On November 6, GRCA and their consultants Pete Zuzek of Zuzek Inc., and Seth Logan of SJL Engineering held an open house in the Venture 13 Lecture Hall to explain measures they were taking to cope with hazards along the Lake Ontario Shoreline from Clarington to Alnwick-Haldimand and north to the moraine. The hazards studied are flooding hazards, erosion hazards and/or dynamic beach hazards. The intent is to have a plan to cope with these – this would primarily involve regulations that would prohibit new development where a hazard exists. In addition, the plan would help “increase the resilience of coastal communities”, reduce coastal hazards and maintain existing public open spaces while ensuring “sustainable coastal development (balance between environment, society & economy)”. To do this, the consultants looked at all the hazards in the study area keeping in mind regulations, policies and legislation.
Since one of the hazards is flooding, this of course meant that there was a big turnout from residents with waterfront properties concerned about flooding due to recent high lake levels. Although billed as an “Open House”, it consisted primarily of a presentation with a Q & A at the end. [Note – the Q & A was dominated by property owners concerned about flooding and blaming it on Plan 2014 and criticizing the lack of Government help].
Cory Harris of the GRCA made it clear that although high water levels are blamed on the recent implementation of “Plan 2014”, they were not involved in that plan and further believed it did not cause the problem: instead unusually high rainfalls were the cause in both 2017 and 2019 and these in turn were due to Climate Change.
The GRCA (Ganaraska Region Conservation Authority) is undertaking this study and public consultation with the goal of creating a “Lake Ontario Shoreline Hazards Management Plan” with a completion date of early 2020. The meeting was to provide a progress report and to get feedback from the public. But the focus of the meeting was not so much about stopping the flooding, but more on understanding and mitigating the effects or “improving resilience”.
But the presentation did discuss the flood and explanations were provided as to how exactly flooding occurred in on Lake Ontario shorelines. At the risk of oversimplifying, and recognizing that this is a report on what was said and that not all agree with this, here is a brief summary:
- In 2019, there has been an unusual amount of incoming water (a 100 year event) – this was mostly because of a fast melt in late May.
- A “100 year event” means a 1% chance of it occurring but it can still happen 2 years apart
- All five Great Lakes, Lake St. Clair, Ottawa River and St. Lawrence River met or exceeded record levels in 2019
- Only Lake Ontario and Lake Superior are regulated.
- Timing of inputs and outputs is critical
- Net Supply to Lake Ontario:
- Lake Erie 85%, local supply 15% (precipitation, snow melt, runoff, rivers/streams)
- Record net supply Jan – Jun, 2019
- Net Outflow:
- Combination of evaporation and outflow to St. Lawrence
- Record outflows Jun – Aug, 2019
- Storm surges – winds from the West – caused this end of the lake to go even higher.
So what about the benefit of regulating the water outflow? Lake Ontario is regulated – does that help?
See the chart below based on measurements and analysis of Lake Ontario.
Notes, comments by consultants:
- Without regulation, peak water levels at Cobourg would have been 37 cm higher (76.21-75.84).
- With the previous plan, peak water levels would have been 7cm lower (75.84-75.77)
- One way of describing the connection between plan 2014 and record high water levels would be to call it a coincidence – that’s what the consultants called it.
- Focus must be on improving community resilience to water level fluctuations and future extremes
As well as flooding, a major hazard is erosion of an average of a foot of shoreline lost each year – measured from 1954 to 2018. This would be worse except that some shorelines are armoured (protected) and winter ice limits erosion in winter months. Because of Climate Change, by the end of the century temperatures here would be 6 to 8 degrees warmer, Lake Ontario would be ice free year round and shoreline erosion would lack the winter ice barriers so erosion would be worse.
Erosion can be limited by various means – some better than others – see full presentation below. There is no “best method” of protection; a competent Engineering company should be hired to make recommendations.
This is where beaches gain and lose sand. One way to mitigate that is what has been done in Cobourg where sand is dredged from the Harbour and deposited onto the beach. For a full discussion see the full presentation in the Links below.
So what should be done to mitigate all these Hazards?
There are four options:
- Avoid: reduce exposure by ensuring new development doesn’t occur on hazardous land
- Accommodate: allows for continued occupation while changes to human activities or infrastructure are made to deal with hazards
- Protect: protect people, property, and infrastructure. Traditional approach and often the first considered
- Retreat: a strategic decision to withdraw or relocate public and private assets exposed to coastal hazards
See the full presentation for more detail on each of these.
See also the primer provided for these strategies by the Federal Government although it’s intended for sea coasts, not lakes. Sea Level Rise Adaptation Primer.
Plan 2014 articles
- Concerns about high Lake levels occurring again – 13 April 2018
- Cobourg Lakefront Properties being damaged by Floods – 17 June 2019
- Cobourg Council Responds to lake Level Flooding – 25 June 2019
12 Feb 2020
The Lake Ontario Shoreline Hazard draft mapping is now on the GRCA web site here. If you look at Cobourg, a 100 year flood (1% chance) extends to the back of Victoria Hall. Scary stuff.