Comments on Water Levels in Georgian Bay

March 2015

Georgian Bay is still mostly ice covered which will assist in higher water levels as loss of water by evaporation is suppressed.

Currently, the water level is at 0.4m above chart datum and at that level it is 0.1m above the long-term average in March.


If the long-term normal trend in water level happens, then the level could possibly increase by another 0.3m by June/July—that is a total of   0.7 m above chart datum.

In practical terms, this means that the water should be always deeper than that shown on the chart.

It seems that even if we have a dry summer, it is unlikely that navigators will encounter seriously low water levels this year.  Safe boating. Cheers!      

September 2014

As this season’s boating approaches haul out, water levels are no longer an issue despite the exhortations of some to “stop the drop”.   

It is worth noting that there has been a shift upwards of  50 cm or 2 feet, above chart datum. This was the elevation predicted by the Hydrographic Service back in June and reported here.  

Our very snowy winter, lots of rain and lower temperatures have moved the water up to more normal values. Furthermore, Lake Superior is quite high and the Lake Superior Board of Control has released higher flows than normal at Sault Ste Marie.

Let’s hope the precipitation in the basin continues to be enough to sustain or raise the levels in the near future. Good sailing and boating.

June 2014

Precipitation over Lakes Michigan-Huron is a random process well illustrated by our recent winter and it seems, as anticipated, the water level will likely go up. Lake Superior is at its highest since 1998 and probably still rising.

The Lake Superior Board of Control is releasing a greater flow from Lake Superior than is currently flowing down the St. Clair River.

The forecast for Lake Huron for May 23 is 28 cm above chart datum. An optimistic prediction by the Hydrographic service indicates that by the end of June, the level could be 176.5m  IGLD or 50 cm above datum. I think that is quite likely and it may even go higher unless the weather takes a surprising shift to producing no precipitation.

Safe boating & sailing everyone.                                            

February 2014

Our snowy winter and ice-covered Great Lakes, that suppresses evaporation, gives rise to the speculation that water levels will attain higher levels this summer.

Last year the level rose from an all-time low to 15 cms above chart datum.

In February, the Lake is still hovering around chart datum. It is entirely reasonable to expect that the rise will be at least the same as last year which takes the level close to average at 25 cms above chart datum. Given the heavy snow accumulations, it is possible that the level could go even higher depending on how the snow melts and how much is lost from the snow pack by sublimation.  Rain may also add to the supply of water to the lakes.

I think therefore, at this early stage, that we could see levels, by July, above the average at 176.70 metres I.G.L.D. or 70 cms  above chart datum.  Time will tell.

Keep warm and think boating.                                                        

November 2013

Lake Huron water levels are the least of our concerns now that boats are up on land until Spring.

Mysteriously, attempts to get up-to-date info. on water elevations from Canadian sources were not available.

The USA, however, obliged. Their data is in inches and the chart datum is not given so conversion of units was  required.

Fortunately, they also use the International Great Lakes Datum that was introduced by Canadian hydrographic officials years ago.  That datum represents the potential energy of the water rather than its elevation relative to a mathematical model of the earth’s shape. This means, for example, that with the same IGLD reading at Toronto and at Kingston, it would be found that the conventional geodetic level would be different because the force of  gravity is not the same at these two places. However, at the beginning of November, the water level of Lake Huron is hovering around chart datum at 176m IGLD. It is 24 cms higher than this time last year which is encouraging. Precipitation and evaporation will determine the outcome in the Spring.  

A substantial flow is coming out of Lake Superior, which is 26 cms above datum, may be useful. Enjoy the winter and think boating.  

August 2013

I have just returned from a trip on the Bay when the water level was stated by the Canadian  Coastguard to be 15 cm above chart datum.  An elevation predicted in previous comments. There has been a lot of hype recently on water levels and hype is what it remains.  Although lake levels have tended to hang around in the lower part of the water level range, nevertheless, the level remains well within its historical range.  

Initially, a lot of attention was directed at the discharge of the St. Clair River while ignoring other influences at work.  Lake levels depend on the difference between the supply of precipitation and the losses owing to evaporation and river outflow. Water in the Great Lakes is influenced by precipitation on the lake itself as the catchment is relatively small compared to the lakes and there is no major river flowing into the lakes.  As the terrain is more or less flat, precipitation is caused by the interaction of cold air from the north and warm air from the south. This is a rather variable process that should not be expected to produce consistent results.  Oddly enough, however, records show a rough cyclic variation of around 11 years.  Some people say that the sunspot cycle of 11 years may have a connection. I do not think so but one never knows.

Obviously, water supplies are neither controllable nor predictable. With the increase globally of unusual weather events—for example, the flood in Alberta—we should not expect to be immune from these kinds of events. It seems now that owing to climate warming, the current long-term dynamic balance between the cold northern air and the humid, warmer southern air may be changing. Great Britain experienced a long, very wet period throughout the country in 2012.

In 2012, we had a very hot summer with excessive evaporation that removed 30 cms more of the lake than usual. If that had not occurred, our current lake level would be 45 centimetres above chart datum.  

Although we have had, recently, somewhat lower net supplies of water, it is entirely possible all that may change. Precipitation may become much less or it may become much more. Also, the same goes for evaporation.

Either case is equally likely. We may, therefore, experience water levels going up rather than declining. It is equally clear that predictions in the long term are unreliable.

Uncertainty for the future demands caution by planners and engineers before embarking on any construction to meddle with water levels.  We may start to experience more water than we need rather than the opposite.  As it stands now, there is currently no real crisis and a policy of masterful inactivity seems to be in order.  Cheers and, good sailing.

May 2013

There has been a lot of agitation and comment
recently about water levels in Georgian Bay.  

In recent weeks, water levels have been something of a hot topic. As predicted previously, the level is now on the rise.

On the 13th May, it was back to 176m or chart datum. Given this level by mid-May, the water level should go all the way up to 176.15 m by July which is 6 inches above datum.

Given the extreme low in mid-winter, a greater recovery is unlikely if normal rates of rise prevail.

Also, hope that we have normal summer weather and not the blistering weeks of last year which evaporated 30 cm more water than normal.

There has been some comment on building some kind of structure at the upstream end of the St Clair River. However, do not hold your breath. Given the uncertainties around climate shifts, it will take quite a few years to get to an international decision to create or not create a control structure that will not interfere with the delicate balance between flow and river cross-section dimensions.

In addition, a structure, artificially raising the lake level, would create a local drop in the water level at the head of the river that would necessitate construction of a lock or locks and probably also canal construction in order to accommodate navigation.

Holding water back would also require considerable discussion with downstream hydro-power-generating stations on their loss of generating capacity.

So what we must do, given things may get measurably worse, (not certain) is to adjust to the new regime. With charts and GPS and know-how, there should be few problems except at locations built up by developers who did not to take into account historical low water levels.

Join us when we go to Henry’s for the rendezvous near the end of June. Enjoy the trip and the good times while there. Cheers and Good sailing.

Mirabile Dictu

For CPS members, application of our piloting and conning skills should avoid embarrassing groundings.

Mirabile Dictu

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Page updated:
11 April 2016

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