On the River Goyt in Stockport, Greater Manchester, there is an 18th Century Grade II Listed Cotton Spinning Mill, called Pear Mill that is now a number of commercial units. The mill was originally powered by a Manhattan steam engine by George Saxon & Co with rope drive transmission but in keeping with its history and geographical position is will now be powered by a 100kW Archimedes Hydroscrew.

The proposed hydro turbine which was based on an Archimedes Screw is 3.5m wide and over 8m in length. It will produce 281Mwh of electricity each year, enough electricity to run 75 standard UK homes, saving well over 150,000 tonnes of CO2 from entering the atmosphere each year.

An Archimedes’ screw is essentially a reversible hydraulic machine and is used for lifting water. In this case, because of the long drop of the screw and the angle of the project, there needed to be a fish pass designed and built so that eel and salmon would be able to migrate up and down the river safely to their feeding grounds. There were limits on the vertical heights and distance the fish could be expected to swim without rest and we needed to balance the flow of the water with the overall height of the damn while providing rest pools for the fish.

We worked closely with the Environment Agency and their guidance on designing fish passes. This included a need for baffles, metal plates that are designed to mimic rocks and are fixed to the ‘fish pass’ the sloped concrete channel, to slow the flow of the water so that fish can swim over the top of them easily. In this way, the fish have access to the aids they would use to move uphill in a natural environment.

One of the issues we faced was that salmon and eels flourish at different water speeds and we needed to account for both. Baffles come in preset modules and so there was not the flexibility of design that we would have liked, however, we overcame this issue and found the correct balance to deliver a solution.

If you have an alternative energy project that needs some structural engineering advice then give us a call on Witney (01993 225085) or Southampton (02381 920656). We can not only help with hydropower projects like the one detailed above but also have extensive experience with projects with close proximity to water and the challenges that it brings.