How much water is diverted?
The Great Lakes in general are very sensitive to high-or-low precipitation years, and this can affect the flow from Lake Erie into the Niagara River, however the levels have been regulated by the International Joint Commission (USA and Canada) since 1910.
The basis for determining the amount of water that can be diverted for power generation is contained in a treaty between the Governments of Canada and the United States concerning the “Diversion of the Niagara River,” dated 1950, and generally referred to as the “1950 Niagara Treaty.”
The treaty requires that during the daylight hours of the tourist season (0800 to 2200 hours local time, April 1st to September 15th and 0800 to 2000 hours local time September 16th to October 31st), the flow over Niagara Falls must not be less than 2832 cubic metres per second (cubic m/s) [100,000 cubic ft. per second (cfs)]. At all other times, the flow must not be less than 1416 cu m/s (50,000 cfs).
The treaty also specifies that all water in excess of that required for domestic and sanitary purposes, navigation and the falls flow may be diverted for power generation.
If the river was allowed to return to natural levels, it would rise probably another 5 metres.
More about the flow of the falls
The term tonnes refers to a metric tonne, also known as a long ton. In this case we are referring to water, which at standard temperature and pressure (STP) weighs one tonne per cubic metre. STP is the weight of water at zero degrees centigrade at sea level which is one atmosphere (atm) of pressure. We can disregard temperature and pressure for this calculation although you should be aware that the mass of water decreases as the temperature rises and/or the pressure decreases.
During the high season, the tourist flow over the falls of 100,000 cubic feet/sec (cfs) converts to 2,832 cubic metres/sec (cms) which would mean that 2,832 tonnes/sec are going over the falls.
The non-tourist flow of 50,000 cfs coverts to 1,416 cms which would mean that 1,416 tonnes/sec are going over the falls.
To convert from tonnes/sec to tonnes/minute multiply by 60. To convert from tonnes/sec to tonnes/hour multiply by 3,600.
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