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.
Bioengineering replacement for blockstone
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.
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.
Plants in Bioengineered versus Blockstone solutions
| BIOENGINEERING | BLOCKSTONE |
| Grasses and Wildflowers | |
| Slender Creeping Red Fescue | |
| Chewings Fescue | |
| Strong Creeping Red Fescue | |
| Hard Fescue | |
| 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 |
