A prohibition may be uneconomic and, engineering-wise, unnecessary. New flood-resistant housing can be built with little difficulty.
We cannot but sympathize with homeowners whose properties are destroyed, damaged or threatened by flood waters. In this context, perhaps out of concern, perhaps out of fear of being perceived as indifferent, politicians rush to implement support policies for property owners who suffer losses. Premier François Legault is no exception. But a bit of caution is in order.
The public discussion we have witnessed in recent days, and also subsequent to the 2017 floods, has been unnecessarily circumscribed: What dollar amounts of compensation are reasonable? Should people be compensated more than once? Should we force individuals out of flood plains?
In times of emergency, to be sure, public resources must be directed to protect lives and property, so there is a public as well as a private interest at stake. Legault has stated his desire to limit compensation and perhaps force individuals out of flood plains, and prevent prospective dwellers from inhabiting them.
We believe it is inappropriate to force property owners or potential dwellers from most areas that are prone to flooding, not just because it impinges upon individual liberties, but because such a prohibition may be uneconomic and, engineering-wise, unnecessary.
People have lived in flood plains for millennia. A vast part of Bangladesh is subject to flooding, for example. If we outlawed dwellings on North American flood plains, most of New Orleans would be a wasteland. After the Hurricane Harvey flooding, Houston-area municipalities did not force residents out of flood-prone areas; instead, they implemented new construction standards.
Land that abuts rivers and lakes provides an opportunity to live in harmony with the elements. For 99 per cent of the weather cycle, these lands are also safe from inundation. It therefore seems uneconomic to prevent the sensible use of such land.
The key consideration is that new flood-resistant housing can be built with little difficulty, without sacrificing the practicality of the buildings. The additional cost in new construction is relatively small compared to the overall construction budget. Existing homes can also be retrofitted, although at significant cost. Still, when compared to the cost of repeated flood damage, the investment makes sense.
The most practical strategies for new construction in Quebec involve a combination of ensuring that appropriate construction elevations (normally the elevations of the ground floor) are chosen with respect to the predicted elevations of flood waters, as well as appropriate waterproofing for any parts of homes built below the expected flood water levels (basements). Calculations are also needed to ensure that the weight of the home is enough to counteract the buoyancy effect of having a waterproof basement completely submerged below flood waters — all relatively straightforward.
Retrofitting existing homes is somewhat more involved. The common global strategy of homes on stilts is somewhat riskier, although not impossible in Quebec. Stilts can be exposed to damage from ice and debris in flood waters. But the most reliable solution for existing homes is lifting and retrofitting with an appropriate concrete foundation structure.
These simple strategies, and other more advanced strategies, are currently being employed successfully around the world to allow people to inhabit flood-prone areas. For proof, we need only look to the retrofitting of homes in New Orleans or to construction practices in the Netherlands, where more than one-quarter of the land is below sea level.
Let us consider all of the available options, and compute the economic cost of a variety of solutions to the challenges posed by flood-plain dwellers, before making a hasty take-it-or-leave-it proposal to property owners. We are living in an age of climate change, and mitigation policies need to be developed that will be in the interests of citizens, and that will not unnecessarily prevent us from living in harmony with the elements.
Evan Irvine is a structural engineer, and partner in the firm SBSA. Ian Irvine is a professor in economics at Concordia University and a research associate at the Montreal Economic Institute.