Hay River flooding has occurred in the past during spring break up. In 1963, Main Street flooded during spring break up - according to the Hay River Museum, this resulted in 'strategic retreat' from the floodplain whereby many of the residents consequently moved out of the floodplain and established a new area of town.
Strategic or managed retreat can be considered when risks are high and flood mitigation efforts or flood proofing efforts are not feasible. A paper Managed Retreat from High-risk Flood Areas: Design Considerations for Effective Property Buyout Programs by Jason Thistlethwaite, Daniel Henstra and Anna Ziolecki (link: https://www.jstor.org/stable/resrep24935?seq=1#metadata_info_tab_contents) notes that "Managed retreat through property buyouts is widely regarded as an effective disaster risk reduction strategy."
The paper notes that cost-benefit analysis may be used to evaluate eligibility for buyout programs:
"Cost-benefit analysis — a method for assessing the economic efficiency of public policies — is often used to project whether the benefits of reducing future disaster losses exceed the costs of acquiring a property. Other criteria used to assess eligibility include damage thresholds (for example, estimated repair costs exceeding 50 percent of a property’s value) and geography (for example, properties located in the 1-in-50 flood zone). The former criterion was used to assess eligibility for buyouts in Quebec in 2017 and New Brunswick in 2019 (Adriano 2019; CBC News 2019), whereas the latter is currently being considered for the buyout program in Grand Forks, British Columbia (Grand Forks 2019)."
More recently in Ontario, 380 cottages /homes on Toronto Island were removed from this historically flood-prone land - see previous post: https://www.cityfloodmap.com/2017/09/toronto-island-flooding-2017-were-lake.html
In Markham, Ontario, flood prone properties on a tributary of the Don River were purchased in order to restore the floodplain and provide storage to attenuate downstream flooding. The business case for the flood control strategy was developed in the Municipal Class EA study that identified the preferred solution including managed retreat - a summary presentation is provided at this link: https://cleanairpartnership.org/cac/wp-content/uploads/2019/09/1.-FINAL-190927-Clean-Air-Partnership-Don-Mills-Channel-Flood-Control-Muir.pdf