Somerset Lake Dam Rehabilitation

Somerset, Pa.

Award of Merit

Submitted By: Michael Baker International

Owner: Pennsylvania Fish and Boat Commission

Lead Designer | Civil & Structural Engineer: Michael Baker International

General Contractor: Thomas Construction Inc.

The $7.6-million dam rehabilitation project, completed within budget in 25 months, included a labyrinth spillway, seepage and filter protection, raising the elevation of the top of the dam and improving the control tower and lake drain system that regulate the water level.

The team discovered sand seams that reached under the existing poorly constructed earthen dam without adequate cutoff. This contributed to uncontrolled seepage that resulted in standing water and wetland formation downstream. To collect seepage passing through and under the dam, the team installed a chimney and blanket along the rebuilt embankment.

When the team found that the existing spillway and dam embankment did not meet stability requirements, they designed a zig-zag-shaped spillway to replace the existing structure, providing additional hydraulic capacity in the existing footprint. They also reduced new spillway widening costs and added storage by raising the embankment 4 ft.

The labyrinth spillway solved a problem with insufficient spillway capacity to safely convey the probable maximum flood event.

An assessment of the existing lake drain revealed that the current conduit, although in “satisfactory condition had an expected design life that was less than the replacement spillway.” To avoid any future upgrade of the lake drain that would probably involve drawing down the lake, the team chose to slipline the full length of the lake drain conduit.