International Lake Superior Board of Control

HIGHER OUTFLOWS AND FIELD DATA COLLECTION THIS SUMMER

2015/04/29

The International Lake Superior Board of Control, under authority granted to it by the International Joint Commission (IJC), expects to increase the Lake Superior outflow for the month of May. The increased outflow is expected to exceed the capacities of the hydropower plants on the St. Marys River in May, and therefore excess will be released through the control structure at the head of the St. Marys Rapids. The outflow of Lake Superior will be adjusted over the next several months to accommodate expected maintenance at the hydropower plants, and to reduce the potential for adverse consequences of high and fluctuating flows in the St. Marys Rapids.

The Board recently requested and received approval from the IJC to temporarily deviate from Plan 2012 to allow for these adjustments.  To maintain more consistent flow conditions in the St. Marys Rapids and minimize the effects on both Lake Superior and Lake Michigan-Huron water levels, the Board expects that flows less than those prescribed by Plan 2012 will be released in May and June, and again in September through November, and that that these flow decreases will be offset by releasing flows greater than Plan 2012 in July and August. At most, the differences in lake water levels in any given month due to these changes are expected to be less than 2 cm on either lake, and differences are expected to be negligible by the end of December.

In consideration of the above, it is anticipated that the gate opening in the control structure at the head of the St. Marys Rapids will be increased from the present setting (equivalent to ½ gate open) beginning Friday, May 1st.  Anglers need to be cautious of the changing flows and water levels in the Rapids on May 1st and the higher flows and levels that will be experienced in the rapids in May. The gate movements will primarily affect water conditions in the main rapids, but water may overtop the Fishery Remedial Dike along the north side of the rapids, and may create a hazard. There will be no change to the setting of Gate #1 which supplies water to the channel north of the Fishery Remedial Dike. 

The Board will reassess conditions on Thursday, April 30th, before setting the final Lake Superior outflow for the month of May and establishing the required gate setting, and this information will be provided at that time. The Board also continues to monitor conditions both on Lake Superior and downstream, and will advise the IJC accordingly on those conditions.

Furthermore, this summer the Board plans to collect extensive data and field measurements in the St. Marys Rapids as part of an International Watersheds Initiative (IWI) study, partially funded by the IJC. The study will provide improved information on the effects of gate movements on flows, velocities, and water levels in the St. Marys Rapids, so that they can continue to be managed in consideration of all interests and stakeholders.