In certain circumstances, riverbanks can become quickly eroded by the action of the river against the face of the bank. This can result in excess silt entering the watercourse causing damage to the river habitat. The eroding bank can also be exacerbated by pressure from stock grazing and lack of trees and other vegetation to bind the riverbank. The use of brash bundles is one of the techniques used as part of Pearls in Peril Project to address this issue.
Brash bundle technique
Posts are driven into the riverbed and on top of the bank for the length of the erosion, ensuring they extend to stable bank at either end. The posts provide anchor points from which to tightly criss-cross wire over brash. Brash bundles are made using willow (or other local wood) and secured with coir rope. The brash is then installed along the bank by piling lots of it into the eroded area. Large willow stakes are driven through the bundles to the riverbed to provide extra stability along with the wire. The section requires stock-proof fencing to ensure it’s success.
Sometimes it can also be beneficial to drill Christmas trees to the front of the posts to provide further protection and beneficial habitat for young fish.
The bundles and willow stakes should grow, protecting the bank, and providing benefits for biodiversity and habitat for fish and other species.
They dissipate the energy of the river, which protects the bank from further erosion allowing time for the bank to recover and naturally vegetate.
Pearls in Peril
This technique has been used in several carefully selected sections as part of the Pearls in Peril Project.
A Flood Defence Consent and careful mitigation was required to undertake the work.
See before and after photos below.