Baffle Type Fish Pass

This project was to construct a fish and eel pass replacing a weir at the site of an old mill building on the River Wylye.

In order to enable migratory fish species to once again colonise the upper reaches of the River Wylye in line with the UKʼs commitment to european legislation called the water framework directive a fish pass was proposed at this location to replace the existing weir left in an old mill structure.

The river itself was temporarily dammed using interlocking steel sheet piles, a plastic membrane and sand bags. This diverted the water diverted down the old bypass channel through the meadow and back into the river further downstream. Pumps were set up on site to deal with the seepage past the dam.

The old weir was removed and the bed of the channel lowered to accommodate the fish pass structure.

A new sub base was formed and compacted before the steel reinforcing was laid in place and tied into the existing structure. The formwork was then constructed before the concrete was poured firstly to form the base of the fish pass with a second pour some days later for the sides

Once the concrete had cured sufficiently the baffles could be installed onto it using resin fixings to hold them in place.

Once the fixings had cured the fish pass was slowly commissioned by removing the temporary dam and setting the new lowered upstream water level.

In order to re-connect the river with the floodplain the raised embankment formed from years of dredging out sediment accumulated upstream of the weir was removed from site to be recycled as top soil at a nearbye licensed waste facility.

Once the raised embankment was removed the river bank was fenced to exclude cattle that are grazed in the fields from the river banks preventing poaching and the resultant increase in erosion and sedimenation that would otherwise occur.