6. Proposed New General Binding Rule 25 - Bank Reinforcement
Following heavy rainfall events in recent years, riverbank erosion caused by swollen rivers has become an increasing land management problem. River bank erosion can result in losses of productive land and damage to fencing, tracks and other infrastructure. But trees or parts of trees can be used to protect eroding banks by cushioning them against the force of the river. These techniques have a number of benefits over alternative ways of protecting riverbanks:
- they don't put banks downstream at increased risk of erosion. This is because some of the force of the river is dissipated as it flows through the tree stems, roots and branches protecting the bank. In contrast, where hard bank protection is used, the full force of the river is transferred downstream;
- if live trees are used, their roots increase the strength of the bank and help create a buffer against diffuse pollution from the surrounding land;
- they mimic natural habitats and so help improve the health of the river.
Land managers have called for a GBR to allow them to carry out this type of bank reinforcement without the need for an application (and hence no application costs) to SEPA.
6.1 General Binding Rule 25
The proposed new activity provides for authorisation of the use of bank reinforcement techniques. The rules to which the authorisation would be subject are designed to ensure:
- the trees used are properly secured in place. This is particularly important where large, heavy wood is used as this can could cause damage to bridges and other structures if washed away by the river;
- the protection does not increase erosion of the bed or banks. The rules require that the protection does not cause steps in the line of the bank that could be triggers for erosion;
- the risk of soils and other sediments getting into the river as a result of the works to install the protection are minimised; and
- risks to one of Scotland's most threatened species, the freshwater pearl mussel are taken into account.
25. The placement of trees or parts of trees in a watercourse to protect eroding banks
(a) Other than in accordance with rule (e), the trees or parts of trees must only be placed in or along eroding banks;
(b) the placement must result in an arrangement of live or dead tree stems, branches or roots which, as the watercourse flows through the arrangement, flex or bend and impede its flow with the effect of cushioning the bank from the force of the watercourse;
(c) the trees or parts of trees must be tied, keyed or staked into the bank or bed of the watercourse so as to secure them in place;
(d) the placed trees or parts of trees must:
(i) follow the line of the toe of the eroded bank at the time of the works; and
(ii) be graded into the existing lines of the banks at either end of the protected section;
(e) the placement may extend beyond the upstream and downstream ends of an eroding bank only to the extent necessary to:
(i) prevent the river from going around the placements and eroding the bank behind them; and
(ii) ensure the line of the placements is graded smoothly into the existing lines of the banks at either end of the protected section;
(f) when placing willow spiling or live willow stakes:
(i) the angle of the eroding bank may be reduced to enable the establishment and growth of the willow; and
(ii) stones may be placed at the toe of the bank to help prevent the bank above being undercut by the watercourse before the willow has become established. The stones used must be no larger than the largest stones that have been deposited by the watercourse on the channel bed in the vicinity of the eroding bank;
(g) all reasonable steps must be taken whilst placing the trees or parts of trees to prevent any exposed soil or other sediments from entering the watercourse and being transported beyond the stretch being protected;
(h) once the trees or parts of trees have been placed, any areas of bare earth on the banks resulting from the works must be re-vegetated to minimise the risk of soil erosion, either by covering with grass turfs or lining with a biodegradable geotextile and seeding; and
(i) where the trees or parts of trees need to be placed on the wetted part of the bed of the watercourse or their placement would otherwise be likely to disturb the wetted part of the bed of the watercourse they must not be placed if there is a reasonable likelihood that there are freshwater pearl mussels in the part of the watercourse that would be affected.