328 CONSERVATION 



since 1880 to control high and low primarily determines cost, namely, the 



stages of the river for navigation. Lake character of topographic basins which 



levels were raised and low, flat lands may be dammed, also varies broadly, 



were flooded. The topographic condi- and according to the distribution of 



tions were favorable and the cost for these two factors we may distinguish at 



lands and improvements submerged least four regions which are unlike in 



was low. In sixteen years the Federal regard to storage possibilities. 



Government expended $i, 525,000. 1 The arid plains and basins of the 



Storage reservoirs for irrigation West afford conditions of minimum or 



waters were established in the arid moderate cost and maximum efficiency 



West by private enterprise in the early f or reservoir storage. The experience 



settlement of the regions, but work on o f the Reclamation Service has been 



a large scale began after the passage cited. 



of the reclamation act, in 1902. The Another region where reservoirs of 



Reclamation Service has twenty-eight moderate cost and adequate efficiency 



projects in various stages of progress. are possible is that of lakes and swamps 



They will make available for homes which lie within the area covered in a 



1,910,000 acres, at a cost of $70,000,000, recent geologic epoch by the great ice 



or $36.65 per acre. 2 sheet. It includes parts of the Da- 



In any particular case the cost per kotas, Minnesota, Wisconsin, Illinois, 



acre-foot of storage capacity depends Indiana, Michigan, and. in a less de- 



chiefly on the topographic situation, g ree . New York and New England. In 



which determines the magnitude and this region there are thousands of lakes, 



character of the structures, and on the eac h one of which is a natural reser- 



value of property to be displaced or vO ir, and many more swamps, each one 



submerged. In general, it costs less o f which is a shallow but practicable 



per acre-foot to store a large body of reservoir site. The experience with 



water than a smaller one. the Government dams on the upper 



The efficiency of a reservoir may be Mississippi gives the best insight into 

 said to be its capacity to retain the the value of these reservoir conditions, 

 water which ought to be stored. If it ,\ third district which may be dis- 

 will hold all the surface flow of its tinguished with reference to the possi- 

 drainage basin, less the amount used bilities of reservoir storage is found in 

 and evaporated during any time, its the prairie states- Iowa, Illinois, and 

 efficiency is 100 per cent. In proper- ( )hi<; and in areas of similar topogra- 

 tion as it fails to do this during floods phy, population, and precipitation. In 

 its efficiency falls below the maximum, that part of those states which lies out- 

 A reservoir which will have an effi- side of the old ice limit, streams as a 

 ciency of 100 per cent is being built rule run in ravines or narrow valleys, 

 by the Reclamation Service on the Rio which, however, have moderate fall and 

 Grande above El Paso. It will retain would, in many localities, afford prac- 

 more than the entire annual precipita- ticable conditions for reservoir storage, 

 tion, approximately three times the The cost of farm lands and town site^ 

 surface flow of the drainage basin, and which must be submerged is such, bow- 

 when it is completed floods which have ever, as to render capacious reservoirs 

 been disastrous will be absolutely abol- too costly, provided any other means 

 ished. of control be practicable. Here the 

 If other conditions are alike, the ef- question of cost will limit the construc- 

 ficiency depends on the amount and dis- tion of large reservoirs. The lands are 

 tribution of the waters from rain and farmed and upon the farmer must rest 

 snow melting. These vary according the responsibility to the Nation for a 

 to broad districts. The factor which proper regulation of the water flow. 



'Annual Report, Chief of Engineers, U. S. Army, part 2, p. 1439, 1906. 



"Blanchard, C. J. : Home-making by the Government. Nat. Geogr. Mag., April, 1908. 



