Flood risk and drainage for developers

What you need to do to deal with flood risk and drainage.

When we make a decision on a planning application we’ll consider flood risk and draining issues. It’s more likely that we’ll approve your planning application if the development will be built on land with a lower flood risk.

Flood risk areas in Bristol

To see areas of Bristol that are at risk of river and tidal flooding, you can look at a flood map at the Environment Agency website. You can also look at a map of areas with a high risk of surface water.

We’ve done some studies to find out more about flood risk in some parts of Bristol. This may be relevant to your planning application. Find out more at planning evidence.

Development in flood risk areas

If you’re carrying out development in a known flood risk area, there may be restrictions to make sure the development will be safe while it is in use.

If you make a planning application to carry out development in a flood risk area, we can carry out a Sequential Test to decide if there are other sites you could use that have a lower flood risk. Look at our Flood Risk Sequential Test Practice Note (pdf, 1.6MB) (opens new window) for more information and to see if this applies to you.

You’ll need to do a flood risk assessment as part of your planning application if your proposed development site is in a flood risk area or is larger than one hectare in size. Find out about flood risk assessments at GOV.UK. (opens new window)

If you’re applying for a major development, we recommend you carry out a Sustainable Drainage Assessment. This will show you’ve followed national and local policies. It should also explain how you’ll maintain your sustainable drainage system. If you get pre-application advice from us, you’ll need to show us a proof of concept for how your site will be drained.

Avonmouth Severnside Enterprise Area project
We're working with the Environment Agency and South Gloucestershire Council to improve flood defences. This is part of the Avonmouth Severnside Enterprise Area Ecology Mitigation and Flood Defence Project.

What to do about surface water drainage

You should consider surface water drainage at the start of your design process, as it is likely this will influence the rest of your design.

You need to use water management measures when carrying out development. This is to reduce surface water runoff and make sure it doesn’t increase the flood risk in other areas.

Sustainable drainage systems (SuDS) are a way of managing surface water to reduce the risk of flooding and deal with any pollution in the water. Find out about sustainable drainage systems at GOV.UK.

All new developments should use sustainable drainage systems where possible. If you’re applying for a major development, you’ll need a detailed sustainable drainage system strategy.

There are technical standards for sustainable drainage systems at GOV.UK.

You should look at the West of England Sustainable Drainage Developer Guide before preparing your planning application:

SuDS case studies

Green roofs:

Ponds, paving and other systems: