floods n.
Skip this Video
Loading SlideShow in 5 Seconds..
Floods PowerPoint Presentation


535 Vues Download Presentation
Télécharger la présentation


- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Floods School: Abdallah Al-Alayly Teacher: Ms. Abeer Abdallah Prepared by: Grade 9 students

  2. What Is A Flood? • Floods are the most common and widespread of all natural disasters except fire. A flood as defined by the National Flood Insurance Program is “a general and temporary condition of partial or complete inundation of two or more acres of normally dry land area or of two or more properties from overflow of inland or tidal waters, unusual and rapid accumulation or runoff of surface waters from any source or a mudflow.”

  3. Kinds of Floods • River Flood: Some floods occur seasonally when winter or spring rains, coupled with melting snows, fill river basins with too much water too quickly. Torrential rains from decaying hurricanes or tropical systems can also produce river flooding. • Coastal Flood: Winds generated from tropical storms and hurricanes or intense offshore low pressure systems can drive ocean water inland and cause significant flooding. Coastal flooding can also be produced by sea waves called tsunamis. • Urban Flood: As land is converted from fields or woodlands to roads and parking lots, it loses its ability to absorb rainfall. During periods of urban flooding, streets can become swift moving rivers, while basements can become death traps as they fill with water. • Flash Flood: Dams are designed to hold a river’s water in reserve for when people may need it. If a dam were to break then all the trapped water would rush down the river at the same time and cause a flash flood. • Ice Jam: Floating ice can accumulate at a natural or manmade obstruction and stop the flow of water.

  4. Causes of Floods • Numerous factors contribute in causing floods. When it rains or snows, some of the water is retained by the soil, some is absorbed by vegetation, some evaporates and the remainder, which reaches stream channels, is called runoff. Floods occur when soil and vegetation cannot absorb all the water; water then runs off the land in quantities that cannot be carried in stream channels or retained in natural ponds and constructed reservoirs. About 30 percent of all precipitation is runoff and this amount may be increased by melting snow masses. Moreover, heavy rain combined with melting snow causes the rivers to overflow their banks and flood. In addition, intense rainfall over a relatively small area may lead to a flood. Furthermore, high tides induced by severe winds over ocean surfaces result in floods. Thus, floods occur due to prolonged rainfall lasting several days, intense rainfall over a short period of time, an ice or debris jam that causes a river or stream to overflow and flood the surrounding area, snow-melt combined with rain in winter, severe thunderstorms, or tropical cyclones that bring intense rainfall to the coastal and inland areas in the summer and fall.

  5. Effects of Floods There are two kinds of flood effects: Domestic and national • Domestic effects are the erosion of people which continues in several places of the effected place, city drainage systems that fail to serve their purpose and the drains that carry the polluted waste water which should have actually gone to a sewerage system for treatment. • National effects are the soil erosion which is one of the main effects of heavy floods; the flow of rivers above the danger level; insufficient stock of food and medicine to cope with the situation; the fact that the affective places remain cut off with the rest of the country; the damage occurred to several hutments, granaries, fisheries and standing crops; the submersion of many roads and relief camps by flood water; catastrophic debris slides can be triggered by flood producing rain; and a great heap of destruction for floods can roll boulders, tear out trees, destroy buildings and bridges and scour out new channels.

  6. What To Do? There are some steps that should be taken before or during a flood. • one should head for higher ground and stay away from flood water . • If one lives in a flood-prone area or think he is at risk, he should evacuate immediately. It is important to move to a safe area before access is cut off by floodwaters. The most dangerous thing one can do is to try walking, swimming or driving through flood waters. • one should follow the instructions and advice of local authorities. • If one is driving, he should avoid already flooded areas. • If one’s vehicle becomes surrounded by water or the engine stalls, and if he can safely get out, he should abandon his vehicle immediately and climb to higher ground.

  7. Places Hit By Floods • Bangladesh:An exceptionally heavy flood affected 3.5 million people in half of the country's 64 districts. • India: the east and north-east of India witnessed floods which killed at least 43 people in landslides yesterday.