We have just completed the fabrication and installation of a ‘spring retarder’ for the Environment Agency at the tidal flap gates on the River Wey at Westham Bridge in Weymouth. The flap gates were installed to stop the ingress of saline water upstream into the River Wey, but they also prevent the upstream migration of fish such as eels, salmon and sea trout.
The spring retarder is a spring device that holds the tidal gate open above level equalisation (the point when the gate would usually close) allowing more saline ingress and the migration of fish past the gate. The size of the retarder for Westham Bridge has been accurately calculated, based on the weight and size of the gate, as well as the degree to which the gate is to be kept open.
It was heartening to see that within minutes of the spring retarder being installed, fish were already taking advantage of the situation as we observed a couple of mullet casually pass up through the now open flap gate! Below are a couple of pictures of the installed spring retarder.