Performance Indicator Summary
Performance indicator: Ice Formation
Technical Workgroup: Hydropower TWG
Research by: Hydropower TWG
Modeled by: PFEG in the shared vision model with inputs provided by the Power Entities.
Activity represented by this indicator: This PI refers to the requirement to reduce outflows as conditions dictate to form a stable ice cover.
Link to water levels: This PI is determined by weather conditions. Ice has historically begun forming in the Beauharnois canal one to two weeks prior to forming in Lake St. Lawrence.
Importance: This PI is critical to all interests. A stable ice cover will allow flows to be released in accordance with the regulation. If the ice cover is weak or if an ice jam or hanging dam forms, then releases will be restricted. This can cause a drop in the operating head, and potentially cause some municipal water supplies to be jeopardized. In the spring, flooding can occur when the jams release.
Performance Indicator Metrics: Ice begins forming when water temperatures approach 0 degrees Celsius (32 degrees Fahrenheit).
Temporal Validity: This PI is critical during the winter months. Ice historically forms in January but historical records show this varies. Water and air temperatures are more reliable indicators of when ice will form.
Spatial Validity: Beauharnois canal and Lake St. Lawrence from the power dam to Ogdensburg, NY and Prescott, Ontario
Links with hydrology used to create the PI algorithm: Velocities of 0.6 m/second (2 ft/second) will promote a stable ice cover. River flows of 6,230 cms (220,000 cfs) will allow for velocities of 0.6 m/second (2 ft/second) upstream of the Moses Saunders facility. For HQ, the flow limitations in the Beauharnois canal during the ice cover formation and for the rest of the winter, were provided to the PFEG.
Algorithm: The flow limitations in plan 1958D are correct, subject to adjustment with the real date of ice cover formation. A new plan should follow a similar pattern. The ice constraints were modeled by the PFEG. It is important these constraints be respected in the proposed plans.
Validation: Calculations by the Corps of Engineers during system design and construction.
Documentation and References:
Risk and uncertainty assessment: There is risk to all interest groups if ice is not allowed to form and stabilize. Flexibility should be built into all plans to allow for flow reductions to form ice.