Somme Parade drop-out repair

Project typeEarthworks / construction of a retaining wall
Project value$6.6M (Waka Kotahi $3.96M / Council $2.64M)
Contractor nameDowner
Completion Date15 March 2024

The Somme Parade drop-out oopposite Axiam Plastics

Significant erosion to about 136 metres of the Whanganui River bank opposite 131 Somme Parade (Axiam Plastics) has made the riverbank footpath unsafe to use and threatens the integrity of the road and gas pipeline under the footpath.

Repairs to this site will cover:

Stage 1 – Secure the gas pipeline. This will require the pipeline to be anchored to prevent damage from further potential bank erosion

Stage 2 – The construction of an inner and outer sheet pile wall to stabilise and protect the area from further erosion. The two walls are driven deep into the river bank and tied together to form a well-anchored and stable structure.

Whanganui District Council’s Roading Alliance partner Downer is doing the repair work. As the riverbank was damaged during Cyclone Dovi in February 2022, the work is jointly funded by Waka Kotahi NZ Transport Agency and Whanganui District Council.

Check out the timelapse video of the awesome progress being made at the Somme Parade drop-out repair site!

Stage 1 – gas pipeline / footpath stabilisation

The footpath area above the eroded section of river bank on Somme Parade

The footpath area above the eroded section of river bank on Somme Parade

Work to stabilise the gas pipeline is scheduled to begin in late June 2023. Heavy machinery will drive a number of 9-metre length steel columns into the ground, and the footpath area will be excavated. The exposed gas pipeline will then be secured to the steel columns.

This work is expected to take two weeks. Both traffic lanes of Somme Parade alongside the worksite will operate during the stage one work period but the roadside car parking lane outside 131 Somme Parade will not be available until completion of the work. The excavated footpath area will also be closed during the work period.

Stage 2 – river bank stabilisation

Indicative cross-section of the Somme Parade river bank repair

The riverbank erosion will be stabilised by driving several 15- to 18-metre length steel sheet piles* into the bank to form the retaining wall. The steel sheet piling is expected to arrive in New Zealand via ship in late July 2023.

Construction of the retaining wall will begin when the steel sheet piling arrives onsite in Whanganui, and Somme Parade will then be reduced to a single traffic lane near the worksite to allow a large crane to operate safely. A special 160-tonne crane will be used to drive the steel sheet piles into the river bank.

Pedestrians have access via two crossing points – near Spier Street and Kaikokopu Road.

(*Sheet piles – most commonly made of steel – are sections of sheet materials with interlocking edges that are driven into the ground to provide earth retention and excavation support.)

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