Persistent dry conditions have resulted in a lower-than-average seasonal rise in water levels for all the Great Lakes. As a result, water levels in both the St. Lawrence Seaway and especially the St. Lawrence River are significantly impacted. This circular letter reminds members of the water level information and tools available for the Seaway and the St. Lawrence River.
Great Lakes and St. Lawrence Seaway
The management of low water levels in the Great Lakes and St. Lawrence Seaway is critical during these dry/drought periods. After seeing record high water levels across the region in 2017 and 2019, Lake Ontario is now well below average this year (June mean was 36cm below average). Lake Erie which flows unchecked into Lake Ontario was 35cm above average for June and the risk of local flooding remains.
The International Lake Ontario and St. Lawrence River Board (ILOSLRB) have approved deviations from Plan-2014 reducing the flows at the Moses Saunders Dam. The Board approved a reduction of 200 m3/s below the applicable Plan 2014 Rule Curve flows. The Board will continue to monitor conditions and the effects of the deviation strategy closely, while tracking weather forecasts and drought conditions. Updated Lake Ontario water flows changes can be found here.
There was a slight gain in the level of Lake Ontario last week and under most potential water supply scenarios, it is likely that Lake Ontario will continue rising slightly before beginning a slow, seasonal decline over the next few weeks. Under dry scenarios, it is possible that Lake Ontario is near its seasonal peak. It is anticipated that if the levels of Lake Ontario decline, water flows may be further reduced affecting available water depths in the St. Lawrence Seaway. As in the past, a draft restriction may be inevitable if dry conditions persist. We continue to work with the Seaway, and will advise members if any draft restrictions are imposed.
St. Lawrence River
The Canadian Coast Guard issues a weekly (or as required) Water Level Forecast Bulletin which provides estimates of the expected lowest water level than can be expected for the upcoming 1-4 weeks. Generally, this means the Coast Guard will endeavor to maintain this level, however there is no guarantee as local or short term hydrometeorological factors may affect the levels. These forecasts are the deviations above/below chart datum for the St. Lawrence River where the main channel is maintained at 11.3m (note some berths are less than 11.3m)
In conjunction with these forecasts is the under-keel clearance (UKC) requirement for vessels transiting between Quebec City and Montreal as outlined in the Annual Notice to Mariners – Section 27C. Generally, vessels are permitted to transit at 7 knots, however wide-beam vessels must base their UKC calculation on 10 knots for the portion of the voyage which is upstream of Batiscan as outlined in Section 27A.
The Federation will continue to monitor and advise members if conditions change.
Please direct any questions to the undersigned
Director, Marine Operations