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Home : Roads and Transportation : Road Safety : Road Safety Advice : Flooding



Floods can occur when rivers burst their banks after a period of heavy rainfall. Large volumes of water can cause flash-floods, or floods in urban areas where the sewers and drains can't cope and there is nowhere for the water to soak away.

Walking ,cycling, riding or driving through flood water can be extremely hazardous and should be avoided. Prevention is better than cure; in the case of flooding this means watching the weather forecasts before you set out on a journey, If flooding is widespread you might be better off cancelling trips that are not absolutely necessary.

If you are in a flood affected area consider moving your motorcycle or car to a place of safety when you first hear the warnings, but also be aware that if flooding has started moving your vehicle could pose a serious risk - never underestimate the dangers of flood water.

Things to consider...

  • Flash floods can come rapidly and unexpectedly. They are usually caused when rivers break their banks. You may not be warned that a flash flood is approaching.
  • Never attempt to drive through a flood that you couldn't walk through and be aware that water hides dips in the road. Worse still, there may be no road at all under the water. Flooding can wash away the entire road surface and a significant amount of ground beneath.
  • Just six inches of water will reach the bottom of most passenger cars; this depth can cause loss of control or possible stalling as water is sucked into the exhaust or washes into the air intake. When negotiating a flooded section of road, drive in the middle where the water will be at its shallowest.
  • Consider other drivers - pass through flooded sections one car at a time and don't drive through water against approaching vehicles.
  • Many cars will start to float in as little as one foot of water - this can be extremely dangerous because as the wheels lose grip, you lose control.
  • Two feet of flowing water can sweep away most vehicles —including large four-wheel drive cars. Don't try driving through fast-moving water, for example approaching a flooded bridge – your car could easily be swept away.

If you intend to drive through a flooded section of road, your first task is to check the depth of the water. In normal vehicles you should never attempt to drive through water that is more than about 25 centimetres deep (or up to the centre of your wheels).

It's also worth checking where the air intake is on your engine. If water is sucked into the engine it will stall, but worse than this, it can cause severe damage that will require the engine to be stripped down in order to bring it back to life. Do not try to restart an engine that has sucked in water - the spark plugs or injectors should first be removed to allow the water to be expelled.

Some four-wheel-drive vehicles are equipped with high level air intakes allowing them to be driven through water several feet deep. However even these vehicles can be washed away in flowing water. If the water is 30 centimetres deep and fast-moving it could wash your car off the road.

Where possible, it is best to negotiate through floods by one vehicle at a time. Wait for approaching vehicles to clear the water before you start to drive through.

If your wheels start to lose grip partway through a flooded section it could be that the car is trying to float. To counter this, open a door and allow some water into the car, this will weigh it down, enabling the tyres to grip again - it's probably best to get a passenger to do this so that you can continue revving your engine and slipping the clutch.

After driving through a flooded section of road or a ford across a river, test your brakes (whilst still driving slowly) and be prepared to dry them off by touching the brake pedal very lightly with your left foot (practice this on an empty stretch of road next time you go out driving to discover whatvery lightly means!).