By John Francis
Our municipality’s Comprehensive Zoning Bylaw regulates where buildings can be put. One of the most complex and important elements of that is establishing storm lines along our lakeshores, especially the shores of Lake Huron and Georgian Bay.
Lakes Huron and Michigan plus Georgian Bay and the North Channel are all one big waterbody — the largest freshwater “lake” in the world. The water level on that huge waterbody fluctuates. A lot. More than any of the other Great Lakes.
Various stakeholders and lobby groups insist that there should be active management of Lakes Michigan/Huron. The St Mary’s River is regulated to keep the water level in Lake Superior within fairly tight limits. The outflow from Lake Ontario, likewise. The outflow from Lake Erie is regulated by a rock weir above the falls. But the St Clair and Detroit Rivers are left to their own devices except when the shipping channels need dredging. The St Clair isn’t even monitored comprehensively, so nobody’s really sure whether the flow is increasing, decreasing or staying the same although the International Joint Commission acknowledges that dredging, gravel mining and erosion of the St Clair River bottom have reduced Michigan/Huron levels by about 50cm.
Lake Michigan/Huron stakeholders, including Georgian Bay Great Lakes Foundation, suggest that — at the very least — there should be flow controls on the St Clair River to mitigate extreme low water events and that outflow from Lake Superior should be managed more equitably during high-water times, to mitigate high water events.
The monthly average water level in Lake Huron/Georgian Bay rose from 175.57m in January of 2013 to 177.4m in July of 2020 — that’s a difference of 1.83m or six feet. At the lowest water level, many shallow bays were dry and the Chi-Cheemaun ferry dock had to be modified so the vessel’s rub rail wouldn’t catch under the mooring fenders. In 2020, the water was so high that storms washed out Cabot Head Road, destroyed Lion’s Head lighthouse and flooded many shoreline properties.
But if GBGLF’s engineers are right (and they have a pretty good track record), there is much worse to come.
Their modelling — which incorporates cyclic phenomena like the El Niño/La Niña cycle, the NAO cycle (~30 years) and the various solar sun-spot cycles (all of which combine to explain most of the variation over the last 200 years) plus projections for global warming — suggests that the amplitude of fluctuations will probably increase in coming decades. They predict that in the next ten to twenty years, low water levels may drop a metre below previous recorded minima. In the decades after that, they expect levels to occasionally reach half a metre above previously recorded highs. (They are not modelling seiche events but rather normal “monthly averages”. Seiches would be on top of that…)
Here is an excerpt from our current Comprehensive Zoning Bylaw (in place since 2002):
“In any zone, no building openings associated with the habitable floor area of a dwelling or structure shall be located at or below the minimum elevation of 179.1 m G.S.C. (587.5 ft) for lands adjacent to Lake Huron and 178 m G.S.C. (583.9 ft) for lands adjacent to Georgian Bay.
or;
In any zone on lands adjacent to Georgian Bay or Lake Huron, all habitable buildings shall be setback a minimum of 15 m (49 ft) measured horizontally from the 177.6 G.S.C. (582.6ft) elevation.”
On flat Lake Huron shorelines, that 15m horizontal setback from 177.6m got to feel pretty inadequate in 1986 and 2020 when the water levels got up above 177.4m. Just imagine how they’ll feel when the water gets up above 178.0m.
And the doors and floors minimum of 178.0 for Georgian Bay may well be awash now and again after 2040.
Just to clarify: if GBGLF’s engineers are right, these levels — highs above 178.0 and lows below 174.8 — will fall within the “normal” 30-year range of variation. And that’s if sensible climate-change mitigation strategies are adopted.
If no such strategies are adopted, it will be much worse. The engineers suggest that water levels might occasionally rise as high as 179.6m by the end of the century. That would be devastating for most Lake Huron shoreline cottages. (That’s almost 2m above current levels…)
It is ironic that the 2017-18 replacement for the CZB was not adopted because a lot of people felt the shoreline building limits were too restrictive.
Based on things that were said at the CZB Public Meetings in 2017, a lot of people seemed to think that as long as they followed municipal regulations, the municipality guaranteed their property would not be flooded. Those people are probably in for the rudest of surprises. The CZB is based on the best guesses, with no guarantees of accuracy.
But going forward, it poses a very interesting question. Should municipal zoning prepare for unprecedented events, based on credible science? Or stay with traditional regulations which are based on past patterns? Should a municipality guess as to what level of climate change mitigation is likely to be implemented? (Because those efforts could have huge effects on water levels…)
If the future is going to be different than the past, should municipal zoning anticipate that change? (And if not now — when?)
