This June marks the 50 year anniversary of a momentous survey operation by the U.S. Army Corps of Engineers, Buffalo District – the dewatering of the American Falls in June 1969.
During the work effort, a cofferdam was built at the east end of Goat Island and was completed on June 12, 1969 (50 years ago today), .
This temporary dam diverted the water from the American Falls to the Horseshoe Falls, allowing for the necessary range of geological surveys to take place. Even now the outflow from Lake Erie through the Niagara River is unregulated, but water in the upper Niagara River, just upstream of the Falls, can be diverted to hydropower plants where the diverted flow is transferred through the hydropower plants and back into the lower Niagara River.
Several factors led up to the decision to re-route nature in such a way. A significant amount of talus (a slope formed by rock debris) had built up under the American Falls as a result of rockfalls, especially major events in 1931 and 1954. Some people thought this took away from the aesthetic appearance of the Falls.
A public campaign started in 1965 by the mayor of Niagara Falls and the Niagara Gazette brought this issue to the attention of the public and the government. The stability of the area near the falls was in question, due to the underlying geology of the site. Water flows there over a more resistant layer of Lockport dolomite, about 80 feet thick, underneath which is a softer layer of about 60 feet of Rochester shale. As the shale gets undermined, and joints open up in the dolomite, pressure builds, the shale falls apart and the cap is thereby undermined.
A partnership was formed: the American Falls International Board, under the IJC, including the Corps of Engineers, the New York State Parks, the Power Authority, and several Canadian offices.
A range of tests were done - 48 core borings, face mapping, “topographic, stratigraphic and structural studies, terrestrial photogrammetry, mapping of rock fractures and joints, installation of piezometers to measure water pressure in rock joints, and installation of instruments to measure horizontal movement in the adjacent rock mass.”
Sprinklers were installed during this project to keep the Rochester shale layers wet so they didn’t crumble apart. It provided a unique opportunity to study the structure and workings of the Falls – according to USACE District Commander Colonel Amos L. Wright, “our geologists are in a dream world.”
The talus at the base of the falls was mapped but ultimately left in place. The cofferdam was removed on November 25, 1969, and the Falls returned to its previous state.
The Corps of Engineers is proud that we were part of this effort and today we continue Building Strong and caring for our Nation’s water resources.