Influencing factors on water levels – Lake Winnipeg
With our ability to increase or decrease the amount of water discharged through the northern channels constructed as part of the Lake Winnipeg Regulation Project, we influence — but don’t control — the lake levels. Many other variables come into play as well to determine what the lake does, including precipitation, wind speed and direction.
Erosion driven by wind
Lake Winnipeg is prone to wind set-up/set-down events due to its large surface area and relatively shallow depth.
Persistent winds on the surface of the lake push water towards its leeward shores. Due to its shallow depth, water is impeded from circulating back to the windward side of the lake and the water effectively piles up on the leeward side of the lake.
During high winds, there has been a reported 2.4 metre difference between the north and south basins. Wind has a far greater effect on erosion than the water level. We can influence the water level but we can’t control the wind.
In 2000, the Province of Manitoba’s Lake Winnipeg Shoreline Erosion Advisory Group conducted an independent series of studies looking at the effect of Manitoba Hydro’s operations on shoreline erosion. The group included south basin municipalities, property owners, First Nation communities, and engineers.
In its September 2000 report, the group stated that “…in most instances erosion, flooding and dynamic beach changes at the shoreline are the result of naturally occurring processes.”
Also called post-glacial rebound, this term refers to the fact that the north end of Lake Winnipeg continues to rebound from the huge weight of glacial ice sheets that existed there thousands of years ago.
Due to isostatic rebound, Lake Winnipeg is gradually tilting from the north so the lake is continually moving southward. The lake has changed significantly in a relatively short period of time and it is still in flux.
Extreme wind storms
In October 2010, a wind storm caused flooding and property damage in low-lying areas of Lake Winnipeg’s south basin.
The wind storm resulted in record-setting low barometric pressure in our province, and it was the strongest ever recorded in the Midwest. Damage was significant.
Conditions were looking drought-like in the spring of 2010. In fact, Manitoba Hydro received calls early in the summer from lake users who wanted the lake level to be increased.
Over the summer, however, precipitation was heavy and inflows into Lake Winnipeg increased dramatically. From 2004 to 2010, our province experienced some of the wettest years on record. Due to excessive rainfall in 2010, water levels in many bodies of water in our province, including Lake Winnipeg, were extremely high.
Manitoba Hydro’s control facility at Jenpeg was at maximum discharge since July 1, 2010.