The brief
To design and deliver a series of works on a National Nature Reserve to prevent further erosion of the canal banks and reduce flooding of the adjacent footpath, while mitigating impacts on the high density watervole population.
Our response to the brief was to carry out detailed surveys and develop a phased delivery plan, implementing a design that was developed in consultation with our watervole specialist sub-consultant, with input from the Environment Agency and Natural England, delivered under strict class licence conditions.
The Solution
The project was delivered across three phases:
Phase 1: Path surfacing works.
Phase 2: Bankside revetment works.
Phase 3: Habitat mitigation works.
Phase 1: Path Surfacing Works.
The adjacent Right of Way had been closed on safety grounds due to the formation of an incised gully resulting from water flow as the canal overtopped its bank. This gully was rectified and the level of the path was raised at key points along a 150m section to prevent water overtopping following high rainfall events.
To match the existing surfacing the newly raised footpath was cambered and dressed with Neogem Path Gravel.
Phase 2: Bankside revetment works.
The bank was reconstructed using a recycled plastic sheet piling and timber kingpost hybrid system driven into the canal bed. This allowed the creation of a stepped bank profile featuring a water-level marginal vegetation shelf, blending hard and soft engineering.
The original line of the bank was reinstated and the retained area backfilled with local gravel, before timber walers and capping were installed to tie the structure together.
Finally the stretch was fenced off to prevent people and dogs entering the canal, and to allow plants to re-establish after the works.
Careful timing was essential to minimise impacts on watervoles. Following thorough surveys a series of works were undertaken to temporarily discourage their use of the area, culminating in physical displacement of any individuals remaining within the work area into the surrounding high-value habitat.
Phase 3: Habitat mitigation works.
The final phase of the project doubled the extent of suitable watervole habitat as mitigation for the bank revetments.
Over stood willow scrub was cleared from the banks of an adjacent ditch, allowing more light to reach the water body and banks, increasing the opportunities for marginal vegetation to form.
Natural recolonisation of these areas was supplemented with planting of Branched bur-reed plugs - a source of food and cover for watervoles.
The outcome
There had been numerous historic attempts to repair this section of bank using natural materials which not been successful in preventing significant erosion of the adjacent footpath.
Finding a suitable proposal that balanced the requirements of Natural England, the Environment Agency, and the client was a challenge but our blended 'hard' and 'soft' engineering approach provides a solution which is both permanent and aesthetically pleasing.
The location is a fantastic wildlife spot and is heavily used by walkers and bird watchers - M:P staff included. With the installation of our sheet piling revetment and the increased path height, the path will remain useable year-round, for many years to come.
