River Till Bank Stabilisation Works
A combination of natural springs and a controlled water hatch structure had led to bank erosion on a private property on the River Till. Historically this stretch of River had been straightened to send water through a working mill, and the hatches were used to impound and release water. This led to fluctuations in water levels and had indirectly caused undercutting of the bankside.
What did we do?
1) We removed an existing timber revetment that had rotted and failed.
2) Operatives hand dug the existing bank to remove undercuts and achieve a square profile
3) Large Alder logs were locally sourced and fixed to the River bed to support the new bank profile.
4) A biodegradable woven geo-textile was installed behind the Alder logs to prevent and gravel and soil fines from washing out into the River Till.
5) 60 tonnes of large and 40mm flint gravels were delivered to site and used to create a sustainable bank slope.
6) Top soil was imported and washed through the gravel to provide a growing medium for plants.
7) Marginal plug plants and a local grass and wildflower seed mix were spread to colonise the new River bank.
How did we do it?
1) Before works began Ecolibrium visited the site and carried out a survey of the River bank and surrounding land. The survey enabled us to evaluate the scale of works, and helped to identify safe methods of working in and around water.
2) Close liaison followed with the client and the Environment Agency, to produce comprehensive drawings, method statements and risk assessments to form a proposed plan of the project and gain planning permission.
3) Due to the site being a SSSI (Site of Special Scientific Interest), we had to avoid the use of machinery and heavy plant. The River bank also had a colony of early Purple Orchids. All work was carried out by hand with minimal ground disturbance.
4) The existing structure was removed and operatives hand dug back to stable bank.
5) We negotiated with the neighbouring land owner to open the hatches to allow us to install the Alder log revetment.
6) Alder logs were imported and fixed to the River bed using Sweet Chestnut posts and mild steel wire.
7) A natural biodegradable geo-textile was fitted to the inside of the Alder logs to prevent gravel and soil fines from spilling out into the River Till.
8) 60 tonnes of large gravel rejects and 40mm flint were imported and placed into the new structure with the use of wheelbarrows. The bank was graded by hand to achieve a sustainable slope.
9) Top soil was imported, hand raked and washed through the gravel to provide a growing medium for plants.
10) A mixture of native marginal plug plants and local wildflower and grass seed was spread to colonise the new River bank.
11) Barrier fencing was erected to temporarily exclude wild fowl from eating the plants and seed.
What were the outcomes?
- The River bank was transformed from a vertical face that was prone to further erosion to a solid and sustainable sloping bank profile.
- Having avoided the use of heavy plant machinery, we minimised disturbance to the ground which enabled a colony of early purple orchids to survive. The following spring yielded the highest density of this plant in that location.
- Additional seeding and marginal plug planting enhanced the biodiversity of the area and provided a haven for many invertebrate species.
- The project was delivered to a high standard and met the client’s expectations.