The Source to Tap forestry pilot is aimed at implementing and monitoring methods of sediment reduction in the Erne and Derg Catchments at sites where harvesting is taking place. These methods are in addition to current forestry best practice already observed by Forest Service NI and Coillte, the agencies responsible for commercial forestry management in NI and Ireland respectively.
Sediment run off increases colour, which is dissolved organic material which gives water a distinct earthy colour, and turbidity, which are tiny particles suspended in the water. This can lead to challenges during drinking water treatment and can potentially impact upon fish spawning grounds.
The focus of these trials is to test measures with the potential to either reduce the volumes of sediment escaping to nearby watercourses or to slow the flow of the receiving watercourse and allow any sediment run-off to settle out.
The results of these pilots will be communicated to forestry managers and operators. Monitoring was undertaken using Time Integrated Sediment Samplers (TISS) upstream and downstream of the mechanisms deployed. Seven mechanisms were trialled at six Forest Service (NI) sites and four Coillte sites. A control site on Coillte managed land, was also monitored during harvesting operations which had no Source to Tap intervention.
Two sites are being trialled with cover crops, one in Killeter Forest owned by Forest Service NI and one on the south side of Lough Derg near Pettigo owned by Coillte.
The crops consist of a mixture of native grasses which were sown in a 10 m wide strip along a 200 m stretch of stream, running through the recently harvested forestry sites. They aim to help bind the soil to prevent sediment loss after the removal of the trees.
A number of check dams, constructed from different materials have been fitted in Coillte and Forest Service NI sites. Geotextile dams were fitted in a stream draining a harvested compartment at Corgary, Castlederg and at Grousehall, Pettigo.
Large logs were laid in streams draining two harvested sites to create “longitudinal log dams” and two further sites in Killeter Forest were used to trial small check dams constructed from either small timber logs or brash bundles.
The check dams aimed to slow the flow and allow any sediment escaping from the recently harvested sites to settle out in the watercourse. Monitoring was carried out upstream and downstream of the dams to evaluate the sediment reduction performance of each mechanism.
Peat dams were also trialled during 2019 but were less successful due to intense summer storms in July 2019.
Minor groundworks took place on a Coillte site near the town of Pettigo making use of the existing landscape to create a settlement area in a borrow pit. High flows from the river were diverted via a newly created channel into the settlement area to slow the stream flow and settle sediment in the base of the settlement area.
Monitoring was carried out above and below the settlement area to evaluate its performance. Results will be made available in a technical report in 2021 at the end of the pilot.