Ditch Blocking

Drainage ditches will be blocked in and around blanket bog on moorland within the Berwyn and South Clwyd Mountains SAC. The restoration work will take place over a total area of more than 4,500 ha, the majority of which is located on the RSPB Lake Vyrnwy Reserve on land owned by Severn Trent Water.

In each year of the project, an estimated 18km of drains will be blocked using various techniques. This will lead to the blocking of a total of 91km of drains over the five years of the project. The drains will mainly be blocked using heather bales to create dams. The drain will be initially shaped using a Hymac digger to fit the shape of the bales. The bales will then be covered with a layer of peat and the surface vegetation replaced. On shallow slopes, the dams will be placed every 5-10m whilst on steeper slopes the drains will be completely filled with heather bales. The spacing of dams on steeper slopes must be close enough to limit flow of water along the drain between dams, and reduce the potential for the water pressure behind the dams building up. As well as raising the water table, it is also hoped that the dams will provide 'bridges' for sheep crossing the drains. The rationale for using heather dams has arisen from a two year trial study carried out on the RSPB reserve at Lake Vyrnwy and consultation with other, similar projects around the UK and Europe. To create the bales for the dams, heather mowing of 2m wide strips, on dry heath, 5m either side of the drain or close by will be carried out. This heather will then be baled and used in the dam.

At some locations, where the drains are small and the slope very shallow, peat dams will be used. In other areas, it may be possible to collapse the sides of the drains rather than filling them directly. Plastic dams will only be used where necessary, as the project is keen not to introduce non-organic materials into the environment.