Project Description
The Forge Bridge over the river Greta in Keswick and its downstream embankments were extensively damaged during Storm Desmond in December 2015. The listed structure, originally constructed in 1817, forms a constriction to river flows and during the storm, the difference in the depth of water between the upstream and downstream sides of the bridge was 5-8m. This created a highly turbulent flow on both downstream embankments, resulting in heavy erosion. This severe scouring and erosion caused the riverside footpath to slip, putting nearby trees and property at risk, including the adjacent Grade 1 listed Smoke Cottage.
The Challenge
The simplest remediation would have been to widen the river, forming a self-stabilised embankment capable of handling high volumetric flow at a lower water velocity. This would cause a loss of supporting ground for the trees downstream however, and would encroach into private land and the river footpath on the upper side of the river bank. The bridge structure, which had also been damaged, was to be returned to its original profile and the private land restored. A steep reinforced wall solution was required which could withstand high flow in flash flood conditions, but faced with materials which remain in-keeping and sympathetic with its location in the heart of the Lake District, renowned worldwide for its outstanding natural beauty. The challenge was to optimise cost, design capability and aim for as natural a finish as possible.
The Solution
A steep concrete revetment was constructed for the lower section of the embankment and faced with local natural stone to protect against the high turbulence generated at the narrow bridge. At the higher levels of the embankment there will be less scour, and ABG’s flexible Webwall geocell system was installed to provide a reinforced soil retaining system, bringing the embankment up to the required garden and footpath level. Locally sourced topsoil was used to fill the front panels prior to planting. The front faced geocell panels help to establish and protect the vegetation roots from erosion in the event of a flash flood. The Webwall geocell solution is highly cost effective and achieves a far lower carbon footprint compared to transporting concrete and stone to site. In addition, it is faster and cheaper to install and the green colour of the front face immediately blends in with the surroundings. In a short period the wall will be completely overgrown and blend in with the other vegetation.
The ABG Service
ABG designed and installed the 45m long and 1.5 to 2.25m high Webwall. The installation was completed over 10 days, supervised by Geogreen.
Contact ABG to discover how Webwall geocell could help you deliver a sustainable, cost efficient and carbon neutral solution.
