Bioengineering solution is cost effective and easy to install
02/05/2001
Maccaferri is working with British Waterways to develop a multi-disciplinary approach to repairing damaged canal towpaths. All works undertaken are required to conform to British Waterway’s own standards of maintenance and, in addition, towpaths and canals must also meet requirements laid down by heritage groups and the environment agency.
Waterways Supervisor at British Waterways, Ian Derby, is in charge of the repair work. He said: “Our remit is to make certain that waterways meet the requirements of various special interest groups, boating enthusiasts, anglers and walkers. We must ensure their differing needs are met and have therefore developed a Bio-Diversity Action Plan for what is very much a working canal. In line with this plan, we asked Maccaferri to help us develop a new solution to the old problem of soil erosion and silt deposit.
Following a site visit, Maccaferri’s Bio-engineering Manager Hugh Ellis was set two objectives for any proposed solution:
- to reinstate the bank profile
- to reinstate the dynamic ecology
The bioengineering design he developed not only fell within the guidelines set by the Biodiversity Action Plan, but also proved to have other operational advantages over conventional sheet piling. Material costs are significantly lower, and the system is very much easier to install, producing dramatic cost savings overall.
And there is no loss of performance – under the right conditions where there is no geotechnical risk of bank failure the system has significantly better properties than sheet piling, with a similar life span.
The design allows a permanent new steep bank edge to be created with dredgings back fill which is stable, will resist boatwash and also satisfy landscape/ecological requirements.
This new approach is currently being taken by British Waterways along a 600-metre stretch of the Staffordshire & Worcestershire canal between Whittington Lock and Caunsall Bridge. This section of the canal is part of a 30-mile section between Wolverhampton and Stourport Basin, which falls under the remit of staff at the Norbury Junction office.
Hugh Ellis comments: “By using wood retaining stakes to relocate the bank profile, a vertical drop is created which also resists boatwash. MacMat-R® reinforced geomat is placed inside the retaining stakes and backed by a layer of biodegradable coir matting. The eroded gap is backfilled to reinstate a new towpath width then planted with native plant species and reeds. Over the years, the root system will reach their full bio-mass and lock up the soil fines, and combined with the MacMat-R® will permanently stabilise the towpath.”
MacMat-R® is a composite material, combining a three-dimensional geomat with Maccaferri’s double-twist hexagonal mesh. This specific type of mesh has a good balance of flexibility and rigidity. Depending on the environmental conditions, general life expectancy is in excess of 60 years. It can be tensioned for construction purposes. The geomat element is manufactured from entangled polypropylene monofilaments heat bonded to create a stable matrix that fills the wire mesh opening. This combination can then hold the newly backfilled towpath in place.
BioMac C, a quilted coir blanket is used to cover the surface of the new towpath, and also lines the MacMat-R® below the water. The quilted coir prevents soil fines washout while vegetation becomes established and plant root systems develop. Fully degradable, it offers excellent soil moisture retention and good conditions for seed germination.
The UK arm of the Maccaferri Industrial Group, headquartered in Italy, Maccaferri Ltd specialises in soil supporting systems including gabions, geotextiles, geogrids and geomats. In addition to a full range of products for retaining structures, slope reinforcement and erosion protection, the company offers an in-house design and consulting service.
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