As northern England and many parts of Scotland count the huge cost of recent flooding, Richard Steel, technical director at independent environmental consultancy practice Atmos Consulting, asks if we need to give the way we design flood defences a fundamental rethink?

Climate change predictions suggest that the unprecedented wet weather we’ve already experienced this winter is destined to become a more common feature of the UK climate. Bringing major disruption to communities, transport infrastructure and local economies, the cost of flooding over recent weeks is already estimated to run into billions.

The traditional approach to flood defence has been to construct flood embankments that force river flows through narrow channels. Meanwhile, the functional flood plain on many UK rivers has been lost as parts of this land are given over to agriculture and commercial and retail development.

Unfortunately, changes to river catchment land use and the management of drainage is leading to increased run-off rates, meaning that water levels on rivers constrained by traditional flood embankments rise much more quickly. When rainfall is as high as it has recently been, these traditional flood defences are overwhelmed, causing the river to reclaim its historic floodplain.

If recent events are destined to become the ‘new normal’, a flood defence strategy focused on building ever larger and higher embankments is destined to fail. Against this background, there is a growing consensus that we need to fundamentally rethink that strategy and to consider approaches that recreate the natural surface drainage storage characteristics of river catchments.

In the case of new developments, this means adopting the principle underlying sustainable drainage systems (SuDS) that surface drainage is stored and attenuated on-site in order to limit the speed and volume of water being discharged outwith the site. To protect downstream communities from flooding, this principle needs to be adopted on a much wider and larger scale, creating the capacity for upstream temporary storage of water that helps to slow downstream flows.

An excellent example of this approach has been implemented in the town of Pickering in North Yorkshire which previously suffered frequent flooding problems. Instead of building large flood embankments, a wide number of measures were implemented in the upstream river catchment through construction of strategically placed ‘leaky dam’ structures and blocking of drainage ditches to provide essential upstream drainage storage and attenuation. During the heavy rainfall of recent weeks, while large parts of Yorkshire experienced flooding, Pickering escaped unscathed.

The key to this approach is to work with local landowners and the farming community to put in place suitable compensation to be able to re-designate riverside zones for temporary flood storage. When areas flood, the associated cost is extremely high, not only in pure financial terms but also for the wider economy and the general well-being of the affected community. In 2014, annual flood damage costs were estimated at £1.1 billion. The cost so far of this winter’s flooding is already estimated at around £5bn.

With this in mind, flood defence budgets could be directed towards purchase of land or providing compensation to landowners for the development of flood plain storage areas within the river catchment. The measures required to attenuate flood water in these areas are relatively low cost. Also, funding should be directed towards slowing the run-off characteristics of upland areas which have been historically impacted by deforestation and drainage.

The permanent purchase of land to be reclaimed as river floodplain offers further exciting opportunities to make ecological gains by developing these areas into natural wetland systems. As well as enhancing biodiversity, these ‘natural sponges’ can also be highly effective in improving water quality by removing pollutants. Just as conservation efforts are most effective when implemented at a large scale, the effectiveness of future flood defences can be significantly enhanced by taking a more holistic approach.

Sadly, without a change of emphasis and a ‘big picture’ approach to managing flood water, the scenes of devastation to properties, businesses and infrastructure we have recently witnessed risk becoming a routine feature of the news headlines. Achieving that change will be challenging but the key is to develop a clear strategy for each river and coastal catchment where flood risk is high, based on strong collaboration between local communities, local government and statutory agencies. Alongside the obvious substantial economic benefits of preventing or reducing flooding, this revised approach to designing flood defences can deliver further important gains in the form of enhanced ecosystems and better water quality.

As we adapt to the ‘new normal’ imposed by climate change, the stakes could not be higher. With flooding still grabbing the headlines, we should seize the opportunity for a fresh approach to flood defence that means we are better equipped to deal with extreme weather events in the years to come.