NIC calls for drainage investment to ease surface flooding

Water companies should be enabled to invest in managing surface water to reduce risks of flooding and futureproof drainage, with a focus on natural and above-ground solutions.

That is according to a report by the National Infrastructure Commission (NIC), which has called on government to clarify its strategic priorities to Ofwat to prepare for surface flooding that will only increase in the changing climate.

In the report released on Tuesday (29 November), the NIC warned 325,000 properties are in areas of high flooding risk, meaning there is a more than 60% chance of them flooding in the next 30 years.

More than 85% of at risk properties are in cities and towns, which is set to increase by up to 95,000 properties due to pressures on drainage systems from urban development.

A further 50,000 to 65,000 homes could become higher risk due to unplanned expansions of impermeable surfaces such as gardens being paved over preventing natural drainage.

Commissioner Jim Hall 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.”

Modelling by the NIC indicated £12 billion of investment over 30 years into drainage infrastructure could reduce the number of at risk properties by around 60%.

“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,” Hall said.

The report described a “solutions hierarchy,” with maintenance and upgrades of existing drainage and sewer systems at the top, above-ground solutions in the middle and below-ground solutions at the bottom. The commission said adopting this hierarchy would ensure the lowest cost options are prioritised while maximising the opportunity for added benefits such as biodiversity.

Local and national collaboration

The report made a series of recommendations for water companies, regulators and central and local government.

At a national level, the NIC called on Ofwat to enable water and sewerage companies to invest in solutions to address surface water flooding including nature-based drainage systems, which would require water companies working closely with local authorities.

The report said the Environment Agency’s (EA) remit should be expanded to model and predict where events could occur. In high risk areas, the NIC called for costed long-term, joint plans to manage surface water by water companies, drainage boards and local authorities. It said these should include targets to reduce risks, assured by the EA and with input from Ofwat.

The NIC highlighted that upper tier local authorities – county or shire councils –  hold main responsibilities for managing risks of surface water flooding. The commission said they should work with water and sewerage companies and drainage boards where relevant to create and deliver long-term management plans. It recommended these be completed by 2026 to inform the following Ofwat price review.

The commission called for developers to be responsible for drainage instead of having a legal right to connect to existing infrastructure. At present including sustainable drainage is encouraged within planning policy, but is not a legal requirement. The NIC called on government to update its technical standards by the end of next year to move away from the automatic right to connect and ensure developers include drainage.

The NIC suggested encouraging households to reduce non-permeable areas by making drainage charges proportionate to how much of a property drains into sewers, excluding parts with natural drainage. It supported Ofwat in encouraging trials to extend area-based charging for domestic billpayers.