168 Irrigation and Drainage 



11. Lessening Destructive Effects of Winds 



In sub-humid climates, especially like those of our 

 western prairies, where there is a high mean wind 

 velocity, and in the level districts of humid climates, 

 where the soils are light and sandy, with a small 

 water capacity, and which are lacking in adhesive 

 quality, the fields may suffer greatly at times, not 

 only from excessive loss of moisture, but the soil itself 

 may be greatly damaged by drifting caused by the 

 winds. Under such conditions, it is a matter of great 

 importance that the wind velocities close to the sur- 

 face should be reduced as much as possible. 



We have, in Wisconsin, extensive areas of light 

 lands which almost every year suffer severely from 

 the drifting action of the winds. On these lands, 

 wherever broad open fields lie unsheltered by any 

 windbreak, the clearing west and northwest winds 

 which follow storms not only rapidly dry out the soil, 

 but often sweep entirely away crops of grain after 

 they are 4 inches high, uncovering the roots by the 

 removal of 1 to 3 inches of the surface soil. It has 

 been observed, however, in these districts, that where- 

 ever there are windbreaks of any sort, even such slight 

 barriers as fences and even fields of grass, a marked 

 protection against drifting has been experienced for 

 several hundred feet to the leeward of them. 



In the case of groves, hedgerows, and fields of 

 grass, the protection results partly from their ten- 

 dency to render the air which passes across them more 

 moist, and partly by lessening the surface velocity of 



