STORAGE RESERVOIRS. 107 



opportunities for the inexpensive storage of water. The dams required are low struc- 

 tures, but the area over which the water is raised by them is so extensive that the cost 

 per unit of volume stored is probably the smallest ever yet realized. 



"These remarkably favorable natural conditions for the storage of water have long 

 attracted public attention and were made the subject of an able official report by Gen. 

 G. K. Warren as early as 1870. Exhaustive surveys followed at a later date, and in 

 1 88 1 actual construction was begun. Up to the present date there have been con- 

 structed five reservoirs, each with an aggregate capacity of 93,400,000,000 cubic feet, 

 at a total cost of $678,300. 



" The average annual storage of these reservoirs is estimated at about 40,000,000,000 

 cubic feet, equivalent to about 5200 cubic feet per second for a period of ninety days. 

 This supply is estimated to increase the gauge height at low water at St. Paul, 357 miles 

 below, from i to 2 feet. 



"The original investigations, embracing the States of Minnesota and Wisconsin, 

 indicated a practicable storage in Minnesota of 95,000,000,000 cubic feet, and in Wis- 

 consin of 79,000,000,000 cubic feet, or a total in the two States of 174,000,000,000 cubic 

 feet. There is probably little doubt that the system could be extended so as to secure 

 a storage of 150,000,000,000 cubic feet in the two States, an equivalent of about 20,000 

 cubic feet per second for ninety days. From the results already obtained, it is 

 probable that this storage would not cost above $2 per acre-foot. The effect upon 

 the navigable stage of the river would, of course, vary with the locality considered, 

 and would diminish rapidly with the distance down stream. But considering that 

 such an improvement is of the most permanent character, depending only upon 

 the maintenance of the dams for its perpetuity, the above cost cannot be considered 

 excessive when compared with the vast outlay for the mere temporary improvement 

 of these rivers by present methods. A permanent increment of. from 10,000 to 20,000 

 cubic feet per second to the low-water stage of even so large a stream as the Mississippi 

 River is not to be passed over as a matter of small importance. 



"The Volga and the Mississippi rivers constitute the only two systems of artificial 

 reservoirs yet constructed, and the only ones designed to improve the navigable con- 

 dition of streams in their natural condition. 



" The construction of reservoirs to feed artificial waterways has been resorted to 

 extensively, particularly in France, and to a considerable extent in this country. Inas- 

 much as the expenditure of water in canals is a matter of very exact determination, 

 the storage required for this purpose can generally be estimated with great definiteness. 



"The construction of reservoirs for municipal purposes is too common a matter 

 to require particular mention. It is sufficient to say that nearly every city in the world 

 of above 100,000 population has storage facilities of greater or less extent to help out 

 its water-supply. 



"The principal development of storage reservoirs for irrigation purposes has taken 

 place in Spain, in France and Algiers, in India, and in the United States. 



