

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