In the 1970s floods replaced lightning as weather's biggest killer. The experts' advise not to drive or wade into flood waters at all, especially if you can't see the bottom. Water over a road, no matter how deep, can hide washed out pavement. As little as six inches of moving water is enough to float a small car and carry it away. That's enough force to punch a car or light truck off a flooded road if the water's up to door level.
Mudslides also can become death traps.
Rain falling onto a hillside can lead to it giving way and tumbling into roads or houses. An on-line graphic and text explains how these form. Alaska Australia Brit.