Case Studies

Larinier fish pass installations on the river Dun

Construction of two Larinier fish passes and by-pass channels on the River Dunn, Hampshire.  The EA and the Wessex Chalk Stream & Rivers Trust since 2015 have been working in partnership to deliver a design to improve fish passage at Holbury and Lockerley Mills on the River Dun in Hampshire. The project involved river modelling and engineering design work which was contracted to the civil engineering company Black & Veatch Limited. Hydraulic modelling was undertaken as part of the initial project design to help ascertain the best means to enhance fish passage at both mills which had various artificial flow regulation measures in place. Five Rivers mission was to build a new off-take on the right bank of the River Dun which will provide a passage through a Larinier bypass channel. The existing mill bypass stream was widened and narrowed downstream through gravel placement. In addition, an eel passage was incorporated within the fish pass and inert stones were placed to reduce the toe erosion process at the confluence between mill bypass and the main channel.

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Digswell Chalk Stream Restoration

 

Five Rivers were contracted by the Environment Agency to design and construct a restoration scheme on the River Mimram. The site at Digswell contains deciduous woodland contributing to the local wildlife. However, the River Mimram is failing to meet Good Ecological Status under the Water Framework Directive. Adjacent to Digswell Lake, the river suffers from over widening, over shading and siltation. For the reasons above, Five Rivers was contracted to undertake habitat improvements over a 300m impounded stretch of the watercourse.
Brash berms and large woody habitat features were incorporated into the stream, as a result, the channel was selectively narrowed. This physical alteration of the habitat allowed to increase flow conditions and fishery conditions. Selective tree thinning was also required to increase light to the channel and provide large woods and brushes for the habitat features.

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Avon Turn Erosion Protection

Five Rivers were contracted by a private riparian owner to carry out bank protection works along the banks of the River Avon. In 2015 the location experienced flooding and a bank collapse due to high flows. In 2018 Five Rivers were tasked with creating a marginal zone and a lower level bank that can be allowed to flood in times of high flows. This included the installation of large woody debris (LWD) to stabilise the bank, coarse woody debris (CWD) to provide fish refuge, and the planting of native aquatic plant species to provide habitat for wildlife and aquatic invertebrates.

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Tank Crossing A River Restoration

Five Rivers were contracted to deliver a multi-benefits project including the reinstatement of a palaeochannel. The project incorporated the lowering of the floodplain and the installation of a variety of wetland features. The overarching goal was to enhance the water quality of the River Avon and enhance habitats. Given a wide design brief, we tailored the works to achieve the best possible environmental improvements.

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Salt marsh restoration, Isle of Sheppey

Works for Southern Water to restore an area of tidal marshland that have been badly damaged and eroded by temporary pipes. Use of bio-engineering techniques including brushwood bundles and retained vegetation designed to trap silt to reestablish the salt marsh habitats.

 

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Flex MSE Bank Protection at Llyn Brenig Reservoir

Works to protect a 100m long section of the reservoir bank using Flex MSE green wall system after wave erosion action undercut the bank, putting the nearby road and SSSI grassland at risk. This project was part of a wider scheme of improvements to Llyn Brenig Reservoir.

For other Flex MSE Schemes see our River Test and Bartley, Hampshire case studies.

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River Restoration on the Amwell Magna Fishery

River restoration works on the Old River Lea at the Amwell Magna fishery to improve past physical alterations to the channel, low flows and lack of management. This NEP Scheme (AMP6) project aimed to reinstate geomorphological diversity to the channel, enhancing river form and function whilst improving vital chalk stream habitat.

For other NEP Schemes see our Petney Abbey and River Bewl case studies.

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Bank Reinstatement using Flex MSE Wall – Bartley, Hampshire

Installation of a Flex MSE geomodular block system wall at a 75-80° angle to reinstate a 10m priority section of the bank at the rear of a residential property within the New Forest National Park. Five Rivers are an approved supplier and installer of flex MSE, for more details click here.

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Reactive Fish Population Surveys

Our team of ecologist provided a reactive response for fish survey requirement. Electric fishing was used to assess the population of five sites.

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European Eel Trap and Transport

On behalf of Southern Water Services our fisheries specialists undertook an intensive European eel trap and transport project at two operational surface water assets. Our team trapped  intensively with the aim to remove land locked eel, allowing them to complete their life cycle by migrating to sea to spawn, increasing silver eel escapement and improving recruitment of a species in decline.

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