Natural Flood Management evidence
Source: gov.uk (2025-02-12)

Summaries of our latest evidence on natural flood management (NFM)

This page contains the summaries for the 2024 Working with natural processes evidence directory.

The research report and literature review can be found on the research project page (https://www.gov.uk/flood-and-coastal-erosion-risk-management-research-reports/working-with-natural-processes-to-reduce-flood-risk-2024).

Working with natural processes (WWNP) aims to protect, restore and emulate the natural functions of catchments, floodplains, rivers and the coast to reduce flood risk. It is also referred to as natural flood management (NFM).

WWNP takes many different forms. It can be applied in urban and rural areas, and on rivers, estuaries and coasts. Measures can be stand-alone or in combination with traditional engineered structures.

What we did

We published the Working with natural processes evidence directory in 2017 (https://www.gov.uk/flood-and-coastal-erosion-risk-management-research-reports/working-with-natural-processes-to-reduce-flood-risk). Since then, researchers have learned more about WWNP measures, their effectiveness in reducing flood risk and providing wider benefits.

We reviewed research from 2017 to 2023 and produced an update to the evidence directory. The update allows practitioners to access recent information on WWNP measures.

In the summaries above, we provide an overview of the evidence around WWNP measures.

We cover 17 individual measures that are grouped into 4 categories.
- River and floodplain management
- Woodland management
- Run-off management
- Coastal and estuary management
We added 3 new WWNP measures to this update because there was an increase in scientific studies in a UK context since 2017.

The new measures are:
- beavers (added to river and floodplain management)
- reefs (added to coastal and estuary management)
- submerged aquatic vegetation (added to coastal and estuary management)
Multiple benefits

We summarised the benefits for each WWNP measure using 8 indicators. The categorisation of these benefits changed since 2017 to reflect Defra’s Enabling a Natural Capital Approach (ENCA) (https://www.gov.uk/guidance/enabling-a-natural-capital-approach-enca). In these summaries, flood risk reduction is used instead of flood regulation.

The 8 benefits fall under 3 categories.

Social – flood risk reduction, water resources, air quality

Environmental – biodiversity, soil, climate regulation, water quality

Cultural – amenity value

We gave each measure an approximate score for the different benefits. These estimates are broad brush and will vary depending on local factors and the context of a measure in the broader landscape.

They are visually represented as a benefits wheel. The multiple benefits wheel tool is only intended to be used as a visual aid to suggest where additional benefits may be sought when implementing the measures for flood risk. It should not be used as part of detailed quantitative analysis or optimisation of options.

For more information about the multiple benefit categories refer to the 2024 Working with natural processes evidence directory report (https://www.gov.uk/flood-and-coastal-erosion-risk-management-research-reports/working-with-natural-processes-to-reduce-flood-risk-2024).

Scientific confidence

We used a scoring matrix to define how confident we are in the science that underpins each WWNP measure. We assigned a confidence limit (either high, medium or low) to the effect that a measure has. We based this on the degree of agreement of scientific studies and the amount of information that is available.

We are not intending to discourage new research if a measure is rated with ‘high confidence.’ A high level of confidence does not necessarily mean a high level of benefit. It is simply that we are highly confident in the effect (either positively or negatively).

Terminology

For consistency, we adopted the following terminology.

For catchment size, the areas were:
- small catchment ≤10 km2
- medium catchment ≤100 km2
- large catchment ≤1,000 km2
The scale of a flood event is measured in annual exceedance probability (AEP). This means that a:
- small flood event is ≥ 10% AEP
- medium flood event is 10%-1% AEP
- large flood event is ≤ 1% AEP