GBA Flipping Book - Spring 2020

2 ≥ www.georgianbay.ca GBA UPDATE Spring 2020 Continued from page 1 What Determines Water Levels in Georgian Bay A quick review of the primary determinants of Georgian Bay water levels might be helpful: ≥ The extent of ice coverage will determine evaporation levels – greater winter ice coverage will decrease evaporation and increase water levels, and vice-versa. It should be noted that the greater the temperature difference between the water (warmer) and air (colder), the greater the evaporation. When this temperature difference is nominal (for most of spring through fall) there is little evaporation. ≥ The number and severity of winter rain storms will play a major role. Recently there have been several major storms each winter. Previously this was rare. ≥ The amount of snow that falls this winter will have some influence, but not as much as ice coverage and rain storms because snow volumes do not change that much from year to year, and 10” of snow is broadly equivalent to 1” of rain. ≥ The flow rate from Lake Superior will have minimal influence, as there are limitations on what can be done to decrease it without adversely affecting Lake Superior’s shoreline infrastructure, coastal flooding, and commercial shipping. Other considerations such as maintaining hydropower output and fish spawning habitat are also taken into account. See: https://www.ijc.org/en/lsbc/ update-lake-superior-outflows-and-expected-conditions- january-2020 ≥ In this context there has been a wealth of disinformation about the extent to which the International Joint Commission (IJC) and the two control boards, at St. Marys and Cornwall, can control water levels. The reality is that when water levels are this high throughout the basin, there is very little they can do. They cannot allow Montreal to flood, and they can only close down commercial shipping channels for limited periods of time. The high flow rate down the Ottawa River last spring placed additional limits on the options available. The Great Lakes are one system and the extent to which water can be flushed down the “drain” (the St. Lawrence River) impacts everything upstream. ≥ There is no control mechanism in place on the outflow down the St. Clair River, but action could be taken to reduce ice jams in the spring break up, which would help. The main driver of current high water levels seems to be increased precipitation, which is in turn directly impacted by climate change. While we can’t definitively say what precipitation levels will do this year, with climate change impacts accelerating, it would be unwise to expect that precipitation trends will return to historically normal levels.  What to Expect in 2020 Given all these influences, it would be prudent to assume that water levels will likely be up again – probably by 10-14 inches over last year’s levels. I would emphasize that this is not a prediction, just the best guess given the information we have. It is important to note that levels last year varied substantially from month to month. Furthermore, high winds also contribute to fluctuating levels as water moves from one side of the Bay to the other and then settles back. With wind strength and duration steadily increasing each year, also due Continues on page 4 Honey Harbour Boat Club (HHBC). South Cognashene. Photo: Steve Jarvis Photo: Tom Halpenny