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lesson 15 - Key Terms and Concepts erosional agent channels...

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Key Terms and Concepts - erosional agent - channels - abrasives - streambed - urbanization - silt - deposition - delta - sediment - floodplain - meanders - oxbow lakes - natural levees - floodwaters - dams - canals - reservoirs - nutrients - salinity - subsidence - channelization - embankments - hydrologic - water table - runoff and base flow - waterborne problems: diarrhea, parasitic, schistosomiasis, sewage, dysentery, polio, hepatitis, spinal meningitis - water pollution - point sources - non-point sources - eutrophication - acid rain - thermal pollution - contaminants - Clean Water Act estuary - watershed (drainage basin) Introduction to River Systems In this lesson, we are going to take a look at another very important water resource. In some ways, this lesson builds upon what you learned in the previous lessons, especially those on geomorphology and groundwater resources.
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Although a mere 0.03% of all freshwater in the world is found in river systems , running water is probably the most important geomorphic agent in shaping the face of the Earth. Review of the hydrologic cycle The hydrologic cycle is a model of the pathways of water movement in the environment. Water exists in several states (conditions) and moves from one state to another in a cyclical manner. The main pathways of movement are: precipitation, evaporation, and runoff. Precipitation is the water supplied to the Earth's surface as rain, snow, sleet, etc. Evaporation is the movement of water away from a surface into the atmosphere. When this surface happens to be a plant, this process is called evapotranspiration . When precipitation reaches the surface, the water can either enter the soil by infiltration y or runoff over the surface. The amount of water infiltrated into the soil depends in large part upon the soil texture. Remember this from the last lesson? Animation of the five processes of the hydrologic cycle. "Together, these five processes - condensation, precipitation, infiltration, runoff, and evapotranspiration - make up the Hydrologic Cycle. Water vapor condenses to form clouds, which result in precipitation when the conditions are suitable. Precipitation falls to the surface and infiltrates the soil [as subsurface flow , where it can recharge groundwater] or flows to the ocean as runoff. Surface water (e.g., lakes, streams, oceans, etc.), evaporates, returning moisture to the atmosphere, while plants return water to the atmosphere by transpiration." Image source: "The Hydrologic Cycle" (NASA Observatorium) [2006] At this time... read this online presentation on "The hydrologic cycle" (WW2010). Pay particular attention to the module section on runoff . Niagara Falls, Canada-US.
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"The Niagara River (a Native American word for "at the neck"), linking Lake Erie and Lake Ontario, flows around Niagara Island, and then plummets over Horseshoe and American Falls, better known as Niagara Falls. The port city of Buffalo, New York is located at the northeast corner of Lake Erie where the river first leaves the lake. The image also includes the infamous Love Canal. In the late 1970s and early 1980s, as a
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