River Watch # 4

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River Watch 2023 # 4

Water Level Update

On Thursday, May 04, the ILOSLRB released the attached graphic which highlights inflows and outflows for those watercourses impacting the St. Lawrence River. The graphic is effective as of May 03. This graphic/chart will give you some idea of why water levels on the St. Lawrence are rising and potentially threatening your properties.

Lake Ontario outflow at the Moses-Saunders Dam (M/S) is shown as being 5,900 cubic meters/second. Flows were further reduced on May 04, to 5,750 m3/sec. Since then, the outflow from the Ottawa River has declined (peaked on May 05) and the Board, as of yesterday evening, has brought the outflow at M/S up to 7,400 m3/sec.

The second major factor affecting levels on the river is the inflow into Lake Ontario. The other Great Lakes inflow enters the lake via the Niagara River. Inflows from rivers, streams and precipitation within the Lake Ontario watershed further add to the level of the lake. As you will note, the combined inflow or supply was 10,510 cubic meters/second. The lake inflow exceeds the outflow at Moses/Saunders, therefore water levels on both the lake and river keep going up. The risk of flooding will be dependent on the Board being able to increase the outflow at the M/S Dam to reflect the inflow more closely. Another major factor would be a precipitation event like what we experience in late April. That might increase flows on the Ottawa River and thereby force the Board to again reduce outflows at the Moses-Saunders Dam.

At the present time, the river level in Augusta is 11.5 inches above what it was on April 21, 2023. That level is without any wind surge. Township staff will continue to monitor river level conditions to keep residents informed.

Should conditions further deteriorate, residents will be advised of the procedures regarding the availability of sand and sandbags. If you have any questions with respect to this bulletin, please email Hans Werner-Mackeler, Community Emergency Management Coordinator at emergplan@augusta.ca.

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