Lake Superior, Lake Michigan-Huron
Levels remain well above average
#LSN_Shipping water levels in the upper Great Lakes
THUNDER BAY, ONTARIO - May 3, 2019 (LSN) Wet conditions continued across the upper Great Lakes basin in April. Water levels of Lake Superior and Lake Michigan-Huron remain well above average, and Lake Superior has the potential to reach or exceed record high levels in May should wet conditions continue. The Board advises all those that may be affected to prepare for coastal impacts similar to those that have occurred during the last few years, as the high levels coupled with potential strong winds and waves are likely to result in shoreline erosion and coastal damages across the upper Great Lakes system.
Lake Superior water levels increased by 13 cm (5 in) last month, while the average water level rise in April is 8 cm (3 in). At the beginning of May, Lake Superior is 38 cm (15 in) above average (1918 – 2018), and 23 cm (9 in) above its level of a year ago. Lake Michigan-Huron rose 20 cm (8 in) in April, which is higher than the average water level climb of 11 cm (4 in) in April. The increases in water levels were driven by above average precipitation, and well above average runoff to the lakes from the basin tributaries and watersheds. Lake Michigan-Huron is currently 65 cm (26 in) above average, and 24 cm (9 in) above last year’s beginning-of-May level. Lakes Superior and MichiganHuron are expected to continue their seasonal rises in May.
The International Lake Superior Board of Control (Board) recently requested approval from the International Joint Commission (IJC) to temporarily deviate from Regulation Plan 2012 from May through November 2019. This deviation strategy is similar to those employed over the past four years, which were also marked by reduced hydropower capacity and high lake levels and outflows. Over the next several months, the Board expects to adjust the gate settings at the Compensating Works in order to offset the effects of maintenance activities at the hydropower plants that are expected to continue through the summer and fall. Over this time period, the total amount of water released through the St. Marys River will be approximately equal to the flow prescribed by Plan 2012 and the deviation strategy will have almost no impact on the water levels of Lake Superior and Lake Michigan-Huron, yet will provide benefits to the St. Marys Rapids directly downstream of the Compensating Works.
The Board expects the total flow in May to be 2,430 cms (85.8 tcfs), which is 340 cms (12.0 tcfs) less than the flow prescribed by Lake Superior Regulation Plan 2012. Actual outflows may vary depending on hydrologic conditions, as well as maintenance activities at the hydropower plants on the St. Marys River. The average St. Marys Rapids flow in May is expected to be approximately 674 cms (23.8 tcfs) and the gates will be raised to the equivalent of four gates fully open on 6 May. This will be achieved by raising Gates #11 through #14 to a setting of 165 cm (65 in) open. There will be no change to the setting of Gate #1, which supplies a flow of about 15 cms (530 cfs) to the channel north of the Fishery Remedial Dike. Gates #2 through #10, #15 and #16 will remain at the current setting of 26 cm (10 in) open. Anglers and other users of the St. Marys Rapids need to be cautious of the changing flows and water levels that will be experienced in the rapids in May.