Sandra Hoffman, age 12, of Dover, Del., for her question:
WAS NIAGARA FALLS ONCE SHUT OFF?
Niagara Fails is one of the world's most memorable natural sights. It is a great waterfall on the Niagara River in western New York and southeastern Ontario, Canada. Back in 1969 part of the waterfall was actually shut off so scientists could study the rivers rocky bed.
Scientists tell us that Niagara Falls was formed about 12,000 years ago when glaciers retreated north, allowing water from Lake Erie to flow over the Niagara Escarpment, a ridge that extends from southern Ontario to Rochester, N.Y. Since that time, erosion has slowly pushed the waterfall about seven miles upstream, forming the Niagara Gorge.
At present the Canadian Falls is receding at an average yearly rate of about five feet and the American falls is being cut away at an annual pace of about six inches. The Canadian Falls erodes at a faster rate mainly because it carries more water.
In 1954 a considerable portion of the American Falls broke off, creating a large talus, or rocky slope, at the base of the cataract. In order to study ways of preventing further rockfalls and to remove some of the talus, the American Falls was "shut off" for several months in 1969 by a dam built between the United States mainland and Goat Island.
The Canadian Falls, also called Horseshoe Fails, is 161 feet high while the American Falls are 167 feet high. The crestline of the crescent shape d Canadian Falls, which carries about nine times more water than the U.S. cataract, is about 2,592 feet long and the fairly straight crest of the American Fails measures about 1,001 feet. A small section of the American Fails near Goat Island is also known as Bridal Veil Fails.
The Niagara's large volume of flow, averaging about 194,940 cubic feet per second, plus its steep drop, give the river great power potential. In 1950 the U.S. and Canada signed a treaty fixing the amount of water that could be diverted from the river for power generation and soon thereafter two major hydroelectric projects were constructed.
The Canadians built the twin Sir Adam Beck Niagara generating stations at Queenston, Ontario. The stations were completed in 1958 and have a 1,815,000 kilowatt capacity.
The Power Authority of the State of New York constructed the Robert Moses Niagara Power Plant near Lewiston, N.Y. It was completed in 1963 and has a 2,400,000 kilowatt capacity.
Both projects are located about four miles below Niagara Falls and are driven by water diverted just above the falls and conveyed by underground conduits and canals to turbines. Much of the hydroelectricity is consumed by industries in the nearby cities of Niagara Fails, N.Y., and Niagara Falls, Ontario.
Niagara Falls is a great tourist attraction. Millions of visitors each year come to see the magnificent display of falling water. The fails may be viewed from parks located on either side of the river, from observation towers, from boats, from Goat Island and from Rainbow Bridge, located a short distance downstream. Visitors also may enter the Cave of the Winds, located behind a curtain of falling water near the base of the American Falls.