EXERCISE 74 

 HOW DOES EROSION AFFECT SOILS? 



Materials. Banks and riffles of a lake, river, or ditch. 



Directions. This study is best carried out by a field visit to a running stream, a lake shore, or 

 a hillside where ravines have been formed. An open drainage ditch will usually furnish a good basis 

 for this work. 



Observe the running water to determine whether it is carrying any soil particles. Does rapidly 

 running water carry more material or larger material than slowly running water? Where does the 

 material come from ? What becomes of this material ? How does the carrying power of water 

 change with changes in its rate of flow ? What evidences upon this question are there along banks 

 and riffles of lakes, streams, and ditches ? 



Additional problems. Arrange an erosion model in a sink in the following manner : Fill one end of the 

 sink with sandy or gravelly soil ; close the outlet of the sink by use of a stopper through which a short 

 glass tube is inserted so that an inch or two of water will stand in that end of the sink before the water 

 overflows ; by use of a tube allow a small stream of water to run very slowly upon the soil farthest from 

 the outlet. Observe the development of channels, and the deposit of materials. 



If in an open field erosion is allowed to continue unhindered, what results will follow ? 



Is it the better or poorer parts of the soil which are usually lost by erosion ? 



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