Sump and pumps
Sump and pump systems are very effective at minimising the collection of flood water beneath a property. Consequently, they are often used in basements that are at risk of flooding or as water removal means for cavity drainage systems. These pumps can be either single or double pumping systems, with the double systems generally costing more but removing a greater volume of water.
These pumps may also be powered using a ‘non-interruptible supply’. This means that they are powered by external batteries or by a generator so that if the mains supply is cut as a result of the flooding, the pump will still be able to function in order to keep pumping the water out.
Cavity drainage and basement tanking systems
Cavity drainage systems are only applicable to cavity-walled construction properties. These systems incorporate the use of drainage channels along the base of the cavity, this will filter any water that enters the cavity into a collection pool. This collection pool will then usually be coupled with a sump pump to extract water out of the pool and away from the house. By allowing evacuation of this water as quickly as possible, the impact of flooding on the building’s structure will be minimised. Cavity drainage systems often contain a full membrane to prevent damp coming through into the wall cavities and help to keep floodwater from entering the property
These systems can block up with silt and sediment carried by floodwater entering the cavity. Consequently, hose connection points are often set into the cavity at various points around the room which can introduce jets of water through the cavity to help clear these blockages.
Cavity drainage systems are often a highly costly flood defence measure and require a lot of work to install. However, these systems can be highly effective and sometimes more cost effective than re-pointing the external plaster on a building and sealing all water entry points.
A basement tanking system applies similar characteristics of a cavity wall drainage system and incorporates them to help protect basements and cellars that are located below ground level.
There are four sections to creating a basement tanking system:
- Wall membrane – the wall membrane ensures that any water that would flow directly into the basement, instead flows down and into the drainage system at the base of the membrane
- Floor membrane – a floor membrane will work in a similar way to the wall membrane however it will ensure that rising groundwater if channelled into the French drainage system around the base of the wall.
- Drainage system – this drainage system then transports any water collected from these walls into a sump pump system.
- Sump and Pump system – the final section of a basement tanking system is the sump pump. This is set into the ground below the floor level and will pump water out of the collection tank and away from the basement.
All four of these sections work together to ensure that water does not flow where it is not wanted but instead flows directly into a pump which will remove the water from the house. Homebuilding.co.uk provides some expected costings of this on their website which can be accessed by clicking here. These costings are given as values per m2 area of the basement requiring tanking.
The following video from a third party company explains how these basement tanking systems work and how they can reduce the impact of flooding in basements and below ground-level dwellings. [The Centre for Resilience does not endorse this company in any way].
Other water removal means
It is now possible to purchase flood vacuums at a relatively low cost. These not only allow flood water to be sucked out of any unsealed service entries but will also allow mud, silt and sand deposited by flood water to be removed alongside the water. On the other hand, these flood vacuums are not automatic and will require manual use as well as an electrical supply either from the mains or backup generators in order to function. However, as an additional emergency water removal means to catch small amounts of entering floodwater, these vacuums can be very effective.