Flood risk assessment for planning applications

Working with an experienced flood risk specialist, you increase your chances of planning approval success.

At Ambiental we generate flood risk assessments (FRA) to meet both basic planning application requirements and to help address complex flood risks that could stand in the way of you getting planning approval. Our services can help you:

  • reduce costs associated with planning delays and design changes
  • speed up the planning process through improved communication with the relevant environmental governing body and local planning authorities
  • improve your chances of securing planning permission.

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Do I need a flood risk assessment?

To satisfy national planning policies you need to submit a flood risk assessment (FRA) or a flood consequence assessment (if you are in Wales) with planning applications for any site over 1 hectare. You also need to submit one for any property or development of any size that is being planned in a zone 2 or zone 3 flood risk area.

The flood risk assessment must show:

  • what the flood risks are and how they could change
  • whether your project will increase flood risk
  • how you plan to manage any flood risk.

We address the first two points by using the most up-to-date and best available flood data. To support you in showing how you plan to manage any risk, we also offer design suggestions, drainage strategies or flood response plans.

To check if your site is in a flood zone, you can contact us or use the country-specific flood zone maps below:

For country-specific policies on flood risk assessments or flood consequence assessments see:

Northern Ireland: Planning Policy Statement (PPS-15) ‘Planning and Flood Risk’

What flood risk assessment services do we offer?

As a flood risk consultancy we tailor any flood risk assessment to address specific issues or requirements that your local planning authority might have.

We frequently consult on and undertake:

  • Flood risk assessments for planning applications under NPPF (formerly PPS25), SPP, TAN 15, and PPS-15
  • 1D computational flood modelling to support planning applications
  • 2D computational flood models to support planning applications
  • Flood risk assessments specifically for proposed renewable energy and energy generation sites
  • Flood risk reports to gain credits for Code for Sustainable Homes or BREEAM accreditation
  • Groundwater flood risk assessments
  • Basement impact assessments
  • Sequential testing
  • Exception testing
  • Surface water drainage strategies (SuDS)
  • Flood response plans and flood warning and evacuation plans



What will the flood risk assessment include?

We tailor each of our reports to match your requirements and will advise you on what you need. For all of them we will combine detailed information about previous flood events, considering water from rainfall, groundwater, rivers and the sea.

Once you give us the information on your plans for the development of the site, we liaise with the governing body (Environment Agency in England, Scottish Environment Protection Agency, National Resources Wales, or the Rivers Agency in Northern Ireland) and your local planning authority to assess their exact requirements. We then request the data we need from the governing body and other sources to assess the flood risk.

At every step we can advise you on design approaches to reduce flood risk. We often act as intermediaries between architects and the EA, passing on design solutions to strengthen your planning approval application.

Below are further brief outlines for what a typical report might cover:

Flood risk assessment reports for NPPF (formerly PPS25), SPP, TAN 15, and PPS-15

The typical flood risk report for planning purposes will include:

  • a clear assessment of the likelihood and extent of potential flooding on site and within the surrounding area
  • a summary of any existing information or history of flooding on the site
  • details of any existing flood alleviation measures which could protect the site
  • outline recommendations for surface water management and sustainable urban drainage system (SuDS)
  • recommendations for measures which may reduce the risk of flooding.

1D and 2D computational flood modelling reports

You may need flood modelling as an additional part of your FRA report if your site falls within a flood risk zone 2 or 3 (medium or high risk) and is close to a river, or to a small river, watercourse or drain for which no detailed flood modelling is available. This assessment requires hydrological modelling to establish the extent of the flood risk. We will need to visit the site to inform the detailed hydraulic modelling we use.

In some situations it can benefit the planning application if the flood risk assessment includes detailed flood modelling of various worst-case scenarios, for example a failure or overtopping of flood defences. We do this using flood modelling software. The output of this includes data and flood maps for the flood depth, velocity and hazard that would result from the potential breach in the flood defences.

Groundwater flood risk assessments

These are sometimes required if a property or asset is being affected by groundwater flooding or where the local planning authority has flagged up groundwater as a potential issue. We develop a conceptual model of the groundwater on site so that we can assess the risk to the property or asset and to provide a basis for designing mitigation measures if required. We review data on the geology, topography, historical land use and hydrology of the site to provide a detailed assessment of the risk of groundwater flooding for the property or asset. In some cases we may need to visit the site to collect data.

Basement impact assessments

Several London boroughs now require that you assess the impact that a basement construction will have on neighbouring properties and the wider environment. Our concise site-specific, basement impact assessment reports will put any risk posed by your proposed basement into perspective.

We consider all relevant local planning requirements in coming to an informed opinion on the likely impact of a basement construction at your property or asset. We give a firm conclusion, and if uncertainties remain, we will recommend how these can be confidently resolved.

Reports to gain credits for Code for Sustainable Homes or BREEAM

See flood risk assessments for environmental accreditations

Sequential testing reports

A sequential test is used to steer new developments towards areas with the lowest possibility of flooding. If your site has not been allocated or tested then you may need to do this as part of your planning application.

This requires a comparative analysis of the flood risk to your development site compared to that of other potential sites that fall within the comparison area. Our consultants can advise you further.

Exception testing

For developments in flood risk areas you may need to demonstrate that the development provides additional sustainability benefits which outweigh the flood risk. The flood risk assessment must also show that the development:

  • will be safe for its lifetime
  • is considering the vulnerability of its users
  • will not increase flood risk elsewhere
  • will seek to reduce flood risk overall.

Our flood risk consultants are experienced in conducting the necessary evaluations for exception testing.



How long does a flood risk assessment take?

FRAs for planning often rely on data supplied by the Environment Agency, the Scottish Environment Protection Agency, national Resources Wales, or the Rivers Agency in Northern Ireland. Over the years we have developed a good working relationship with these agencies. This means we can deliver flood risk assessments both quickly and efficiently.

If you are short on time we can write a letter to the local planning authority telling them that we have been commissioned and have requested the necessary data. The local planning authority will sometimes put the application on hold then until they receive the flood risk assessment report though.

A fast-track report

If your timescales are very tight we can help. We can complete a fast-track flood risk assessment to help get your planning application validated, and then complete the full assessment and report when we have all the data from the relevant agency. This helps avoid any delays in the planning application process.

Not sure what you need?

Daniel Cook is one of our most experienced flood risk consultants. Call him for advice on a flood risk assessment for your property or asset.

Call Daniel on 0203 857 8540 or email fra@ambiental.co.uk

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