Guidance

Defining which areas and properties benefit from investment

Published 3 March 2026

Applies to England

1. What a benefit area is

A benefit area for a flood risk intervention refers to the geographic area that would experience measurable flood or erosion risk benefits because of the investment. It should cover any area of land that would benefit from the investment.

The output of defining a benefit area is a shapefile which defines the spatial area benefitting.

1.1 What types of properties benefit from investment

The properties benefitting from flood and coastal erosion risk investment includes the number of residential and non-residential properties.

Examples of residential properties include:

• houses
• apartments
• caravans with an address
• care homes

Examples of non-residential properties include:

• schools
• hospitals
• industry
• retail
• leisure

Properties may benefit from investment if projects result in a reduction in the:

• likelihood of flooding
• depth of flood water, for example from property level interventions
• rate and extent of coastal erosion risk

The number of properties benefitting from investment can be used to calculate the economic benefits of an investment.

The 2025 flood and coastal erosion risk management (FCERM) funding policy sets out that existing properties are to be included in the property counts benefitting from investment. This includes those built after 2012. Only properties that are constructed should be counted. Properties that are included in plans but not yet constructed should not be counted.

2. How to define an area benefitting from investment and count the properties within it

The next section explains the methods used to inform the:

• benefit area
• number of properties that would benefit from the investment.

The methods depend on the:

• source of risk
• type of project planned

2.1 For projects building new assets 

For these projects a map identifying the areas of risk can be found using:

• Check your long term flood risk – this shows flood risk from rivers and the sea and flood risk from surface water
• National coastal erosion risk mapping – this shows a map of coastal erosion risk

The maps can help you consider the extent of the area benefitting from an investment.

Once the location of risk is known, you can draw a polygon to define the spatial extent of the investment benefit area. Table 1 shows you where you can draw and download these polygons. The links are also to data for those with or without access to GIS software. Environment Agency staff can also use AIMS:PD Spatial or internal mapping tools.

The benefit area should be based on the current mapped extent of flooding downstream or landward of the defence should it be built.

Table 1: Risk source and how to draw a polygon 

Risk source	Use if you have GIS software	Use if you don’t have GIS software
For risk of flooding from rivers and the sea	Download Risk of Flooding from Rivers and Sea spatial data on the Defra Data Services Platform	Draw a polygon on the Defra Data Services Platform
For risk of flooding from surface water	Download Risk of Flooding from Surface Water spatial data on Defra Data Services Platform	Draw a polygon on the Defra Data Services Platform
For coastal erosion	Download National Coastal Erosion Risk Mapping (NCERM) spatial data on the Defra Data Services Platform	Draw a polygon on the Defra Data Services Platform

Counting properties can be done in different ways. Proposals should consider the scale of impact they are reasonably likely to have and count properties where risk is reduced due to the investment.

For smaller areas benefitting, the number of properties can be counted from:

• maps
• reports
• local knowledge

If you have GIS software available, you can use the National Receptor Dataset (Partner Version) to count the number of properties that would benefit. You must be a member of the Public Sector Geospatial Agreement (PSGA) and be logged into the Defra Data Services Platform to access the National Receptor Dataset. If you are not a member of the PSGA and are not logged in the link will not work.

You can use postcodes to determine the number of properties benefitting from investment if:

• the area benefitting from investment is large
• GIS software is not available

For flood risk from rivers and the sea, you can use postcodes in areas at risk to help identify the number of properties at risk within the postcodes within a benefit area. This is available from the Defra Data Service.

Postcode data can also be downloaded from the:

• Open Geography portal
• Postcode resident and household estimates, England and Wales: Census 2021 - Nomis - Official Census and Labour Market Statistics

You should refine the number of properties that could benefit from the investment using:

• local knowledge
• historic flood information
• local reports

Your proposals should:

• consider the scale of impact they are reasonably likely to have
• only count properties which are likely to see a reduction in flood probability and flood impact due to the investment

For coastal erosion risk, projects should use the present day, no future intervention 2055 and 2105 outlines to count properties that would benefit. You should supplement these datasets with:

• shoreline management plans
• local knowledge
• historic flood information

This will help you to refine the number of properties that could benefit from the investment.

2.2 For projects refurbishing or replacing existing assets

For the refurbishment or replacement of existing assets, the benefit area should reflect the flood outline that would otherwise see an increase in flood probability if refurbishment or replacement work did not occur.

Property counts should be based on evidence and kept proportional to the scale of work and standard of protection. Two examples of a proportionate approach are provided below.

Example 1 - the refurbishment of a small defence offering a low standard of protection

This might only offer measurable benefits to areas shown to be at high or medium risk. However, refurbishment of a much larger defence may also offer measurable benefits to areas shown to be at Low risk.

Risk areas are defined by the Risk of Flooding from Rivers and Sea dataset

Example 2 - a large flood storage area

This may reasonably expect to provide benefits across high, medium and low risk areas for a significant distance downstream of the defence. A smaller investment such as a short, raised embankment may only expect to provide benefits across a small area and perhaps to only high and medium areas.

Risk areas are defined by the Risk of Flooding from Rivers and Sea.

For refurbishment or replacement projects managing flood risk from rivers and sea

The present day Flood Map for Planning - Flood Zones will help you to consider the area of the land that would be at risk if the asset failed. This is because existing defences are not included in these outlines. You should use this alongside the data sources referenced above.

For refurbishment or replacement projects managing coastal erosion

Use the National Coastal Erosion Risk Mapping (NCERM 2024) present day, no future intervention 2055 and 2105 scenarios to count the number of properties benefiting. Projects should supplement this approach with expert knowledge and local analysis to refine the number of properties benefitting. For example, the scale and shape of the benefit area that is used with the coastal erosion data to count properties benefitting may vary across different locations due to local factors.

2.3 Natural flood management

For standalone natural flood management (NFM) projects under £3 million that aim to reduce flood risk from river and/or surface‑water flooding, begin by estimating the effective storage created by the NFM measures.

Effective‑storage multipliers, provided in Chapter 3 of estimating the benefits of natural flood management, can be used to convert design storage into effective storage for this purpose. Alternatively, the NFM benefits calculator can be used to calculate these values.

Once you have estimated the effective‑storage volume, you should apply a standard downstream distance to identify the places that may benefit. The standard distances are:

• projects providing 200 to 5,000 m³ of effective storage will benefit areas up to 1 km downstream
• projects with 5,000 to 10,000 m³ will benefit areas up to 5 km downstream
• projects with more than 10,000 m³ will benefit areas up to 10 km downstream

The benefitting area is the stretch of catchment from the most downstream point of the NFM interventions to the relevant downstream distance. This includes land on either side of the river falling within the high-risk areas defined by the:

• Risk of Flooding from Rivers and Sea map
• Risk of Flooding from Surface Water map

For standalone NFM projects under £3 million that aim to reduce sea‑flooding or erosion risk, the benefitting area can be calculated as the area:

• below the NFM intervention that falls within the high-risk area or
• within the present day, no future intervention 2055 or 2105 outlines of the National Coastal Erosion Risk Map (NCERM).

The benefitting area for NFM projects which are part of a project with hard‑engineered interventions or other resilience measures, should be based on the benefits of the main intervention or assets.

2.4 Sustainable drainage

Benefit areas and property counts should cover areas where surface water flood risk is likely to be reduced. SuDS primarily reduce risk in smaller, more frequent flood events. Benefit areas and property counts should focus on areas defined as high risk by Risk of Flooding from Surface Water. You should use this unless there is evidence that the investment would also provide benefits to medium or low risk properties.

Benefit areas should exclude locations that only receive wider benefits without a measurable reduction in surface water risk. For example, greening or biodiversity gains. SuDS features that contribute to wider environmental or amenity benefits may also be located outside the surface water benefit area itself.

2.5 Property flood resilience (PFR)

Benefit areas and property counts should focus on areas defined as high risk by:

• Risk of Flooding from Rivers and Sea map
• Risk of Flooding from Surface Water map

Areas where there is a risk of flooding greater than 60 cm may not be suitable locations for PFR.

2.6 Groundwater

Project benefit areas should use local knowledge, reports and historic flood information to define the number of properties that could benefit from investment.