Mangaweka deviation facts for kids
The Mangaweka Deviation is a special 7-kilometer (about 4.3 miles) section of the North Island Main Trunk (NIMT) railway line in the middle of New Zealand's North Island. It's located between the towns of Mangaweka and Utiku, just south of Taihape. This new part of the railway was opened on November 18, 1981, by the Prime Minister at the time, Robert Muldoon.
Building this deviation took eight years, from 1973 to 1981, and cost $17 million. The main reasons for building it were to move the train tracks away from land that was often unstable and prone to slipping. It also replaced old, difficult-to-maintain steel bridges, including the large Mangaweka Viaduct. This project was the biggest and most important change to the NIMT railway since it first opened in 1909.
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Why the Railway Needed a New Path
The original railway line in this area was built in 1904 as part of the NIMT. Most of the route from Marton up to Taihape was built on the west side of the Rangitikei River. It mostly followed the flat areas, called terraces, within the river valley. Only south of Marton did the railway cross the Rangitikei River on its way to Palmerston North and Wellington.
Challenges of the Old Route
Between Mangaweka and Utiku, the land on the western side of the river is very steep. There aren't many flat terraces, and the hills drop sharply into tall river cliffs. The Kawhatau River also joins the Rangitikei River here, making the landscape even more challenging. Despite these difficulties, the original surveyors found a way to keep the railway on the cliff tops. However, this route included a steep climb at both ends, a large bridge (viaduct), and several tunnels.
Safety Concerns for the Old Line
By the 1940s, people started worrying about how stable the land was where the railway ran. The Mangaweka area is known for landslides because of its steep hills, heavy rain, and soft rock called papa rock (a type of mudstone). The railway, being on cliff tops and having tunnels, was especially at risk from erosion and collapse.
At the same time, there were also concerns about State Highway 1, which is New Zealand's main road. This road, built after the railway in the same area, was also steep, narrow, and winding. It was prone to slips and caused traffic jams, especially for larger vehicles.
Because of these problems, investigations began to find ways to improve both the railway and the highway. They even looked into whether they could build a new route that both the train and the road could share.
Building the New Railway Line
From many ideas, different routes were chosen for State Highway 1 and the NIMT railway. It turned out to be possible to rebuild much of State Highway 1 along its existing path. The work on State Highway 1 was finished in stages between 1972 and 1980.
The New Railway Path
The new NIMT railway route was chosen from one of the ideas that had considered sharing the path with the road. Construction started in 1973 and finished in 1981. This new railway path crosses the Rangitikei River twice and the Kawhatau River once. This meant building three huge bridges, called viaducts. The new route also removed the steep climbs at each end of the section.
Key Features of the Deviation
- From the south, the new railway line leaves the old path near the Mangaweka tunnel.
- It then crosses State Highway 1 and passes much closer to the Mangaweka town than before.
- After going under State Highway 1, it crosses the South Rangitikei Viaduct. This bridge is 315 meters (about 1,033 feet) long. It has six sections, each up to 56 meters (about 184 feet) long. Its unique twin-leg piers rise up to 76 meters (about 249 feet) above the Rangitikei River. These piers are designed to sway during an earthquake to prevent damage.
- During the construction of the South Rangitikei Viaduct on May 5, 1975, 200 tonnes of steel and concrete fell to the valley floor. This accident led to changes in how the Ministry of Works and Development planned and built temporary structures for bridges.
- The railway then runs along the eastern side of the river for about 2 kilometers (1.2 miles). It goes through a long cutting (a trench dug through a hill) and then across the Blind Gully embankment, which is New Zealand's largest.
- Next, it quickly crosses the Kawhatau Viaduct (73 meters or 240 feet high over the Kawhatau River) and the North Rangitikei Viaduct (81 meters or 266 feet high). The North Rangitikei Viaduct is the highest bridge on the entire NIMT railway line.
- Both the Kawhatau and North Rangitikei viaducts have a 160-meter (525-foot) long single center section and two shorter 25-meter (82-foot) sections leading up to it. They are built with a cantilever design, which is different from the South Rangitikei Viaduct.
- The new line then rejoins the original NIMT path about 1 kilometer (0.6 miles) further north, just south of Utiku.
After the deviation was opened in 1981, the old railway tracks were removed. The Mangaweka Viaduct, which was part of the old line, had been built between 1902 and 1903. It was 946 feet (288 meters) long and 158 feet (48 meters) high. This old viaduct was taken down in 1982.
The new section of the railway was later set up for electric trains between 1984 and 1988, as part of the wider NIMT electrification project.
What Remains of the Old Railway Line Today
Much of the old railway line can still be seen today. For most people traveling on State Highway 1, the most obvious parts of the old line are the bases of the Mangaweka Viaduct. These can be seen on the hillsides on each side of State Highway 1, just north of where the railway now crosses the road.
The old formation (the prepared ground where the tracks used to be) can still be followed on both sides of where the viaduct once stood. To the south, however, it is slowly being covered by growing bush. The tunnel at the top of the climb on the old line is almost completely blocked by a landslide at its northern entrance. North of the former viaduct, the old railway path runs through farmland. The five tunnels on this side of the old line are mostly still in good condition.
The old Mangaweka railway station closed in 1981, and the old Utiku railway station closed in 1986.
External links
Photos -
- Mangaweka Viaduct in 1903, 1904, 1908, 1909, 1910, 1912 and 1935
