Flood Defences Overview
Flood defences falls into three main areas concerning home flood defences, coastal flood defence and town flood defences. Pumps, building driers and vent covers are typical of domestic items needed. Our Flood Advice section has a wealth of good practical tips for people as to how to prepare for a flood and how to best recover after a flood....more
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Flood Defences Explained
In recent years the issue of flooding has become a key concern to both the Government and the public. Insurance companies have paid out millions of pounds when entire communities have been affected by flooding. Flood insurance in areas susceptible to flooding has become increasingly difficult to secure and hence individuals and communities are now looking at all angles of flood defence measures.
A risk assessment of a flood scenario usually identifies areas of likely ingress to be doors, floors and airbricks.
BS 1188 PAS-3 is relevant to many flood products and PPG25 offers government guidance upon development within flood plains. The Environment Agency is the key government body taking responsibility for flood warnings, flood advice and flood prevention.
Vent Covers / Air brick covers
One of the main areas where water ingress is suffered in a flood situation is through the airbricks which are evident in most external walls of houses. The airbricks are used to introduce ventilation either into the brickwork cavity, or more often to provide cross-ventlation underneath a suspended floor. Traditionally this suspended floor would be timber floor joists and the ventilation would avoid dry rot and wet rot forming. In modern block and beam construction of ground floors, ventilation is also required and this is to prevent build up of gases or decaying deleterious matter.
Vent covers or airbrick covers are now available in several forms which can be fitted to airbricks in the event of a flood situation to effectively seal the airbrick making it watertight. Permanent automatic airbricks with covers are also available which form a permanent installation and these are often referred to as 'Smart air bricks'.
Front and rear doors form a key area of exposure in times of flooding and the marketplace has developed a wide range of door barriers that can be fitted very quickly in times of flood. Most of these are characterised by fixing clips or other mechanical fixings that are pre-fitted in prior preparation for a flood situation. Putting the door guard in place then becomes a simple job at the time of the flood. Such door barriers are often GRP, fibreglass or aluminium with appropriate rubber seals.
Similar types of barriers are available to form window flood defences but it is important to bear in mind that if water rises above 1 metre in height, this restricted flood water forms very large hydrostatic pressures and there is significant danger of structural collapse. For this reason once a flood reaches window height it is often recommended to allow the water to flood into the building thereby equalising the pressure on the walls of the structure. Most floods however (95%) do not exceed window cill height.
General flood protection panels are available as door protectors and for more general flood applications.
Flood doors are becoming increasingly available whereby a very heavy duty and well sealed door is fitted with a correspondingly heavy-duty waterproof doorframe. Flood door manufacturers have to be mindful that such doors can readily still be opened by small children in the everyday use of the door.
A feature of many floods is the speed at which conditions change. Rapidly rising water levels can easily go undetected during the night or if people are away from home at work or on holiday. Automatic flood alarm systems can be installed which have an auto dialler to notify owners of any changes in conditions.
Commercial flood barriers
Many councils and The Environment Agency are considering the installation of commercial flood defences that protect entire streets or communities from the effects of flooding. These floodshield barriers may be permanent or demountable flood barriers whereby aluminium posts and panels are fixed to pre-fitted anchoring points in pavement areas.
Inflatable building skirt systems can be used to protect entire houses or commercial and industrial buildings.
Flood Drying Equipment
After a flood the most important action is to remove all standing water since materials like concrete and brickwork are relatively slow to absorb water, but once saturated they similarly take months to dry out. Electric heaters and gas propane heaters are commonly used to speed drying and ventilation as at this stage it is important to continually remove damp moist air from the building as soon as possible.
In the later stages of drying, a building a dehumidifier or building drier can be used. This requires the building to be sealed relatively tightly so the vapour in the air can be frozen and collected hence lowering the humidity of the air. This then encourages water to leave the structure, as a humidity gradient has been established.
An excellent test as to whether a concrete floor has dried out is to place a piece of polythene sheet on part of the floor overnight. The amount of water on the underside of the sheet will give a good indication if further drying is required.
Simple electric submersible pumps are ideal for removing water from flooded buildings. If a sump or low area can be identified, these will quickly clear almost all standing water. Since they rely upon electricity however, a small petrol generator is usually required as in most heavy flood situations mains grid electric power or power within the building is usually lost immediately. A small investment in a submersible pump and generator is a 'must have' for any potential flood victim.
The 'Flood Advice' section elsewhere in this website has an abundance of good practical advice. This advice is for people preparing for a flood or who have just suffered a flood and it is an invaluable resource for anyone needing further information.