Net water supplies to Lake Superior were below average in March. The level of Lake Superior fell 5 cm/2 in. last month, while on average the lake declines 1 cm/.39 in. in March. The Lake Superior level at the beginning of April is 14 cm/5.5 in. above average, 11 cm/4.3 in. below the level recorded a year ago at this time, and 17 cm/6.6 in. above its chart datum level. The level of Lake Superior is expected to begin its seasonal rise in April.
The International Lake Superior Board of Control, under authority granted to it by the International Joint Commission (IJC), has set the Lake Superior outflow to 2180 cubic metres per second (m3/s) for the month of April, effective April 4th. The outflow is as prescribed by Plan 2012 and may at times vary due to weather events and changes in hydrologic and ice conditions.
Maximum flows will be discharged through the three hydropower plants in April. Accounting for required maintenance outages expected at the plants this month, their combined capacity is expected to be a total of 1954 m3/s.
Most of the remaining flow (approximately 215 m3/s) will be passed through the St. Marys Rapids. To achieve this, it will be necessary to increase the gate setting at the Compensating Works. This will be done as soon as ice conditions permit and is expected to occur before the beginning of May. The current setting equivalent to one-half gate open will be maintained until that time. There will be no change to the setting of Gate #1, which supplies a flow of about 15 m3/s to the channel north of the Fishery Remedial Dike.