Impact of Cyclone Gabrielle and other severe weather events on the rail system

MURRAY KING TALKED TO Daniel Headifen, KiwiRail’s Civil Engineer in charge of the Hawke’s Bay recovery, and others.

During January and February, the North Island was subject to three severe weather events (as defined in the Severe Weather Emergency Recovery Legislation Act 2023): Cyclone Hale, from 8 - 12 January, the Auckland Anniversary Day storm from 26 January - 3 February, and Cyclone Gabrielle from 12 - 16 February. All of them affected the railway system, but most of the impact was from Gabrielle.

The North Auckland Line was damaged by slips and washouts in a number of places. There were 10 major sites where temporary works were unlikely to be viable, in particular a major slip at Tahekeroa, about 20 kilometres north of Helensville. A hillside in rolling farmland gave way and poured debris across the railway and a local road. This is still being stabilised and cleared. There are more than 30 further sites where specific engineering investigation and solution development are required. Other sites are still being discovered.

There was also damage to the North Auckland Line within the metro area, particularly from the Anniversary Day floods. These did not impact operations for very long, but repairs are still ongoing.

Cyclone Gabrielle in particular caused significant damage to the railway in Hawke’s Bay, which will take many months to fix. This initially cut off both Napier and Hastings, and Napier and Napier Port are still cut off. Napier Port is a key destination for rail traffic in Hawke’s Bay. This article focuses on the damage in Hawke’s Bay.

Work on repairing the line south of Clive began immediately, as well as preparations for a temporary bridge at Awatoto, including clearance of a large amount of debris at the bridge site. For north of Napier, the recovery team has built on experience with the restoration of the Main North Line in the South Island following the Kaikoura earthquake, and has taken time at the beginning to work out what is needed, and what the priorities are. This process resulted in some changes to the number of sites, the estimates of damage at some sites, the work required to fix it, and the priorities. To assist with this, the team developed a triage tool, classifying the damage at each of the nearly 600 sites (on the whole line) into five categories:

• No obvious railway damage despite adjacent land being damaged – in case of rail damage later became apparent;

• Minor damage – localised damage readily cleared e.g., short track misalignment, ballast loss;

• Moderate damage – shallow landslides covering the track with surface soils and vegetation, track subsidence, repairable damage to bridges, more serious track misalignment;

• Major damage – track and formation are buried, pushed out of alignment, or lost. Culverts collapsed, and bridge foundations were undermined. A full formation rebuild is needed. Bridge repairs up to six months; and

• Extreme damage – track and formation damaged over more than 500 metres, track deformed and displaced, damage to tunnel portals, life safety threats for access. Bridge repairs in excess of six months. There were 15 such sites in Hawkes Bay, 14 of them north of Napier.

Digitising lidar (light detection and ranging), drone and aerial maps enabled rapid assessment of the work required, particularly temporary and make safe work, including quantities of material to remove or replace, and how the task should be approached.

A reconstruction alliance (Transport Rebuild East Coast Alliance – TREC) has been formed with KiwiRail, Waka Kotahi NZ Transport Agency and contractors Fulton Hogan, Downer and Higgins. This type of alliance worked well in the aftermath of the Christchurch and Kaikoura earthquakes, though in the Hawke’s Bay case, there is less opportunity to share works as road and rail run on largely separate routes (apart from through Eskdale, Clive to Napier and some shorter sections).

Reopening to Hastings

The line between Woodville and Hastings had damage over most of its 161km. Fortunately, most sites were not major; the worst was the washout of a bridge embankment at Waipawa. This was repaired and the line reopened by 3 April. There is still follow-up work to be done in this section to bring the line back to full standard.

With the line open to Hastings, road bridging of traffic - especially to the port - became feasible (see pic on page 20). KiwiRail has used customer sites at Team Global Express (TGE) in Hastings and Heinz Wattie’s nearby at Tomoana as transhipment points for freight. The TGE site is used for handling containers moving meat, dairy, machinery and other freight to the port. The daily pulp movement from Karioi in the central North Island, which is breakbulk rather than containerised, resumed in early June. This could not move to the port at all while main highways were blocked, and as the mill did not stop producing, its output had to be stockpiled off-site. After the reopening of the state highways, the traffic to the port was moved by truck to keep customers’ supply chains flowing. Now it is back on the rail, using Heinz Wattie’s site at night, when Heinz Wattie’s was otherwise not using the area.

Log traffic from south and north to the port is currently hauled by truck.

The floods stranded a number of locomotives and a heritage railcar in Napier. Once the line was open to Hastings, the stranded locomotives were shifted there by road. The railcar was roaded back to its Pahiatua base.

Hastings to Napier

In this 20km section, there were a small number of minor sites which have largely been fixed, and a major site, at Bridge 217 across a branch of the Tutaekuri River at Awatoto. Sixty metres of this 260m-long bridge was ripped apart by the flood waters. Three concrete piers and even more spans were washed away, and two further piers were potentially undermined and not safe to reuse. Some of these piers and spans have not yet been found. The rails were bent at right angles and broken off by the pressure of the flood and debris. Bridges are designed to withstand the build-up of debris, and also designed against scour, but the combined effect was too much this time.

A temporary bridge is being built, on the current alignment. This is using second-hand spans held for such an emergency (something the American owners in the 1990s thought should be sold!). It will include six new piers and five new 40-foot spans, with a further 20ft spans at each end. The piers are being formed from steel casings (railed from Belfast) which will be filled with concrete. As of mid-June, about half the new casings were in place. The bridge and the line through to Napier Port are expected to re-open later in the year.

A temporary bridge was chosen as it enabled quick design, procurement and construction to enable the line to be available again, including for access for rail equipment to any rebuilding effort north of Napier.

A permanent replacement will come later, on an alignment and with features like span length and height that will take into account the need for future flood protection and other transport improvements.

North of Napier

The line to Wairoa and Gisborne was mothballed in 2012. In 2019, it was reopened as far as Wairoa, to carry logs to Napier Port.

Along this 116km section were 70 per cent of the total damage sites on the line north of Woodville, and nearly all of those sites were classed as extreme. Damage included bridge damage, under and over slips, gully erosion and flood damage. In particular, it was concentrated on the 39km section from just north of the SH2/SH5 junction at Bay View to Kahika.

In the 7km section along the lower Esk Valley, through Eskdale (where the railway runs parallel to SH5), which is relatively flat, the damage is a result of floodwaters scouring out track and formation, distorting track, depositing debris and, in particular, silt. Not only are there mountains of silt to be cleared, but it is also potentially contaminated and may need to be treated as hazardous to work with.

It is not the first time it has flooded in the Esk Valley – in 1938 a similar massive flood closed the line for a time. For many years, the flood level was marked on the goods shed and later on a notice. The same flood damaged many bridges over an area roughly the same as Gabrielle.

In this section, the track materials are likely to be written off. It will have to be cleared of debris, and be rebuilt. The whole of the Esk Valley flats has been provisionally declared by the local authorities to be level 3 (where a currently unacceptable level of future risk means it may no longer be safe for people to live there), which illustrates the level of risk and damage to the railway. Any work on the railway here will need to be coordinated with Waka Kotahi and Hawke’s Bay Regional Council.

In the next 24km section, from the Esk River bridge up the steep sides of the Esk Valley through Waikoau to Tutira, there is extensive damage from underslips (washouts) and overslips. In contrast with the lower section, embankment washouts are the most common form of damage.

The Esk River bridge (see picture on page 8) appears to be standing but, in reality, has lost piers at the ends and cannot be used. The deck of the bridge is covered in debris. It didn’t stop there, as some even got deposited on the top of the truss! Records from the 1938 flood levels on this bridge show the 2023 water levels were a reasonable amount higher.

Further north, there are deep gullies and damaged bridges. In the first 16km of this section, the line rises almost continuously on a grade of 1 in 60 along a steep face up to more than 100m above the Esk, a rise of about 270m in total. The 8.5km section at the top of the Waikoau bank has the highest number of major sites. The last 6km to Tutira also has some major sites.

Many months of work will be necessary on this before reopening can be contemplated.

Conclusion

Natural disasters play havoc with roads and railways, especially in steep country like that north of Napier. The railway in Hawke’s Bay has been damaged before by floods and restored. This time, there is a significant amount of work to be done, particularly to the north of Napier, but the first priority is to