218 WJMCGEE OUTLINES OF HYDROLOGY 



The primary basis of the fourth stage is the 30,000 cubic miles of 

 ■water anniiall}' distilled from the clouds over the lands of the globe, of 

 which amount some 50 per cent is evaporated (thus serving to temper 

 climate), while an average of some 20 per cent flows seaward in streams, 

 and i^erhaps as much more becomes ground watex", leaving a considerable 

 fraction to be consumed in organic growth or inorganic chemical combi- 

 nations; the secondary basis (in both positive or injurious and negative 

 or beneficial aspects) comprises the earth -matter carried into the ocean 

 in solution, in suspension, and in saltation — that is, about 1 cubic mile, 

 20 cubic miles, and say 3 cubic miles respectively every year. 



In humid regions generally the primary water-supply is disregarded or 

 deemed appurtenant to the land and the off -wash is complacently ignored, 

 while in arid regions men early began to realize that productivity and 

 even habitability are dependent on the retention of water and the preven- 

 tion of wash ; indeed, under the bitter strife for existence amid sun- 

 scorched sands, water became a vital currency, eventually engendering an 

 altruism which ripened into world-civilization and spread from the deserts 

 of the globe to blend in modern culture. 



Partly by reason of the fundamental differences between humid and 

 arid regions, the customs and laws of the world's nations respecting the 

 control and use of water are diverse : Several states among the world's 

 countries provide for the appropriation (or expropriation) of water, for 

 the diversion of streams, and in same cases for retaining storm waters in 

 reservoirs; in a few cases forestation or other agricultural devices have 

 been adopted at least partly to equalize stream-flow by diminishing storm 

 run-off and increasing the volume of ground water ; but the development 

 of a common-law doctrine on a practically riverless island in a humid 

 zone, with concomitant juridical precedents and procedure on differently 

 conditioned continents, has greatly retarded recognition of the real inter- 

 ests involved, and it is only recently that a comprehensive system has been 

 proposed for the control and utilization of the entire water-supply of a 

 single nation — the United States. 



The modern plan contemplates complete diversion — that is, artificiali- 

 zation — of the natural water movement both on and below the surface, 

 in such manner as (1) to prevent floods by so managing the soil and soil 

 cover that the local rainfall will be absorbed where it falls; (3) to spare 

 the soil, and so save the stream from contamination; (3) to increase 

 productiveness by checking erosion and secixring better distribution of 

 the groimd-water ; (4) to equalize and clarify the streams by preserving 

 and maintaining ground-water seepage, as well as by diminishing fresh- 

 ets; (5) to coordinate works connected with water-supply, navigation, 



