Alum Creek Lake
| Alum Creek Lake | |
|---|---|
Alum Creek Dam and Lake. View is to the northwest.
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| Location | Delaware County, Ohio |
| Coordinates | 40°11′09″N 82°58′00″W / 40.185718°N 82.966636°WCoordinates: 40°11′09″N 82°58′00″W / 40.185718°N 82.966636°W |
| Type | impound |
| Primary inflows | Alum Creek |
| Primary outflows | Alum Creek |
| Basin countries | United States |
| Built | September 1974 |
| Surface area | 5 sq mi (13 km2) |
| Max. depth | 68 ft (21 m) |
| Water volume | 134,815 acre·ft (166,292,000 m3) |
The Alum Creek Lake reservoir was built in 1974, covers 5 sq mi (13 km2) and has a maximum capacity of 134,815 acre feet (166,292,000 m3).
Alum Creek Dam which was constructed between 1970 and 1974 is located on Alum Creek, a tributary of Big Walnut Creek, which drains into the Scioto River. The dam is a rolled earth-fill embankment 10,000 ft (3,000 m) in length with a maximum height of 93 ft (28 m) The spillway is located high on the right abutment with the raceway dropping off in front of it to the stilling basin below. Control is provided by three 34 by 25 ft (7.6 m) tainter gates supported by 8 ft (2.4 m) wide concrete piers resting on concrete ogee sections. The ogee sections have a crest elevation of 878 and are founded at elevation 839.
On April 24, 1975 during a periodic inspection of the completed dam, the US Army Corps of Engineers expressed concern about the safety of the spillway monoliths. The rock underlying the dam is Ohio Black Shale which is a largely hard, massive silt shale. It is highly fractured below the base of weathering. Within this shale are several light gray, silty to clayey shale seams up to 1 ft (0.30 m) thick. It may be possible that the spillway monolith and its underlying bedrock could slide forward on one of these seams, opening a gap between the monolith and the rolled earth dam leading to rapid and catastrophic erosion of the dam.
Twelve, 6-in. diameter core holes were drilled in the raceway directly in front of the ogee weirs. At least six of these cores exhibited a clayey seam about elevation 830 (nine feet below the ogee foundations). Testing of this material and deep-seated sliding analysis indicated that the dam did indeed face a safety issue.
To prevent the concrete monolith from sliding forward, it was decided to install seven cable anchors deep into the bedrock. Each anchor consisted of bundled, high strength steel cables that were concreted into the bottom of the holes. They were then hydraulically tensioned and the holes filled with grout. Anchors were installed at a 45 degree angle to a depth of 813, or 26 feet (7.9 m) below the foundation of the ogees. On March 2, 1977 the project was bid to VSL Corporation for $254,777. Drilling for the anchors began on June 7, 1977. The final loading on each anchor was 1300 kips. On September 28, 1977, one of the anchor's foundations failed and had to be re-concreted. By 1978, the project was completed.
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