Advice on driving in flood waters

ARRIVE Alive has issued a warning to motorists to be cautious when driving in flowing water or crossing bridges built over streams and rivers. It advises motorists to take the following into consideration when crossing or driving in flowing water, standing water and to slow down as speeding may cause your vehicle to aquaplane.

• Flowing water applies pressure to contact areas. The higher the speed the higher is the pressure.
• With water that is one meter high it will flow out at a speed of 4.47 meters per second or 16 km/h. The pressure is one metric tone per square meter.
• With a wheel half under water is the area 0.4 sq m and the force 0.4 tonne per wheel. For the four wheels it becomes one and a half tons and for 2m of water it becomes 2 ton per sq m.
• Be careful, water that has fallen only 0.4m reached a speed at 3.2 km/h and can sweep your car off a road bridge.
• When the side of the body of a vehicle makes contact with the water the force increases rapidly but the water now also acts on the underside of the vehicle as well and starts to lift it. It is now able to float like as ship. The weight of the vehicle will not be able to hold it on the road. Every cubic meter of space in a vehicle can lift one tonne.
• Be careful, 0.6 meters of water can float a car. Only vehicles that are open and let the water through will behave differently.
• Establish the body area of the vehicle and its mass. From this calculate the how deep will the vehicle sink in the water before it floats. For a truck that is 8.5 meters long and 2.5 meters wide and with a mass of 12 tonne it will float at a level of .532 meters above the body base and be able to float down the river.

• Danger of standing water

Standing water does not exert side pressure but will also lift the vehicle and float it. Then it will be impossible to move it forward.

• Speeding vehicles and aquaplaning

When vehicles are moving fast over a layer of water the vehicle can start to aquaplane. If the tyres are worn, it is easier to happen. Under these conditions an untrained driver may easily loose control over the vehicle.