LYCOS RETRIEVER 
Floods: Waters
built 637 days ago
Floods are the result of a multitude of naturally occurring and human-induced factors, but they all can be defined as the accumulation of too much water in too little time in a specific area. Types of floods include regional floods, flash floods, ice-jam floods, storm-surge floods, dam- and levee-failure floods, and debris, landslide, and mudflow floods.
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The 1953 floods were caused by a major storm surge which coincided with a naturally high spring tide. Storm surges are caused when air pressure and strong winds push a volume of water across large distances. The result is an elevated body or 'hump' of seawater which can move towards the coast and overtop sea defences. Small changes in atmospheric pressure can result in large volumes of water being displaced. The storm surge that caused the 1953 floods resulted in sea levels rising almost 3 meters above normal high water marks. Most sea defences along the east coast of England were not designed for such events and most could not prevent the oncoming wave of water.
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During the last Ice Age (18,000 to 12,000 years ago), and in multiple previous Ice Ages, cataclysmic floods inundated portions of the Pacific Northwest from Glacial Lake Missoula, pluvial Lake Bonneville, and perhaps from subglacial outbursts. Glacial Lake Missoula was a body of water as large as some of the USA's Great Lakes. This lake formed from glacial meltwater that was dammed by a lobe of the Canadian ice sheet. Episodically, perhaps every 40 to 140 years, the waters of this huge lake forced its way past the ice dam, inundating parts of the Pacific Northwest. Eventually, the ice receded northward far enough that the dam did not reform, and the flooding episodes ceased.
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Zealand Experience summarizes the wealth of observation and analysis of floods and droughts in New Zealand. Chapters are contributed by 20 hydrological scientists and water resources professionals, who have worked on many different aspects of floods and droughts. Some chapters present observations of historically significant floods and droughts, and review different approaches to their analysis. Other chapters consider the cause-and-effect relationships between floods and droughts, land use changes, instream uses such as ecosystem maintenance, erosion and sedimentation processes, and the behaviour of groundwater resources. A final pair of chapters focuses on approaches to management of floods and droughts that are being developed in the country, and discuss four specific case studies.
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Just weeks ago, since floods hit Western Pennsylvania, The Salvation Army has provided nearly $150,000 in support services in Allegheny County. 450 households were seen on a case-by-case basis receiving clothing, food, temporary lodging, cleaning supplies and personal hygiene items. 400 flood clean-up kits, 150 mops, 100 shovels and two pallets of bleach were distributed. And, since the waters hit, three canteens or mobile feeding units have served 7,800 meals.
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The type of land use in an area ... affects the nature of floods. In totally forested areas, rainfall is readily absorbed into the ground and flows slowly into streams through groundwater pathways. The presence of snow cover or frozen ground can worsen flood conditions because rainwater does not soak slowly into the ground. Likewise, roadways, parking lots and rooftops in developed areas shed water quickly and channel it directly into streams, resulting in more damaging floods.
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