Slow the Flow - Natural Flood Management at Hardcastle Crags

At Hardcastle Crags, we're working with nature to reduce flood risk. Most of what we do is achieved with the help of local volunteers and through partnerships.

The background

Take a walk through our woods after a heavy rain shower, and you’ll notice dozens of tiny streams which form on the steep valley sides. Since 2016, the National Trust has been working with our community partners Slow the Flow, using generous funding from the Environment Agency, to manage that water flowing through Hardcastle Crags. We’re using natural methods to try and reduce the impact this water has on our downstream neighbours.

Slowing the flow

Water from Hardcastle Crags runs into Crimsworth Dean Beck and Hebden Water, which then flows into the River Calder. We’re using logs and brash (branches and leaves) to create leaky dams across these smaller streams. These leaky dams give the water more time to pool and soak into the ground, rather than running straight into the rivers. We’ve also been thinning our beech trees in some parts of the woods. This allows more sunlight to reach the woodland floor, encouraging native woodland plants to grow. These plants then help intercept storm water on the steep valley sides. All this work is helping to reduce flood risk in the Calder Valley, thanks to an army of volunteers.

Volunteers have helped create hundreds of leaky dams
Slow the flow volunteers move a log into position to form a leaky dam
Volunteers have helped create hundreds of leaky dams

Helping wildlife

As well as reducing flood risk, our work in the woods is benefiting nature too. Our beech trees are being replaced by a variety of native species that are more suited to the woods, like oak and blackthorn. More light to the forest floor means smaller plants can flourish. We’ve also left behind deadwood habitats; a haven for roosting bats, nesting birds and insects. Our work is also reducing the amount of silt which reaches the streams and ponds. This helps amphibians, invertebrates and fish.

Volunteer days

Every two weeks, Slow the Flow and the National Trust run volunteer days where people can help us build leaky dams and help with other natural flood management tasks. The enthusiasm and hard work of local people means that together we’ve built over 500 leaky dams. Slow the Flow have helped bring hundreds of volunteers to work in Hardcastle Crags.

You can see evidence of our natural flood management throughout Hardcastle Crags and can help us monitor how our leaky dams behave in storms and change over time. Look out for numbered fixed-point photography posts with white tops – you can use your phone to capture images and submit these to

Find our more about Slow the Flow;

Slow the Flow are working with the National Trust
Volunteers walk into the woods
Slow the Flow are working with the National Trust