Silt and sediment management in river restoration works
This project highlights the successful implementation of a low carbon, sustainable solution that provides an engineered embankment which blends in with the natural environment, whilst providing ecological benefits such as high benthic invertebrate population, flora and fauna.
A hybrid soil bioengineering solution was designed on the banks of the River Derwent in Workington, Cumbria as a direct alternative to previous rock armour and blockstone revetments.
It was created for long term asset protection of an access road that was destroyed during the major floods of Storm Desmond in 2015 to the pumping station and an 18th century weir.
Protecting an important river for fish
The River Derwent is an important habitat for various fish species including Atlantic Salmon, Lamprey, Sea Trout and Brown Trout as well as an important drinking water supply.
Recent flood events accelerated bank erosion on a reach of the River Derwent, east of Workington, Cumbria compromising an access road to the Yearl pumping station and threatening the structural stability of the Yearl weir.
Salix were enlisted as the appointed contractor to reinstate the 160m length of bank in this ecologically sensitive site. They identified that strong environmental protection would be required throughout the duration of the project including silt control.
The risk of silt pollution associated with the disturbance of the fine, unconsolidated mud depositions on the river bed and weak alluvium soils on the bank was high.
Sensitive silt management products
We worked alongside the team at Salix to advise on the method of work to minimise silt and find a low-cost silt control solution that did not use chemical treatments.
The decision was to surround the work areas with Silt Wattles, untreated Floc Mat® and Silt Mats™ which, in combination, created a pool where flow could be limited to enhance the settlement of silts and provide a natural fibre filter, restricting the suspended solid load entering the main river flow.
Managing silts in river restoration works is critical to success
In addition to this a further silt barrier was installed in the form of a bubble curtain, this is made up of two lines of ¾” diameter Bubble Tubing®. An air compressor located on the bank pushes air through tiny holes in the Bubble Tubing® to create a wall of bubbles.
The bubbles create a flow pattern that hold the sediment back, whilst the centre of the bubble curtain baffles and augments the water to prevent the transition of silts downstream.
Silt control in river restoration schemes is a critical part of any project’s success.
It relies on assessing and addressing environmental risk in the planning stages. Salix exemplify good environmental practice during their river works, mitigating the potential impact of silt on the river and maintain high dissolved oxygen levels that benefit the salmonid populations.
We can provide silt control guidance and materials. Contact us to discuss your project.
