Natural Flood Management

Flooding: a growing risk

Hundreds of thousands of us live and work in areas at risk of flooding,with 165,000 Londoners at risk from rainfall alone. In our towns and cities, we have lost water storage by replacing landscapes with artificially impermeable surfaces stopping water soaking into the ground, so more water flows to drainage networks. And we have straightened our river channels so that they now move water very quickly.

With climate change, the risk of flooding is increasing. Winters are becoming warmer and wetter, and there are also more extreme rainfall events during the summer in London. Conventional hard flood defences can reliably protect some communities, but are often very expensive and can harm the environment: destroying aquatic habitat and disrupting natural flood alleviation and water purification processes. Hard defences can also increase the risk of flooding downstream.


Trialling Natural Flood Management in London

Healthy river catchments store water in the landscape, in uplands and on river floodplains, reducing the volume and slowing down the flow of water downstream.

Natural Flood Management (NFM) is the practice of using and enhancing the natural landscape’s ability to do this. The aim is to work with nature to restore the natural functioning of river catchments, but where that isn’t possible, to emulate natural processes. Depending on the character of the local area, that could involve creating storage ponds, planting trees, reducing soil compaction, restoring meandering rivers, creating wetlands, or leaky dams with local woody materials.

NFM trials in several rural areas have demonstrated effective reductions in flood peaks, but there are not enough real world examples, especially in urban areas.  That is why we are working with the Environment Agency and Lead Local Flood Authorities to pilot NFM in greater London. The trial, funded by by DEFRA (Department for Environment, Food & Rural Affairs) will investigate whether it can work as a method to protect homes, businesses and valuable, productive land.

Thames21 is trialling NFM in four areas in London: Hillingdon, Harrow, Enfield and Havering (the latter as part of the Land of the Fanns project). Working in partnership with local communities and organisations, we will identify suitable locations to slow down and store floodwaters, improve local habitat diversity and monitor the outcomes.



Working with nature and communities to tackle flooding

Local communities have valuable local knowledge of the land which statutory organisations can learn from. We believe that involving communities will lead to better flood-proofing solutions.

By creating many small-scale flooding interventions, we aim to slow the flow of floodwater and store it higher up in river catchments, especially during and after periods of heavy rainfall. Creating natural flood barriers will allow more water to soak into the ground, complement existing flood defences and protect more land, homes, business and infrastructure from flooding in London.

It also has the potential to reduce soil erosion, create more habitat for birds, mammals, fish and invertebrates, to store carbon and improve access to enhanced green space, helping boost wellbeing and quality of life for urbanised communities.

With the help of a designated app, professional modelling and citizen scientists, the programme will be intensively monitored and evaluated over the next three years, and the results fed back to DEFRA and the wider public.

The aim is for what happens in London to help inform best practice nationally on how to respond to the increasingly urgent threat of flooding: how to reduce existing flood risk and future-proof ourselves from the increased flood risk in future.


Volunteering and training opportunities

There are many ways that you could get involved in any of the four NFM projects across North London. These include helping to install leaky dams, monitor their effectiveness at storing water and tracking changes in habitat, soil moisture and ecology that result from their installation.

We post all volunteering events on our events calendar and we will be running more NFM training courses this summer. There are also ad hoc volunteering opportunities for monitoring that plays a vital part in the project.

For more information please contact Stephen Haywood. Email:

Meanwhile, we encourage you to take photos of our leaky dams and NFM installations in action and send them to us using our Slow Flow NFM app, by email or social media to @Thames21 with hashtag #Thames21NFM.