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UKFB STAFF BLOG: Construction Director, Tom Jarratt shares his views on the importance of passive so


Systems that have to be constantly put up and taken down are also much more prone to damage that could render them ineffective at the crucial moment.

Tom Jarratt
Construction Director

Passive flood defences are rapidly becoming the protection of choice as the climate changes bringing with it increased risk of flooding.  Passive flood defences are those that require no human, mechanical or electrical power to operate and will remain in place, doing their job, 24 hours a day, 7 days a week.  The importance of passive flood defences is increasingly being recognised by both private and public sector clients, especially when considering the whole-life costs of schemes.

The two big advantages of passive flood defences over active measures (i.e. those that do require some form of intervention to operate, be it human, mechanical or electrical) are that:

  • They reduce risk
  • They reduce whole-life costs


It is obvious to say it, but flood defences only work when they are in place.  Where there is plenty of warning that a flood is coming active flood measures may be an appropriate choice.  However, flooding occurs from many sources, some of which are highly unpredictable and some of the worst floods occur in ‘flashy’ catchments, i.e. areas where water levels rise very quickly following a rainfall event, giving little time to respond.

When a flood occurs, it is naturally in poor conditions.  The weather is almost certainly going to be bad, making travel difficult, with this localised flooding may be occurring, again affecting travel.  A flood can occur at any time day or night, at weekends, or on public-holidays and there may well be power cuts due to the bad weather.  All of these factors can affect the deployment of flood defences which require human, mechanical or electrical intervention.      

A local example of this occurred in Upton-Upon-Seven, Worcestershire during the floods of Summer, 2007. Severe weather meant operatives were delayed in getting to their destination, ultimately not getting there at all, resulting in no barriers being in place leaving parts of the small village underwater.

When a flood defence is in place, however, ready to do its job at all times, there is much less chance of the wrong person, or key, or piece of equipment, being in the wrong place at the wrong time.  Systems that have to be constantly put up and taken down are also much more prone to damage that could render them ineffective at the crucial moment.

For these reasons the risk of the flood defences not working is dramatically reduced by using passive defences.  This has been recognised by the Environment Agency whose preference is always for passive defences on a flood protection scheme.

The risk to the welfare of operatives who have to go and erect demountable flood defence systems during a storm event is also reduced by the use of passive systems.  In the conditions leading up to a flood on-call operatives who have to go out to deploy the flood defences are at risk from the environmental conditions and travelling in poor weather.  This risk is again eliminated by the use of passive defences.

The initial capital costs of flood defences is only part of the investment required.  Some demountable systems are very labour intensive to deploy and must be erected every time there is a flood warning.  Passive defences however have zero deployment costs and a crew of operatives does not need to be paid to be on call to deploy them.  Maintenance of passive defences tends to be less than for active systems too,  which can be prone to damage and are often more complex then passive ones.

It is for these two key reasons, i.e. a reduction in cost and a reduction in risk that passive flood defence systems are the systems of choice.

To find out more about our range of passive flood defence solutions, contact us.

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