Articles & Case Studies

Fish Pass Clean Water Test

Posted: Wednesday 18th February 2009

Siltbuster, experts in solids/liquids separation technology, have collaborated with the Environment Agency Wales (EAW) to treat and remove silt contaminated water from a new constructed fish pass at Osbaston Weir, on the River Monnow, Monmouth.

Salmon reserves in the Wye Valley fishery have been given a helping hand, (or should that be facilitative fin) thanks to the silt busting expertise of Welsh water treatment specialists Siltbuster Limited. Historically the migration of Salmon up the river Monnow, a major tributary of the Wye, had been prevented by a man made weir at Osbaston, Monmouth. During an independent construction project to build a small hydroelectric plant, the Environment Agency Wales took the opportunity to build a new fish pass re-opening the Monnow to migratory Salmon.

James Hepburn, Environment Officer for the EAW explained: “The new fish pass at Osbaston was needed as it opens up some prime spawning grounds and ensures full access to the upper reaches of the Monnow, which in turn helps safeguard the Salmon populations of the river Wye.

However, during construction works, heavy rainfall led to flooding in the Osbaston area and deposited tonnes of sediment in the fish pass.

“The site contractors tried to remove the silt prior to commissioning the fish pass, but in doing so some of the silt was released to the river causing some discolouration downstream. We were under strict time restrains to get the project completed before the fish began their migration and we needed a quick and effective solution to the siltation problem. We contacted Siltbuster because they could provide a temporary treatment plant to counteract the environmental damage caused by flooding and reduce the harmful effects on the aquatic life before the fish migration began,” explained Mr Hepburn.

Siltbuster provided a temporary treatment plant including a Hopper Bottom HB50 lamella clarifier and associated chemical dosing equipment with Polymer Dosing Kit and Pipe Flocculator.

Dr Richard Coulton, Siltbuster’s Managing Director, said: “There was a significant volume of sediment in the pools that form the fish pass which would be remobilised to the river when the full 1m3/s of flow was released through the fish pass. This could have had a major effect on the local river life so we provided a temporary treatment plant to remove the solids laden water.”

To achieve effective solids/liquids separation Siltbuster treated the water with a coagulant followed by an ionic flocculant, dosed on a flow proportional basis. The resultant solids were then separated from the water using a Siltbuster HB50 lamella clarifier and the treated water returned to the head race above the fish pass. The separated solids were then recovered from the hopper bottoms fitted to the HB50 unit and removed offsite for disposal.

Andrew Osbaldiston, Environment Management Team Leader (Lower Wye) for the EAW concluded, “We had initial concerns about any potential discharge into the Monnow and needed an indication of the loads of silt and the chemicals that would be used to ensure the treatment process didn’t have any adverse effects on the river.

“After discussions with Siltbuster we were confident the water could be treated in an effective and non harmful manner. We are extremely happy with the results achieved by Siltbuster as the water conditions have been improved and all work was completed before the start of the fish migration season in early November.

“The fish pass is now open allowing the migration process to continue and the Salmon to reach their important spawning grounds further up the Monnow.”

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