Open day at Surrey Hills Siphon

On Sunday (12th May, Mother’s Day!), we ran a public open day at the Surrey Hills Siphon. We felt it was a very successful event and, with the assistance of the Hinds & District Lions and great support from a number of our contractors and service providers, we estimate we had over 700 people come up and take the opportunity to ‘walk the siphon’.  We even had a group of mountain bikers ride the tunnel (and back) at the end of the day.

We had sausages, ice cream, and coffee available (all very popular). Our contractors and consultants sponsored all of these refreshments. The Lions were on hand to assist with car parking, driving the vans to bring the tunnellers back to the start, and collecting donations which were very forthcoming. The proceeds are all going to the Lions, with a provisional estimate of over $3,000 raised on the day.  

The Surrey Hills Siphon is a 2.7km long tunnel that is one of nine siphons along the RDR. It is the longest siphon on the scheme but, interestingly, wasn’t part of the original scheme design when they started construction in 1938. The main canal had been progressed some way along Surrey Hills leading up to Xmas 1938. After the Xmas break, the crews returned to find the hillside had slipped away, taking some of the partially constructed canal with it. A big rethink was required. It was decided the Surrey Hills hillside was too unstable and, instead, the canal would have to be moved to the bottom of the hill. To avoid losing all the elevation of the canal, an inverted siphon was designed for the 2.7km run along the toe of the hill. A pipe factory was constructed nearby, and over 700 large pipes (12 foot diameter and 12 foot long) were constructed to fit together to form the Surrey Hills Siphon. The lowest point of the tunnel is approximately 40m below the inlet, but it then rises up to the outlet which is only 5m lower than the inlet. Given the resources of the day, it is an amazing engineering accomplishment.

Fun facts:

  • the whole RDR goes through the siphon and the water takes 1000 secs (16 minutes) to travel through. The mountain bikers did it in 7 mins (and the walkers about 40 mins).
  • the open day proved that the acoustics of the tunnel are such that less than 10 noisy children can sound louder than the whole of Ashburton
  • the water coming out of the tunnel would fill an Olympic swimming pool in 90 seconds.
  • there are 743 pipe sections in the siphon  

Tony McCormick, RDRML CEO, commented “We are extremely grateful to the various groups that supported us in running the very successful open day.  It was such a pleasure to see the enjoyment all our visitors got from the event, and we appreciate their generosity with donations. We say the RDR is the lifeblood of Mid Canterbury, and the turnout on Sunday shows that our community recognises and appreciates the importance of the scheme to their region.”

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