Groundwater, which also rises in the case of higher water levels, endangers even low-lying districts that are further away from the Rhine. Even when the flood recedes, there is a risk of inundation from the still rising groundwater. You should therefore check your basement rooms more often and take precautionary measures.
You should vacate basements, garages and lower-lying rooms sufficiently early. Ideally, do so from the outset, so there is no need to carry the same furniture several times. If necessary, organise professional help from removers.
The fire service can help only in exceptional cases! You should also continue your own contribution during the flooding period. If necessary, take leave from work and do not rely on others. Help your neighbours too!
During the flooding phase, the fire service essentially does not provide pumps to pump water ingress out of basements and other rooms. If you pump for yourself, please bear in mind that large differences in pressure can result in indentation of basement floors and walls. Co-ordinate with your neighbours!
Protect your heating system. Switch off burners, heating appliances etc. in good time, so they can be removed in cool condition. Bear in mind: local heating engineers have a lot to do when flooding is imminent. Do not forget to close the gas valves on gas heating.
Use proper fixings (e.g. anchoring) to secure your oil tanks and power cables against lifting. To reduce the pressure in the case of rising flood water, you can also have your tanks completely filled in good time. Remove containers with used oil, chemicals, paints, varnishes, washing and cleaning agents from rooms at risk of flooding. Oils and other substances that are hazardous to water pollute not only the water and your rooms but also the surroundings and the environment. If environmentally hazardous substances leak out despite all precautions, inform the fire service immediately. Any time delay will exacerbate the damage many times over.
Water pressure and lift
If water levels are high then the groundwater rises above the level of the foundations. Water pressure and lift forces on the building arise here. Watertight buildings with few storeys do not normally have the necessary deadweight against the lift.
Measures to prevent lift
Flooding basement rooms is a short-term way to increase the weight of the house. Moreover, this equalises the pressure on the side walls. Flooding with clean water can reduce consequential damage.
In the event of flooding, the water level in the sewer network rises, as the sewers back up in the case of overload due to large volumes of rainwater and groundwater (in the case of leaking sewers) or due to the high water level of the outlet channel. This rise in the sewer network water level continues through the outlet pipes and domestic connections, potentially into the building. If no protective equipment is in place, e.g. such as backflow traps or wastewater pumping stations, then the water level rises in the mains network of the building concerned up to the level of the water in the sewer network. This can result in water leaks from the sanitary installations or similar in the building.
Black tank / internal seal
In the case of water-permeable soil types such as sand or gravel, a rise in the groundwater level must be expected in the event of flooding. Close to the river, it may be assumed in simple terms that groundwater level = flood level. The following animations show options for sealing a building.
Black tank / external seal
A fully enclosed seal of the building areas concerned is described as a black tank. This seal is generally implemented as an external seal with bitumen or plastic sheeting. It is technically much more difficult and expensive to apply such a seal to the inside of the building. An additional internal trough is required here in order to absorb the water pressure acting on the seal. An internal seal against water under pressure should therefore be used only in isolated cases for retrospective upgrading of old buildings.
The formation of the external walls and foundation slab as an enclosed tank made of waterproof concrete is described as a “white tank”. No additional sealing membranes are required. Regardless of the nature of the seal, building floors and walls must be assessed for the expected loads from water pressure. For the reinforced concrete building floor, this generally means installation of an additional, upper reinforcing layer.