Hardcastle Crags & Broadhead Clough

A river flowing shows how leaky dams slow the flow of water at various sections.

Slowing the Flow

Across both landscapes, volunteers from Slow The Flow have been rolling up their sleeves and helping protect Calderdale since 2016. Their Natural Flood Management (NFM) work is reducing flood risk by slowing water as it runs from the hillsides into the River Calder.

Formed in response to the devastating 2015 Boxing Day floods, Slow The Flow is a passionate, volunteer-led charity. Their volunteers protect Calderdale by using Natural Flood Management (NFM) to slow water running from the hillsides into the River Calder, reducing local flood risk. Their mission is driven by community spirit, resilience, and hope.

NFM began at Hardcastle Crags in summer 2016, and their exciting journey expanded to Broadhead Clough started in January 2024.

Implementation & activities

Hardcastle Crags

The goal is simple yet powerful: reduce downstream flood risk by working alongside nature. Active projects include:

Over 1,000 leaky dams built: Volunteers have crafted more than 1,000 woody dams by hand. They even use a local shire horse to move heavy logs without damaging the valley floor.
Strategic woodland management: By thinning out overgrown trees, our team opens up the forest canopy. This allows sunlight to reach the ground, prompting new plant growth that boosts biodiversity and naturally slows down rushing rainwater.

Broadhead Clough

Here, volunteers and the Yorkshire Wildlife Trust are restoring and expanding rare wet woodland bogs, precious ecosystems that act like giant natural sponges to slow down floodwaters.

The team has already installed 20+ leaky woody dams, cleared overgrown holly to bring sunlight back to the forest floor and maintained and rebuilt existing dams to keep the system thriving.

Together, these efforts are strengthening one of the South Pennines’ most important habitats.

Fallen tree branches and logs in the foreground at Broadhead Clough, with several people in high‑visibility clothing standing and working among the woodland in the blurred background.

Community Involvement

Slow The Flow is powered by people. Every dam built, every habitat restored, and every step taken up a steep woodland path reflects the dedication of local volunteers—many inspired by their own experiences of flooding.

Through grants and generous donations, and with support from the Community Foundation for Calderdale, Calderdale Council and the Environment Agency volunteers have installed a community weather station and flow monitors, with an upcoming dashboard to share real-time data with the public.

Some volunteers have been so inspired that they’ve gone on to study Natural Flood Management academically and even become trustees of the charity. This is community action at its finest.

River Level Recorder box at Broadhead Clough

Impact & Outcomes

Hardcastle Crags

Studies show great success here. The hand-built dams slow down flood water by 30 to 105 minutes. This gives local towns vital time to get ready when it rains.

Broadhead Clough

Tests are still new here, but the results already show great signs. The woods are healthier, nature is growing, and the land holds more water.

This work does more than fix the land. It helps volunteers gain confidence and learn new skills. It also brings peace of mind to local people. They can rest easy knowing these natural defenses protect their homes day and night.

Close‑up of dried bracken on the ground at Hardcastle Crags, with several people in high‑visibility clothing working in the blurred background among trees.

Looking Ahead

Slow the Flow will regularly return to both Hardcastle Crags and Broadhead Clough to maintain and expand these vital natural defences. As local enthusiasm grows, Slow The Flow also plans to spread natural flood management education and activities beyond Calderdale in the coming years.

Get Involved!

You can help protect our communities, learn new skills, and make a real difference on the ground. Visit https://www.slowtheflow.net to volunteer, donate, or learn more.