Our second volunteering session at Yorkshire Wildlife Trust’s site at Broadhead Clough in Mytholmroyd was a particularly productive and highly enjoyable day. We had a great bunch of volunteers and trustees – about 15 in total, some regulars but encouragingly lots of new faces. The weather wasn’t great but at least the heavy rain of the previous days and weeks had subsided a bit.
We continued to work on the tributary we started worked on at our previous volunteering session in January. Splitting into two groups, one group worked on completing the leaky dams we had already started; the other group set to preparing for installing leaky dams at the higher reach of the tributary. Being able to climb like a mountain goat was a distinct advantage – the terrain was steep and slippery and entailed a considerable amount of climbing. Unperturbed, this group did a great job spotting sites to install leaky dams and collecting material to carry out this task at our next volunteering session. The group thinned out a small cluster of silver birch trees which were about end of their life – the trees had grown too close together and were competing for light and nutrients as well as blocking out light to the woodland floor. Opening the ground to more sunlight will increase the diversity of fauna and flora and the roughness of the vegetation will help slow the flow of rainwater as it travels in sheet flow down the hillside.
The second group of volunteers spent their time completing the four leaky dams previously started and adding a fifth to the lower reaches of the tributary. Our approach to building leaky dams is to only use natural material that is already on-site and preferably close by where we will put it to use. We site leaky dams according to the profile of the land and where it makes sense and is safe to do so. The availability of build materials is also a consideration. In terms of design and construction we try to build leaky dams to allow for ‘base flow’, the typical flow of a water channel, to pass through without interruption. The leaky dam is designed to slow the flow at higher than ‘base flow’. This means that when a potential flood event occurs there is storage capacity behind each leaky dam. Each of the leaky dams we have installed at Broadhead Clough will be capable of storing up to two cubic metres of water. As we are likely to install about ten leaky dams on this small tributary you can imagine the impact of doing this work on multiple tributaries across the catchment; cumulative small actions can make a big difference.
Posting the results of this work on social media generated an informative discussion about leaky dam design and construction.
We volunteer at Broadhead Clough on the third Sunday of every month. To book your place please see our Eventbrite page
We look forward to seeing you.
