The advantages of Salix Bioengineering Solutions V Blockstone on two Welsh Rivers – Case Study Evidence

willow stakes taking well on the River Cleddau

Willow stakes taking well on the River Cleddau

Bioengineering replacement for blockstone

Salix completed erosion control riverbank revetment works on two Welsh rivers, the Cleddau in 2010 and the River Ebbw in 2005. It’s always interesting to revisit sites to monitor how the Bioengineering solutions we designed and built have performed.

The Cleddau works were undertaken after a request by Natural Resources Wales to provide a more sustainable, cost effective solution to reduce the amount of blockstone revetment initially required adjacent to a bridge.

Our solution has not only provided long term erosion protection but has greatly improved riparian vegetation (also see independent study on River Ebbw) and hydromorphological conditions supporting aquatic ecosystems and providing physical habitat for biota such as fish, invertebrates and aquatic macrophytes.

Salix bioengineering proposal for bank stabilisationBlockstone next to bioengineered solution on the River CleddauBlockstone next to bioengineered solution on the River CleddauWillow stakes taking well on the River Cleddau
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Blockstone next to bioengineered solution on the River Cleddau

 

At the toe of the river bank Salix installed our pre-filled 2m x 300mm Rock Rolls. Live willow stakes were placed either side of the Rock Rolls to provide a rough surface that will slow down the flow during periods of high flow and encourage re-growth of willow. (On smaller watercourses, or where willow is not required, it is perfectly feasible to omit the willow and just use the pre-filled Rock Rolls or Rock Mattresses).

Above the Rock Roll toe detail, long term slope erosion control was provided by the use of our VMax³ C350, a high performance erosion control geomat. This was laid over the hand seeded topsoil to fully protect the newly emerging vegetation and provide permanent turf reinforcement in this high energy area.

VMax³ C350’s 3-D matting structure increases the shear resistance of vegetation by up to 576 Pascal and flow velocities exceeding 6m/sec.

The River Ebbw project is now nearly 14 years old. It was one of Salix’s first large Design and Build projects completely replacing the original design of over 1km of blockstone.

Huge benefits in terms of carbon reduction and biodiversity over traditional blockstone hard revetment can be clearly seen.

Graphic showing difference in C02 Blockstone versus Bioengineering

Plants in Bioengineered versus Blockstone solutions


Bioengineering Blockstone
Grasses and Wildflowers
Slender Creeping Red Fescue
Chewings Fescue
Strong Creeping Red Fescue
Hard Fescue
Smooth Stalked Meadow Grass
Brown Top Bent
Bird’s Foot Trefoil
Small Leaved White Clover
Betony
Black Knapweed
Bulbous Buttercup
Meadow Buttercup
Oxeye Daisy
Perforate St John’s Wort
Selfheal
Yarrow
Reed Canary Grass Reed Canary Grass
Lesser Pond Sedge
Ragged Robin
Water Mint
Brooklime
Purple Loosestrife
Hard Rush
Soft Rush
Marsh Marigold
Water Figwort
Fools Water Cress
Hemlock Water Dropwort
Trees
Alder
Ash
Grey Willow
Goat Willow
White Willow
Oak
Invasive
Japanese Knotweed Japanese Knotweed