Tips on how to do a safe river crossing

BARRY PARK
Last updated 07:01 24/08/2012
Make sure you know the risks, and be properly prepared, before attempting a river crossing.
Fairfax NZ

KNOW THE RISKS: Make sure you know the risks, and be properly prepared, before attempting a river crossing.

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Water crossings have to be one of the most challenging parts of off-roading.

The golden rule is that you should never attempt one without first knowing the depth of water you'll be driving through.

Even familiar stretches of river can change overnight as rainfall kilometres away builds the up the current, shifting stones and other obstacles hidden below the river's surface including submerged logs, patches of sand and deep depressions.

Walking the river before crossing it, following the path of that the left wheels of the vehicle will take and returning along the path the right wheels, will take will often show these up and help with planning the shallowest route across. Take a stick, too, so you can get a sense of the river bed's firmness.

Before attempting a crossing, wind down the electric windows and unlock all the centrally locking doors so that if you do get stuck and the vehicle's electronics fail, you can still get out of the vehicle.

If the water is particularly deep, you may need to cover the front of the vehicle with a tarp to stop water washing in over the engine – and, crucially, into the air intake, where it can cause terminal engine damage.

The golden rule is to pick a low-range gear, enter slowly, don't change gears, and only drive fast enough to get a small bow wave appearing in front of the vehicle. Other important factors are the ease of entry to the water, and how difficult it will be to get out the other side, particularly if other vehicles have already turned the bank into a slippery slope.

Water is extremely deceptive. A calm-looking surface can hide fast currents underneath, particularly if the river is shallow, and it does not need to be very deep, either, to carry enough force to push a vehicle sideways as it crosses at a right angle to the river's flow.

Vehicles will also tend to float slightly, and the rear end may bob around a bit if it has more buoyancy than the engine-laden front end. If the side panels are dipping into the water, the sideways force is a lot higher than if the water was pushing against the wheels alone and there is more chance the water could sweep your car downstream. Most stock off-road vehicles only have a wading depth of between 300mm and 500mm (it's the serious 4WDs that approach the latter figure), which means the water should only come half-way up a wheel.

However, with a few modifications such as a snorkel and breather pipes, a vehicle can safely attempt deeper crossings.

For a deep crossing, it pays to attach a recovery strap to another vehicle. If one becomes stuck half-way across, the second vehicle is still able to provide some instant support if things start to go pear-shaped.

If your engine stalls mid-way through a crossing, don't attempt to restart it. The risk is that the engine may have sucked water inside it, and because water does not compress very well, you'll damage the cylinders and pistons and rack up a huge repair bill.

-Fairfax Australia

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