We found this on the Burnmoor Tarn track above Boot in Eskdale. I have not seen one being built before. I assume that they are excavating to install a pipe down to a turbine hall at the bottom. I was wondering why the water needs diverting down such a long pipe. The water mill at the bottom will have a short mill race but the water in the stream will have gained energy by its natural fall. I found this https://en.wikipedia.org/wiki/Micro_hydro which explains an equation power P=QH/k. Looking at https://www.gov.uk/government/publications/national-trust-renewable-energy-limited-application-made-to-abstract-water-and-impound-water-npswr023281/national-trust-renewable-energy-limited-application-made-to-abstract-water-and-impound-water says that they will abstract 792 cubic metres per hour or 13.2 cubic metres per minute. This is 2904 gallons per minute. For a 100kW scheme, that gives a head H of 183 feet. Burnmoor Tarn is at 250 metres and is about 200 metres above Boot. 183 feet is only 60 metres of vertical drop so that works.
