Working in partnership with frog environmental, Mackley has successfully deployed ‘silt wattles’ to help control sediment on a flood alleviation scheme in West Sussex.
The innovative solution has been used at the Clay’s Lake Flood Prevention Scheme which Mackley – as part of Team Van Oord – is delivering on behalf of the Environment Agency.
The Clay’s Lake scheme comprises the removal of an existing dam which is being replaced with a larger dam. This will increase the lake’s capacity from 10,000 cubic metres to nearly 400,000 cubic metres, thereby reducing the risk of flooding to more than 280 homes in the area, and to Gatwick Airport.
Natural silt wattles are used as check dams in rivers, ditches, swales and gullies to reduce the speed of water and aid natural sediment deposition. The natural media supports silt trapping and can also be used in conjunction with a floc mat to enhance sediment capture and reduce downstream turbidity.
Silt wattles can also be used to control soil erosion, protect surface waters or break sheet flow on slopes; their low permeability supports natural ground infiltration and helps to contain dirty water.
At Clay’s Lake the wattles were used to help control sediment discharged from a large excavation that had to be regularly pumped throughout the winter.
The wattles were used to contain muddy water pumped from the excavation, and replaced straw bales that had previously been used for this purpose.
Unlike the straw bales, the wattles did not break down or degrade over time. This reduced maintenance and resource demand in the winter months when the site was shut down.
The design of silt wattles, which are manufactured in the UK by frog environmental, ensures they are malleable and will fit to the contour of uneven surfaces, where they can be staked in place or tied off.
Other innovative techniques to reduce silt pollution are being trialled at Clays Lake, these include Water Lynx blocks to aid water settlement and flocculation mats to trap silt in water before entering the watercourse.
frog environmental has also provided silt control training at two Mackley sites – Clay’s Lake and the Shoreham Adur Tidal Walls Scheme – as part of wider efforts to prevent silt pollution and maintain and improve environmental performance.
01 June 2017
