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.
ABG offer a number of products for the creation, repair and reinforcement of flood embankments, which act both as erosion protection against flood water and for flood water storage.
Webwall is a flexible geocellular retaining wall system, which provides green faced walls up to near vertical faces. Installation is quick and easy, with the added benefit of using site won materials as fill. Webwall can also be constructed as a Flood Bund, and provides a visually pleasing alternative to gabion baskets for Riverbank Restoration.
Erosaweb geocell is designed for the reinforcement of weak soils and has many applications, including retention of soils on steep slopes and erosion control. The perforated geocells retain the fill material, while allowing water through and reducing run-off velocity.
When used in conjunction with Erosamat and Abgrid, ABG can provide a single solution for Flood Management systems, backed-up with design advice and support from our Technical Team.
ABG offers a range of permanent and biodegradable Turf Reinforcement and Erosion Control Mats, from low cost soil cover to reinforced spillway protection systems, as well as permanent geocellular solutions.
Permanent erosion control is provided by ABG’s Erosamat Type 3 range of Turf Reinforcement Mats, designed to meet the requirements of CIRIA 116. Manufactured here in the UK, Erosamat Type 3 is in widespread use on projects throughout the country, offering reduced lead-times and a lower delivery carbon-footprint.
Temporary erosion control is provided by ABG’s Erosamat Type 1, Type 2, and Type 4 range of jute and coir mats. These mats offer between 18 months and 4 years life-spans, allowing for the establishment of vegetation whilst protecting the subsoil.
All Erosamat products are secured using biodegradable anchor pins, steel pins or helical pins, for which Pinning and Installation Guides are available.
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.
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.
Our experience across many areas of infrastructure, including current AMP frameworks, means we can ensure you get the right product for your specific application. All ABG products come with design advice and technical guidance from our in house Chartered Civil Engineers.
Click to view our recent Water Projects.
ABG’s Terrex and Gridtex geotextile products include a range of woven and non-woven polypropylene options to meet a variety of separation, filtration, reinforcement, protection and drainage design functions.
Geotextiles are used in multiple applications, such as: under rock armour in Coastal Protection, beneath Pond Liners, French drain filters, sub base separation, embankment starter layers, basal reinforcement and ground stabilisation.
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.
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