WATER 105 



a regular supply to the streams. Like other reservoirs, the 

 ground water reservoir is the great equalizer between the ex' 

 tremes of scarcity and floods. 



EROSION 



Man can't control the basic character of the soil any more 

 than he can control the slope of the land. Nevertheless, he can 

 do a lot to control run-off. He can plow his fields in such a way 

 that the furrows will hold the water. On badly eroding slopes 

 he can plant close-growing crops, such as clover, which pro 

 tect the surface of the soil with a thick sod. He can stop de 

 stroying the forests. He can pl^ig gullies and put check dams 

 in run-off ditches. 



Anyone who has read the newspapers in the last four or five 

 years knows why there is so much interest in run-off. Run-off 

 is the key to water erosion, and water erosion has already de 

 stroyed 100 million acres of what was once productive farm 

 land. Every year 400 million tons of soil are washed out of the 

 Mississippi region alone. 4 



But that is just the beginning of the trouble that has come 

 from this barrier that man has thrown across the absorption 

 route of water. The soil that is carried from one field may be 

 left on the field below. In that case the fine silt which has been 

 washed down from above will choke the pores of earth where 

 it is deposited. Thus the new land will have increased run-off 

 and in turn it too will be eroded. Eventually, the final end of 

 that silt will be some stream, and through that stream it will 

 flow to some major river system and finally into the sea. Ero 

 sion debris is not always silt, however. Sometimes it is much 

 coarser material, such as gravel, and even on rare occasions, 

 boulders as big as small houses. Again, it may be a solid mass 

 of fluid mud. In these cases, the results of erosion are just as 

 destructive as a deposit of silt. 



4 Person, o>. cit., p. 2. 



