WATER CIRCULATION AND ITS CONTROL 



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



(Continued) 



Outline of Methods of Control 



ENGINEERING CONTROL OF SURFACE FLOW 



THE engineer aims to regulate sur- 

 face flow through methods of 

 storage, diversion, or confinement 

 in an established channel. His selection 

 of method is determined by the topo- 

 graphic conditions of the particular lo- 

 cality primarily, and also by the balanc- 

 ing conditions of need and cost. The re- 

 sult is a reservoir, canal, or other struc- 

 ture designed to be permanent, to meet 

 the greatest emergency which may arise, 

 and to supply such water or aflford such 

 relief from water as conditions require. 

 When practicable the investment should 

 return to the people at least a fair in- 

 terest on the cost. These limiting con- 

 ditions are so well understood and en- 

 gineering practise is based upon such 

 a thorough knowledge of fundamental 

 mechanical principles that in any given 

 case the engineer's calculation may be 

 implicitly trusted, provided that the 

 factors of run-off, fluctuation, and sedi- 

 ment, which are fundamental elements 

 of the problem, do not at any future 

 time exceed the maxinumi limits which 

 past experience leads him to assume. 

 This provision implies that the progress 

 of settlement and the exploitation of 

 our natural resources should not unfa- 

 vorably modify the relation of run-off 

 to ground storage and evaporation. 

 Through ignorance, carelessness, and 

 greed, the farmer, herdsman, and lum- 

 berman are constantly violating this 

 provision, as we shall see when we 

 come to the consideration of the specific 

 relation of their activities to the parti- 

 tion and distribution of precipitation. 

 The engineer is now called upon to reg- 

 ulate run-off, the irregularity of which 



is persistently aggravated by these 

 widespread activities ; he is required to 

 take care of sediment whose volume is 

 constantly increased by vicious meth- 

 ods of agriculture, grazing, and defor- 

 estation, and the Nation collectively 

 spends millions on engineering while 

 the people individually render the ex- 

 penditure useless. 



The engineer urgently needs the sup- 

 port of an educated, enlightened public 

 opinion which will control individuals. 

 In proportion as every landowner man- 

 ages his property intelligently with re- 

 gard to its perpetual value and the 

 welfare of the commonwealth, the engi- 

 neer's problem will shrink within those 

 limits of reasonable magnitude and cost 

 which it now threatens to exceed. 



Let us consider some of the examples 

 of the engineer's methods of regulating 

 surface flow by storage, drainage, di- 

 version, and canalization. 



The construction of reservoirs for 

 the storage of waters is, in compari- 

 son with its possibilities, very slightly 

 developed in the United States. A few 

 examples will illustrate the magnitude 

 and purposes of existing works. 



The Croton reservoir system cost 

 Greater New York $86,359,562 up to 

 1898; and estimates on extensions and 

 improvements are $161,000,000. The 

 city can afford it, for the system sup- 

 plies pure water to 4,000,000 persons, 

 among whom, considering one benefit 

 only, the death rate from typhoid fevet 

 was, in 1905, sixteen per 100,000, as 

 against more than 100 per 100,000 in 

 certain cities supplied with polluted 

 river water. 



On the upper Mississippi a reservoir 

 system has been gradually installeii 



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