1.3km low carbon erosion protection
location
Leigh, Kent
Type
Flood storage
Services used
Pipeline, Infrastructure Flow
Overview
The Leigh Flood Storage Area was built in 1982 to reduce flood risk for Tonbridge and surrounding communities. With climate change driving more intense rainfall and flows, the probability of embankment overtopping has increased. The Environment Agency committed to a £21.5m upgrade programme, part of which required a new erosion protection system for the 1.3km downstream face, capable of withstanding flows up to 7.7 m/s.
Challenge
The existing grass cover on the downstream face was not sufficient to manage extreme flows, and earlier design proposals involved articulated concrete blocks — effective but carbon-heavy and intrusive. The client required a solution that combined robust performance with a lower carbon footprint and minimal long-term maintenance.
Solution
Hesselberg worked with designers JBA to develop an OSA-based design. A 200mm layer of Open Stone Asphalt was placed on a 100mm granular drainage layer across the slope, with 150mm OSA on the crest and toe. The asphalt was installed in phases over five months, then covered with topsoil and seeded to restore a natural finish. The use of OSA provided both hydraulic resilience and a significantly reduced carbon impact compared to concrete.
Result
The project was completed in 2022 and now delivers long-term protection for the Leigh Barrier embankment. The downstream face is resilient against high velocity flows, while the grassed finish maintains the site’s environmental and amenity value. The scheme provides a benchmark for low-carbon flood defence upgrades, balancing climate resilience with sustainability and biodiversity.
