i>o THE IMPROVEMENT OF RIVERS. 



for this purpose would only be following out and perfecting the plan upon which nature 

 has operated for an indefinite period. If the overflow into this basin in a great flood 

 like that of 1882 is equivalent to a depth of 6.5 to 7 feet upon its overflowed area of 

 6706 square miles, it is at least a reasonable question to ask why this flooded area cannot 

 be reduced to one-half or one-third its present size, be given a depth twice or three times 

 as great, and the water be prevented from flowing out until the following low water. 

 The slope of 120 feet in the length of the basin would seem to make possible a division 

 into separate reservoirs by means of moderate embankments such as Mr. Seddon sug- 

 gests, making five or six basins of an average depth of 10 to 15 feet, with longitudinal 

 levees to restrict the lateral area. The water thus stored (and it could be stored with 

 such an arrangement, whether there were a high flood or only a moderate one) would 

 give to the lower river in low water an increment (based upon the overflow of 1882) 

 of 141,000 cubic feet per second for a period of one hundred days. This would give 

 a low-water flow of at least 300,000 cubic feet per second, and would radically improve 

 the navigation of the Mississippi from Helena to the sea. From Helena up, the slack- 

 water system through the basin itself, with five or six locks, would carry the deep water 

 to Cairo. How far the imperfectly known topography of the St. Francis basin would 

 lend itself to this project, and whether or not the cost would be prohibitory, exhaustive 

 surveys alone can tell. 



"On the Missouri River the case with regard to reservoirs is somewhat different. 

 The annual flood of that stream, which is known as the 'June rise,' is essentially a head- 

 water flood. The earlier floods are generally, although not always, from the lower 

 river, and very rarely from the extreme upper sources. The June rise is the mountain 

 flood, bringing down the snow-water, and generally augmented by the spring rains 

 both in the mountains and on the plains below. Not infrequently it meets with heavy 

 contributions all the way down, and is the result of a general high water over all its 

 drainage area. Ordinarily, however, as already stated, it is a head-water flood, and 

 coming as it does while the banks are still soft and yielding from previous high water, 

 it does its full share of the destructive work peculiar to the Missouri River. 



"That a complete system of reservoirs in the mountains and plains portion of the 

 watershed of this stream, which should embrace its many tributaries and contain the 

 waters from melting snows and spring rains, would materially reduce the magnitude 

 of the June rise is highly probable. To take off the flood excesses at Sioux City, men- 

 tioned by Mr. Seddon in the first section of his memoir, would require a storage of, say, 

 48,400,000,000 cubic feet, corresponding to a reduction in stage of 2.8 feet. A storage 

 of 100,000,000,000 would probably give the very material reduction of 6 feet. Allow- 

 ing a reservoir efficiency of only 50 per cent, as elsewhere explained, and assuming that 

 no one of the great floods of the Missouri has its origin in more than one-half of its 

 watershed, it would seem that a reservoir system of 400,000,000,000 cubic feet, distrib- 

 uted over the watershed above Sioux City, would quite effectually control the floods 

 of the river. This amount of storage is about the percentage of total flow required 



