Decision Support Tool

What is the Decision Support Tool?

The Decision Support Tool is an interactive, computer-based tool that brings together a collection of data to help inform decisions regarding outflows from Lake Ontario when water levels are at extremes in the Lake Ontario-St. Lawrence River basin. It was created by the Great Lakes-St. Lawrence River Adaptive Management (GLAM) Committee, which is conducting the expedited review of Plan 2014.

The new tool will be used by the International Lake Ontario-St. Lawrence River Board (Board), a six-member group that oversees Lake Ontario outflow management in accordance with the regulation plan known as Plan 2014.

The Board is involved in the direct management of outflows from Lake Ontario when water levels reach extreme high or low thresholds, which gives the Board authority to “deviate” from the current regulation plan. The Board attempts to provide relief, to the degree possible, from extreme conditions by setting outflows that differ from those specified by the regulation plan. However, the outcomes of deviation decisions are measured in centimeters and inches, not feet and meters.

Board members have reported that when making their decisions they could make use of more information about the potential outcomes of a particular outflow strategy and whether it may help or harm the various interests across the regions. In response to this request, the GLAM Committee worked with experts from government agencies, academia and the private sector and consulted with its Public Advisory Group and the Board to create a Decision Support Tool (DST).

The DST presents data and information in graphs, charts, and maps that allow the Board to assess how outflow decisions might influence water levels and associated impacts

Fundamentally, the DST makes use of recently collected data and other information that correlates many sorts of impacts to extreme water levels at the time the impact occurred.

For example, the data show how many shoreline homes may be inundated across the entire system at different lake and river levels. There are analyses of how marinas, municipal infrastructure and services, and public and private water system may be affected at various water levels at specific locations.

The DST presents these data and information in graphs, charts and maps that allow the Board to assess how outflow decisions might influence water levels and associated impacts at different points of the lake-river system under a range of forecast, weather-driven, water inflow conditions. This helps better inform the Board and will better prepare them for the next crises.

Interactive decision-support applications are used regularly in many disciplines. Members of the Lake Ontario – St. Lawrence River Board have begun learning working with the DST that was developed during Phase 1 of the expedited review of Plan 2014 and Board members say it will be valuable in future extreme events to include both high and low water levels.

More information needed

Tradeoffs are situations in which a potential deviation strategy may bring relief to one interest or region but may threaten to make conditions worse for another.

Tradeoff situations are not uncommon during extreme events because of competing interests within the system. Lake Ontario, the upper St. Lawrence River and the lower St. Lawrence River each react differently to a change in outflow.

An outflow increase may slightly relieve flooding on the lake shore but worsen flooding considerably on the lower river. Interests such as commercial shippers, the lake and river ecosystems and recreational boaters may suffer negative impacts from outflow decisions intended to help others. The Board members wanted more information about potential consequences of proposed deviation strategies.

Informational shortcomings were due to limited details about impacts on different interests and regions at water levels that had never been experienced before, while other challenges relate to uncertainties about future climate, weather, and water supply conditions. Existing forecasts of precipitation and other weather factors are only reliable several days into the future, which makes it very difficult to predict the amount of water entering Lake Ontario in future months and this uncertainty continues to create a challenge for Board decision-making.

The tool makes use of data about on-the-ground impacts of the extreme high water in 2017, 2019 and early 2020 plus other information that was gathered by the GLAM Committee and its associates.

Benefits of the tool

When the Board has authorization to deviate from Plan 2014, the Board’s technical experts present Board members with a range of potential outflow strategies. They know from analysis and experience how each of those outflow strategies will influence water levels in the lake and river system in the short term for a given forecast of water supplies.

The Board can now use this additional tool to see maps, charts and graphs that display how water levels and associated impacts might change if a certain outflow strategy were pursued. The tool makes use of data about on-the-ground impacts of the extreme high water in 2017, 2019 and early 2020 plus other information that was gathered by the GLAM Committee and its associates. Additionally, thanks to those who participated in an online questionnaire about impacts, the tool also incorporates responses and data from over 3000 shoreline property owners’ responses.

What the Decision Support Tool includes:

  • The DST displays broad-based metrics indicating the number of buildings on Lake Ontario and the St. Lawrence River shorelines that would be expected to be inundated by floodwaters under certain scenarios. It considers the impact of waves and storm surge.
  • The DST also supplies localized metrics for impacts on Lake St. Lawrence, a section of the St. Lawrence River that reacts sharply to changes in outflow because it is immediately upstream of the dam where outflow is controlled.
  • The DST has a section with direct comparison of impacts on potentially competing interests: commercial navigation, property owners on the lake, upper river and lower river shorelines, the ecosystems, and recreational boating on Lake St. Lawrence.
  • A total of 11 locations were identified in the DST to assess impacts including seven communities on the Lake Ontario shoreline, two on the upper St. Lawrence River and two on the lower St. Lawrence. Categories of increasing severity were included to characterize the impacts at each location on shoreline properties, municipal infrastructure, parks, recreational boating, marinas and yacht clubs, and public and private water systems and to allow for a comparison of severity from one community to another.

Addressing an unpredictable water supply

The Great Lakes–St. Lawrence River system is a dynamic natural system and the major factors affecting water supply to the Great Lakes are precipitation, evaporation, and runoff. None of these can be controlled and all are difficult to accurately predict.

By testing an outflow strategy in multiple water-supply scenarios over a six-month period, the Board can see how that decision may play out over the coming months under a range of possible conditions.

What the tool does not do

The DST will help inform the Board, but it will not make decisions for the Board. Board members will consider possible deviation strategies presented by technical support staff.

The Board will continue to determine which deviation strategies, if any, will be made to address extreme water level conditions.