How to cope with flash floods?

Updated: Sep 25, 2020

Among the effects of global warming, rising temperatures are causing abnormally rapid melting of the ice caps around the world. The melting of glaciers at the poles causes sea levels to rise, while the melting of glaciers at the tops of mountains presents an additional risk of flash flooding for people living downstream. In the future, these floods will become more frequent. How can we better cope with them?

TLDR: For many living beings, the risk of flooding represents a real danger to their lives. Climate change will increase the frequency and intensity of flooding, and we must be prepared for this. This does not necessarily mean migrating, even if it is sometimes the only solution left.

Through human and property damage, a flood can put you at risk. Flooded homes, broken furnitures and devices, pollutants released by flooding; these are all risks that can be reduced or even eliminated by appropriate measures. Effective flood protection is possible with a little anticipation.

The first thing to do is to identify how much you are at risk from a flood. If you have already been taken by surprise by the outburst of your neighbouring riverbed, or if you know that this has already happened without the local government having taken satisfactory action in the meantime to prevent future events, then you can consider yourself to be at risk. If you are in any doubt, you can consult your community, your neighbours or your local government.

Assessing the weak points

Whether you are assessing the risks to your home, neighbourhood or city, you need first to identify entry points of water: doors, ventilation, evacuation, sewers, streets, walls... Think of all possible access, especially near ground level. Recording these accesses on a map can be useful, especially in the case of large structures or repeated risk. This can avoid costly disorganisation in terms of time and resources later on.

Building your home in a risky area

If you are in the process of building in an area that presents flooding risks, you would consider choosing a zone least exposed to the risk. In any case, raising the habitable floors from 0.5 to 1.5 meters can help protect your possessions. Ideally, establish the liveable level above the highest known waters level, to protect your life in the event of a flood. Ultimately, facilitate run-off by leaving regular openings around the field for example. The drying and cleaning of your home must be simplified as much as possible, especially with a natural ventilation system and not electric, which is likely to break down: opposing openings in the direction of the prevailing winds create a natural draught.

Establishing a refuge area

If you do not have the possibility to design your home in order to make it a refuge in itself when water starts rising, you might consider choosing a refuge area. The structure must be strong enough to ensure good reliability under water pressure. For its walls, avoid materials that allow water to rise by capillary action. Heavy materials such as cinder blocks and bricks are resistant to flooding; generally, only the lining needs to be redone. Metal-framed partitions offer the advantage of easy access to the electricity network. The use of water-repellent materials can be considered if they retain their characteristics after 72 hours of immersion. In all cases, trust the specialists in charge of the building's construction. In extreme cases, the use of amphibious platforms can keep the building above the water level by passing on the Archimedes' thrust. A few projects have been carried out in this way around the world, but the investment remains such that it is rarely interesting if one can afford to build elsewhere.

Reacting to floods

If possible, try storing sensitive objects and devices in the safest area of your home. It should be located above the highest known water level. If not possible, quickly move vulnerable elements when the first signs of flooding appear. Place all water-sensitive elements in the non-submersible area, high up or upstairs, out of the reach of floods. This includes, devices, documents, food, water, medicine... In case you lack of preparation or a flood occurs in an area that is usually safe from these risks, water is coming to your door and you have very little time to react. So what can you do? After securing your vulnerable relatives and pets, cut off electricity and gas, then take care to prevent material damage as much as possible.

Covering openings

Close previously identified entry points as much as possible. An inflatable floor dam can be installed quickly and allows large openings to be plugged quickly. Make sure that accesses are watertight. We don't think about it often enough, but a tarpaulin is perfectly capable of protecting a piece of furniture. Of course, it must be perfectly positioned to be truly effective.

Putting bags filled with sand can help form a barrier to limit the penetration of water. The sand will also filter it out if there is any pollution. This technique is mostly used to seal openings such as entrance door, bay window, gate... Above a certain height, the water pressure is such that it may be preferable to let a flow through to reduce the risk of breakage. Access to the interior must remain possible for emergency services. To protect a neighbourhood or city, removable low walls can prevent water from entering. Several of these walls can be linked together depending on the area to cover. Be careful, however, to ensure that the highest known water level cannot exceed the height of the equipment and plan the management of diverted water (final destination, expected flow).

Use absorbents

Before the flood: stored in strategic locations in the form of intervention kits, sorbents allow a rapid initial reaction in the event of moderate flooding. Be careful to place them in places that allow effective deployment. The use of sorbents during a flood can limit water infiltration. For example, all-liquid absorbent pads are an excellent alternative to sandbags. They can also collect regular drips. The pads are placed at the bottom of doors to retain a moderate flow. Absorbent sheets can be placed just about anywhere on your premises.

Manage the after

The receding water level does not mean the end of the dangers. Particular attention must be paid to any electrical appliances that may have been affected. They must be reconnected by professionals. Beware also of the risk of contamination. Household products must be placed at a high level to prevent them from contaminating the water. And check with the town hall very quickly to find out if the tap water is still drinkable.

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- Another look at plastics: the German deposit system






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