5-14 - Floods and mitigation What Is A Flood? An event...

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What Is A Flood? An event where water covers a normally dry area for a period of hours or days. Floods are the most common and widespread of all natural disasters-except fire. What Is A Flood? Floods result from: Overflow of lake, river or tidal waters, Unusual and rapid runoff mudflows Flood Types Downstream floods : In mature rivers, take days to develop may persist for days to weeks. In large river systems, high water in tributaries may not cause floods in main river. Flood Types Upstream floods: Floods that only affect small localized basins, or small streams. Includes road flooding Water may rise rapidly and violently in minutes, a “flash flood” . Flood Severity Factors: Flood Severity Factors: Amount of precipitation. Flood Severity Factors: Amount of precipitation. Rate of precipitation Flood Severity Factors: Amount of precipitation. Rate of precipitation Amount of surface runoff. Flood Severity
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5-14 - Floods and mitigation What Is A Flood? An event...

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