The main challenge for flood protection schemes is often to maintain grass coverage onto embankments and spillways during over-topping and rising flood water level events. Grass is a good short-term erosion protection solution, however it suffers from potential weak areas due to die back or poor growth which can lead to washout and erosion.
Bare soil gives rise to soil erosion by wind, rain and water and more frequent and intense rainfall increases the risk, with studies such as CIRIA Report 116 finding that well established grass can only withstand flows of 4.5m/s for up to one hour. In addition, with steeper slopes there is a risk of landslip where subsurface flows can cause blow out further down the slope.
Permanent turf reinforcement erosion control consists of mats and webs that provide immediate protection to bare soil for the lifetime of the project, protecting the soil even if there is die-back of the vegetation.
Flood Embankments & Reservoir Spillways
In accordance with the CIRIA 116 guidelines for “Design of Reinforced Grass Waterways” a robust open permanent Turf Reinforcement Mat (TRM) is recommended. The proven ABG Erosamat 3/20Z500M erosion control matting is suitable for flood embankment projects to meet this requirement. The ABG Erosamat Type 3 is a non-biodegradable solution, with a predicted life span of 120 years. The TRM permanently protects the soil in non-grassed areas and reinforces the roots in grassed areas to withstand flow velocities up to 7 m/s.
Long Duration Field Trial
Following construction of the Aller Moor levels spillway, vegetation was not fully established before the winter of 2013/14. Subsequent prolonged heavy rainfall led to extensive flooding, where the new flood defence measures worked well – with no significant loss of soil due to erosion.
Independent data collected by Black and Veatch during the 62 day flood reported the spillway and TRM functioned as intended. This data demonstrated that unvegetated Erosamat Type 3/20Z 500M provided sufficient protection to the spillway for velocities exceeding 4 m/s over prolonged periods and fully vegetated Erosamat 3/20Z 500M provides protection for flow velocities of 7 m/s.
Unlike typical lab simulation results from short duration tests (10-50 hours), the Erosamat 3/20Z 500M performance parameters are demonstrated during active flood conditions, over an extremely long duration of 62 days. Erosamat is therefore a proven TRM system that provides a high level of protection for vegetation and the underlying soil during high flow/long duration events.
62 days of flow rate data following January 2014 floods
Flow depth and velocities were recorded on Aller Moor spillway during flooding on 23 January 2014.
Soil retention systems
ABG’s Erosaweb geocell contains topsoil onto steep slopes to stabilise embankments, enabling a natural grass finish to establish and providing a light-weight and low carbon alternative to wire mesh for veneer stability.
ABG Erosaweb geocell GWX 200/300 for soil retention on steep slopes
The ABG Erosaweb cells retain the topsoil fill whilst still allowing water to drain through. The large 4m x 6m GWX 200/300 panels have a cell size of 200mm deep x 300mm diameter and are simply stretched out into position down the slope before pinning into place.
Filtration geotextiles are designed to be used as separators for hydraulic coastal and river defence structures. They are placed at lower permeability depths to prevent the escape of fine particles while permitting the free passage of water to provide a stable and consistent bedding layer, often replacing the need for rock armour. The fine pore size and high permeability properties make Terrex SNW an ideal choice for demanding filtration applications such as coastal engineering.
Ponds, Swales & Lagoons
Water containment applications such as the creation of attenuation lagoons and swales (for SuDS applications) are facilitated with our range of geomembranes and GCLs. Geosynthetic lining systems such as GCL and HDPE are useful and long-lasting methods of forming ponds. Liners can be pre-fabricated to size before delivery, or welded on site to the required profile. Geosynthetics also contribute to the construction of efficient swales and conveyance channels, by providing resilient protection from damage caused by erosion. Where suitable, steep banks can be constructed using geosynthetics to increase plot size on housing developments.
Trench soakaway systems
Geotextiles have long been an integral element of soakaway systems, providing a vital treatment process as collected water is filtered through the fabric. They provide a separation function for granular stone layers and filter water within the drainage systems to reduce the environmental impact of construction. They are an important component in many applications, including in the construction of roads, car parks, embankments and wrapping SuDS Infiltration/Attenuation Tanks.
Typical Client Profile
- Environment Agency
- Local Councils
- Drainage Engineers
- Coastal protection engineers
- Geo-environmental engineers
- Agricultural engineers
- Highways engineers
- Reservoir engineers
- Local Drainage boards
- Canal & River Trust
- Housing Developers
- Water & sewerage authorities