This page contains a Flash digital edition of a book. Sustainable bio-engineering

Many of today’s engineering requirements effecting the movement of water, be it revetment, channel, river or open drain will, more often than not, require a significant bias to the projects program, to improve or maintain the environment. During the 1960’s a large number of rivers in England were artificially straightened to reduce flooding. It is now acknowledged that far from reducing flooding, this straightening of channels increased flood events. As a consequence, over the last 20 years, there has been a vast increase in the use of vegetation and bioengineering solutions within fluvial schemes to replace meanders, control erosion and enhance straightened river channels. Sustainable aquatic bio-engineering was developed in Germany and introduced into the UK by MMG Civil Engineering Systems, subsequently incorporated into the A.G.A. Group, who have since pioneered many of the applications and methods commonly in use today for erosion control, revetting and bank support.

Supporting river banks

Bank-side erosion is a common riverine problem, particularly in fast flowing (artificially straightened) channels , while there are a number of revetment techniques which can be employed, the choice of the erosion prevention measure will be heavily dependent on site conditions and as such there is no one cure-all. Hard engineering solutions can be effective but carry their own set of disadvantages. Coir turf reinforcement mats (TRM) are a very effective natural material for sustaining vegetation which can either be under-sown prior to installation or laid and seeded within applied top-soil. More recently some clients are adopting the use of TRM’s

pre-vegetated with grass and wild flower mixtures and grown to order under controlled conditions at A.G.A.’s Merton aquatic plant nurseries.


Where the sides of bank are heavily eroded it may be more effective to build a new robust bank-side and back fill the voids caused by the erosion. Bio-engineering methodology employed by the A.G.A Group proves an extremely effective solution. The use of pre-planted coir fibre rolls placed on faggots or rock rolls will immediately stop erosion. The aquatic plants root systems rapidly grow and develop a permanent bond with the toe of the revetment.


straightened river channels

Where no opportunity exists to reinstate meanders to artificially straightened rivers, techniques can be employed that will enhancing the channel and provide good habitat for fish and plant species.

Marginal planting is a common enhancement practice which acts to improve habitat and provide spawning areas for fish communities. This can be achieved using a number of techniques that introduce a variety of desirable aquatic species into the water course or margins, for example, Lesser Reedmace (Typha angustifolia), Flowering Rush (Butomus umbellatus), Reed Sweet- grass (Glyceria maxima), Reed Canary-grass (Phalaris arundinacea), Sweet Flag (Acorus calamus), Arrowhead (Sagittaria sagittifolia) and Water Plantain (Alisma plantago- aquatica). Pre-grown coir pallets offer an excellent natural solution to establish marginal aquatic

vegetation. The success of the coir pallets lies in their diversity, they are so versatile and can be used to protect against erosion or provide habitat. These coir pallets help to quickly establish aquatic plants in the area and increase biodiversity of sites by providing habitat for a number of ecologically key species.

Another useful enhancement technique is recreating pool/riffle sequences, this effectively alters the flow regime of the river and creates sections of fast flowing shallow water which are ideal for migratory and non- migratory species to spawn. Riffles are particularly beneficial as they act to oxygenate the water, as with any areas where the air water interface is increased dissolved oxygen levels recover, naturally improving water quality.

Reinstating natural meanders

Multi-span growing facilities at A.G.A. Group’s Merton nurseries

Reconstructing meanders will mitigate against flooding by restoring a slower more natural flow regime to the river allowing the water time to work through the fluvial system. This of course assumes that there is ample floodplain to allow the river to come out of its banks without the consequence of threatening life and property. A.G.A. Group’s integrated approach to the management of aquatic planning takes into account the interaction of the entire systems environment and ecology. No part of an aquatic ecosystem should be viewed in isolation so every project may need to consider the appropriate bioengineering systems put into place.

There are and always will be cases where hard engineering products will be needed, sheet piles gabions and concrete structures will be required to overcome high velocity and turbulent conditions. Bioengineering systems are probably the most effective way to soften the appearance of this hard engineering, creating an acceptable


aesthetic appearance while creating habitat and access to mammals and invertebrates.

Clear sets of aims and outlines must first be decided before embarking on river restoration and enhancement projects; these plans must incorporate future goals and constraints to ensure the project’s blueprint is one for success. It is only through a thorough understanding of fluvial processes that informed management strategies using bioengineering can be formulated. A close relationship with the client is essential as this type of work will often require consultation with the Environment Agency, Local Authorities and other statutory bodies. The A.G.A. Group are leading specialists in sustainable aquatic bio- engineering, our nurseries are the largest in the UK devoted to growing and supplying a range of pre- vegetated coir products and aquatic plants, additionally supplying a wide range of associated materials including geosynthetics. A.G.A. are also specialist in the installation of their materials and products. The Aquatic Consultancy division offers professional advice on issues including fisheries management, conservation, environmental management, environmental impact assessment and larger scale integrated projects. The consultants provide assessments of all relevant environmental issues and undertake the steps required to obtain consents for the client from ‘Concept to Completion’.

Vegetated coir pallets installed on the river margin behind pre- vegetated coir rolls that are temporary protected from wildfowl damage by anti-grazing cages.

Erosion Control

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