The two factors that contribute to flash flooding are rainfall intensity and duration of the rain. Most flash flooding is caused by slow-moving or stationary thunderstorms.
Imagine the actual weight of a gallon of water: over eight pounds per gallon! Now imagine millions of water rushing across the ground seeking drainage.
Flash flooding can tear out trees, destroy homes and wash away bridges with only waters weight used as force.
Avoid walking through any flood waters. If it is moving swiftly, even water 6 inches deep can sweep you off your feet. Beware of snakes and other critters in the floodwaters. It is NEVER safe to play even after the rain has ended.