328 



CONSER\'ATION 



since 1880 to control high and low 

 stages of the river for navigation. Lake 

 levels were raised and low, flat lands 

 were flooded. The topographic condi- 

 tions were favorable and the cost for 

 lands and improvements submerged 

 was low. In sixteen years the Federal 

 Government expended $1,525,000.^ 



Storage reservoirs for irrigation 

 waters were established in the arid 

 West by private enterprise in the early 

 settlement of the regions, but work on 

 a large scale began after the passage 

 of the reclamation act, in 1902. The 

 Reclamation Service has twenty-eight 

 projects in various stages of progress. 

 They will make available for homes 

 1,910,000 acres, at a cost of $70,000,000, 

 or $36.65 per acre.' 



In any particular case the cost per 

 acre-foot of storage capacity depends 

 chiefly on the topographic situation, 

 which determines the magnitude and 

 character of the structures, and on the 

 value of property to be displaced or 

 submerged. In general, it costs less 

 per acre-foot to store a large body of 

 water than a smaller one. 



The efficiency of a reservoir may be 

 said to be its capacity to retain the 

 water which ought to be stored. If it 

 will hold all the surface flow of its 

 drainage basin, less the amount used 

 and evaporated during any time, its 

 efficiency is 100 per cent. In propor- 

 tion as it fails to do this during floods 

 its efficiency falls below the maximum. 

 A reservoir which will have an effi- 

 ciency of 100 per cent is being built 

 by the Reclamation Service on the Rio 

 Grande above El Paso. It will retain 

 more than the entire annual precipita- 

 tion, approximately three times the 

 surface flow of the drainage basin, au'l 

 when it is completed floods which have 

 been disastrous will be absolutely abol- 

 ished. 



If other conditions are alike, the ef- 

 ficiency depends on the amount and dis- 

 tribution of the waters from rain and 

 snow melting. These vary according 

 to broad districts. The factor which 



primarily determines cost, namely, the ■ 

 character of topographic basins which "I 

 mav be dammed, also varies broadly, 

 and according to the distribution of 

 these two factors we may distinguish at 

 least four regions which are unlike in 

 regard to storage possibilities. 



The arid plains and basins of the 

 West afford conditions of minimum or 

 moderate cost and maximiun efficiency 

 for reservoir storage. The experience 

 of the Reclamation Service has been 

 cited. 



Another region where reservoirs of 

 moderate cost and adequate efficiency 

 are possible is that of lakes and swamps 

 which lie within the area covered in a 

 recent geologic epoch by the great ice 

 sheet. It includes parts of the Da- 

 kotas, Minnesota. Wisconsin, Illinois, 

 Indiana. Michigan, and. in a less de- 

 gree. New York and New England. In 

 this region there are thousands of lakes, 

 each one of which is a natural reser- 

 voir, anrl many more swamps, each one 

 of which is a shallow but practicable 

 reservoir site. The experience with 

 the (iovernment dams on the upper 

 Mississippi gives the best insight into 

 the value of these reservoir conditions. 



A third district which may be dis- 

 tinguished with reference to the possi- 

 bilities of reservoir storage is found in 

 the jrrairie states — Iowa, Illinois, and 

 ( )hio — and in areas of similar topogra- 

 phy, population, and precipitation. In 

 that part of those states which lies out- 

 side of the old ice limit, streams as a 

 rule run in ravines or narrow valleys, 

 which, however, have moderate fall and ^ 

 would, in many localities, afford prac- 

 ticable conditions for reservoir storage. 

 The cost of farm lands and town site^ 

 which must be submerged is such, how- 

 ever, as to render capacious reservoirs 

 too costly, provided any other means 

 of control be practicable. Here the 

 c|uestion of cost will limit the construc- 

 tion of large reservoirs. The lands are 

 farmed and upon the farmer must rest 

 the responsibility to the Nation for a 

 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. 



