Concept of Flooding As a Natural Disaster

Concept of Flooding

Flooding is a natural and recurring event for a river or stream. Flooding is a result of heavy or continuous rainfall exceeding the absorptive capacity of soil and the flow capacity of rivers, streams, and coastal areas (Nelson, 2011). Flooding is an overflowing of water onto land that is normally dry. Floods can happen during heavy rains, when ocean waves come on shore, when snow melts too fast, or when dams or levees break. Flooding may happen with only a few inches of water, or it may cover a house to the rooftop. They can occur quickly or over a long period and may last days, weeks, or longer. Floods are the most common and widespread of all weather-related natural disasters (Nelson, 2011). A flood is a situation in which water temporarily covers land where it normally doesn’t. This water comes from the sea, lakes, rivers, canals or sewers. It can also be rainwater. A flood is a hazard that can happen in any part of the world. Floods bring misery to those that live in the area. They can cause loss of life and often cause a great disruption of daily life mostly transportation: water can come into peoples houses, drinking water and electricity supplies may break down, roads can be blocked, people cannot go to work or to school. Floods all over the world cause enormous damages every year like economic damages, damage to the natural environment and damage to national heritage sites (Maria & João, 2018).

Types of Flooding

Floods can be described according to speed, geography or cause of flooding (DTLR, 2002) Coastal flooding Coastal flood is when the coast is flooded by the sea. This is caused by severe storm. The storm wind pushes the water up and creates high waves. A storm is formed in al low pressure area, beneath a low pressure area the sea level is higher. A flood starts when waves move inland on an undefended coast or overtop or breach the coastal defence works like dunes and dikes. The waves continuously attack the shore. When it is a sandy coast, each wave in a storm will take sand away. Eventually a sandbank may collapse that way.

River Flooding

Rainfall over an extended period and an extended area can cause major rivers to overflow their banks. The water can cover enormous areas. Downstream areas may be affected, even when they didn’t receive much rain themselves. With large rivers the process is relatively slow. The rain water enters the river in many ways. Some rain fall into the river directly, but that alone doesn’t make the river rise high. A lot of rain water run off the surface when the soil is saturated or hard. It flows to small rivers that flow to larger rivers and these rivers flow into even larger rivers. In this way all the rain that fell in a large area (catchment area) comes together in one large river. When there is a lot of rain over a long period, the river rises gradually as it is fed with water form smaller rivers. It takes time for all the rainwater to reach the river, but once it is in the river it flows downstream to sea (Pradhan, & Pokharel, 2017). When a dike or a dam breaks and a lot of water is released suddenly, the speed of the water at the breach can be compared with the speed of a flash flood. As a larger area gets covered the speed will be reduced. The water spreads out as much as possible flowing to the lower lying areas before slowly rising. A breach is very dangerous for the people living close to it. The strength of the water may carry cars, trees and even houses away and cause loss of live. According to Stephen (2014) This type of flooding affects villages surrounded by large stretches of water; roads are blocked creating transportation and communications problems.

Ponding (or pluvial floods)

Ponding is a type of flooding that happen in flat areas. Rain water falling in an area is normally stored in the ground, in canals or lakes, or is drained away, or pumped out. When more rainwater enters a water system than can be stored, or can leave the system, flooding occurs. In this case, rain is the source of the flood: not water coming from a river, but water on its way to the river. That\'s why it is also called \"pluvial flood\". Puddles and ponds develop on the land, canals are filled to brim and spill over; gradually a layer of water covers the land.