Construction of Fish Passage Weirs

This project was to replace an existing weir with three lower weirs to enable fish passage further up the river. Restoration works to re-model the river channel and improve fishery habitat were then carried out downstream of the new weirs.

The designed water level in this impounded stretch of the Little Stour was very important for both farm land irrigation and historical aesthetics. Therefore the new weirs were designed to maintain this water level yet reduce the height and enable fish passage over them by means of a central notch.

The access to the working area was through nearbye old gravel pits that were now a fishing club and then several hundred metres up the river bank to get to the existing weir which was quite remote.

The setting out of the new weirs was carried out and then the sheet piles were driven to form their structure using a long reach excavator fitted with a piling hammer.

A temporary diversion channel was then excavated and a temporary sand bag dam installed across the river to divert the flow around the location of the new weirs.

The sheet piles were then clad in recycled plastic and stone was imported and placed as rock armour to protect the banks of the weir pools.

The old weir was then carefully removed and more stone placed upstream of the new weirs to increase the velocity of the river on the approach to the new weirs and prevent silt building up above them as had happened with the old weir.

River restoration works were then carried out downstream of the new weirs for several hundred metres to create meanders, pools and riffles improving the fishery habitat.

The temporary dam was removed and the weirs commissioned. The temporary diversion channel could then be filled in and the working area tided and seeded with grass.