Salmons Brook: Cutting flood risk in Enfield

Flooding poses a threat to people, property and productive farmland across the UK and this risk is increasing due to the effects of climate change. This is no different in Greater London where thousands of us live or work in areas threatened by flooding.

Parts of the borough of Enfield, north London, have suffered from severe flooding in the past. The Salmons Brook Flood Alleviation Scheme was completed in 2016 at a cost of £15.3 million and has reduced the risk to more than 2500 homes. However, some areas still remain at a higher risk. Now, a Natural Flood Management (NFM) scheme is being piloted in Enfield to investigate if further reductions in flood can be achieved at a reasonable cost.

 

The Salmons Brook Natural Flood Management project

NFM is the practice of using and enhancing the landscape’s ability to store and slow flood waters using natural measures. Depending on the local area, NFM could involve creating semi-natural water brakes with large wood, such as leaky dams; wetlands; planting trees; or reducing soil compaction to make it easier for rainwater to infiltrate and be stored in the ground. Hydrogeological modelling is being carried out by Thames21 to help us understand the best places in the catchment to install these features to have maximum impact on reducing flood risk.

A leaky dam: one example of natural flood management

The Salmon’s Brook Catchment

The Salmons Brook NFM project is concentrating on the upper, higher elevation area of the Salmons Brook catchment within the Greenbelt; north of Enfield Road, through Trent Park and as far as the Ridgeway Road, where there is a large amount of agricultural and park land. This includes the Merryhills Brook and the Leeging Beech Gutter.

Local communities have valuable local knowledge of the land which statutory organisations can learn greatly from. We believe that by working together we can create better solutions to flooding issues that are multi-beneficial and long lasting.

By installing many small NFM interventions appropriate to location, we aim to slow the flow and store water higher in the rural areas of the Salmons Brook catchment, especially in and after periods of heavy rainfall.  Allowing more water to infiltrate into the ground will reduce the amount of water flowing downstream and complement existing flood defence structures – giving an increase in flood protection to property and infrastructure.

The Salmons Brook NFM programme is a partnership between the London Borough of Enfield Council, the Environment Agency, and Thames21. We are turning to land owners, farmers, Friends of Groups, and other interested parties to help us plan and install these interventions. In addition several complimentary projects have arisen that have brought extra partners to the overall project. These include various parcels of tree planting, habitat and flood storage pond creation, and a cross-political border landscape-scale land use management review.

 

The Multiple-benefit approach

This project (alongside similar projects in Hillingdon, Harrow and Havering that Thames21 is working on) is being intensively monitored and evaluated to enable the results to be fed back to DEFRA in March 2021. We aim to demonstrate the costs, benefits and lessons learnt of carrying out NFM in the urban fringe – and this will inform best practice nationally.

As well as increasing protection from flooding for at least 20 more properties in Enfield, our vision for the Salmons Brook is that the scheme will help improve the health of the river by regulating flows, stabilising the soils on the land, and enhancing the value of the green space for wildlife and people.

Using specially designed visual surveys, project partners are able to record how the features are performing in different weather and flow conditions as well as report any changes observed in the ecology. The MoRPh citizen science survey method is monitoring changes in geomorphology over a longer period of time to reveal how the streams habitats are changing.

Digital monitoring devices called Freestations are also providing vital data of the water level changes with increased rainfall before and after NFM interventions have been installed, sending data via telemetry to online databases. More information on these can be found here.

Freestation L181 – Live data

 

Volunteering opportunities

There are many ways that you could get involved in this project of one of our other 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 the second NFM training course 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: Stephen.Haywood@thames21.org.uk

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.

This will enhance our understanding of their performance and be a visual check to compare with our Freestation data.