Flash flooding is the number one weather-related killer in the United States. Flooding kills almost twice as many people each year as tornadoes and hurricanes combined! Unlike hurricanes, floods are a threat in every state.
Most flash flooding is caused by slow-moving thunderstorms, thunderstorms repeatedly moving over the same area (called "training"), or heavy rains from hurricanes and tropical storms.
Nearly half of all flash flood deaths are auto-related. Even 6 inches of fast-moving flood water can knock you off your feet and at a depth of 2 feet will float your car.
Water weighs 62.4 pounds per cubic foot and is typically flowing downstream at 6 to 12 miles an hour.
When a vehicle stalls in the water, the water’s momentum is transferred to the car. For each foot the water rises, 500 pounds of lateral force are applied to the car.
The biggest factor is buoyancy. For each foot the water rises up the side of the car, the car displaces 1,500 pounds of water. In effect, the car weighs 1,500 pounds less for each foot the water rises.
Two feet of water will carry away most cars - 1,000 pounds of lateral (or side force) plus 3,000 pounds of buoyancy!