Source: New Zealand Transport Agency
New resilience work is underway this week at Utiku south of Taihape, on land between State Highway 1 and the railway corridor.
Work has now begun onsite and is expected to continue for at least four months.
During the work, crews will install new drainage in the area to boost the resilience of SH1 through this area and reduce risk to the road, which has been affected for many decades by a large, slow-moving landslide.
NZ Transport Agency Waka Kotahi (NZTA) Project Manager Gareth Howie says drainage is critical to any project, but drainage for this project is particularly crucial as it will redirect water away from the hillside, road and railway elsewhere in the existing stormwater system.
“This work, to redirect the water from the hillside and improve drainage, will boost the safety and reliability of the state highway and ultimately the efficiency of travel for all road users, hopefully minimising disruptions in future,” says Mr Howie.
In August 2023, cracks in the road meant emergency repair work needed to be undertaken, in addition to the installation of monitoring.
Over the next four months, NZTA is planning to install up to 3 incline drains (drains running up the hill) at the site, subject to approvals, which will reduce risk to the main trunk railway line as well as SH1.
Each drain will consist of four ‘fans’. At each of the fan locations in the drain, groundwater will be intercepted and will flow through the drain and be redirected.
“Water will be directed through the slotted drains from the upper levels into one exit point at the base of the drain, then filtered through the open swales, down into the culvert system and into existing culverts and then down to the Hautapu River, which is the direction the water is trying to take naturally,” says Mr Howie.
“We are working with mana whenua to ensure that water discharged from the drains remains in the same catchment, and effects on the Hautapu River, wetlands and watercourses are minimised as much as possible.”
Each drain will take up to four months to install and NZTA will monitor the effectiveness of each one before moving on to install the next. There will be minimal impact to road users as a result of these works.
Other work at the site this construction season to ensure a more resilient and safer road includes the felling of trees overhanging the road, and application of a second coat seal on the road following the 2023 emergency works.
This work is likely to involve some traffic management.
NZTA is also planning to install more instrumentation in the area to enhance monitoring with real time capability for response.
We will keep people updated as these works progress.
Site for first drain.
