Weekend Herald


It’s best to avoid driving in flooded areas at all. But if you have to . . .


There was extensive flooding this month in Canterbury and surroundin­g areas of the South Island. It’s a timely reminder that it can happen unexpected­ly, especially in our winter months.

Flooding occurs when the input of water is greater than drainage can take away. This can be caused by a significan­t amount of rain or by a river bursting its banks — or even a burst water main.

The key advice for motorists is to avoid travel in situations where you could encounter flooding or other road hazards, unless it is absolutely essential. Always follow the advice of Civil Defence and emergency services and check for road closures before you head off. You could also run into insurance hassles, so it’s best to check your (or your company’s) vehicle usage policies before setting out.

Don’t, but if you do . . .

If you have to drive when there’s been heavy rain and flooding, make sure your vehicle is capable of the task. If you have an SUV, ute or vehicle with raised suspension you could be able to pass through water that is deeper than a standard car can manage. The standard car sill height can be around 15-20cm; in water a foot deep, most cars would start to float or feel a bit light, and double the depth could be present a danger of being swept away in flowing waters.

Don’t exceed 5km/h when driving through water, so you don’t overtake the bow wave generated at the front of the vehicle. If a vehicle is coming in the other direction, let it past first so that your two bow waves don’t meet. If you’re following another vehicle, wait for it to clear the flood, because if it becomes stranded you don’t want to be trapped behind it and lose momentum.

The aftermath

If a vehicle drives through shallow flood waters, it will usually dry out by itself after a few kilometres of driving. The brakes will dry off with heat, so the driver should lightly apply them after exiting the water to ensure they will operate safely next time they are needed.

The AA recommends you have your air filter checked by an automotive vehicle service and repair provider if the pressure wave in the front of the vehicle was near bonnet level, as this is usually where the engine air intake is.

If a vehicle sits or drives in deep flood water

Driving into deep water at speed is like driving into a wall. The resistance of the water will slow your vehicle down very quickly. Water will be pushed in a wave ahead of your vehicle, going under the bonnet and could be forced into the engine, damaging parts (water doesn’t compress, so even a small amount inside can be enough to bend internal components).

If you find your vehicle has been caught in flood waters

Even if water hasn’t seeped inside the vehicle, it is not recommende­d the vehicle be driven.

Contact your insurance company and seek advice. The vehicle will need to be sent to a service and repair provider to have all the driveline components checked and may require transmissi­on and differenti­al fluids replaced.

In some instances, even the CV joints in the axles of some vehicles may need to have the grease replaced, as water may have seeped in through any cracks/ holes in the rubber boots or ventilatio­n valves. The brakes may have trapped mud or silt and require a thorough check and clean to ensure they work safely.

In the unfortunat­e event a vehicle is trapped in flood waters and has water inside, do not attempt to power up the system or start the vehicle, as water could be inside the engine and electrical systems. We recommend calling your insurance company and follow their recommenda­tions.

There is a high chance of a submerged vehicle being written off as the electrics, safety systems, engine and drivetrain could be full of water and may not recover, even if dried out. The cost of replacing all the electrical and safety systems alone could cost more than the value of the vehicle.

Check Waka Kotahi NZTA’s website for road closures and visit AA Insurance and AA Auto Centre for advice.

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