What's interesting about this is that it was constructed with shotcrete, a technique developed in the early 20thC.
http://en.wikipedia.org/wiki/Shotcrete
Also used on the Ffestiniog railway in 1976 at which time it was still quite novel in the UK.
http://en.wikipedia.org/wiki/Ffestiniog_Railway
See para 'The Llyn Ystradau Deviation'
Well by looking at the picture i'd say with some certainty the drain hole (maybe fits a giant plug for summer heatwave swimming) in the middle has something to do with the drainage. I love skating bowls thought, i usually prefer them in L.A mind.
Well by looking at the picture i'd say with some certainty the drain hole (maybe fits a giant plug for summer heatwave swimming) in the middle has something to do with the drainage.