Weekly Regulation Summary

Summary for Week Ending 19 February 2020

A partial ice cover remains in the Beauharnois Canal. The high Lake Ontario outflows along with ice accumulating downstream of Lake St. Louis causes water levels on Lake St. Louis to rise. The Lake Ontario outflow has been adjusted in recent days to ensure Lake St. Louis remains below flood levels. Mild temperatures are expected to return and this may allow outflows to be increased again soon. Outflows continue to be maintained as high as possible and will continue to be adjusted as necessary, according to conditions in the St. Lawrence River.

  Week Ending: Wed, 19 Feb 2020 Average this time of the year (c) 
Lake Ontario -    
         Actual end of week level: 75.11 m  (246.42 ft) 74.62 m  (244.82 ft)
         Computed Plan 2014 Level (a): 75.24 m  (246.85 ft)  
         Computed Preproject Level (b): 75.98 m  (249.28 ft)  
         Weekly Mean Outflow: 9480 m³/s  (334800 ft³/s) 7050 m³/s  (249000 ft³/s)
         Weekly Total Supply: 8790 m³/s  (310400 ft³/s) 7170 m³/s  (253200 ft³/s)
Lake St. Lawrence at Long Sault Dam Weekly Mean Level:  72.82 m  (238.91 ft) 72.51 m  (237.89 ft)
Lake St. Louis at Pointe-Claire Weekly Mean Level:  21.89 m  (71.82 ft) 21.35 m  (70.05 ft)
Montreal Harbour at Jetty #1 Weekly Mean Level:  7.30 m  (23.95 ft) 6.87 m  (22.54 ft)
Ottawa River at Carillon Weekly Mean Outflow: 2180 m³/s  (77000 ft³/s) 1850 m³/s  (65300 ft³/s)
Preliminary Lake Ontario Outflow for Week Ending Fri, 28 Feb 2020: 9000 m³/s  (317800 ft³/s) 7170 m³/s  (253200 ft³/s)

Levels are in metres (feet) IGLD 1985.  Supply and flows are in cubic metres (feet) per second m³/s (ft³/s).  

(a) Levels that would have occurred with strict adherence to Plan 2014.

(b) Levels that would have occurred had there been no Lake Ontario regulation.        
(c) For comparison purposes, Lake Ontario water level data since 1918 are used to be consistent with those published in the  US and Canadian Great Lakes bulletins (https://www.waterlevels.gc.ca/C&A/bulletin-eng.html). Other averages are for the periods as follows: Lake Ontario outflows and levels at Long Sault and Pointe-Claire since 1960; Montreal since 1967; and Ottawa River outflow at Carillon since 1963.

The regulation plan for Lake Ontario specifies a weekly average outflow from Saturday through the following Friday, inclusive.  To provide timely information for the coming week to the hydropower and Seaway operators, and our readers, we complete the regulation plan calculations each Thursday.  Our calculations use the data available at the time, which are from the previous seven days (Thursday through Wednesday). Since the two time periods do not exactly coincide, their data are usually slightly different.

The table shows the actual flow for the week ending Wednesday.  It also gives the preliminary flow for the coming week ending Friday.  We emphasize that this is the preliminary flow, since unforeseen flow changes may occur after we have issued our notice.  When these flow changes occur, they are reflected in the subsequent week's notice.

Information in this report is compiled from provisional data provided by: Environment & Climate Change Canada, Fisheries and Oceans Canada, Hydro Quebec, Ontario Power Generation Inc, the New York Power Authority, and the U.S. National Ocean and Atmospheric Administration.