Rock Rolls, Rock Mattresses and Brushwood Fascines preventing erosion on the River Crouch

Rock Rolls, Rock Mattresses and Brushwood Fascines were the Bioengineering solution to erosion management on the River Crouch in Essex.

The toe of the Essex block revetments on the upper reaches of the tidal River Crouch are protected by salt marsh which in some areas had been eroded. The Environment Agency in conjunction with JacksonHyder investigated options to reinstate the salt marsh, thus protecting the toe of the revetment and mitigating future deterioration.

The initial option of using gabion mattresses was considered to pose a hazard to trapping of dog paws on this popular dog walking route, MLM Consulting Engineers came to us for a product solution and we proposed to use a combination of Rock Rolls and brushwood faggots.

This solution also had the benefits of being easier to manhandle on the river bed at low tide and as a large proportion comprised timber elements was both sustainable and low carbon.

Inter tidal rivers are notably difficult to manage when it comes to erosion control, historic hard engineering is not the best solution in such a dynamic environment.

Inter-tidal rivers create unique challenges for bio engineering solutions as the water quality and tidal changes in levels, long periods of inundation and turbidity alongside salinity and wave action make it a difficult environment for many solutions to last.

Our brushwood fascines, Rock Mattresses and Rock Rolls have all been used because they are able to intercept the surface drainage of receding and residual tidal waters and cause sediment to build up.

Where sediment builds up vegetation self colonises and will further stabilise the soils through the root systems. This recreates the natural processes which are able to prevent erosion.

Rock Rolls and Rock Mattresses have been proven through research with Swansea University (opens YouTube video of Dr Ruth Callaway) to be excellent revetments for use in areas of environmental sensitivity, proven out in the toughest of environments they not only protect assets, they also prevent soil loss by encouraging vegetation whilst creating a habitat for invertebrates as they accrete silt.