STORAGE RESERVOIRS. 119 



The floods of the Mississippi do not come from this direction. They are formed by 

 the heavy rains in the low regions east of the ninety-eighth meridian, and very largely 

 come from east of the Mississippi itself. The great controlling element, in fact, in all 

 the lower river floods is the Ohio River. 



" The magnitude of these floods also depends very largely upon fortuitous com- 

 binations of the floods in its tributaries. No single flood from any one of these tribu- 

 taries, except the Ohio, can produce serious consequences in the main river. But if 

 two or more of them discharge excessive floods in the main stream simultaneously, then 

 it is that great disasters follow. Very fortunately, nature has caused these flood-waves 

 to arrive generally at different periods, and the more disastrous combinations are not 

 of frequent occurrence. 



"It is apparent, therefore, that a reservoir system which should exercise any appre- 

 ciable influence on the lower-river floods must embrace the three great upper tributaries, 

 and particularly the Ohio. What the magnitude of the storage required would, have to 

 be may be inferred from the fact that the total discharge of the Mississippi at Cairo, 

 above the bankful stage, during the late flood, was 2,368,000,000,000 cubic feet, or 

 4250 square miles 20 feet deep, the assumed average depth of reservoirs. The largest 

 artificial reservoir ever built viz., that at Lake Winnebigoshish, Minn. has a capac- 

 ity of 45,000,000,000 cubic feet. To store all this excess would take fifty-two such 

 reservoirs. 



" While it might seem at first thought that this amount of storage could be found, 

 still it would be very difficult to find it. Particularly on the upper Ohio and its southern 

 tributaries favorable sites are understood to be of rare occurrence. It is probable, how- 

 ever, that in all the watershed of the Mississippi sites could be found that would insure 

 a reduction of a flood discharge at Cairo like that of 1897 by one-fifth of its maximum. 

 The ease with which the writer was able to find storage amounting to 11,000,000,000 

 cubic feet in the State of Ohio at the very head waters of streams along the divide 

 between Lake Erie and the Ohio convinced him that the natural facilities for storage 

 are rather greater than is commonly supposed.* 



"As already stated, the difficulty is not so much a physical as a financial one. To 

 store, say, 500,000,000,000 cubic feet of water, equivalent to 11,500,000 acre-feet, 

 would cost, even at the rate of only $5 per acre-foot, $57,500,000. This one fact con- 

 demns the project as a system for the exclusive purpose of flood prevention. But 

 whenever such reservoirs have other and more immediate purposes for their construc- 

 tion the increment which each will form in the . grand total necessary to produce some 

 influence in the Mississippi floods is an element in its favor worthy of consideration. 



" The only direct and effective reservoir project, if any such be possible, for impound- 

 ing floods of such vast magnitude as those of the Mississippi is that pointed out by Mr. 

 Seddon in the second part of his memoir. The project for utilizing St. Francis basin 



* See Report on Ohio Canal Surveys in 1895, House Doc. No. 278, Fifty-fourth Congress, first session, 

 p. 56; printed also in Annual Report of the Chief of Engineers for 1896, part 5, p. 2973 et seq. 



