Gareth Pedley describes a workshop carried out with volunteers from the Culdaff River Community Angling Club, the Inishowen Rivers Trust and the Loughs Agency to learn about techniques for tackling excessive bank erosion — and does some valuable work too!
Back in 2017, we undertook two days’ of walkover assessments on the Culdaff River catchment in Inishowen, Ireland for the local Culdaff River Community Angling Club, identifying a range of factors affecting the river, both positively and negatively, and highlighting several areas where simple improvements could be made by the Club. Through the efforts of a few enthusiastic members, and funding from the Waters and Community Office, in October 2018 the Club hosted a WTT habitat workshop (with Inishowen Rivers Trust and the Loughs Agency) to learn about techniques for tackling excessive bank erosion.
We chose two sections of high, steep riverbank, where a history of grazing and the associated lack of vegetation and tree regeneration has led to major bank destabilisation and erosion. It’s very easy to overlook the impact of grazing on erosion, but a loss of vegetation, tree regeneration and root diversity within the riverbank is often the underlying cause. Fencing-out livestock from the riverbank is therefore usually a pivotal part of protecting it long term and a requirement before investing anything more into its protection. Fortunately, for us on the Culdaff, the farmer agreed to fence off the river.
For three days, we installed bank protection at the two sites, using a range of natural, locally-sourced brash materials. The concept works by creating a line of brash along the base of the bank, dissipating the flow and encouraging silt to settle in among the brash, helping to rebuild the bank. This settled silt then makes an excellent place for trees and plants to take root and provides a footing for any slumping bank material, hopefully holding it in place long enough for it to consolidate and assist the natural bank regrading. The end goal is a well vegetated, naturally regraded bank that is more resilient to erosion.
First-off, we identified the bank line to be reinstated, dictated by the original and current bank line; posts were whacked in to mark our new line (photo below). It’s important to allow sufficient space inside the posts for the installed brash to go hard-down on the riverbed, to prevent it becoming undercut. When the brash goes in, we leave its riverside edge deliberately scruffy and irregular, helping to soften the edge and prevent undercutting — tidy, straight lines are a definite no no.
The lack of vegetation and smaller shrubs (from sheep grazing) was clearly evident at the sites, but the issue was really highlighted when within minutes of bringing freshly cut willow brash to site for the work, sheep began to browse it, despite all the grass in the field. It just shows how much sheep love to graze shrubs (particularly willow), even right next to lush grass.
At the upstream site, we used dead conifers, since other brash was in short supply. Unlike willow, cut conifer branches won’t regrow but, being really dense, they can be used to create a very tight ‘brash mattress’, with good potential for trapping very fine sediment. As much of the brash was only in short lengths, it was secured in place with regular posts driven horizontally into the bank over the brash and secured to the vertical posts along the new bank line (photo below).
At the downstream site, we used mostly willow brash which doesn’t pack down so tightly but the longer sections give greater structural integrity to the bank protection, with the added bonus of regrowth any bits buried in water or mud. That in itself can be good and bad: it often creates better long term stabilisation but does require subsequent maintenance. The longer lengths of willow available also meant that the structure could be secured with long willow branches over the top of the brash, held in place by a post at either end and, where necessary, an additional one in the middle.