What do you mean by ‘flood’?

0 June 21, 2018 at 4:20 pm by

When a homeowner gets water in the house, they call it a flood. It doesn’t matter to them how it happened (pipe or municipal water main break; toilet, water heater, dishwasher or washing machine failure; seepage; sewer backup; riverine; storm surge; tsunamis) it just matters that it happened and that it get fixed right away.

Exactly how the water damage happened, on the other hand, matters a great deal to insurers.

First of all, depending on the cause of the water damage, an insurance policy may or may not respond.

Second, the nature of the advice that would be given to prevent or mitigate a repeat of the loss would depend on the nature of the occurrence. For instance, the advice ICLR would give to prevent damage from a riverine flood is very different from the advice that would be given for a sewer backup that happens as a result of a heavy rainfall event (i.e. an urban flood).

Now, granted, there is some degree of crossover: For instance, a backwater valve could be useful to prevent surcharge of sewage into a basement if an overland flood in an adjacent area inundates the sanitary sewer system. This happened during the 2013 flooding in Calgary (many of the basement floods documented occurred quite a piece away from rivers). Disconnecting foundation drains from the sanitary and running them to a sump system may also prevent surcharge should the sanitary sewer system be inundated from an overland event.

However, if you have water up to the main floor windows, a backwater valve or sump system isn’t going to help you, just as gently sloping landscaping, window well covers, clean eavestroughs, or disconnected extended downspouts and the other best practices to prevent basement flooding aren’t going to help.

It is key that the nature of the mitigation advice match the hazard, and for the most part, giving basement flood risk reduction advice for riverine flood risk is a non-starter.

At ICLR, we have six booklets in our ‘Protect your home from…’ series (i.e. Protect your home from snow and ice storms, earthquake, extreme wind, hail, wildfires and basement flooding).

We do not have a booklet for riverine or overland flood and we may never have one. There are not only serious public health and safety matters to consider with this hazard, but also deep philosophical concerns about the wisdom of advising homeowners how to face down an overland flood. We are uncomfortable with the moral questions surrounding the issue, largely because the nature of the measures needed to prevent or mitigate riverine flood risk are very different from the nature of the measures that are needed to mitigate sewer backup or other hazards.

First of all, the best way to prevent riverine flood damage is not to locate assets in flood hazard areas. As an absolute minimum, new structures should never be built in the highest hazard area of a floodplain – often referred to as the floodway, the portion of the flood hazard area where flows are deepest, fastest and most destructive. In our view, assets located on floodways should be moved or abandoned whenever possible (this is where government buyouts would come into play) or protected by dams, levies or other defensive infrastructure. But considering the legacy risk that exists (i.e. all the older parts of communities where entire downtowns and neighbourhoods were built on floodways), this can be difficult.

The next consideration is for those assets located on the fringe, the portion of the flood hazard area that is outside the floodway (i.e. the remainder of the floodplain after the floodway is considered).

Ideally, structures should not be located in the flood fringe. Where there are no other options, structures located on the fringe should be flood proofed (though it is still preferable to avoid constructing vulnerable development, like homes, in these areas whenever possible).

This leads to the second main consideration: How should this be done?

Generally, flood protection in the floodplain should involve raising structures above the potential flood level, plus an acceptable freeboard (or safety factor). This type of advice is extremely context-dependent. A qualified engineer should evaluate the hazard level, the structural integrity of the building, whether fill pads will negatively affect the flow of the river, etc.  This can also be expensive, especially if the intent is to retrofit an existing home. Homes will also be largely inaccessible during flood events, creating life safety hazards.

Other types of flood proofing are fraught with risk. For example, with dry flood proofing (where there is an attempt to design the building to be watertight), hydrostatic and hydrodynamic forces around foundation walls caused by the force of flood waters can cause a great deal of damage, even destruction, of a home. There can also be buoyancy forces working to cause the home/basement to float. Hence, dry flood proofing is rarely a good idea. Where it is applied, it should be completed with the assistance of a qualified engineer who can assess the hazard level, the structural integrity of the home, and then make recommendations for reinforcement of building foundations to ensure they can withstand the extreme static and dynamic forces that are often associated with river flood events.

With wet flood proofing – where buildings are specifically designed to allow water to safely enter the home during a flood — there can be issues around contamination of flood waters (which may include agricultural runoff, human sewage, fuels, chemicals, and subsequent mould growth). Even when water-friendly materials (such as marine lumber and water resilient drywall) are used to wet flood proof, these materials may still need to be ripped out post flood and replaced due to contamination. A homeowner will also have to remember that they will still experience substantial contents damages and may have to relocate from their home while remediation is performed.

Further, with both dry and wet flood proofing there is always the possibility that a storm will exceed design, leading to property damage and even injury or loss of life.

So there is a lot at stake when advising property owners about protecting their properties from riverine flood and, thus, the provider of the advice must really know their stuff.


Here are a few guidelines on how insurers should approach the issue of providing flood mitigation advice to property owners and others:

1) Recognize that property owners view all unwanted water as a ‘flood’, regardless of the source.

2) When advising about flood prevention/mitigation, providers of info (‘experts’) must be explicit about what type of flood they are referring to (eg. riverine/fluvial or urban/pluvial, storm or sanitary sewer backup, seepage from groundwater or surface water etc.).

3) When referring to more than one type of flooding, experts must be clear about how the types differ – in cause, damage incurred, and with regard to risk mitigation.

4) When providing advice for riverine flood risk reduction, the expert must explicitly outline the risks (some of which can be life threatening) that are present in living with – and confronting – this hazard.

5) The expert must clearly outline both the upsides and the downsides of certain approaches (eg. dry versus wet flood proofing).

6) The expert’s advice should include counsel as to whether the property owner should continue to reside in the at-risk location.

7) When referring to ‘flood insurance’, experts must be explicit about what kind of insurance they are referring to (sewer backup or overland).

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