26 POPULAR SCIENCE MONTHLY 



irrigated lands if there is any remote likelihood of having homes, prop- 

 erty and lives wiped out in floods from bursting reservoirs. 



Granting, then, that the reservoirs are feasible, there still remains 

 the question of expense in constructing the number necessary to place 

 one or more in each of the most important tributaries. Estimate 

 the expense most generously, letting each one cost a third more 

 than the Engle dam above El Paso, and the total figure then is less 

 than what has already been spent on the Mississippi system. But 

 there is another important factor to be considered — the tremendous 

 possibilities which lie in the development of water power from each 

 reservoir. The question of future motive power for industrial purposes, 

 as the coal supply decreases, is a problem which must soon be met in 

 this country, and probably will be solved by the use of water power 

 either directly or through electricity. In fact, even now, water rights 

 are being rapidly acquired and developed on every hand, as the advance 

 guard of the change that is to come. A sample of what a storage 

 reservoir will do can be seen in the case of the comparatively small 

 irrigation project at Minidoka, Idaho, which will develop about 30,000 

 horse power per year. Eenting this power at the very low figure of 

 $10 per horse power per year would pay for the entire Minidoka 

 project, reservoir, irrigation-canals, gates and all, in six years. The 

 amount of power generated by the Mississippi system is variously 

 estimated high and low, with 60,000,000 horse power per year as an 

 intermediate figure. Much of this amount is not directly available, 

 but granting on a conservative basis that a series of impounding reser- 

 voirs would develop immediately 2 per cent, of that amount, there 

 would be 1,200,000 horse power to be turned into electricity and dis- 

 tributed to factories. A purely nominal rental would be ample enough 

 to repay in two or three decades the entire original expense of the 

 system, besides a good income on the investment. The reservoir sys- 

 tem, however, must be intimately associated with forest conservation as 

 a vital factor in regulating surface drainage and in checking the 

 amount of soil erosion which supplies sediment to the river. 



The proper building of reservoirs in the headwaters, therefore, 

 offers what no other plan can possibly offer : it promises effective regu- 

 lation of river stages and water supply for all time to come, removing 

 entirely the liability of destructive floods, checking the erosion of banks 

 and preventing much of the formation and shifting of sand bars and 

 the pollution of water which the presence of sediment means. At the 

 same time it provides a way of actually paying for itself in short order, 

 aside from all idea of the savings to shippers and river interests in 

 general which would be in excess of the cost. The importance of this 

 latter consideration is emphasized best by a brief comparison with the 

 system now being followed. The levee-revetment system, as mapped 

 out, calls for an expenditure of $60,000,000 for its completion. From 



