That’s a great video - thanks for sharing. The gravel mounds you mentioned are in fact spoil heaps from when Tarmac company were constructing the dam in the early 1960s. They discovered that most of the raw material they needed for the dam was in the valley itself, so they literally quarried it from where we now see the mounds of gravel. The intention was to actually landscape the area before it was totally submerged, but the lake filled in much quicker than they anticipated. They had thought it might take between 3 and 4 years to fill - but it filled to the brim in 8 months due to the exceptionally heavy rainfall in the winter of 1964-65.
@@arwelagrimachinery I don’t think the material they needed was near the dam site. The rock and gravel they needed was further up the Tryweryn valley, close to where the village is.