Thousands more homes could be at high risk of surface floods driven by climate change and urbanisation in the coming decades, government advisers have warned.
A new report from the National Infrastructure Commission (NIC) warns the number of homes and properties in England that are at risk of surface water flooding could rise from 325,000 today to 600,000 in the next 30 years.
Without action, the risk of surface water flooding could increase as climate change brings more intense and frequent heavy downpours, new development puts more pressure on drainage systems and paved-over front gardens worsen water run-off, the report said.
The NIC said stricter controls on new property developments, along with around £12 billion in investment in drainage systems are needed over the next 30 years to prevent thousands more homes and businesses from flooding.
And there needs to be more focus on “nature-based” solutions such as roof gardens, green gullies, drainage ponds and rain gardens to tackle the problem.
The Commission said that localised floods across England last month, following major flooding incidents in London in 2021 which affected 1,500 properties and hit hospitals and public transport, highlighted the risks posed by surface water flooding.
It occurs when there is too much rain for drains to cope with and the ground to soak up, filling streets with water which can flood into buildings and disrupt infrastructure.
At present, 325,000 English properties are at a high risk from surface water flooding, with a 60% chance of being flooded in the next 30 years.
But a combination of climate change, bringing more intense and frequent heavy rainfall, and increased pressure on drainage caused by new developments could see as many as 230,000 more properties in the high risk category by 2055, the report said.
In addition, the unplanned spread of impermeable surfaces, such as the paving over of front gardens, reducing the ability of rainwater to seep away into the ground, could put a further 65,000 properties into high risk areas, it said.
The Government needs to strengthen legislation and standards for new developments to reduce the use of existing drainage systems for surface water run-off, which risks overloading drains, and increase sustainable measures such as green gullies and flood storage ponds.
It also needs to review options for managing the growth in paved surfaces, the report said.
Action to expand drainage capacity and better maintain existing systems, will improve the resilience of towns and cities to more frequent and heavier downpours, the NIC said.
Lower-cost, above-ground measures – which also benefit wildlife – such as grassy channels, rain gardens and ponds, should be considered before digging more pipes and sewers, it said.
There also needs to be more joined-up, targeted governance and funding for the issue, with the Environment Agency actively involved in assessing flood water risk and the Government setting national risk reduction targets.
Local authorities and water companies should work together to develop plans that deliver locally-agreed targets with funding devolved to local areas, the commission recommends.
The new infrastructure involved will cost an estimated £12 billion, spread over 30 years, split between public and private funding from water companies.
The investment could move 250,000 properties out of the high risk category for surface water flooding, and boost protection for many more.
Action on new developments could prevent a further 95,000 homes and businesses from facing a high risk of surface water flooding in their area.
The £12 billion figure could be reduced by action taken under separate plans for £56 billion of spending to reduce combined sewer overflows, which tip sewage into rivers and the sea during heavy rain to prevent systems becoming overwhelmed, the commission suggested.
Professor Jim Hall, National Infrastructure Commissioner, said: “It’s clear that faced with more intense rainfall and increased urbanisation, we need to start taking this type of flooding far more seriously.
“The solution is clear – reducing the amount of water flowing into drains, whilst also improving the capacity of those drains.
“That means stopping urban creep from increasing the amount of storm water that drainage systems have to cope with and giving nature more opportunities to hold on to excess water, as well as targeted investment to ensure sewers can cope with growing pressures.
“While sustained investment is needed, the estimated additional costs are relatively modest.
“At least as important is a more joined-up approach to owning and acting on the problem,” he urged.
A Government spokesperson said: “We are tackling surface water flooding through our £5.2 billion flood defence programme, with over 30% of 2,000 new flood defences, including sustainable drainage systems, set to improve surface water management.
“The Government has completed a review about mandating sustainable drainage systems in new developments, with more information set to be published shortly.
“This will help address both surface and sewer flooding, alongside our Storm Overflows Discharge Reduction plan, which requires water companies to deliver their largest ever infrastructure investment of £56 billion to tackle storm sewage discharges.
“We will closely consider the findings of the NIC’s report ahead of publishing our response in 2023.”