21 May 2004

Tangiwai Bridge construction start soon

Work to protect the bridge over the Whangaehu River on State Highway 49 at Tangiwai from a possible lahar from Mt Ruapehu will begin shortly.

Transit New Zealand today let a $3.5M contract for the improvements, which will see the bridge deck lifted and bridge supports strengthened to withstand a flow of mud, lava and water should the tephra dam at Mt Ruapehu’s crater rim collapse.

Transit regional manager Errol Christiansen said all the necessary consents for the project were in place and construction would get underway almost immediately.

“A 60-metre-long Bailey bridge is in place to act as a detour, and its sealed carriageway and approaches are nearly completed. Because Bailey bridges are one-way only, traffic signals will be in operation. But given the traffic volumes on this highway, we expect this to cause few, if any delays.”

Mr Christiansen said although the Bailey bridge work would be completed in the next few days he did not expected it to be used for several weeks as the early work on the strengthening of the main bridge would not interfere with traffic.

“The first stage of work involves driving new piles alongside the existing bridge abutments. They are 1.8 metres in diameter and will be driven deep into the ground to withstand the very deep scour that could occur from a worst-case scenario lahar. The next stage will see the bridge deck raised by two metres. It will be jacked up and the bridge piers extended to the new height.”

The Department of Conservation predicts a lahar from Mt Ruapehu could travel at an average speed of up to six to seven metres per second, and could have a bow wave of up to two metres.

Smith Bridge Ltd of Mt Maunganui will carry out the improvements, which should be completed by the end of November.

Mr Christiansen said contractors would be able to work through winter because the project did not involve major earthworks. A risk management plan had been developed in case of a smaller lahar in the interim period or any other flash flooding that might occur on the Whangaehu River.

He said Transit was grateful for the co-operative manner in which all the parties had worked together and responded to help get the project underway quickly.

ENDS

© Scoop Media