Natural capital value of SuDS outweighs costs

January will mark two years since sustainable drainage systems (SuDS) became mandatory in Wales - a move which could soon follow in England. Welsh Water’s managing director of wastewater Steve Wilson tells Utility Week that during that time SuDS have vastly reduced the use of combined sewer overflows (CSOs), increased biodiversity and saved hundreds of properties from flooding.

Amid a rising tide of public outrage at the extent of CSO use in England, Defra has suggested mitigating some of the pressure by following the example of Wales and including SuDS in all new developments.

From January 2019 Schedule 3 of the Flood and Water Management Act 2010 came into play requiring any 100m² or more of impermeable area – buildings, roads, car parks etc – to obtain consent from the SuDS approval body (SAB), a role local authorities hold in Wales.

Wilson tells Utility Week the change has been positive but has added extra steps for developers to comply with and has made more work for local authorities, which are already stretched. He explains there are variations between planning authorities as they gain the skills and knowledge to implement SuDS. In Welsh Water’s region there are 22 local authorities acting as SABs, meaning 22 slightly different interpretations of the rules.

“We are behind the intent because we absolutely see it is one of the most critical things to make development more sustainable, deal with climate change and the agenda around the use of CSOs. One of the long-term, sustainable, low-carbon ways of addressing the frequency of operation of sewer overflows is reducing the amount of impermeable area.”

Urban creep and housing needs have meant an increase in impermeable land, even areas with less housing growth have green space as homeowners add extensions, lay patios, or tarmac over gardens to park off street. The loss of green spaces together with ever more intense storms leaves more surface water with less ground to absorb it.

Wilson points to two significant projects in south Wales where SuDS were retrofitted – in Grangetown, Cardiff and Llanelli, Carmarthenshire.

“You get multiple benefits: reductions in surface water into the sewer network which reduces the risk of flooding in bad weather, it reduces CSO operation, and enhances the public spaces. What we’ve seen from that is communities positively adopting that space and taking more pride in it.”

At Llanelli the company invested £95 million in the scheme that removes around 1,070 megalitres of surface water each year from the wastewater network. Wilson says flow monitors show a “huge reduction” in the operation of CSOs into the Loughor Estuary since completion in May.

“Some sites were operating around 80 times a year, down to 10. That’s included periods of very wet weather in August this year, so it’s been really successful.”

Similarly, the Greener Grangetown project in a built-up area of Cardiff with few green spaces has reduced the operation of CSOs into the River Taff and a reduction in the running costs of the pumping station downstream as less water is coming down thus electricity costs are lower.

The company is now undertaking studies into the efficacy of SuDS in removing pollution and microplastics from the water as it makes its way to the Taff.

“We expected a reduction, but when we measured it we were all gobsmacked at how different it was. We are now trying to find the best way to measure and quantify things like microplastics, but it’s another easy-to-see benefit.”

An alternative would have been expanding the capacity of the sewers; however Wilson argues that with climate change and the intensity of rain and storms growing, that capacity will be beaten.

In October 2018 much of the Carmarthenshire area was affected by flooding but the SuDS scheme prevented Llanelli from being flooded and diverted 1,690 tonnes of flood water from reaching the sewer system.

From a natural capital accounting point of view the biodiversity benefits are clear, however Wilson warns it’s not cheap.

“I could build a concrete pipe or storage box as cheaply; the cost is very similar. This needs a lot more public engagement in the early stages to gain support to add surface planters that may cost parking spaces. It can be more disruptive and take longer. However, if you go through that engagement to add the green space, the finished product is well-received.”

A downside, particularly as the legislation is new, is SuDS can be seen by developers who are unfamiliar with the system as another upfront cost and could be put off by the extra steps required to get approval from the local authority SAB.

Developers can pay a commuted sum for SuDS being included in a new build and work out over 30 years what the maintenance costs would be, build it, then lave the local authority to manage the SuDS. Wilson said there is debate around the right value, because there is insufficient experience in the long-term maintenance of the assets, which can put developers off.

“There is a clamour to build our way out of this recession and we shouldn’t be putting barriers in the way to growth. A green recovery approach means sustainable urban drainage is a good way to build our way out of this in a more sustainable way. It enhances the public realm and nature.”

The Welsh government is now considering standalone SuDS legislation in consultation with the water company. It could include extension of powers held by water companies to lay sewers across private third-party land to also allow land drainage to be added.

Wilson concludes: “Everyone reconnected more with nature during lockdown, which is one reason we’re seeing a lot more concern about CSOs and river quality. If we go down this route it might be more expensive to put SuDS in the ground in the short term, but the longer-term benefits are multiple.”