Flood Risk and Drainage

Our highly experienced team of Engineers offer Flood Risk and Drainage services for a range of Clients and industries including Education, Commercial, Industrial, Residential, Local Councils and more. We have experience of working on a variety of projects from small scale single unit conversions to large scale community developments of over 1,000 units for both the private and public sectors.

Our services cover:

• Flood Risk Assessments
• Drainage Strategies
• Environmental Impact Assessments

How can we help you?

Some projects are quite advanced before the advice of a Flood Risk / Drainage Consultant is sought. We are often the bearer of bad news, for example; having to advise Clients that the masterplan needs amendments, or that the site is not suitable for the development that is proposed.

We recommend getting in touch at the initial stages of a project, even before the masterplan is drawn up. This is especially important when the site is located in a medium or high-risk flood zone!

We can then advise upon an initial assessment of the site and highlight any potential issues that we foresee based on the information provided.

Even if no formal assessment is required under national legislation it is valuable to get us involved early as we can provide input into the masterplan and determine the most effective locations for any drainage and water attenuation features. This can help minimise abortive work.

Flood Risk Assessments – When are they required and what are they?

Flood Risk Assessments (FRAs) are a planning requirement when a site is:

• Located in a medium or high-risk flood zone (2, 3a, or 3b)
• Located in a critical drainage area
• When a development site is over 1 hectare in size

The purpose of an FRA is to assess the development proposals and determine if the site is at risk of flooding and/or it is likely to increase flood risk to downstream or surrounding catchments. Following the assessment, if the answer to either of the above questions is yes, mitigation measures are introduced to remove the impact of the development proposals.

Drainage Strategies

If an FRA is not a planning requirement, the Local Planning Authority will still require a Drainage Strategy to demonstrate how the surface and foul water flows from the development can be managed.

In liaison with the design team we will advise on suitable Sustainable Drainage (SuDs) measures. These will be assessed specific to each individual site circumstances.

The strategy will assess how the foul effluent from a given development will be drained. It will cover the proposed route of the sewers, where they will discharge, discharge rates, capacity and specify the design criteria.

We also undertake the detailed design of surface and foul water drainage networks (including SuDS) from Planning Approval through to As Constructed status. Refer to our Infrastructure Design section for more details.

Environmental Chapters

Mayer Brown provide Water Resources and Flood Risk Chapters for Environmental Impact Assessments. We will assess the potential impacts of a development on water resources, flood risk and drainage and examine them in accordance with national planning guidance and Environment Agency requirements.