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Penn Forest dam wins ASDSO award

The Penn Forest dam has won the US Association of State Dam Safety Officials’ (ASDSO) National Rehabilitation Project of the Year Award. The largest RCC dam east of the Mississippi river (pictured here before, during and after rehabilitation), Penn Forest was built to replace the old dam at the Penn Forest reservoir, which was built in 1956-58 to provide 62% of the City of Bethlehem’s raw water supply.

The original dam was a 588m long, 44m high, zoned earthfill/rockfill embankment with a central impervious core wall founded on rock. In 1960, high rates of seepage caused a sinkhole to develop in the upstream slope of the embankment near the reservoir’s surface. The embankment was repaired and over 200 piezometric instruments were installed to monitor the seepage, but by 1994 it had progressed to the stage where either a major repair or replacement of the dam was unavoidable.

After reviewing several options a new 55m high, 625m long RCC dam was built.

ASDSO found the project noteworthy in several respects:

•The existing spillway and diversion and intake structures were retained by building just upstream of the original dam.

•US$20M was saved by using the original embankment as a buttress, allowing for a steep downstream face.

•Retaining the old site limited the environmental impact of the new dam.

Also nominated for the award were the Hopewell dam reconstruction in Florida, Ottowa State Fishing Lake rehabilitation in Kansas, the Tongue river dam in Montana, Robinson’s Branch dam rehabilitation and the Douthat and Hungry Mother dams rehabilitation.