Features of a Flood

A flood is basically an overflow of water so that land which is normally dry is covered by the water. Floods can result from heavy rainfall and from melting ice or snow. When a river, ocean or lake area exceeds its capacity, it will spill over along river banks or shore lines. Floods may result in human injuries or death and property damage, or can be minor as in the case of the annual flooding of the Nile. Different types of floods have various characteristics.

Flood Features

• River water levels increase and decrease; this is known as the flood wave. As a river overflows, the water will slow down and congest the downstream areas. In Arctic basins, floods can result when ice blocking the lower part of the river melts. A "storm surge" results when an impending hurricane forces ocean waves onto shore. A "flash flood" may occur after a short, heavy rainstorm causes torrential overflows or when a man-made or natural levee or dam bursts due to a rainstorm. The condition of the soil may affect how often floods occur based on its saturation level and permeability.

Types Of Floods

• Floods are categorized according to the length of duration. Slow-onset floods may last for a few weeks and sometimes even months, resulting in possible damage to livestock, roads or railway links. Rapid-onset floods typically last for just a few days, but a rapid-onset flood can actually result in greater damage because of the lack of notice to prepare for such an emergency. Flash floods often cause the greatest damage and can arise in minutes after an intense rain or tropical storm or due to dam or levee break.

  Floods are also categorized based on their locations. Coastal floods, for example, occur in coastal areas when hurricanes or tropical storms cause heavy rainfall, ocean water is driven on to the coast, or when volcanoes or earthquakes cause huge tidal waves.

  A river that is usually dry is known as an "arroyo," and when a storm moves into such areas, it will typically develop into an "arroyo flood" along the gully. A river flood results when the water in a channel exceeds its capacity due to melting snow or an intense spring rain. Urban floods affect areas with paved roads, where a large amount of rainfall cannot be absorbed into the ground.

Flood Control Measures

• Planting ground cover on slopes, building small dams and constructing terraces to increase soil infiltration may help detain runoff. Other flood control measures include constructing levees to inhibit the flow and straightening or dredging a channel to improve the flow. Examples of flood control projects in the U.S. exist alongside the Mississippi River and the Hoover Dam on the Colorado river.