Slow The Flow Calderdale

Third Sector • Calderdale

Exploring natural flood prevention measures and solutions to slow the volume of water flowing into the River Calder, in West Yorkshire.

Slow the Flow's story

Over Christmas and Boxing Day 2015, Pennine areas in the North of England had over 60mm of rainfall in 24 hours and some locations had over 100mm. During this time, the Calder Valley suffered the most significant flooding event in recent times. 2,781 homes and 4,416 businesses were flooded all along the Calder Valley causing unparalleled and significant damage. Recorded flooding events in the Calder Valley go back as far as 1615, so it’s clear that some action needs to be taken to look at why this is happening.

As the climate crisis continues to worsen our flooding problems, Slow The Flow (STF) was founded by local residents to look at the issue of why and how the Calder Valley floods; to look at natural flood prevention measures and solutions to slow the volume of water which comes down the hillsides into the River Calder. Since 2016, STF has worked as a charity to advance the education of Natural Flood Management (NFM) and Sustainable Drainage Systems (SuDS) approaches, which are an essential part of the toolkit to mitigate against the consequences of future flood events.

Members are mostly local and are all volunteers giving up their time to secure a future for the Calder Valley and all who live, work and visit locally. We carry out practical work contributing to flood prevention in the Calder Valley, whilst enjoying the outdoors. We will not stop flooding events, but if we work together, we can reduce the risk of serious flooding. Building walls are not the only solution and our measures will support traditional measures.

STF’s most successful project to date is at local National Trust site Hardcastle Crags. Volunteers have built over 859 woody leaky dams with another 100 built by local contractors in harder to reach locations. These interventions mimic the natural environment by pushing excess water onto the forest floor, slowing its flow to the main river channel. This helps to reduce the height of the flood peak in our towns and villages further down the catchment, at Hebden Bridge, Mytholmroyd and beyond. These leaky dams also provide more environment benefits like diversifying natural habitats for animals, insects, flora and fauna. Dedicated teams of volunteers have worked tirelessly every month to build more than 10-12 new dams every month and there are plans to continue this work here for many years to come.

In addition to activism, STF educates about NFM and SuDS; providing people with ways to ‘slow the flow’ of flooding themselves through online resources and support programmes for people with land from small gardens to larger farmlands.

STF’s local ‘Artist In Residence’ Anne Fox records the group’s flood prevention interventions and to produce a body of work that reflects, celebrates and raises awareness of the unique and fragile nature of our environment and helps promote the ways in which people can work together to make positive changes. Annes’ work with STF can be found at:

Useful learnings from Slow the Flow

As a small organisation of volunteers we were motivated by the need to do something (anything!) active. We were supported by individuals with technical advice and links. The early evidence we gathered through student dissertations enabled a pilot programme to be funded by our partners, the National Trust. We found there was a myriad of consents and organisations that we needed to engage with at the outset.

It was important to develop a track record for competence early on within the process and here we were supported by organisations, such as the National Trust and institutions such as the University of Leeds and University of Huddersfield. As we have developed we have focused on education- this is an area where we need to engage future generations. It is also an area within which the (statutory) organisations are not active. It also made our application to the charity Commission more straightforward. Our future strategy (including our fundraising) strategy has stemmed from this. We have needed to become quite agile in terms of funding and manage our own expectations.

Slow the Flow's metrics

So far:
1000 volunteers
1000 leaky dams
40 hectares of woodland managed
10 attenuation dams
20 schools worked with

Feeling inspired? Discover more about this story...



Response to climate crisis

Mitigation & Adaptation




Third Sector, less than 9 people

Shared by

Carbon Copy

Updated Feb, 2024

Recommended for you

  • Climate Friendly Bradford on Avon

    Climate Friendly Bradford on Avon

    Working in association with local organisations to become carbon neutral by 2030.

    Buildings & Places
  • Earth Cubs

    Earth Cubs

    Educating young children about climate, sustainability and the environment.

    Buildings & Places
  • Hay Community Assemblies

    Hay Community Assemblies

    Running community assemblies to make better decisions that serve the needs of all.

    Buildings & Places
  • NWG Innovation Festival
    Newcastle upon Tyne

    NWG Innovation Festival

    Finding innovative solutions to water industry challenges.

    Buildings & Places