FLUVIAL ENGINEERING

River restoration and enhancement

The A.G.A Group undertake a whole range of river management and restoration projects. We formulate clear sets of aims and outlines before embarking on restoration and enhancement developments; our plans will incorporate future goals and constraints to ensure the project’s blueprint is one of stability and sustainability for long life. When working with dynamic fluvial systems we emphasise that this planning stage is crucial both from an environmental and health and safety standpoint since mistakes can prove disastrous.

It is from our understanding of fluvial processes that informed management strategies are formulated. With this type of undertaking we will often work in consultation with the Environment Agency, Local Authorities and other statutory bodies.

Restoring meanders to straightened rivers

In England during the 1960’s many rivers were artificially straightened to reduce flooding. It is now acknowledged that far from reducing flooding events, straight channels may increase the chances due to volumes of water pushed rapidly through the waterway.

The A.G.A. Group carry out projects for the reinstatement of natural river meanders, which effectively mitigate the problem of flooding by restoring a more natural flow regime to the watercourse.

Enhancing straightened river channels

Where the opportunity to reinstate meanders to artificially straightened rivers is unrealisable, we offer a number of other management techniques which can be used to enhance the channel and provide good habitat for fish and plant species.

Marginal planting is a common enhancement technique, this acts to improve habitat and provide spawning areas for fish communities, by using desirable aquatic species such as the more popular 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), Water Plantain (Alisma plantago-aquatica).

Another useful technique we could adopt is by recreating pool/riffle sequences, effectively altering the flow regime and creating sections of fast flowing shallow water, ideal conditions for migratory and non-migratory species to spawn.

Riffles will also help to oxygenate the water, as with any areas where the air water interface is increased, so dissolved oxygen levels increase, improving water quality and enhancing fish health.

Revetting and Supporting River Banks

Bank-side erosion is a common riverine problem and one which the A.G.A. Group is particularly prominent in successful remediating practices.

There are a number of revetment techniques which we employ to control or repair bank erosion. The choice of erosion prevention measure employed is heavily dependent on site conditions and, as such, there is no ‘one cures all’.

The A.G.A Group will, wherever appropriate, focus on aquatic engineering which incorporates bio-engineering techniques that reduce erosion by using such materials as coir, willow, vegetation and other natural materials to support and rivet banks. These traditional techniques will often provide erosion control without the need for further hard revetment methodologies

Pre-vegetated coir rolls offer excellent protection by effectively building a new bank which can be back filled to provide a natural effect. By using pre-planted coir fibre rolls placed on faggots or rock rolls we can create ‘new’ bank-sides so erosion can be effectively stopped.

Coir is a very effective natural material which can be laid in mats which help to reinforce the bank or used as edging to act as a barrier to erosion. After the turf reinforcement mats (TRMs) are laid down and pegged in position, plant species soon colonise or they can even be seeded after installation, then the coir acts as the perfect germination medium. Depending on the time of year banks can look naturalised again in as little as 6-8 weeks.

Rock rolls can be incorporated into many river restoration projects and provide long term stabilisation.

We do not exclude hard engineering solutions, these are effective and have their place, we will however where possible, incorporate our bio-engineering systems to soften the appearance and vegetate these structures thus making them environmentally enhancing.

Utilising silt from the river bed to backfill behind the new structure, not only helps as a robust erosion prevention technique, but also allows the removal of a quantity of silt from the river bed without the need for consents.

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