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.
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
- The foundation exhibited significant water loss during the water pressure
- 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.
is no low level outlet for the reservoir.
REPAIRS TO THE DAM/SPILLWAY
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.
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.
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.
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.