Are Sandbags Effective for Flood Protection?
In the UK, the annual level of rainfall received has gradually been increasing over the last 40 years. Average yearly rainfall levels are now approximately 162 millimetres greater when compared with levels from the 1980s.
These changes may not appear like much, but averages can mask extremes. 1 in 100 year (1% Annual Exceedance Probability- AEP) and even 1 in 1000 year (0.1% AEP) rainfall events are becoming more common; it is these intense rainfall events which are catching many people off guard, and sadly resulting in flooded homes.
Sandbags are a common sight in flood prone areas; however, the Environment Agency (EA) acknowledges that they are “ineffective” in mitigating flooding, and are only used as they are “Cheap, easy to obtain and can provide protection for short periods of time”. Sir Michael Pitt conducted a review following the extensive 2007 floods, which also found sandbags to be ineffective.
Despite this, thousands of people across the UK continue to opt for sandbags when there is an increased risk of flooding.
But are sandbags really the best way to protect your home from flooding?
Many people are under the impression that sandbags are an effective means of preventing flood water from infiltrating into a property, and that they act as a flood barrier. However, this couldn’t be further from the truth, in fact it is quite the opposite.
In a recent test conducted at an accredited British Standard Institute test tank, by Mary Dhonau OBE and Simon Crowther BEng (Hons) C.WEM MCIWEM, sandbags were tested for their effectiveness at preventing water ingress. Four sandbags (a similar number to if a local authority had issued the sandbags to a household) were placed in front of a door and were subjected to a steady flow of water. After just 59 seconds, these four sandbags were breached by the water. When 10 sandbags were positioned at the door, they held back the water for just two minutes before being breached.
The Side Effects of Using Sandbags
Not only can sandbags fail to prevent water ingress, but they may also make your home more susceptible to future flooding.
Sand often escapes from within the sandbag during a flood event, which can collect and build up in the local drains surrounding a property; or alternatively can build up and block existing flood mitigation measures already in place such as puddle pumps (the sand pollution blocked one of the puddle pumps utilised in the BSI test tank mentioned above). This may impact the ability of drains to alleviate floodwater come the next heavy rainfall.
Sandbags are single-use only and can be extremely difficult to remove and dispose of in the aftermath of a flood event. They are highly likely to be contaminated from the flood water and can harbour bacteria.
Alternatives to Sandbags
Currently, the UK is due to spend £5.2bn on flood defences over the next six years, with regions such as the East Midlands, Southeast and Central London receiving the most money to fund flood protection measures. However, many local authorities and individual personnel continue to use sandbags during flood events.
Whilst investment is often required to protect homes effectively against flooding, the risk of flooding is only increasing. Therefore, the provision of sandbags should be phased out, and instead communities should be made more aware of proven Property Flood Resilience measures.
Property Flood Resilience is a term used to describe measures that reduce the risk of flood damage to properties and help speed up the recovery time following a flood, such that residents can move back into their homes more quickly. When installed, Property Flood Resilience measures are unique to each property, and aim to address the most likely source of flood risk.
Property Flood Resilience measures may include:
- Non-return valves
- Flood resistant self-closing airbricks
- Sump pumps
- Flood barriers
- Waterproof plaster
- Raising electrical outlets
- Recoverable kitchens
- Tiled flooring
Preventing flood damage isn’t just about building bigger defences. Smarter house planning and designing will play a huge impact in how communities are affected by floods.
It is accepted that proven PFR measures require investment. Sandbags are often seen as ‘cheap’, and whilst not always the case, there are measures which can be utilised even on limited budgets. This may include creating and enacting a Flood Action Plan and signing up to receive flood warnings. On receipt of a warning, belongings should be relocated above the flood level and cars moved to higher ground to minimise damage. Tape, sheeting, boards, and ballast may help reduce the ingress into a property. The only instance we have found for sandbags to be useful is as a weight to hold sheeting in place, however even then we would recommend filling the bags with gravel instead of sand. The gravel will not wash out of the bag and will not set hard.
How Can We Help?
Flood Protection Solutions Ltd are a renowned team of Flood Risk Consultants, Engineers and Environmental Professionals who specialise in flood mitigation to homes and businesses.
We have an extensive background at undertaking Property Flood Resilience Surveys, Surface Water Assessments and Flood Surveys to assess the flood risk to a property, and provide recommendations tailored to each individual property to combat flood risk at your home. We can assist in providing proven flood mitigation measures to manage and minimise your flood risk