Flash Floods

Flash floods occur when water levels rise rapidly and inundate low-lying areas. The United States National Weather Service defines flash floods as floods that occur within 6 hours of their cause, which may include heavy rainfall, ice dam breakage, and dam or levee failures. Flash floods cause minor to severe damage, injury, or death, and often disrupt transportation systems. Although some regions are more likely to experience flash floods than are others, they can occur anywhere in the world.

Flash floods often occur when heavy rain falls on less permeable surfaces such as clay soils, soils already saturated with water, and concrete. Urbanization therefore contributes to flash flood hazards in two ways. Instead of infiltrating the ground, the water flows over land surfaces and through streets, ...