Flash Floods

Flash flooding is flooding that was not expected. Flash floods are the most dangerous of all floods because of the element of surprise. Intense rainfall over a significant period of time can cause flash flooding. The speed with which a flash flood can occur makes it even more dangerous. Flash floods often occur in dry areas where the ground is baked hard. When torrential rains do come, water immediately fills arroyos, or dry stream beds, turning them into raging rivers. The torrent of water rushes through with enough force to wash away sections of concrete road.

Flash flood waters move very quickly and can move boulders, tear out trees, and destroy bridges and buildings. Sometimes a wall of water 10 to 20 ft (3 to 6 m) high carries a huge amount of debris. The worst flash floods are created when a dam or levee breaks and a huge amount of water suddenly pours downstream, destroying everything in its path. Inland flooding has been the number-one cause of deaths from hurricanes in the past 30 years. In 1999, Hurricane Floyd caused 56 deaths. Fifty of them were people who drowned due to inland flooding. Inland flooding occurs when a slow-moving storm is accompanied by heavy rains. Inland flooding is a threat to communities hundreds of miles from the coast. Over a third of the people who drown during an inland flood are in their cars. Some are trying to escape the flooding, while others are attempting to abandon the cars. Even a foot of water can cause a car to float, and if that water is rushing down a street, the car can be swept away.

All kinds of floods cause problems for people. The worst consequence of floods is loss of lives. Property damage is a major problem with flooding. Houses can be completely demolished or even carried away down a turbulent river. Even houses left standing after a flood usually have substantial water damage and some have structural damage as well. Also, when the water subsides, it leaves behind a thick, sticky coat of mud filled with debris. So even if there is no structural damage, cleaning up after a flood is a big job.

Floods can also spread disease. Water flowing through an area can pick up chemicals and waste products and move them to another place. Most diseases are more easily spread through water than through air. That is one reason it is so important for those in a flooded area to drink only bottled or boiled water. Besides damaging homes, floods can cause other problems to agricultural areas. Soil can be eroded and crops already in the fields can be ruined. Floods also damage reservoirs and rivers where they deposit the load of soil the water picked up from the fields.