Jackson Civil Engineering worked with client Environment Agency and suppliers Salix to produce a sustainable and soft engineering solution to strengthen an embankment that was in the early stages of failing at Maylon’s Sluice on the River Crouch, Essex.
The failure was due to the natural erosion of the salt marsh that was protecting the existing embankment.
Jackson and the EA investigated options to reinstate the salt marsh and raise the existing embankment to help prevent future deterioration and lower the risk of flooding. The river is used by local sailing clubs who expressed concern about the embankment’s condition. It had been reported that spectators of the sailing events had been cut by wires protruding from gabion baskets that had corroded and rusted away over the years.
Inter-tidal rivers, such as the River Crouch, are notably difficult to manage when it comes to erosion control, and in our experience, hard engineering is not the best solution in such a dynamic environment. From an engineering perspective, the structure must cope with tidal flux, strong currents and wave action. Biologically, the system must cope with changes in water quality, salinity, seasonal effects and daily exposure and inundation.
The site team, in conjunction with Salix designed a Bioengineering solution using chestnut timber pegs, rock rolls and brushwood faggots that would also encourage future salt marsh growth.
Saltmarshes are highly valued because of the range of ecosystem services that they provide. For example, as they are amongst the most highly productive ecosystems, they support a biodiverse and complex food web that is particularly important to wading and over-wintering birds. In consequence, they are an important component in maintaining biodiversity while efficiently capturing carbon and other pollutants and also providing a high amenity value.
As an alternative to importing clay to site, the site team worked closely with the landowner to obtain planning permission for a borrow pit to be excavated in the field behind the embankment. The borrow pit was shaped and planed with ecologists to provide the best possible habitat for the local wildlife.
As a result, the clay only had to travel approx. 1km by dump truck from where it was dug to where it was placed, instead of being bought to site by tipper lorries which could not be taken directly to the work area, meaning the material would have to be double handled and still transported the last 1-1.5km by dump truck along the farmers haul routes.
In an attempt to avoiding plastic materials, the team installed Eronet, an untreated hessian mat, to hold the topsoil on the embankment long enough for the grass to take hold and prevent further embankment erosion. This was secured with small timber pegs instead of steel pins as the matting is designed to degrade over time. Therefore the pegs will degrade in the same way, rather than leaving an embankment full of steel pins in future.
At the embankment toe, gabion rock rolls were placed to hold brushwood against the embankment. Both are anchored by chestnut stakes.
The system is designed to trap silts in the brushwood bundles and rock rolls. This will result in the reformation of the salt marsh, creating habitat and providing natural protection to the embankment.
This soft engineering solution also had construction benefits: Lighter materials made it easier to manhandle the component parts on the soft muds, and from a sustainability perspective, the materials selected maximised the use of renewable resources, thus lowering the project’s carbon footprint.
During this project, the site team also ran a plastic clean-up initiative which helped to clear three 1-ton aggregate bags of loose plastic debris that had accumulated along the estuary. John Abraham, EA Project Manager said: “I really see this as very positive behaviour from the Jackson team as well as something that should be shared wider within and outside our organisation. If every construction site adopted something like this then maybe we can start to make a difference in the amount of plastic waste within the environment. There is only one thing better than looking at a job well done, but a litter free job well done, regardless of where that litter originated from.”