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50 years ago the U.S. turned off their part of Niagara Falls

In 1969 Niagara's American Falls were "turned off" so engineers could study the effects of rock falls on the flow of the water.

In 1969, engineers 'turned off' the American Falls to study the rock below

In 1969 the American Falls, one of the three making up Niagara Falls, were dried up so engineers and geologists could study rockfalls and erosion there. 1:33

Back in the summer of '69, some tourists at one of Ontario's biggest shows might have been there to see what was not on display. 

Niagara Falls, which is actually comprised of three waterfalls — the American, the Bridal Veil and the Horseshoe — was diminished by one, as the American fall was reduced to just a trickle, so it could be studied by U.S. engineers and geologists.

Over the course of a few days that June, a dam was built over the Niagara River, between the American shore and Goat Island.

'The water was shut off'

The mighty Horseshoe Falls, still at full power in 1969 when the American Falls were "turned off." (CBC National News/CBC Archives)

With the diversion of the water to the Canadian side of the river, for the American Falls, the CBC's Sheldon Turcott reported, "the water was shut off" on June 12.

"Here, exposed, a massive rock pile," he said, adding that the river poured "10,000 cubic feet of water into the Niagara Gorge every second."

Building of the dam over the Niagara River, in the 1969 shut-off of the water to the American Falls. (CBC News/CBC Archives)

Rock falls in 1931 and 1954 had caused the water drop to be shortened and were threatening to mar the beauty of the waterfall at the American Fall by shortening the length of the curtain of water.

The erosion threatened to "flatten out the American Falls and make them disappear altogether," he said.

The exposed rock where the American Falls usually flowed, with just a trickle of water, in 1969. (CBC News/CBC Archives)

About a month later, CBC's The Day It Is visited the site, for some in-depth exploration of the project and the near-dry river bed.

With a dam built to divert the water to the Canadian side of Niagara Falls, the rock of the American Falls was exposed for examination. 1:37

As U.S. Army Corps engineer Maj. B.R. Schlapak explained, the building of the cofferdam — in this case a temporary structure erected to enable the draining of the river bed close to the fall ledge — had gone well, and work had begun on studying the rock.

Schlapak said the purpose of the project was to check the feasibility of clearing away the "[fallen] rock from the foot of the American Falls" and "to see if it's possible to stem the erosion of the falls."

'There wouldn't be a falls anymore'

With the water diverted, geologists were able to test and examine the rock types at Niagara Falls. 3:55

Sitting below the escarpment, host Warren Davis spoke with the project's chief geologist, T.A. Wilkinson.

"I've heard it said that if something isn't done, eventually Niagara Falls would become a long rapids, that there wouldn't be a falls anymore," Davis said.

"Yes," Wilkinson agreed, adding that it was a particular threat for the American Falls and less likely for the Horseshoe Falls.

"There's a greater volume of flow," at the Horseshoe, he further explained, because "something like 90 per cent of the water flows over the Horseshoe Fall" and this volume "scours the basin," preventing accumulation of the fallen rock there.  

'Faith in the cofferdam'

The American Falls, just before they were 'de-watered' by a cofferdam in 1969. (CBC National News/CBC Archives)

With the camera sweeping the ridge where the river's water normally fell, Davis raised a point which made the geologist smile.

"By the way, if the cofferdam gave way, we'd be under water?" Davis said.

"Yes," Wilkinson agreed, "we'd be in the region of the river here at this point."

"Let's have faith in the cofferdam," Davis laughed.

The flow of water to the American Falls was restored on Nov. 25, and according to a report the next day in the Toronto Star, Niagara Parks Police were quoted as having said that "'two or three times' the normal number of visitors viewed the falls this year."