Source: Environment Agency
If you’re imminently at risk of flooding, read What to do when it floods.
If you know your property is in an area that could flood, buy protection equipment and prepare your property well in advance to reduce the risk of flood water getting inside. Remove flood protection equipment once the water has gone to help dry out your property.
If your property could flood through the ground, a pump will be the best way to keep water out. Other methods such as sandbags will be ineffective because water comes up through the ground. You are likely to have to pump water for days, weeks or months. Pumps work best when the inlet is installed in a low point where water can drain (a sump).
Pumps can be electric or petrol/diesel. Electric pumps may be the most convenient, but you will need to take care using an electric pump near floodwater. You may need a back up generator in case of power cuts during a flood. Contact a qualified electrician for further advice. Petrol or diesel pumps can be noisier and will require refueling. Position the generator outside as generators produce carbon monoxide fumes which can kill.
Only pump out water when flood levels outside your property are lower than inside to reduce the risk of structural damage. Contact a structural engineer before pumping very deep water from basements.
A good quality pump should last around 10 years. However, this depends on how often it is used and the acidity and dirtiness of the water. Regularly check and test your pump. Remove and thoroughly clean the pump at least once a year. Disconnect the pump from the power source before you handle or clean it.
Pumping from one place to another may cause flooding elsewhere. You must not pump water into the public foul sewer. When deciding where to pump water, you should contact:
Prepare your property in advance to reduce the damage floodwater might cause inside, making drying out and cleaning up quicker and easier.
If your property could flood from groundwater, there are things you can do in advance to reduce damage.
Fit a pump in a basement or under-floor void so you have a way to extract flood water. This will also help to dry out the property .
A reinforced concrete floor with a continuous damp proof membrane can be effective where groundwater pressures are low. Take particular care where the floor and the walls join as water can penetrate through this point.
If there’s enough headroom, you could raise the floor level either by laying a reinforced concrete floor directly onto the existing floor or by creating a suspended floor. Remember that water exerts considerable pressure: a 300mm depth (1 foot) of water pressure will lift a 125mm thick (5 inch) concrete slab. It’s this pressure that makes groundwater flooding difficult to prevent.
Suspended floors create a void beneath the floor which will flood before water rises to enter the house. They may be built from timber or concrete, but flooding beneath wooden floors will often cause the timber to rot so get specialist advice before carrying out this work.
Basements are prone to flooding and it’s difficult to prevent. ‘Tanking’ materials are available, but these are best applied on the outside walls. This is often impractical and you may have to construct an inner wall. Specialist advice is strongly recommended. Sealing the walls can lead to an increase in water pressure which may cause structural damage.
Foul sewage is the waste from sinks, baths and toilets, which often backs up and causes problems during groundwater flooding. What you can do to prevent sewage flooding depends on your system.
Main drainage systems: Report any flooding problems with main drainage systems to the water company or housing association that operates them. For further advice you can also contact Ofwat, the economic regulator of the water and sewerage industry. If you have a continuing problem with sewage flooding which the authorities are unable to solve, you can try fitting non-return valves. Get guidance on these from the Construction Industry Research Information Association (CIRIA).
Septic tanks: These frequently have problems when groundwater levels rise. You may need to hire portable facilities, or arrange to have your tank emptied and the contents tankered away by an appropriate contractor. Adding a pump to the outlet side of the tank may help keep your system working and pump the sewage to high ground above the groundwater table. You must contact the Environment Agency if you want to do this as you may need a permit to discharge, which will be dependent upon local circumstances. You should take steps which are reasonable and practical in the circumstances to minimise pollution and advise us as soon as practical. The design of pumped sewerage systems is complex and you should always seek specialist advice.
Cesspits: If these are well built, they should not be a problem. Rising groundwater will test the integrity of the structure and small leaks may occur which will quickly fill the tank. Be aware that if you call a tanker to empty a septic tank or cesspit when the toilet will not flush, but the tank has not been installed with a sufficient concrete surround, there is a risk it could float the tank or it will quickly fill with groundwater.