Climate Change

One of the most immediate impacts of climate change is the increased frequency of extreme flooding. To experience flooding is a traumatic experience for both households and businesses. It can take eighteen months to recover from and clear up. February 2020 was the wettest February on record, and in Gloucestershire there were anxious moments when a repeat of the devastating floods of 2007 was feared. Although water levels in the River Severn nearly reached those recorded in that year, the number of properties flooded was much lower. Since 2007 almost £50 m had been invested by the County Council in flood defence and resilience. These projects were all bespoke, designed for the specific flooding circumstances of the locality. This is the central message of  remarkable book by Ed Barsley Retrofitting for Flood Resilience: A Guide to Building & Community Design. Flood risk is inherently site specific. Copying and pasting  approaches without a holistic understanding of the context and potential consequences can be foolhardy and dangerous, warns the author Ed Barsley. Founder and Director of The Environmental Design Studio. He is a specialist in environmental design in architecture aiming to improve the resilience of communities and the built environment.

Through six clear sections, each with exceptional charts and illustrations, the author guides the reader through an understanding of flood risk contexts and consequences, identifies the type of flood risk and describes the tools and techniques to understand the risk. A hugely valuable section deals with catchment and community flood risk management before subsequently discussing building – level strategies. In the final section he outlines how we can mitigate and adapt to the causes and effects of climate change in the way we design, plan, build and manage the built environment.

Wealth of Examples

What makes this book outstanding and justify a place in the library of every building professional are the wealth of examples drawn from around the world of innovative building schemes that have been designed to protect people from flooding. These include the BIG U – a 16 km system designed to protect Manhattan from flooding and a neighbourhood wide Sustainable Urban Design System (SuDS) underway in Copenhagen. Covering an area of over 105 hectares it brings together a variety of SuDS strategies. Streetscapes are being retrofitted into “Cloudburst Roads”, which provide green routes for cyclists, pedestrians and vehicles. They also function  in the event of heavy rainfall as channels through which water can be slowed, stored, conveyed and discharged into Copenhagen harbour. These examples of retrofitting schemes to increase flood resilience raise a fundamental question. Should we be building in huge flood risk areas at all?

Building in the floodplain?

In 2016/17 around 24,000 homes were built in these areas in England. A large proportion are protected by flood defences, which is why the Environment Agency did not object to them. Flood defences alone will not always be sufficient to protect properties. The increased likelihood of the severity of flooding, because of climate change, means that there will have to be changes to how new housing is constructed. Bright Blue, a centre ground think tank has recommended a reform of building regulations for homes being built in the most flood – prone areas. By 2025 resilience measures should be mandatory for all new – build properties in flood risk zones 2 and 3 ( where the annual probability of flooding is greater than 0.1%).

 Natural Flood Management

If, because of the pressure to build more houses, the solution of simply not building in flood risk areas is not always open to planning authorities, catchment flood risk management is a proven cost – effective option. Natural Flood Management (NFM) which aims to slow, store and filter water as it moves from upper, to middle and lower catchment levels, is particularly promising. The system has the added benefit of reducing erosion, encouraging biodiversity and habitat creation. Where capital is scarce for large – scale engineering schemes, NFM interventions can support the need for targeted flood prevention schemes. These will help combat the more extreme conditions associated with climate change. In the Slad Valley, Gloucestershire, made famous by Laurie Lee`s personal story of growing up in this secluded countryside near Stroud, the Environment Agency has worked with the local authorities and land owners to coppice trees along the river bank. These are then used to form “leaky” dams that hold back the flood water upstream and help regulate the flow of water together with bunds in the fields. The Slad Brook is a tributary of the River Frome which flows through Stroud and which experienced severe flooding in 2007. Over a fifth of the Frome catchment area has now been drained using a range of interventions.

The future of the Thames Barrier

I vividly recall as a Building magazine correspondent, standing with others on a barge anchored down- stream of the Isle of Dogs, as we waited with bated breath for the barrier gates to be raised for the first time. The barrier was built in 1983 to protect London from tidal surges from the North Sea until 2030. The Environment Agency has now forecast that the design life of the barrier can be extended  to 2070, as current projections of sea level rise give a standard of protection much higher than originally expected.

Fluvial Flooding

Critics point to the increasing use of the barrier to prevent fluvial flooding in West London, and this was not anticipated.  Fluvial flooding primarily occurs when rainfall from periods of sustained or intense downpour enters watercourses such as rivers and cause water levels to exceed the capacity of the channel. Closing the barrier provides more capacity in the Thames to accept this flood water.

The current stance of the Environment Agency that maintenance and upgrading  of other flood defences in the catchment area together with  monitoring of sea levels  can take us to 2070 is contested by many including Dr Richard Bloore. He was chief project manager on the construction of the original barrier. In an interview with Building magazine he commented that “We have to at least start thinking about what comes next now rather than decades into the future.” This outstanding book and the questions it poses has a particular resonance for London. It should be on the bucket list of all the mayoral candidates for London`s elections, now postponed because of the Covid-19 pandemic, until May 2021.

This blog is based on an article  published in  Planning in London Issue 113 April – June 2020 and which can be purchased on-line.