EAS328_Lecture6_Part1_flooding - EAS 328 Natural...

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EAS 328: Natural Environmental Hazards Lecture #6: Friday, March 4, 2016: PART 1 Plan for this lecture: 1. Define Flooding 2. Learn basics of river and water basins 3. Learn the physics of: -­‐ floodings 4. Study the impacts and best management pracRces for dealing with these events Some slides are adapted from: Keller, DeVecchio; Natural Hazards ; by Tim Frazier
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River Flooding: Natural process of overbank flow Related to: 1.Amount and distribution of precipitation in drainage basin 2.Rate at which the precipitation soaks into earth 3.How quickly surface runoff reaches river 4.Amount of moisture in the soil Inland Urban Flooding : no river needed, simply too much water for the urban run-off system. Coastal Flooding : Natural process of beach inundation Related to: storm surge or large waves RIVER FLOODING AND COASTAL FLOODING
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PRECIPITATION EXTREMES VS. FLOODING EVENTS In the Northeast US: -­‐ The largest rain events occur in late summer and fall. -­‐ River flood events are most frequent in later winter and spring The disconnect between the rainfall and the floods is related to the surface condiRons. In summer/fall, the land is drier* and the rivers have low water so it is more difficult to flood. In the late winter and spring the snow melt fills the streams and river, and then a small rain produces more snow melt and floods the waterways. *one complicaRon: if the land is very dry and the rainfall is very intense, there might not be Rme for the water to soak in to the soil before it generates a hazardous amount of run-­‐off
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Flooding related to amount and intensity of precipitation and runoff Catastrophic floods produced by infrequent, large, intense storms Smaller floods may be produced by less intense storms that occur more frequently Recurrence interval or Return Period Average time between flood events of a certain size Example: 10-year flood Can be expected about every ten years Probability of this size of flood in any given year is 1/10 MAGNITUDE AND FREQUENCY OF FLOODS RAINAMOUNT = RATE * DURATION
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Less frequent floods Cause tens to hundreds of billions of dollars of damage Loss of human life goes into the thousands or even hundreds of thousands Storms over a long period of time Stationary atmospheric rivers over a period of a week or longer. MEGAFLOODS
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Contours: sea level pressure anomalies (solid indicates high pressure anomaly Shading: verRcal velocity in pressure coordinates (i.e., dp/dz) TAKE HOME MESSAGE: strong anRcyclone key for these flood events.
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Floods were number one disaster in the United States in twentieth century All areas of the United States and Canada are vulnerable to floods A single flood can cause billions of dollars of property damage and more than 200 deaths Developing countries suffer much greater losses due to lack of monitoring facilities, warning systems, adequate infrastructure, etc.
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