Impact of the 2019/2020 summer drought on roads on the Hauraki Plains - FAQs
Why do drought cause damage to the roads on the Hauraki Plains?
- A large proportion (about 44 per cent or 230km) of the Hauraki District’s local roads are on unique, moisture sensitive soils (organics, marine muds/clays) on the Hauraki Plains.
- During the recent drought, these soils dried out and contracted more than usual, causing widespread damage such as cracking, slumping, rutting, and settling of the road surface.
- The drought didn’t affect roads outside of the Hauraki Plains as markedly, as they are on different soils.
- Some roads will require full width repairs in places, and others are half width. Overall it equates to about 10 kilometres of road length.
How widespread is the damage?
There is some damage to most roads on the Plains.
- Some roads need full width repairs in places and others are partial width.
- Overall, we need to repair an equivalent of about 10 kilometres of road.
- The drought damage programme of work is about 3.5 times larger than our normal road repair programme.
- The work will take place over two construction seasons (i.e. over a two-year period) as a Second Coat seal, which provides a thick durable surfacing layer, can only be applied after the First Coat has received some trafficking, ideally within a year of the initial repairs.
Why haven’t all the roads been repaired yet?
- We’ve fixed areas that presented an immediate safety threat.
- However, we’ve waited to repair other Plains roads until after winter 2020 to allow ground moisture levels an opportunity to ‘normalise’.
- Doing the repairs while the ground was still drying out and moving may have resulted in them failing and needing to be done again when moisture levels returned to normal.
What will it cost to fix the damage?
About $2.8M. Waka Kotahi NZ Transport Agency will pay for most of the work through their Emergency Works programme, and the balance will be funded by Council across the 2020/21 - 2023/24 financial years.
Which roads are Council responsible for?
- We look after local roads.
- Waka Kotahi NZ Transport Agency looks after state highways.
- State Highway 2 and State Highway 25 run through the Hauraki Plains.
How do droughts cause damage to roads?
- Some soils, particularly those that provide the foundation for the roads on Hauraki Plains, shrink considerably when they dry out. Some soils will expand once they become wet again but regretfully the damage is already done. Other soils stay in the “shrunk” state once the moisture is removed.
- The shrinkage causes deformation of the road surface and in some cases this causes ruts and large bumps. In other cases, it results in cracking of the sealed surface which in itself is not that noticeable and generally does not cause a problem until the rain comes again. When the rain comes the cracks let water into the road pavement. When water gets through the seal, potholes form and the pavement can lose its strength.
- Climate change is likely to result in more extreme weather events such as droughts so we are researching and studying the timing of repair work and the type of repairs to learn what will be most effective in the future.
What precautions should road users take on the Plains roads over summer?
- We encourage everyone to take extra care on the Plains’ roads over summer.
- Some surfaces will feel uneven, so keep both hands on the steering wheel so you are prepared for any unexpected movement from the wheels of the car or bike.
- There will be various road construction crews out and about, so be prepared to slow down or stop.
- Road users also need to expect the unexpected on rural roads – tractors, ducks, pheasants, hares and even livestock can take you by surprise.
- Thanks for your patience and extra care on the road as we complete this work.