Roots of the plants hold the soil together and

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Unformatted text preview: above 100- year flood level ParLal dam across floodplain, with narrow channel under bridge Deep water under bridge flows faster, causes erosion, undermines pilings supporLng bridge Bridges Urbaniza1on Fig. 12- 19, p. 341 Urbaniza1on Increases ‘100- yr flood’ Magnitude Fires, Logging and Overgrazing Why does removal of vegeta1on cause more surface runoff and thus more erosion? a)  b)  c)  d)  e)  All of the plants covering the surface slow the runoff. Roots of the plants hold the soil together and prevent erosion. It reduces the amount of vegetaLon available for forest fires. It permits more water to directly strike the ground and run off. It results in increased grazing and compacLon of the soil. Yellow River, N China 1887 Avulsion, Flooding, Famine: 1M deaths Fires, Logging and Overgrazing Channel deepened, water table (groundwater supply) & downstream deposiLon lowered Levees Reten1on Basins Trapping Debris Flows People Feel Safe Levees Aeract Development in Floodplain Unintended Consequences of Levees Boeleneck Effect Levee Construc1on Increases Upstream Flooding Levee Construc1on Increases Downstream Flooding What effects do levees NOT have on a stream? a)  b)  c)  d)  e)  They raise the flood level. They increase the water velocity next to the levee. They raise wa...
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