CSP’s SuperSpan Arch saves time and money at Mangorewa Gorge

The $4.5 million Mangorewa/Kaharoa Gorge Improvement project, which is being carried out on behalf of the NZTA by the Rotorua District Council, involves the replacement of the one-lane Ohaupara Stream and Mangorewa Stream bridges with two-lane bridges, and realignment and widening of a 900m section of road. The section of road is situated midway along SH36 in the Mangorewa Gorge 25km north of Rotorua and carries around 2300 vehicles per day.

The Mangorewa Stream offered the designers several challenges when deciding the best way to upgrade the current single-lane bridge and roadway whilst allowing SH36 to operate during construction. CSP's SuperSpan Arch was the chosen option offering road access during construction and a considerable cost saving compared with building a complete new two-lane bridge.

"To build a two-lane bridge to replace the old single-lane bridge would have meant closing the road for many months," said Joe Habets, Area Sales Manager Central North Island for CSP. "In choosing our SuperSpan Arch the road can be kept open at certain times of the day and the road alignment would mostly remain as it is. There is a huge difference in cost and convenience between the two options."

Mangorewa Gorge has significant historical and cultural importance. The gorge has World War II fortifications contained within it and is rich in Maori history and folklore. The project site was also the original water stop for the Rotorua/Tauranga stagecoach. The area is challenging to work in with no mobile phone coverage, no power or other amenities available and icy road conditions in winter due to limited sunlight reaching the bottom of the gorge.

The treacherous speed environment and the single lane bridges have seen serious vehicle crashes in the past, including several large trucks that have crashed into the gorge and lost their loads into the streams.

"We began installing the footings in the stream in April," said Bruce McLachlan, Project Manager for Downer EDI Works, Tauranga. "We had limited time in which to install the footings as the stream is closed between May and November for the spawning of trout."

Once the footings were installed and the required panels were on site the arch was assembled in just two weeks. Sections were pre-assembled on the side of the road and winched into place where the Downer EDI Works staff bolted each section into place.

"Once the arch was built we had to raise the ground level by more than 3 metres with fill," added Bruce. "The old bridge was removed once the level was high enough, keeping the road closures to an absolute minimum. Joe Habets from CSP was a huge help during the whole process. He pre-instructed our staff on the sequence to follow when assembling the arch and provided guidance and periodic site checks throughout the construction."

The project is targeted for completion by March 2010.

Principle:New Zealand Transport Agency (NZTA)
Customer:Rotorua District Council
Contractor:Downer EDI Works, Tauranga
Consultant:Opus International Consultants Rotorua
Location:SH36, Mangorewa Gorge
Product:SuperSpan high profile arch
DateOctober 2009

Bridge Rail from CSP® makes for a good looking retrofit!

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