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By Simon Crowther

Founder, Flood Protection Solutions

TODAY'S OTHER NEWS

Investment strategy – is surface water the biggest flood risk?

February 2020 was the wettest ever recorded in Britain, with Atlantic Storms Ciara and Dennis depositing vast amounts of rainfall across the country.

According to the Met Office, a UK average of 202.1mm of rain fell during the month, surpassing the February 1990 record of 193.4mm.

Flooding was widespread with some of the worst-hit areas including Ironbridge and Bewdley along the River Severn.

The media focus tends to be on fluvial (river) flooding, as this tends to be more predictable and longer lasting than flash floods, making them easier to film and report on.

This often means other types of flooding can go ignored by the media, resulting in both less public and government interest.

Of all the flood risks to the UK - from coasts, rivers, groundwater, sewers and surface water – it is surface water flooding which threatens more people and properties than any other form of flood risk.

Over three million properties in England are at risk of surface water flooding, which is greater than the number at risk from rivers or the sea (2.7 million).

The most worrying thing here is, most do not know they are at risk. If you don’t live near a river or the sea, it’s not unreasonable to think that you are not at risk of flooding, however this may not be correct.

Surface water flooding occurs when intense rainfall overwhelms drainage systems. It is reported that 35,000 properties were affected by surface water during the major floods of 2007.

It is also important to note that surface water flood maps are not designed to be used to identify if an individual property will flood. They do not take into account drainage connections and therefore an experienced flood risk consultant is needed to translate what the flood mapping is showing to what would likely happen on the ground, at property level.

It is important to remember that surface water flooding may not come with any warning.

Surface water flooding does not just hit homes and businesses, but also has far reaching effects across society, disrupting road, rail, utilities of towns or cities. It is a risk area which is growing.

An increasing population and drive to build new homes will mean more concrete and fewer areas for rainfall to safely drain away. The government set a target in 2015 to build 200,000 houses a year, so that by 2020 one million new homes would have been built.

Incredibly, this target was deemed too small and in 2017 it was increased to 250,000 homes a year with the suggestion that the target should rise to 300,000 a year.

Alongside new developments, changing land uses and deforestation will exacerbate flood risk as interception and infiltration rates are reduced. Climate change will bring more frequent and intense rainfall, bringing more flash flooding and overloading of our ageing sewer network.

 

Government-funded Environment Agency flood mitigation schemes are not designed to protect against surface water flooding. It is a risk which tends to affect built up urban areas. Poor urban areas are the most susceptible of all because there are a lot of people, with paved drives and roads which don’t absorb the rainwater.

If there is a possible upside to surface water flooding, it would be that it generally does not last as long as river flooding, and therefore there is a greater chance of keeping the water out of properties using property flood resilience measures, such as flood barriers, water pumps, and anti-flood airbricks.

Moving forwards, we urgently need to reduce carbon emissions to limit climate change, or the risk of surface water flooding will keep increasing. Alongside this, warnings need improving, as generally surface water flooding occurs without warning.

Any new developments should be resilient to flooding, and not exacerbate the risk elsewhere through well-executed (and maintained) sustainable urban drainage schemes.

Alongside this, catchments should be managed better to reduce overland flow, by reforesting and contour ploughing to slow the flow. It is important to remember that there will always be a residual risk, and therefore property flood resilience is a key part of the flood mitigation jigsaw.

With 67% of the population not knowing their flood risk, we have a long way to go to drive changes in behaviour!

*Simon Crowther is a Civil Engineer and Chartered Water & Environmental Manager. Simon founded Flood Protection Solutions Ltd in 2012, and as a 2007 flood victim he has huge empathy with his clients.

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