Flood control walls, dikes or dams serve to protect and reduce damage. But particularly given the rising intensity of weather phenomena, the potential hazard remains a realistic threat, as dikes can break, flood walls can be deluged and dams overtopped. In all your proactive measures, it is crucially important that you detect the weaknesses at your location in order to undertake very targeted, appropriate, additional precautions for your property’s flood protection.
The points at which creeks and rivers pass through narrow stretches, including at bridges and culverts, are the spots prone to be blocked by flotsam, with the result that hardly any water can flow through the usual passage. The formation of such debris jams are a common threat during flood events. The problem specifically is that larger volumes of water with a high flow velocity can suddenly force through the jam, carrying away a particularly large amount of flotsam. This then frequently causes devastating damage by expanding the extent of the flooding and creating expansive deposits above the point where the debris jam occurred.
Therefore, pay attention to bridges or culverts on the waterways in your neighbourhood. The potential flooding areas shown in maps can quickly expand in the wake of a debris jam. You can also contribute to reducing this risk of having a lot of loose materials accumulating during a flood to create a large mass and a large mess by taking care in your own backyard. Make sure that you do not have material that could potentially contribute to a debris jam, such as all kinds of kitchen and garden waste, as well as bulky and construction waste.
What do you know about the condition of your home’s foundations?
The stability of buildings in the immediate vicinity of a river or brook may be at risk in the event of incorrect construction. In the worst cases, the foundations of the building can be washed out. And the longer the flood lasts, the more soil is removed from under the foundation. The resulting lack of earth under the foundations can even lead to the building’s subsidence.
Flotsam is another underestimated threat of damage to buildings. It is not just the side of the building facing the oncoming flood that will be affected; all side walls can suffer scratches and impacts caused by flotsam.
So that basement rooms stay dry even when the groundwater is high, they must act like a "tank" that could "float" in the worst case scenario. Such tanks are needed particularly in basement apartments and basement living areas.
As basements built from water-impermeable concrete do not require additional sealing, they are called "white tanks". If, on the other hand, the walls and foundation slab are not water-tight, then the basement needs an additional exterior waterproofing – as these materials are all black in colour, this is called a "black tank".
One scenario that you will certainly know is actually easily preventable; that’s when heavy rains very quickly overflow roofs and rain gutters.
If the spilling waters then spread over sealed grounds, such as paved terraces or garage driveways, where they cannot – due to their sheer volume – seep through the ground, those waters will accumulate and can run into entrances and other low positioned openings of the building. This is another source of significant damage.
Is your home situated in a hollow? Then you must protect it from the risk that rainwater will collect at the lowest point of the hollow. This happens if it cannot seep through or drain away quickly enough. This is particularly the case where there is asphalt or paving or also where there is a lack of gradient, but it also affects frozen or icy ground, and water-saturated soils, because they can simply no longer absorb the volume of water.
On a location like that even the drainage capacity of a sewer – if there is one at all – will often prove insufficient.
In the event of heavy rainfall and other flood incidents, water will quickly gather in this depression. If the house is situated at precisely that point, it will be engulfed. Consequently, the water is literally invited to penetrate through all the building’s openings: beginning in the lowest areas, such as via light wells, basement windows and ground-level doors… bringing danger and damage.
Built too close to the hillside? If the slope is sealed by pavement, cobbles etc., or if the soils are icy or already saturated, there is a high risk during periods of heavy rainfall of large volumes of water draining from the hillside, running, in the worst-case scenario, directly into your home. The situation is comparable to a building located in a depression, but with water flowing into the building on one side only.
A further danger may arise with long-lasting rainfall: If the slope is not covered with plants, or only with plants that do not have deep roots, then the upper reaches of this slope’s unprotected soil will get completely soaked and become unstable. It is highly probable that this situation will lead to one or more landslides, running off the hill to the low-lying building below it and entering through its openings.
Is your house located in a potential flow path of a raging torrent caused by heavy rain? It is not just river beds that pose a risk; urban streets and canyons of varying sizes are perfect pathways for flood waters to rip through, sweeping everything before them.
Flash floods occur during heavy rainfall – within a very short space of time. Most vulnerable are sealed surfaces, as well as saturated or icy soils. The waters run off the gradients and accumulate in dips on roads and trails, where they can build incredibly quickly into raging torrents. If a building is located on the flow path of such a torrent, the water can rip through the building, especially through (un)favourably positioned windows and doors. Be aware, that there is increased danger due to the high speed of those torrents.
After heavy rainfall or during a flood the following scenario often arises:
Wastewater and sewage from a building no longer drains away properly. Instead it collects, for example, in the basement and causes considerable damage.
How on and in earth can this happen?
Heavy rain or flooding can lead to a back-up in the public sewer. The rain water can no longer run off completely. As a result, water from the public sewer system pushes into the private property pipes. Thus, sewage from the house can no longer flow into the sewer. Instead the opposite happens: In the basement as well as the lower floors, this back pressured wastewater spills from toilets, sinks, floor drains etc. throughout the building.
Even imagining this is deeply unpleasant. You can increase your chances of never being affected significantly by this, by taking appropriate and simple measures. For example, non-return valves or sewage lifting systems may have to be installed depending on the building’s situation.
When connecting rain gutters to the wastewater system, take care to install a non-return valve behind the flap.
If installed incorrectly, the rain water will enter the building.
There are many ways water can enter a building. Here are some examples: