Retrofit revolution required for Suds

As approaches to flood prevention and alleviation become increasingly politicised before the general election, David Schofield calls for greater commitment to retrofit solutions.

The UK is still some way from having the robust and workable policies it needs to underpin sustainable urban flood protection, adaptation and mitigation. Last winter’s severe flooding certainly raised both public and political awareness, and the conflict between protecting at-risk areas and cutting public spending is likely to make flooding a much-debated election topic.

During 2014, policymakers sought expert views and evidence during public consultations. Surface water management measures have the potential to make a significant contribution. After a consultation last autumn, new planning regulations in April should encourage the implementation of sustainable drainage systems (Suds) in England, but only for new developments of more than ten properties. Different arrangements apply for Scotland, Wales and Northern Ireland.

In surface water management terms the run-off from new developments is a relatively small component of a much larger problem. To materially reduce urban flood risk, extensive retrofitting using a range of contemporary Suds techniques (natural, engineered and manufactured) is required.

The challenges for retrofitting Suds in both practical and policy terms can be complex and lengthy. But if the UK is ever to make substantial improvements in managing the quantity and quality of surface water run-off, future governments will have to rise to the challenge.

At the end of last year, Hydro Consultancy was invited to present evidence to the inquiry into Innovation in Flood Risk Management, held by the All Party Parliamentary Group (APPG) for Excellence in the Built Environment.

We recommended the City of Portland in Oregon to the committee as a best practice case study, where, along with other US cities such as Philadelphia and Seattle, larger scale retrofit programmes have been hugely successful in reducing the amount of surface water reaching overcapacity below-ground drainage systems.

Portland’s response to decades of river pollution was the Big Pipe programme, its most ambitious public works programme to date, which resulted in the construction of three substantial flood storage tunnels.

However, Big Pipe was only half the story. Impressive clean-up targets were achieved, and overflow spills dramatically reduced, but only with the considerable contribution by Portland’s Green Streets programme. Wholly reliant on public acceptance and participation for its success, without Green Streets the Big Pipe infrastructure would have needed to be substantially larger and more costly.

Green Streets promoted the retrofitting of Suds such as rain gardens, roadside swales, surface water street planters and green roofs. Hugely successful programmes of downpipe disconnection and impermeable area de-paving were also rolled out that wholly engaged local communities in Portland.

While in Portland surface water assets are generally owned and maintained by one public body, in the UK surface water assets are the responsibility of a patchwork of different authorities, including the Highways Agency, water and sewerage companies, local authorities, internal drainage boards, the Environment Agency and other landowners near rivers and waterways. In the UK finding the right balance between underground storage and above-ground at source Suds is more difficult to achieve and can polarise opinions by raising impassioned debate.

Ensuring the correct arrangements for whole-life ownership and adoption is vital, because without it long-term maintenance of surface water features can be neglected. The recent Suds planning consultation suggested that a range of different organisations could be tasked with long-term inspection and maintenance of new Suds features; there is no reason why this principle could not be extended to retrofit schemes .

One major opportunity to reduce surface water entering the sewer network could be to incentivise industrial and commercial landowners to retrofit Suds on their sites in return for reduced surface water charges payable to water companies. Incentivisation schemes have proven to be successful in the US.

There are also ways of improving the flow of water within the sewer network to increase flood resilience, as an alternative to extending the network or building more storage. Water companies model their networks to identify any unused storage capacity. To make use of any available volumes, the pass-forward flow at key locations needs to be controlled and the storage carefully managed to avoid surface flooding. Strategic positioning of vortex flow controls can be used to deliver this retrofit solution. This approach could be used alongside above-ground retrofit Suds measures to also limit the inflow of surface water into the sewerage network.

If we are to collectively achieve sustainable flood protection, adaptation and mitigation, taking into account climate change, then finding political and technological approaches that facilitate retrofitting has to be high on the policymaking agenda.

David Schofield, associate director, Hydro Consultancy