Helping clients overcome flood risk issues to facilitate developments: a recent success story

The effects of climate change, together with recent guidance from the Environment Agency (EA), mean that an increasing number of developers now have to take measures to overcome flood risk issues. This need not be the onerous task it appears to be.

A Flood Risk Assessment is a planning requirement for developments in medium and high risk flood zones (zones 2 and 3), if the development is more than one hectare in size and if the development is in a critical drainage area. (When we talk about critical drainage areas we mean areas such as central urban locations where extensive hard surfaces lead to poor surface water drainage.)

Here at Mayer Brown we work with a large range of clients to overcome flood risk issues and enable suitable developments to progress. We engage with planning authorities and the EA, helping clients create developments that meet planning requirements whilst staying on course with the original vision for the development.

How is a Flood Risk Assessment done?

One recent success story is a site in Southwark, South London, where Mayer Brown was commissioned to undertake a Flood Risk Assessment (FRA) for a proposed residential development.

The proposal included:

  • A change of use of the existing Grade II listed building from offices to residential dwellings.
  • An extension to the rear of the existing building.
  • A new three-bedroom dwelling in the existing courtyard.
  • Alterations to the existing courtyard to provide shared amenity for the development.

The site was in high risk Flood Risk Zone 3. This means that despite the protection of the River Thames flood defences, it’s still necessary to plan for the eventuality of a breach in those defences.

The challenge of being in a Flood Risk Zone 3

The location in Flood Risk Zone 3 meant that EA and Southwark Council required:

  1. Measures for the protection of dwellings at lower ground floor (beneath breach flood level).
  2. The floor level of the new dwelling in the courtyard to be located above the breach flood level.  
  3. A reduction in the rate and volume of surface water discharging to the local sewage network.

Our solution

We liaised with the EA and Southwark Council to agree a solution. It comprised:

  1. Protecting lower ground floor dwellings through the creation of duplex apartments across two floors. With no sleeping accommodation at lower ground floor level, the design provides residents with internal access to upper floors in the event of flooding.
  2. Raising the entrance to the courtyard to above the flood level to prevent floodwater affecting the proposed 3-bedroom dwelling.

Demonstrating to the planners that there was a reduction in impermeable areas to meet statutory requirements. This was achieved through a natural reduction in surface water discharging to the local sewage network, via more grass areas and soft landscaping. (This method of surface water reduction removed the need for additional attenuation structures, saving additional expenditure for the client.)

The result

The application has since been submitted to, and approved by, Southwark Council.

Keep costs down with early planning

As you can see, it just takes a little of the right experience and expertise to overcome flood risk issues and facilitate developments.

Developers can keep costs down further by working on planning drainage schemes from the outset of development design. By integrating calculations for permitted drainage systems at the early stages of the development, the most cost efficient draining methods can be part of the overall design, reducing the requirement for designing in costly Sustainable Drainage Measures later in the process.

If you’re working towards a new development, think about planning for flood risk now. Give us a call at Mayer Brown – our innovative and creative team are always happy to talk through your options.

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