New report on 2017 Lake Ontario and St. Lawrence River flooding

By on June 25, 2018

A report released June 21 by the International Lake Ontario-St. Lawrence River Board (the Board) provides a detailed account of the historic 2017 flood, and the Board’s actions under Plan 2014 to regulate Lake Ontario outflows in the face of high inflows and record-breaking precipitation.

The report finds that extreme weather and water supply conditions were the primary factors that caused Lake Ontario and St. Lawrence River water levels to rise to record breaking levels last year.  It also finds that Plan 2014 did not cause or exacerbate the devastating floods and associated damages that occurred in 2017.  Under extremely wet weather, the rules of Plan 2014 essentially reflect how the Board operated under the former regulation plan.

During 2017 Lake Ontario outflows were largely dictated by extreme conditions, including upstream and downstream flooding, highly variable ice formation, and hazardous high flows in the navigation channel.  Throughout the spring, the Board was releasing water from a flooding Lake Ontario into a flooded St. Lawrence River.  The Board would have faced these conditions under the old regulation plan, and outflows would have been very similar.

The Board recognizes that for many residents and businesses on the shores of Lake Ontario and the St. Lawrence River, the flooding, erosion and other coastal impacts that occurred in 2017 were devastating.  By providing this comprehensive review, the Board hopes to add clarity and transparency to how its outflow regulation under Plan 2014 took the needs of all interests into account and reduced the upstream and downstream impacts to the extent possible.

While regulating Lake Ontario outflows can help reduce flood damages, it cannot prevent major floods from occurring under extreme water supply conditions.  The Board hopes this report will increase public understanding of that reality.  To reduce future flood damages, shoreline communities must become more resilient, particularly since climate change increases the uncertainty regarding future high water events and their frequency.

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