River Yoe, Long Sutton. Somerset
Client: Environment Agency, Bradney Depot, Somerset. Summer 2008
Project Brief: The River Yoe runs through farmland in raised flood embankments south of Long Sutton, Somerset. A fifty metre section in the river bend had become degraded by cattle descending the slope to drink. A soft engineering solution was required, and Willow Spiling was rejected as inappropriate and a turf reinforcement option proposed by Salix was adopted.
The solution: The bank was to be steepened so as to deter the cattle from descending. The forty five degree slope was created by in filling the eroded scour with compacted subsoil. A three hundred millimetre layer of topsoil was required to generate a reliable south facing grass slope. This was held on the slope by placing the soil between contour bands of faggots at half metre centres tied to driven chestnut stakes. The soil was seeded and covered with North American Green (NAG) C350 Turf Reinforcement Mat.
The result: This mat provided immediate erosion protection against rain and also against floodwater of four metres per second. Once the grass has established the bank is protected against flows of six metres per second for about forty eight hours. At the base of the slope at the waterline a Pre-Established Coir Roll anchored the leading edge of the NAG C350 and ensured the new reed margin would establish to provide erosion protection against the river flow.
Materials used: Grass seed mix and NAG C350 Turf Reinforcement Mat, Dead Brushwood Faggots, Pre-Established Reeds in Coir Rolls.
Typical cross section
The erosion scar
New profile creation
Topsoil held by faggot lines on subsoil wedge
Seeded topsoil covered by NAG C350 erosion
protection
New reeds and grass growth through NAG C350 matting after 3 months
