Flood Risk Assessments

Herrington Consulting specialises in delivering complex technical reports for challenging projects which are located in areas sensitive to flooding, drawing on excellent numerical modelling capabilities and a diverse technical workforce. Having produced over 2,500 Flood Risk Assessments in the last 18 years, including numerous Strategic Flood Risk Assessments, we have become an experienced market leader in flood risk management.

Our team of specialist consultants provide high quality expert advice and appraisals of the risk of flooding from rivers, the sea, groundwater, surface water runoff, sewers, reservoirs, and other man-made sources. We have a wide spectrum of clients, ranging from private developers to government organisations, and regularly work alongside large design teams.

How we work

Our proven track record of success is founded on our expertise and the ability this brings to providing bespoke and innovative solutions. Our flood risk assessments are not just a collection of data and mapping products that are simply downloaded from the internet – we provide expert advice and treat every project as a bespoke technical assessment. Our team of professionally qualified analysts and consultants are involved in the whole process and strive to deliver the best solution tailored for your site.

What is a Flood Risk Assessment?

Flood Risk Assessment (also known as an FRA) is a study to assess the risk to an area or site from flooding, now and in the future. It also assesses the impact of any change, or development, might have to flood risk  at the site and elsewhere. It may also identify, particularly at more local levels, how to manage those changes to ensure that flood risk is not increased.

Why is a Flood Risk Assessment needed?

An FRA is required to satisfy the requirements of National Planning Policy and Local Planning Policy for the location in which the development is sited. An FRA may also be required to outline the risk of flooding for potential purchasers of a site or home, to support insurance applications, or simply for homeowners looking to protect their home against the potential impacts of climate change.

When is a Flood Risk Assessment needed?

An FRA is required if a site falls within Flood Zone 2 or Flood Zone 3 as identified on the Environment Agency’s flood map. An FRA is also required if the site is greater than 1 hectare, or if the Local Planning Authority (LPA) deem it necessary, regardless of which flood zone the site is located within. For sites located within a London Borough, an FRA will also be required if the local authority’s Strategic Flood Risk Assessment (SFRA) identifies the site as being located within a Critical Drainage Area (CDA).

We also undertake assessments for sites in Scotland and Wales. The requirements in Scotland and Wales differ slightly to those in England but we would be happy to review your site to confirm if an assessment is required. As a starting point, an assessment will likely be required for sites in Scotland shown by the Scottish Environment Protection Agency (SEPA) online mapping to be in a risk area, or in Wales for sites shown by the TAN 15 Development and Flood Risk Development Advice Maps to be at risk. Our team or experts would be happy to assist with the specific requirements in Scotland and Wales.

How long does it take to prepare a Flood Risk Assessment?

As far as timescales are concerned, we are often constrained by the 20 working-day response time of the Environment Agency. Typically, we anticipate that the assessment will take between 3 and 4 weeks from commission and receipt of all required information. Notwithstanding this, we do hold copies of a number of Environment Agency modelling studies on our system and therefore, in some circumstances we may be able to move the process along quicker. Consequently, we would encourage you to contact us directly if time is of a major concern/constraint to your project.

How much does a Flood Risk Assessment cost?

The cost of a flood risk assessment is dependent on the nature of the development and site characteristics. We provide a bespoke service and prefer to gather as much information about the site and the development as possible, to enable us to provide a competitive and accurate free-of-charge quotation.

Why do I need a Flood Risk Assessment on a site that has not flooded?

Although a site may not have flooded in recent or living memory, the site could still fall within a flood zone, which may suggest that the site could flood during an extreme event in the future. In this instance, it is still necessary to submit an FRA so that the risk of flooding can be appraised in greater detail. For example, whilst a site might currently benefit from flood defences, flooding could still occur as a result of waves overtopping the defence infrastructure during an extreme event, or flooding might occur as a result of the defence failing. The FRA will identify and appraise these risks, which in some circumstances may involve undertaking detailed numerical modelling.

The development is only a change of use/extension, so why do I need a Flood Risk Assessment?

Even if the development is only a change of use, or an extension to an existing building, an FRA may still be required if the development falls within a flood zone on the Environment Agency’s Flood Zones Maps and is of a certain size. This is because the risk of flooding may be increased as a result of the development proposals.

For example, by changing the use of a building from commercial use to one of residential use, the risk to human life is considered to be increased as occupants are to be permanently located within a flood risk area. In the case of an extension, it may be that the development results in displacement of floodwater and consequently, flood storage compensation may need to be considered.

What is a Sequential Test?

The Sequential Test is a decision-making tool designed to steer new development to areas with the lowest risk of flooding. The Sequential Test is a key component of the hierarchical approach to avoiding and managing flood risk.

The Sequential Test does not technically form part of the FRA and undertaking it is the responsibility of the Local Planning Authority (LPA), however, we are increasingly finding that the LPA has insufficient resources to undertake the test and will request that the developer undertakes a Sequential Test to support the application.

It is important to consider the Sequential Test at the early stages of a project because if the Sequential Test shows there is another site available that is capable of delivering a similar scale of development in an area at lower risk of flooding then it is unlikely the council will support the application. The Sequential Test should be undertaken ignoring the presence of any proposed mitigation measures, therefore, even if the flood risk to a site could be mitigated (for example by raising internal floor levels), if another site at lower risk of flooding is available for development, the Sequential Test is considered to be failed.

Our FRAs do include a brief statement on the Sequential Test, which for many small developments is sufficient to satisfy the LPA’s requirements. Some larger or more complex sites do, however, required more detailed research into planning policy and historic applications and such work is outside of the scope of the FRA. We would, nevertheless, be happy to provide a fee quotation for undertaking or assisting with this work if required.

What is the Exception Test?

The Exception Test is applied following the application of the Sequential Test. If the Sequential Test is passed, it is necessary for any development located within Flood Zone 2 or 3 to then also consider whether the Exception Test must be applied. The application of the Exception Test will depend on the type and nature of the development, in line with the Flood Risk vulnerability classification set out in the NPPG.

The Exception Test consists of two parts – Part A and Part B as defined below. Both parts of the test will have to be passed for development to be allocated or permitted.

  • Part A: the development would provide wider sustainability benefits to the community that outweigh the flood risk; and
  • Part B: the development will be safe for its lifetime taking account of the vulnerability of its users, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall.

Undertaking Part A of the Exception Test is outside the scope of the FRA, however, our team or experts will work alongside you and your consultants to assist with this Part where applicable. The main aim of an FRA is typically to demonstrate that Part B of the Exception Test can be passed.

What is a Strategic Flood Risk Assessment?

A Strategic Flood Risk Assessment (SFRA) is a large scale assessment of the flood risk within the boundary of a local authority. In some cases, a combined SFRA may be prepared for adjacent local authorities. An SFRA identifies all of the different mechanisms and sources of flooding and is designed as a high-level strategic document to aid Local Planning Authorities in applying the Sequential Test, as well as to aid the preparation of site-specific FRAs. The SFRA document will often contain an array of flood and hazard maps that cover the Council’s district/borough and will also identify any specific planning policies that relate to the risks that have been identified. SFRAs will typically also confirm where a council has any specific requirements for undertaking FRAs.

Herrington Consulting Ltd have been responsible for the production of a number of SFRAs including for Canterbury City Council, Medway Council, Dover District Council, Folkestone and Hythe (formerly Shepway) District Council and Thanet District Council.

Numerical modelling

Some Flood Risk Assessments may require more detailed analysis to quantify the type, depth and velocity of flooding at a site and to facilitate this, we employ state-of-the-art numerical modelling software to provide high resolution flood simulations for a wide range of scenarios, including:

  • 1D and 2D river flows
  • Flood propagation
  • Coastal breaches and wave overtopping
  • Rainfall runoff and surface water flows

What our Clients say

“I have to say it is had been a very smooth process from start to finish.
 I definitely plan to use yourselves again on future projects.”

Private Client