INTRODUCTION

Canonsburg Lake is a 76-acre Commonwealth-owned impoundment located south of Pittsburgh in Peter’s and North Strabane townships, Washington County, Pennsylvania. The lake is very popular with outdoor recreation enthusiasts in southwestern Pennsylvania.

A dam is located on Little Chartiers Creek. Water from the lake flows over the spillway, then continues north for approximately ¼ mile where it meets the main branch of Chartiers Creek. Chartiers Creek continues for approximately 25 miles until it meet the Ohio River in McKees Rocks. Computer-aided hydraulic models indicate that failure of the dam would inundate approximately 300 residents and 100 homes.

DAM AND APPURTENANCES

The Canonsburg Lake Dam is a reinforced concrete gravity dam approximately 525 feet long and 45 feet high. Alcoa corporation completed construction on the dam in 1943. The impoundment was to be used as an industrial water supply for Canonsburg Forging Plant during World War II. A small structure built immediately below the dam to house the pumps that was to transport water to the forging plant remains on site today. The piping in the pump house is still intact, however, it is considered to be inoperable. Unlike most dams, Canonsburg dam was built without any kind of drawdown control. The Commonwealth, acting through the Fish and Boat Commission, acquired the lake, dam and adjacent property in 1958 for public fishing and boating.

DEFICIENCES OF THE DAM

In 1996 the PFBC contracted Schnabel Engineering Associates to assess the dam. The study revealed the following:

• The concrete exhibited minor surface deterioration (concrete spalling and surface cracking).
• The foundation exhibited significant water loss during the water pressure tests.
• The spillway has insufficient capacity to pass the Spillway Design Flood (SDF) without over-topping the non-overflow sections of the dam.
• Both the spillway and non-overflow sections of the dam fail to meet the required sliding factors of safety for several loading conditions.
• There is no low level outlet for the reservoir.

REPAIRS TO THE DAM/SPILLWAY

Schnabel’s Engineers recommends remedial measures include patching and sealing the exposed surfaces of the non-overflow sections, installation of post tensioned rock anchors to strengthen the dam and allow overtopping of the non-overflow section (safe passage of the SDF), foundation grouting in association with the post tensioning (to be coordinated with the anchor drilling and installation), and conversion of the existing 14 inch suction line to a low level outlet. The conceptual level cost estimate for the project (including engineering and construction) is $1,040,000.

DREDGING THE LAKE

Like many aging impoundments, Canonsburg Lake is gradually filling with silt. At some point in the life of any impoundment, dredging is required to maintain the pool at desirable depths. The depths at the upper end of the lake have lowered to the point that, in some circumstances, boating is difficult or impossible. The PFBC has been asked to estimate the costs of a project to dredge silted material from Canonsburg Lake and move it to upland locations away from the project. The PFBC has had the silted material tested and found that it does not contain contaminants requiring special disposition.

A project to dredge Canonsburg Lake would be costly and would face challenges related to the configuration of the Lake. Preliminary estimates of the cost of a dredging project range from $2 million to $20 million depending on the amount of silt removed from the lake and the location to which it is moved. For example, a concept to remove 3 feet of dredged material from the area upstream of McDowell Lane is estimated to cost about $3 million.

PFBC PARCIPTATION

The Fish and Boat funds managed by the PFBC, including federal fund augmentations for these funds, do not contain money to support either a dam rehabilitation or dredging project at Canonsburg Lake. Any such projects would need an alternate funding source. The Fish and Boat Commission will cooperate with local and state efforts to identify funds for, and undertake, such projects. The PFBC is currently working with Washington County Watershed Alliance, Chartiers Creek Watershed Association, and the Washington County Conservation District to secure funding. The partnership has secured $250,000 from the Army Corp of Engineers for an Environmental Restoration Study on the lake.

PFBC DAM FUNDING NEEDS

While Canonsburg Lake remains at normal pool level, the PFBC currently manages five (5) lakes drawn down in recent years to address dam safety concerns. The Commission continues to work to secure funding for repairs on all the dams.

The Commission remains optimistic that a funding source outside of the day-to-day operating revenues in the fish and boat funds will be found and will be available for the substantial infrastructure improvement needs the Commission has. The total need for dam repairs alone is estimated at more than $83 million.

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