WATER CIRCULATION AND ITS CONTROL 



By BAILEY WILLIS, E.M.C.E., United States Geological Survey 



(Concluded) 



CONTROL OF RUN-OFF THROUGH GRAZING 



ABOUT twenty-five per cent, of 

 the area of the United States 

 is so situated with reference 

 to topographic and climatic condi- 

 tions that it will best raise hardy 

 grasses and must be devoted chiefly to 

 grazing. The principal area is that of 

 the great plains, extending from north- 

 western Montana around the base of 

 the Rock Mountains to Texas, but in- 

 cluding also portions of the basin re- 

 gion on the west. Within this area the 

 governing condition is a meager pre- 

 cipitation. The soils are appropriate 

 to agriculture, the mountain ranges 

 above the plains are suited to forestry, 

 but both agriculture and forestry re- 

 quire more water than the grass that 

 feeds herds, and they are accordingly 

 limited in distribution in this region. 

 The herdsman's prosperity depends ab- 

 solutely upon the grass. It is proved 

 beyond dispute that overgrazing injures 

 the grass, partially removes the protect- 

 ive cover, and promotes erosion. Ero- 

 sion eventually results in the removal 

 of all herbage, produces bare, gullied 

 badlands, and makes restocking with 

 grass impossible. 



The method available to the herds- 

 man for the limitation of run-off and 

 the prevention of erosion is to increase 

 the stand of the natural grass cover, 

 upon which alone his herds depend. 

 In some small areas he may find it 

 necessary to adopt the usual methods 

 of agriculture to check erosion, estab- 

 lish soil, and re-cover the surface with 

 grasses, but in general that which any 

 intelligent herdsman does to main- 

 tain the range upon which his herds 



live is that which he must do to pre- 

 vent erosion and to limit run-off. Thus 

 intelligent grazing promotes both in- 

 dividual and general welfare. 



The preservation of grass upon the 

 semiarid plains is of vital interest, 

 probably, to the farming states, Minne- 

 sota, Iowa, and Missouri, and even 

 more so to eastern Nebraska and Kan- 

 sas. If it be true, as stated in the 

 opening discussion of conditions of pre- 

 cipitation (p. 265), that radiation from 

 the hot plains checks rainfall, it would 

 follow, should they be eaten bare and 

 eroded to badlands, that the semiarid 

 climate would extend eastward. The 

 plains themselves would become more 

 arid, the farming districts adjoining 

 them would be affected by prolonged 

 droughts, and the climate would be 

 unfavorably modified as far east as the 

 western margin of the moist-air cur- 

 rents that flow north from the Gulf. 

 Iowa is interested in the grass that 

 grows in western Nebraska. 



FOREST CONTROL OF PERCOLATION AND 

 RUN-OFF 



The areas which must be kept for- 

 ested in North America comprise 

 twenty-six per cent, of the whole conti- 

 nent. Of the United States nineteen 

 per cent, requires forest protection or 

 will grow trees more profitably than 

 any other crop. The necessity for this 

 amount of forests rests on two impera- 

 tive economic conditions, (i) the value 

 of forest products, and (2) the protec- 

 tion forests afford to other essential 

 needs and activities of civilized com- 

 munities. 



It is not proposed here to discuss for- 



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