Alum Creek Lake

The Alum Creek Lake reservoir was built in 1974, covers 5 sq mi (13 km2) and has a maximum capacity of 134,815acre.ft.Dam construction (1970–1974)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 10000ft in length with a maximum height of 93ft 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 25ft tainter gates supported by 8ft wide concrete piers resting on concrete ogee sections. The ogee sections have a crest elevation of 878 and are founded at elevation 839.Potential dam failure and retrofit (1975–1978)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 1ft 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.TestingTwelve, 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.