06 Apr Surprise Climate Change Allowance Changes for Flood Risk Announced

Developers and Councils have been taken by surprise by the Environment Agency’s (EA) sudden revision to guidance for flood risk assessments and flood defence projects.

Surprise Climate Change Allowance Changes for Flood Risk Announced

Updated climate change allowances for flood risk assessments were published in February and changes to advice for flood defence projects planning followed in March.

The allowances feed into National Planning Policy Framework (NPPF) guidance which is used by local planning authorities when preparing local plans and considering planning applications.

Based on climate change predictions and different scenarios of CO2 emissions to the atmosphere, the allowances set out likely changes in peak river flow, peak rainfall density, sea level rise, offshore wind speed and extreme wave height.

Most predictions remain the same but peak river flow allowances have been changed in many river basin districts.

“It appears that this guidance was put out very quietly and a large number of our consultant members are struggling to know how they should apply it” said Alastair Chisholm, head of policy at the Chartered Institution of Water and Environmental Management (CIWEM).

Concerns have been expressed about how the EA’s new guidance will be applied at property development scheme level. The new, higher peak river flow allowances, now mean that sites originally earmarked for development on zoning plans by council planning teams, may have to be redrawn as the flood risk boundaries widen to accommodate the higher risks.

For some river basin areas, such as in the South East and Thames, peak flow increases have been revised upwards to 105% and 70% for the upper end allowances respectively by the 2080s.  This redrafting of the allowances will therefore have a substantial impact on flood risk zones and also for viability of schemes now within the orbit of these wider risks.

Flood risk assessments need to demonstrate that large developments in flood zones 2 and 3, will be safe from flood risk and not increase flood risk elsewhere.

For more information on EA Flood Risk Zones and their impact on Climate Change Allowances read this useful blog from GeoSmart Information, www.geosmartinfo.co.uk/flood-zones-explained/

The new guidance is likely to mean more flood mitigation and attenuation measures will be required and this will in turn increase scheme costs for developers.

While this affects the viability of traditional housing developments with conventional drainage, it provides a clear opportunity to enable sustainable drainage systems (SuDS) to attenuate the flash flows into river courses that would exacerbate peak flows if left unchecked.

The guidance for flood and coastal risk management authorities includes extreme climate change scenarios to stress-test flood defence projects in case climate change turns out to be much worse than currently expected. There is equal concern though, that these scenarios don’t go far enough.

But according to Daniel Johns, the Committee on Climate Change’s (CCC) head of adaptation, they do not go far enough.

“These scenarios aren’t that extreme when compared to scenarios prepared for us by the Met Office last autumn… flood defence projects usually assume peak river flows shouldn’t increase by more than 120%. However our research suggests 290% increases in peak river flows are plausible.”

In the House of Lords debate on the Housing and Planning Bill, which is still ongoing, amendments are being discussed that will make developers liable for flood damage to their projects.

The government is currently reviewing its national flood strategy, which has received much criticism of late from experts. DEFRA says flood risk calculations will be among the areas reassessed.