EARTHSC 2GG3 Lecture : Lecture 35.pdf
5 Sep 2014
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Force of water against car can wash it downstream. Deep erosion may not be visible underwater. Difficult to escape from submerged and sinking car. Picture: even shallow floodwaters can lift a vehicle and wash it downstream. Bridges: raise roadway above 100-year flood level, partial dam across floodplain, with narrow open channel under roadway bridge. Without a bridge the river spreads over its floodplain during a flood (shown a left). Bank erosion from river currents or waves. Piping or seepage through levee, sometimes reaching surface as sand boil: every time a levee is built, also reduces width of flood-flow part of river and raises water level during flooding, levees act to: Constrict flow and raise upstream water levels. Severe drought in provinces downstream of the three gorges dam. Improper maintenance: landslide into reservoirs, earthquakes that weaken earth-fill dams, reducing flood damage, annual costs of flood damage in the usa increased tenfold from 1929 to.
