Flash Floods

(Important for Prelims, Geography)

Q. What are Flash Floods?

· A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice or snow flowing over ice sheets or snowfields. Flash floods may also occur after the collapse of a natural ice or debris dam, or a human structure such as a man-made dam.

·   This specific type of flooding occurs within a short frame of time after a precipitation event, which is generally less than six hours. It takes place in areas near rivers or lakes. However, it can also take occur at places with no water bodies nearby.

·      These are characterized by very fast rise and recession of flow of small volume and high discharge, which causes high damages because of suddenness.

Q. What are the causes of Flash Floods?

·     A flash flood is often the result of a heavy or excessive rainfall. Whenever it rains, the soil acts as an absorber, and absorbs the precipitation. However, in cases of heavy rain, the soil may be saturated to capacity and unable to absorb any more water.

·       Flooding can also occur after a drought, when the soil is too dry and hardened to absorb the precipitation. This is why, flash floods are a common scene in desert landscapes after heavy rainfalls. The other reason of flash floods are cloudburst or thunderstorm. It is common in places such as hilly, not too hilly regions and sloping lands.

·   Depression and cyclonic storms in the coastal areas of Orissa, West Bengal, Andhra Pradesh, Karnataka, and Tamil Nadu also cause flash floods. Further, the states of Arunachal Pradesh, Assam, Orissa, Himachal Pradesh, Uttarakhand, the Western Ghats in Maharashtra and Kerala are more vulnerable to flash floods caused by cloud bursts.

·   In addition to these, sudden release of waters from upstream reservoirs, breaches in landslide dams and embankments on the banks of the rivers can also lead to disastrous floods. The severe floods in Himachal Pradesh in August 2000 and June 2005, and in Arunachal Pradesh in 2000 are a few examples of flash floods caused by breaches in landslide dams.

·     Floods in Assam, Bihar, Uttar Pradesh, Orissa and Andhra Pradesh are generally caused by breaches in embankments. Incidents of high intensity rainfall over short durations, which cause flash floods even in the area where rains are rare phenomena, are on the rise and the problem needs to be tackled in a scientific manner.