Every year flooding affects communities around the UK. The Chartered Institute for Water and Environmental Management recently contended that although there has been expert agreement for many years about reforms, policy change has been slow. In part, this is due to the complex governance system within which flooding occurs. In this article, Professor Graham Haughton and Professor Iain White (University of Waikato) suggest a simple new target to help to break this deadlock.

• A clear target to require all towns and cities at risk from flooding to improve water retention by 10%, should place an initial emphasis on large developments such as master-planned communities and implementing measures on publicly-owned land.
• This policy will focus on reducing the peak water flows that can overwhelm rivers and drainage systems.
• We need to coordinate and combine ways of retaining and slowing down water, not just where problems manifest themselves through flood events but also up-stream within catchments (river basins).

Working with nature

There is widespread agreement that flood policy needs to place more emphasis on reducing the peak water flows that can overwhelm rivers and drainage systems. In effect, the preferred approach has become working with nature, rather than against it and retaining water for longer closer to where it falls. Hard flood defences and improved urban drainage systems still have their place and need investment, in addition to being costly to build and maintain, they need help as climate change and urbanisation increase runoff. Policymakers and urban planners need to design towns and cities strategically, finding ways of retaining and slowing down water that moves beyond ‘at risk’ areas to include up-stream parts of river catchments.

This kind of thinking has inspired considerable work internationally, captured by terms such as Sponge Cities (now widely adopted in China), Sustainable Urban Drainage Systems (SUDS), and Green Infrastructure. We have a range of policy tools available that we know can help improve retain water locally, from simple things like using more water butts, permeable paving, tree planting, or creating road-side swales.

Less permeable cities

But, despite this knowledge towns and cities are becoming less permeable. Not least because of large-scale building projects on brownfield sites, developing urban infill projects, and encroachment into surrounding greenfield areas. There has also been a continuing practice of adding impermeable surfacing to existing housing, such as paving over front and back gardens for car parking, reduced garden maintenance, or the desire for large patio entertainment spaces. These incremental changes collectively add up to reduce local water retention and to add pressure on urban drainage systems.

More positively, we have seen an explosion of interest in nature restoration schemes. These can have positive flood risk benefits, from restoring bends in rivers decades after they were first straightened, to encouraging revegetation alongside riverbanks by reducing grazing, re-planting hedgerows and trees, restoring upland peat bogs by blocking up former drainage channels, and the iconic reintroduction of beavers to help create permeable dams that again help retain water for longer upstream.

A 10% target for new developments and existing urban areas

What is lacking then is not so much ideas, as a clear strategic approach to application, funding and targets, which is where our 10% water retention proposal seeks to make a difference.

Major new developments such as the new towns currently being proposed can play a significant role in enabling housing affordability, but without careful thought, they may also increase flooding. This policy would mean their master planning would be designed to retain water over and above pre-development levels, which would actually lessen risk downstream.

This 10% water absorption gain is similar to, and supportive of, the current plans requiring 10% biodiversity gain on all major new developments. It would create multi-functional greenspaces that can store water, assist nature and enhance liveability.

Logistics and benefits of the 10% approach

While it may be easier to implement at the design stage for new development sites, there are also opportunities to retrofit a 10% improvement in water retention in our existing towns and cities. This could be over say a ten-year period and coordinated by city-region authorities and local governments through their plans, with all public authorities mandated to insert the target into their corporate plans.

Given the difficulties associated with existing property rights, the multiplicity of actors and agencies who own land, and the need for a strategic plan, it makes sense to prioritise changes to public land first. In every local authority area, a significant amount of space is controlled by government funded and statutory agencies – from roads to recreation areas, and the public realm more generally.

Using Local Authority data on local flooding and flow paths, our proposal provides an incentive for all public land to be potentially re-designed to retain water and give drainage systems and defences time to cope. More can also be done by local authorities to educate and persuade land holders, home owners, landscape gardeners, and others on the value of improving permeability at site and household level, not just to help alleviate flood risk but also potentially to improve their property values. Discussions with the insurance industry on property level certification that might reward those taking flood protection measures is already underway, which might help, but such are the complexities and tensions involved this would need to be a national initiative.

The proposed 10% water retention approach to improving on- and off-site water absorption on to the land will also require work to test its technical and practical feasibility, though this should not be too onerous. There is a wealth of existing data on which measure would work best where. Government have already consulted widely on related technical guidance for achieving biodiversity net gain and green infrastructure standards.

The counter-argument to our proposal might be that it will impose further costs on landowners, developers and public bodies. We prefer to think of it the other way around, it is a way of making sure developers and homeowners do not impose further avoidable costs on others. Demonstrably better flood protection should also help reduce insurance costs and potentially increase house sell-ability, inward investment, and indeed house prices.

The 10%+ water retention approach opens up opportunities to encourage nature recovery at scale, creating bigger, better and more joined up areas to support biodiversity and flood protection.