FLOODS
Floods are rare events in which a body of water temporarily covers land that is normally dry. Floods also occur around lakes, wetlands and the sea coasts. However, river floods occur naturally and in many cases, are beneficial for ecosystem functioning because they allow the river to exchange water, sediments and nutrients with the floodplains. Such floodplains provide habitat for a wide range of aquatic and riparian (situated on the banks of a river) organisms. River floods are typically caused by excessive rainfall or sudden melting of snow and ice.
During rainy seasons, most of the rivers overflow their banks, causing minor floods. Moderate floods might occur in every five to ten years, and very large floods might only occur once in fifty or a hundred years. The average time period over which a flood of a particular magnitude occurs is called that flood's recurrence interval or return period. For example, very large flood occurs, on average, once in a hundred years as happened recently in Kerala, 2018. Earlier in June 1924, such a heavy flooding occurred in Kerala, causing extensive damages in different parts of the state. The 1924 incident is commonly referred to as the "Great Flood of 99", denoting Malayalam calendar year 1099.
Flash floods are caused by heavy rains falling on soil already wet or frozen and therefore have limited capacity to absorb more water. Flash flood may occur on land covered in snow or ice. In such situations, the soil has limited capacity to absorb water so that the melting snow adds to the runoff. Flash floods are highly dangerous because the people downstream do not get enough time to get informed or prepared. Human activities such as development in the watershed and modifications of the river channel can change the frequency and severity of floods. In particular, expansions of urban areas increase the frequency and intensity of floods. This happens when roads, parking lots and buildings prevent drainage of water.
Floods make considerable changes to the width and depth of river channels. Rivers overflowing their banks inflict severe losses to men, property, animals and plants. Floods cause severe environmental problems too. Floods result in serious economic and social disorders. Deforestation is a major factor aggravating the damages due to floods. Felling of trees on the banks of rivers and their plains escalate the damages. In fact, the river plains and nearby wetlands are nature's flood control systems into which overflowing rivers could spill water. As such, any modifications in wetlands and plains will affect their water holding capacity. As a result, tonnes of valuable soil are getting swept away during floods when rivers flow through unexpected routes. Mining, extractions, excavations, etc., lead to landslides. During floods, topsoil and subsoil are carried into sea. Thus ultimately, all these result in huge losses to men and property.Mining, extractions, excavations, etc., lead to landslides. During floods, topsoil and subsoil are carried into sea. Thus, ultimately, all these result in huge losses to men and property. Floods are rare events in which a body of water temporarily covers land that is normally dry.
You must be logged in to post a comment.