River Thaw Enhancement, Cowbridge, South Wales
Client: Environment Agency Wales
Salix were asked by Environment Agency Wales to advise on methods to restore a 100 metre reach of the River Thaw which had been subject to physical degradation by overgrazing and cattle poaching. Salix conducted a basic walk over survey and concluded that the degraded reach was 25-30% wider than unaffected reaches up and down stream. The over wide channel had lost much of its physical habitat value due to the poaching.
Salix undertook channel restoration works as part of a larger flood defence scheme and were designed to mitigate habitat loss due to the infrastructure works. Coir Rolls were installed to return the average channel width by 25-30%. The rolls were backfilled with locally won soil. The narrowing has had a dramatic impact on the flow of the channel, with a deeper faster base flow being sustained. This has allowed submerged vegetation to re-establish and provide excellent physical habitat structure within the channel. The Pre-Established Coir Rolls have rapidly controlled bank erosion and have provided a physical habitat with the diverse vegetation establishment of marginal and bankside species.
Materials used: Coir Rolls.
Over wide channel caused by over grazing
and cattle poaching. The over wide channel was
lacking physical habitat structure and both
bankside and in-channel vegetation
Pre-Established Coir Rolls were set 1 to 1.5m into the channel on both banks to recreate a more natural channel size
The same reach 12 months on. Note the
diverse bank side planting from the Coir Rolls
and the physical structure provided by the
in-channel vegetation
The channel narrowing and establishment of in-channel and bankside vegetation types has created a more concentrated base flow, with locally complex flow diversity
