Sir James Bevan KCMG, Chief Executive of the Environment Agency, has warned that surface water is the UK’s biggest flood risk and highlighted potentially dire consequences if action is not stepped up to tackle the issue.

Speaking at this week’s CIWEM Surface Water Management Conference, he described surface water flooding as “a real and growing threat” to life, property, the economy and the country which impacts the whole infrastructure – road, rail, utilities etc – of a town or city,

Sir James told delegates that surface water flooding threatens more people and properties than any other form of flood risk. Over 3 million properties in England are at risk of surface water flooding, even more than the 2.7 million at risk from rivers and the sea.

The risk also extended to other countries – the recent flash flood in Majorca which killed two British nationals, was a surface water event. “The Dutch, who have been so successful in fighting sea flooding and are rightly regarded as world leaders in the field, are themselves struggling to manage a serious surface water risk building behind their mighty sea walls.” he added.

He warned his audience that surface water flooding is a risk which is growing - an increasing population with more people in cities means more people are at risk. Development also meant fewer places for rainwater to drain safely away, while more frequent and intense rainfall as a result of climate change will make flash flooding and overloading of the sewer network more likely and more frequent.

Sir James outlined a nightmare scenario where London was overwhelmed by intense rain during the summer leading to flash floods, resulting in deaths and the city grinds to a halt, warning:

“This nightmare could happen. London is prone to high intensity thunderstorms and has an ageing Victorian sewer system.“

He referred to a smaller version which did happen, in London in 1975 when in a localised thunderstorm got more than three months of rain in three hours. Four of the capital's main-line railway stations were flooded and closed, while much of the Underground was brought to a standstill as tunnels were inundated and the electrics failed.

Summer floods in 2007 “ a wake up call for all of us”

He went on to describe the 2007 summer floods which left 13 people dead, 44,600 homes flooded and caused £3 billion in damage as “a wake up call for all of us.”

The event led to the 2008 Pitt Review, which concluded that much of the flooding had arisen not from rivers over-topping but from surface water. The Pitt review led to the Flood and Water Management Act (2010), which provided clarity on the roles and responsibilities of the Environment Agency, local authorities, water and sewerage companies and others who manage flood risks.

The Environment Agency chief said the Agency had made many changes in the light of the review, including better information on areas at higher risk from surface water flooding, improved forecasting and a record £2.6 billion investment in flood defence construction projects to better protect 300,000 homes by 2021.

The Agency had also taken up the Pitt Review recommendation to improve the way it works with natural processes by using nature to help manage flood risk and adopting greener approaches to engineering.

Future challenges are growing and will only be met by working together

Sir James warned that future challenges are growing, including:

• climate change, which will bring more extreme rainfall.
• development and building more houses, all of which have potential to increase the risk of surface water flooding
• constructing modern infrastructure which does not increase the risk of surface water flooding and is more resilient to it when it happens.

The challenges would only be met by “pressing all the buttons that are available to us, and by doing it together” to improve how we manage surface water flood risk both now and in future.

Defra’s Surface Water Management Action Plan published in July 2018, he said this seeks to strengthen the current arrangements by improving collective understanding of the risks and helping those responsible to manage them effectively. It also promotes better partnership working across all the flood risk management authorities, better risk assessments, better data sharing, and better guidance.

However, surface water flooding is the hardest of all to predict, he warned, and at present is “sometimes just not possible at all.”

Sir James emphasised the need to design resilience into towns and cities, part of which involved Sustainable Drainage Systems. “The EA is working with developers, local authorities and the water companies to support the integration of SUDs into as many locations as possible”, he added.

However designing in resilience was “about a lot more than SUDs” and meant starting “far upstream in the planning process so that new developments are themselves laid out in ways which reduce surface water and other risks.”

“Wrong kind of farming in the wrong place can cause significant surface water flooding”

It also meant recognising that some of the causes of surface water flooding are neither urban nor to do with concrete.

Sir James went on to warn that “the wrong kind of farming in the wrong place can cause significant surface water flooding.” There had been a dramatic increase in maize production over the last few years, primarily to feed Anaerobic Digestion plants. However, maize is normally harvested in late autumn, when the ground is wet - combined with the use of heavy harvesting machinery, leading to compacted which can’t absorb rainwater. This resulted in surface water runoff, which in turn can cause local flooding and pollute watercourses.

Sir James emphasised the need for greater public awareness to ensure people at risk were better prepared - whether by putting in property level protection or encouraging their local council to ensure that the risks are mitigated.

He concluded by telling his audience:

“So if there is somewhere you don’t want water to be, like people’s houses or the local supermarket, a community centre, a power station, a railway line, an underpass or a road, you’d better make sure that you have the right measures to stop it going where it wants to go .... because this really, really matters.”