There are a number of dangers to be aware of when driving through flood waters. Apart from shorted-out electrics on petrol cars, there is also a risk of the engine sucking in water which will cause it to lock solid (hydraulic lock), smashing connecting rods, pistons, even crankshafts. If the water is fast-moving, there is also a risk that the car could be carried off, with you inside.
More than half (54%) of UK drivers would endanger themselves and their vehicles by driving through moving flood water, according to a joint Environment Agency and AA survey in October/November 2013. The research of 21,165 AA members also revealed that more than a quarter (27%) of respondents would drive through moving flood water deeper than 30cm, which is enough to move a car. The Environment Agency and the AA strongly advise not entering flood water that is moving or more than 10cm deep.
According to the AA, a third of flood-related deaths involve a vehicle because drivers take unnecessary risks.
So what should you do when you meet a flood behind the wheel?
1. Look for an alternative route
Firstly, you should try to avoid the flood water, but if you can’t, you should make sure there is not more than six inches of standing water or four inches of moving water.
Parking up and watching how other drivers attempt to negotiate the flood can be a good way of checking to see how deep it is. In particular look out for hidden dips and gullies where the water could be deeper.
3. Go forth (slowly!)
If you decide to go through, stay on the crown of the road where possible and crawl through the water very slowly in first gear. Avoid the temptation to make a quick exit, as going at speed can push water into the engine bay. Keep the engine revs up by slipping the clutch if necessary, to avoid water entering the exhaust pipe.
4. Got a 4×4? Make waves!
Experts at Land Rover advise entering the water slowly (about 1-2mph), before accelerating to about 3-4mph. This creates a bow wave in front of the vehicle, which will create a depression in the engine bay and keep the air intake clear of water. However, it warns that this technique won’t work with beam-axled 4x4s, as the water tends to hit the front axle beam and squirt straight into the engine bay.
5. Be aware of ‘gung ho’ drivers
Watch out for the less clued up drivers coming the other way. You might be observing all the best advice, but giant 4x4s or trucks racing though in the opposite direction can create such bow waves they drown your car.
6. Exit with caution
When you make it through the water, don’t assume that you have emerged unscathed. Dry the brakes by using them gently and continue to test them for several miles. At the earliest opportunity check the radiator matrix for blockages.