This page last updated on 28-Mar-2007 EENS 204Natural DisastersTulane UniversityProf. Stephen A. NelsonFlooding Hazards, Prediction & Human InterventionHazards Associated with FloodingHazards associated with flooding can be divided into primary hazards that occur due to contact with water, secondary effects that occur because of the flooding, such as disruption of services, health impacts such as famine and disease, and tertiary effects such as changes in the position of river channels. Throughout the last century flooding has been one of the most costly disasters in terms of both property damage and human casualties. Major floods in China, for example, killed about 2 million people in 1887, nearly 4 million in 1931, and about 1 million in 1938 The 1993 flood on the upper Mississippi River and Midwest killed only 47 people, but the U.S. Army Corps of Engineers estimates the total economic loss at between 15 and 20 billion dollars (Click HEREfor U.S. Army Corps' web site). Primary EffectsAgain, the primary effects of floods are those due to direct contact with the flood waters. As seen in the video last lecture, water velocities tend to be high in floods. As discharge increases velocity increases. zWith higher velocities, streams are able to transport larger particles as suspended load. Such large particles include not only rocks and sediment, but, during a flood, could include such large objects as automobiles, houses and bridges. zMassive amounts of erosion can be accomplished by flood waters. Such erosion can undermine bridge structures, levees, and buildings causing their collapse. zWater entering human built structures cause water damage. Even with minor flooding of homes, furniture is ruined, floors and walls are damaged, and anything that comes in contact with the water is likely to be damaged or lost. Flooding of automobiles usually results in damage that cannot easily be repaired. zThe high velocity of flood waters allows the water to carry more sediment as suspended load. When the flood waters retreat, velocity is generally much lower and sediment is deposited. After retreat of the floodwaters everything is usually covered with a thick layer of stream deposited mud, including the interior of buildings. zFlooding of farmland usually results in crop loss. Livestock, pets, and other animals are often carried away and drown. zHumans that get caught in the high velocity flood waters are often drowned by the water. zFloodwaters can concentrate garbage, debris, and toxic pollutants that can cause the secondary effects of health hazards.Page 1 of 8Flood Hazards, Prediction, & Mitigation3/28/2007
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