Forestry felling practices, if not managed carefully, can place pressures on rivers and lakes, and their wildlife, by generating large volumes of sediment which impact on water and habitat quality. It also can make water treatment in source drinking water catchments more costly and energy intensive because sediment run-off increases colour and turbidity. The colour arises due to higher concentrations of dissolved organic material, which gives water a distinct earthy colour, and the turbidity is tiny particles of solids suspended in the water.
Source to Tap opened a dialogue with Forest Service NI and Coillte (the agencies responsible for commercial forestry management in NI and Ireland respectively) on how current best practice for sediment reduction, during and after felling, could be further enhanced with additional, low-cost, repeatable measures, which we called ‘Best Practice plus’.
Download our Forestry Pilot Literature Review to find out more about current best practice forestry, felling silt reduction measures and the various methods reviewed and considered for our ‘Best Practice plus’ measures.
In partnership with Forest Service (DAERA) and Coillte, the project trialled various ‘Best Practice plus’ mitigation measures to reduce soil erosion and sediment run-off to watercourses draining forestry compartments/coupes. The project developed innovative, sustainable, and low-cost measures to mitigate the impact of forestry activities on water sources and provide evidence of the benefits of enhanced measures to protect water quality.
The trials proved that low cost, readily available materials can be used to create sediment reduction measures following harvesting operations and that further reduction of sediment loss can be achieved by combining current best-practice with additional measures, to benefit ecosystem services.
Download our Forestry Pilot Technical Report to find out more about the ‘Best Practice plus’ measures and their effectiveness in further reducing sediment loss from forestry felling operations.
Two sites trialled the sowing of cover crops, one in Killeter Forest, County Tyrone, owned by Forest Service (DAERA) and one near Pettigo, on the south side of Lough Derg, County Donegal, owned by Coillte.
The crops consisted of a mixture of native grasses which were sown in a 10-metre-wide strip along a 200-metre stretch of stream, running through recently harvested forestry plots at each site. The cover crops were used to help bind the soil to prevent sediment loss after the removal of the trees.
To find out more about cover crops and their effectiveness download our ‘How-to’ guide to Cover Crops.
A number of check dams, constructed from different materials were installed at Coillte and Forest Service NI sites. The check dams aimed to slow the flow and allow any sediment escaping from the recently harvested sites to settle out in the forest drainage channels, before reaching nearby rivers and streams. Monitoring was carried out upstream and downstream of the various check dams to evaluate the sediment reduction performance of each mechanism.
Geotextile dams were fitted in a stream draining a harvested compartment at Corgary Forest, Castlederg, County Tyrone and at Grousehall, Pettigo, County Donegal. Download our ‘How-to’ guide to Geotextile dams to find out more about their installation and their
Longitudinal log dams comprising large logs were laid in streams draining two harvested sites to test their ability to capture sediment in suspension. Download our ‘How-to’ guide to Longitudinal log dams to find out more about their installation and their effectiveness.
Small twig-bundle and timber dams were installed in forestry drainage channels at sites in Killeter Forest, County Tyrone, to slow and collect sediment, in suspension. Download our ‘How-to’ guide to Small twig-bundle and timber dams to find out more about their
installation and their effectiveness.
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 former gravel 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.
Download our ‘How-to’ guide to Settlement Areas to find out more about their installation and their effectiveness.
Results of the Forestry Trials
Download our Forestry Pilot Technical Report to find out the results of all our Forestry ‘Best Practice plus’ measures and their effectiveness in further reducing sediment loss form forestry felling operations.