Loch Laggan outlet

This is the man made, or at least man deepened, cut through channel from Loch Laggan to Laggan Dam reservoir. The Lochaber Aluminium smelter hydro scheme has a catchment of about 300 square miles. The upper reaches of the Spey are intercepted and diverted by tunnel through to Loch Laggan. The pressurised head does not start at Laggan dam as this is itself simply reservoir storage which is decanted to Loch Treig via another tunnel. In turn a 15 mile tunnel (which has an additional 11 hill stream intakes) runs through the mountains to the portals above the works then overground penstock plunges to the power house. Output is close to 100 megawatts. While the Spey upper reaches were added in the second world war the main scheme was completed in 1929.
It is a fine example of civil engineering, both in concept and execution in an era long predating GPS and laser measurement.