Semington Brook Bankside Revetment

Semington Brook Bankside Revetment:

A private residence on the banks of the Semington Brook was experiencing an accelerated rate of erosion due to signal crayfish damage and other external factors. A hydro-electric scheme exists upstream of the property, which leads to regular fluctuations in water levels, and has resulted in some areas of the river bank becoming undercut and slumping. We were tasked with the job of stabilising this steep river bank by hand due to the limited access for any machinery.

What did we do?

1.     Installed a sediment barrier at the downstream end of the works to catch any fine sediment.

2.     Constructed a temporary geo-textile curtain to catch any soil from the failing bankside.

3.     Sensitively de-constructed the existing bankside revetment in order to build a new structure in its place. This Adhered to the stipulations outlined in the Environment Agency’s permit.

4.     Built a fifty-metre bankside revetment using chestnut stakes and geo-textiles to form the new line of the River Bank.

5.     Imported over 30 tonnes of flint gravel by hand to provide a robust River bank frontage, preventing signal crayfish from being able to burrow and stopping any potential undercutting of the bank.

6.     Additional gravel was introduced to the channel to provide extra bank protection and riffles.

7.     Imported over six tonnes of top soil and seeded the upper bank to sympathetically match the existing upper lawn area of the garden.

8.     Back wired the new revetment to help prevent any of the chestnut stakes from being pushed forward by the weight of the gravel and topsoil.

9.     Erected a low-level fence to mark the edge of the top of bank.

How did we do it?

1.     A sediment barrier made out of natural hessian was fixed to the river bed using chestnut stakes prior to the commencement of works to trap any fine sediment.

2.     Geo-textiles were loosely rolled out and lightly tacked on to the back of chestnut stakes, in case any top soil slumped into the channel.

3.     Operatives carefully dismantled the existing rotting revetment by hand, and hand dug any areas of River bank to be able to build the new structure.

4.     Chestnut stakes were hand driven in at 500mm centres to form the new line of the River Bank.

5.     A layer of three types of geo-textile were secured behind the new line of the chestnut stakes.

6.     Chestnut stakes were hand driven into the upper bank at 2m centres and the structure was back wired to anchor the front posts, preventing them from moving forward from the weight of the infilled material.

7.     Over thirty tonnes of flint gravel were imported using wheelbarrows and placed into the new structure to form a robust bank frontage.

8.     Top soil was also wheelbarrowed in and lawn seed was sowed to match the existing profile of the garden.

What were the outcomes?

1.     The project was delivered on time and on budget.

2.     The new structure is now robust and can withstand the fluctuating water levels.

3.     The revetment is solid enough to withstand any signal crayfish from being able to burrow into the bank.

4.     The addition of extra gravel into the stream to form riffles in places has increased the potential for any fish spawning on this reach of the Semington Brook.