Flood risk area

“That field floods every year, how on earth can they be allowed to build houses there?!”

Words to that effect are ushered by hundreds if not thousands of local residents every year when planning permission is granted for development in a flood risk area within their neighbourhood.

The demand for new housing stock and limited land supply means new development is often proposed and permitted on land which may have previously posed too many constraints, including areas of floodplain.

Flooding is an increasing problem.

Building in a flood risk area is a controversial issue. Flooding is becoming more frequent and more devastating. Long-standing flood records are increasingly being broken and flooding has begun impacting areas that previously had little more than a puddle to worry about during a storm. How can development be allowed a flood risk area when we know the problem is getting worse?

Why is development permitted in areas of flood risk?

Put simply, all planning applications for development in areas of known flood risk must prepare a Flood Risk Assessment (FRA). Since the Flood and Water Management Act was brought into law in 2010 flood risk is now at the top of every planning consultant’s checklist when determining the suitability of a site for development.

A Flood Risk Assessment is technical review and appraisal of the flood risk to a site. Any flood risks must be reviewed against the potential impacts of a proposed development and an FRA must demonstrate that any flood risk can be mitigated, whilst also ensuring that the development does not exacerbate flood risk outside of the site. Flood mitigation often requires a mixture of hard and soft engineering solutions. An FRA must also consider the vulnerability of a development and the impacts that residual flood risk may have on the proposed buildings and occupants.

An FRA will be reviewed by the Environment Agency and Lead Local Flood Authority as part of a planning application to determine whether the proposals adequately address any flood risk issues at a site. Where the assessment is insufficient to satisfy the EA and LLFA that flooding is appropriately mitigated and managed, they have the power to object to the development proceeding, or may request that further assessment is undertaken to ensure the development is acceptable.

(See our page explaining in further detail what an FRA comprises and when one may be required).

The impact of development.

The hydrological characteristics of undeveloped vs. developed sites are significantly different. Changes in ground levels and new buildings can alter flood flows, extents, and depths. Where this is the case flood storage compensation may be required to ensure displaced flood water does not increase flood risk outside of a site.

Rainfall runs off tarmacked roads and tiled roofs far quicker than undeveloped agricultural fields. This increase in run-off must be managed within the drainage design for a development so as not to increase flows into watercourse and subsequently increase flood risk downstream of a site. Surface water run-off must mimic the characteristics of an existing site wherever possible, and Sustainable Drainage Systems (SuDS) should be utilised wherever possible.

What about Climate Change?

The National Planning Policy Framework (NPPF) also requires that the predicted effects of climate change are considered when assessing flood risk; whether that’s considering increased flows and higher peak flood levels in rivers, sea level rises, or increases in rainfall intensity. New development must account for these changes within the flood mitigation measures they propose.

Assessing flood risk.

The assessment of flood risk is not an exact science. As with all statistical modelling there are uncertainties and assumptions. However, the Environment Agency, Natural Resources Wales and the Scottish Environment Protection Agency, alongside Local Authorities in the UK provide some of, if not the best and most comprehensive, national flood risk datasets in the world. This data is used to inform developers about the flood risks, and assists in undertaking the technical review that underpins a Flood Risk Assessment.

There will almost always be a residual flood risk within a site, but following a review and assessment of the risks, and development of engineered mitigation solutions, it can often be demonstrated that development is safe from flooding even in extreme scenarios.

How can FPS help with your project?

It is vital that flood risk is considered at the outset of any development project. FPS Environmental Ltd can assist in helping property owners and developers understand the flood risk at their site, and what work be required in order for their development project to become reality. Please get in touch to see how we may be able to assist with your project.

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