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Managing & Maintaining our water channels Bank


Stabilisation an alternative to blockstone revetment


BY RICHARD EDWARDS, SALIX RIVER & WETLAND SERVICES LTD


The scouring effect of fast flowing, frequently high volume water flows can have a destructive effect on the stability of channel banks. This can be of particular concern in ubran areas where there is likely to be development on the adjacent land. This example, in Swansea, was threatening the stability of a road and housing development.


The developers were looking for a cost effective, natural looking solution to the problem as opposed to installing blockstone revetments. but the solutions would have to offer high energy scour protection inorder to protect the bank.


The developers approached a consulting engineer who in turn recommended Salix, who have expertise in this area.


Starting with a very steep gradient channel with high flows and a bed that was down cutting, Salix had to design a solution that offered high energy scour protection and bank stabilisation.


T he solution was to bury rock rolls below the bed, pinned into place. This would prevent the toe scour and bank undermining. The rock rolls were designed to allow accretion and vegetation establishment by the use of small stones within high tensile nets.


The embankments were graded back before being covered with a turf reinforcement mat called VMax C350. This is a UV stabilised permanent turf reinforcement mat that reinforces the vegetation on the banks allowing the grass to take flows of up to 6m/sec without soil loss. (Unvegetated, it will provide protection against flows of 3.2m/sec).


Pre-established coir rolls were used between the rock rolls to provide marginal plant establishment.


Graded slope to have 100mm topsoil. Hand seeded prior to erosion control matting being laid. Slope angle as shallow as possible.


Graded slope.


Existing eroded bank. Slope angle & height varies.


Pre-established 200mm coir roll.


C350 high performance geomat.


C350 taken under top rock roll.


Low flow level


Existing cobble bed.


rock rolls in place protecting the toe


the graded bank, covered with the VMax C350


just 3 months later


12 months later The result is a natural looking channel offering high scour protection and bank stabilisation


22


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