Lake Superior is 11 cm./4 in. above the 1918 to 2017 average, but 14 cm./5.5 in. below the level at this time last year, as seasonal water level rise continues. The U.S. National Weather Service says that Lake Superior rose about 5 in./13 cm. from June 13th through July 13th. Usually the lake would rise about 3 inches during this time period. This equates to about 2.75 trillion gallons of water.
Lake Michigan-Huron is currently 45 cm./18 in. above average, 4 cm/1.5 in. above last year’s beginning-of-July level, and the highest since 1997. Seasonal water level rise is expected to continue on Lake Michigan also.
The above-average levels coupled with strong winds and waves continue to result in shoreline erosion and coastal damages across the upper Great Lakes system. Additional shoreline erosion and coastal damages may occur this summer, should active weather continue.
Lakes Huron and Michigan Two Feet Above Average
In a July 19th public conference call, several callers criticized the Lake Superior Board of Control for releasing too much water to Lake Michigan and the lower lakes. Last year, more water was released from Lake Superior than at any time during the last 32 years. Shoreline damage is a driver for criticism as Lakes Michigan and Huron are approximately 2 ft./61 cm. above their historical average. They are also half an inch or 1.27 cm. higher than this time last year. The situation is like dumping more water from Superior into an already full bathtub.
Over the next several months, The Lake Superior Board of Control expects to adjust the gate settings at the Sault Ste. Marie control structure or “Compensating Works” and release flows greater than those prescribed under recent regulations. Under authority granted to it by the IJC, the Board set the Lake Superior outflow to 2,800 cubic metres per second (m3/s) for the month of July. This is actually 390 m3/s more than current regulations prescribe. This special measure is necessitated by reduced flows due to maintenance at the two hydro-electric generating stations on either side of the St. Marys River. Flow through these hydro-electric stations is critical in managing Superior’s water levels.
Primary Driver is Hyrdologic Conditions, Not Control Structures
The gate setting at the Compensating Works was increased on 9 July 2018, from the current setting of approximately two gates fully open to a setting of three gates fully open. The Lake Superior Board of Control stresses that hydrologic conditions are the primary driver of water level fluctuations. Water levels of the Great Lakes cannot be fully controlled through regulation of outflows, nor can regulation completely eliminate the risk of extreme water levels during periods of severe weather and water supply conditions. It is not possible to accurately predict such conditions weeks in advance, but given the current levels of the lakes and the possibility that wet conditions may continue, the Board advises all those that may be impacted to prepare for the possibility of high water levels, should they occur this summer and fall.
Related November 23rd, 2017 Infosuperior Post: “Interactive Tour – Lake Superior Outflows”