Chapter II

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CHAPTER II Types of Calamities Flashfloods Flashfloods, dangerously fast moving floods caused by a large amount of heavy rain, are basically a natural hydrological phenomenon. This torrential downpour comes from a normally calm area into a devastating river of death in a short period of time, the main reason many people are caught unprepared. Flash floods are somewhat different from normal floods. Normal floods involve water rising and overflowing from its normal path. However, flash floods app
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  CHAPTER IITypes of CalamitiesFlashfloods Flashfloods, dangerously fast moving floods caused by a large amount of heavyrain, are basically a natural hydrological phenomenon. This torrential downpour comesfrom a normally calm area into a devastating river of death in a short period of time, themain reason many people are caught unprepared. Flash floods are somewhat differentfrom normal floods. Normal floods involve water rising and overflowing from its normalpath. However, flash floods appear quickly and move swiftly across land with littlewarning. The water in a flashflood moves at such a high velocity that it can moveboulders, uproot trees, demolish buildings, and destroy bridges. The walls of water insuch a flood and be anywhere from ten to twenty feet tall and usually carry a substantialamount of debris.(http://library.thinkquest.org/03oct/00758/en/disaster/flood/flashfloods.html)  Flashfloods commonly develop in hilly and mountainous terrains where the slopeof the river is rather steep. The prompt development of the flood is due to the extremelyshort concentration time of the drainage catchment which means precipitation falling on apoint in the catchment farthest from the river takes only a short time to reach the riverchannel and become part of stream flow. Thus, the amount of stream flow rapidlyincreases and, consequently, the rise in water level. When the flow capacity of the stream  is exceeded, the channel overflows and the result is a flash flood.(http://kidlat.pagasa.dost.gov.ph/genmet/floods/cause_types.html) As land is converted from fields or woodlands to roads and parking lots, it losesits ability to absorb rainfall. Urbanization increases runoff two to six times over whatwould occur on natural terrain. During periods of urban flooding, streets can becomeswift moving rivers, while basements and viaducts can become death traps as they fillwith water. Flooding occurs in known floodplains when prolonged rainfall over several days,intense rainfall over a short period of time, or an ice or debris jam causes a river orstream to overflow and flood the surrounding area. Countries having four seasons,melting snow can combine with rain in the winter and early spring; severe thunderstormscan bring heavy rain in the spring and summer; or tropical cyclones can bring intenserainfall to the coastal and inland states in the summer and fall.Floods are also caused, indirectly, by seismic activities. Coastal areas areparticularly susceptible to flooding due to tsunamis (seismic sea waves). Sinking of landdue to earthquakes reduces the elevation of land areas. In the vicinity of lakes and rivers,these areas become flood-prone. Likewise, the uplifting of lake and river beds fromseismic causes sometime results in the overflowing of these bodies of water. The waterthen inundates the surrounding and adjacent areas. To a certain extent, astronomicallyinfluenced phenomena such as high tides coinciding with the occurrence of heavy rainfallfrequently cause flooding.Occasionally, floods occur unnaturally. These are usually the result of humanactivities. Some of these undertakings are: blasting causes landslides in the slopes of hills  and mountains which may result in the unintentional damming of rivers and streams;construction of temporary dams this produces an obstruction to the flow of a river orstream which then results in an overflow; failure of hydraulic and other controlstructures result in the entry of an enormous quantity of water in a protected area such asaccidents like the breaking of a dike; and mismanagement of hydraulic structures resultsin an untimely and sudden release of large amounts of excess water, control structureslike dams which are utilized for various purposes are usually operated according to whatis known as an operation rule and mismanagement which the violation of the rule maythe root of such catastrophic event.While not quite so obvious, human activities that tend to alter the ecologicalsystem in a river basin will have an impact on the hydrology of the catchment. Thiscould, in the future, result in frequent floods. Foremost among such activities is thedenudation of forest and watershed areas.(http://kidlat.pagasa.dost.gov.ph/genmet/floods/cause_types.html)    Flash floods have a variety of effects that affect the lives of people living in flood-prone areas. Economically, flash flooding is a natural disaster responsible for millions of dollars in property damages every year. Flashfloods are among the most frequent andcostly natural disasters in terms of human hardship and economic loss. As much as 90percent of the damage related to all natural disasters (excluding droughts) is instigated byfloods and associated debris flows ( Talking About Disaster: Guide for Standard  Messages , 1999). Disaster stricken place caused by flashfloods lose their houses(appliances and things inside), livelihood especially in agriculture and etc.. Afterflooding, government has to input many resources for aiding or reconstruction such as  police force, aid worker, resources used for resisting flood which also brings loss tosociety.Environmentally, flash floods carry unconceivable damages. Floodwaters haveenough strength to damage or destroy buildings, sometimes washing them completely off their foundations. Some floodwaters can destroy roadways, wash out bridges and wipeout most anything in their path. This dangerous effect of flash flooding can trap people intheir homes and make roads impassable, rendering victims helpless to escape from thedanger. Air rescues are sometimes necessary to pull people to safety.The sudden rise in the water level can often destroy sewer and drainage systems,making a potential health hazard anywhere that has been affected. Human waste andother hazardous materials can wash out into the streets and into homes and potentiallycontaminate drinking water supplies.Flash flooding can also quickly evict people from their homes. Rising water maynot even give residents time to save their belongings before they must evacuate. Familyphotos and expensive or sentimental possessions can be washed away or destroyed.People who are forced from their homes must find shelter and may not be able to returnto their homes for an extended period of time. Even when the water recedes, there arelikely mold problems, which also pose a health threat. Rebuilding and treating homesdamaged by flooding can take weeks or even months depending on the severity. In themeantime the victim families must find alternative housing which will likely only lead tomore stress and anxiety.
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