WATER CIRCULATION AND ITS CONTROL 



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



Circulation of Waters 



THE moisture which falls upon 

 North America in the form of 

 rain and snow comes chiefly from 

 the Pacific Ocean. A smaller propor- 

 tion rising from the Gulf of Mexico 

 and the West Indian seas falls upon the 

 eastern United States. A part of this 

 precipitation returns to the air ; another 

 part flows to the streams ; a third enters 

 the ground. It all sooner or later re- 

 turns to the oceans. In this great gen- 

 eral circulation there' are many short 

 cuts and many stop-overs. Rain which 

 falls upon the sea has taken a short cut.' 

 Snow which gathers in banks and gla- 

 ciers, water which lingers in lakes, 

 swamps, and especially in the soil and 

 deeper recesses of rocks underground, 

 has stopped over for a longer or shorter 

 time. On the whole, the great body of 

 moisture moves constantly, circulates 

 in various forms through the air, on 

 the earth, and through all parts of the 

 superficial crust of the earth, and in its 

 constant flow is the most vital element 

 affecting the life of plants and animals. 

 The very air itself is not more neces- 

 sary than the presence of an adequate 

 and fairly regular supply of moisture. 

 These vast movements of moisture 

 transcend our control, but their effects 

 do not. Has not man through intelli- 

 gent skill converted the desert into a 

 garden ? And has he not through obsti- 

 nate ignorance turned the garden into a 

 desert? The path of our race from 

 Asia across Europe has led through 

 many such gardens ; it is marked also 

 by such deserts. 



Says Irving in the charming intro- 

 duction to The Alhambra : 



Though there are exceptions in some of 

 the maritime provinces, yet for the greater 



part Spain is a stern, melancholy country, 

 with rugged mountains and long sweeping 

 plains destitute of trees and indescribably 

 silent and lonesome, partaking of the savage 

 and solitary character of Africa. What adds 

 to this silence and loneliness is the absence 

 of singing birds, a natural consequence of 

 the want of groves and hedges. The vulture 

 and the eagle are seen wheeling about the 

 mountain cliffs and soaring over the plains, 

 and groups of shy bustards stalk about the 

 heaths ; but the myriads of smaller birds 

 which animate the whole face of other coun- 

 tries are met with in but few provinces in 

 Spain, and in those chiefly among the 

 orchards and gardens which surround the 

 habitations of man. 



No better description could be writ- 

 ten, not only of Spain but of Asia 

 Minor, \vhere the marbles of Grecian 

 civilization mark the sites of lost cities ; 

 or of Dalmatia, where barren plateaus 

 have replaced the forests from which 

 Rome built her navies ; or of many 

 other parts of southern Europe and 

 northern Africa, where man has helped 

 to rob nature of her charm and 

 transformed her gentleness into stern 

 severity. 



We Americans have left these desert 

 mountains behind in Eurasia ; but we 

 occupy the last land that lies toward 

 the setting sun. Our children and our 

 children's children for countless gener- 

 ations are to enjoy the gardens or be- 

 wail the deserts we create. 



In the general circulation there is 

 just one point where agencies under 

 human control can directly affect the 

 course of the movement. It is where 

 rain strikes the ground or the vegeta- 

 tion covering the ground. From this 

 point three routes are open to the mois- 

 ture. It may evaporate, it may run off, 

 or it may sink in. That which evapo- 

 rates is lost to man's immediate use ; 



'To appear in the Report of the National Conservation Commission. 

 262 



