THE IMPROVEMENT OF RIVERS. 



flood discharge is already vety great. The effect of the proposed reservoirs on the 

 flood of the Rhone iinnu-diately below the junction 'would be to diminish its height by 

 less than 1.3 feet. 



"The following tabular summary shows the magnitude and cost of the foregoing 

 works: 



"The result of these works and of this expenditure may be summarized as follows: 



"Over the 24,700 acres of submergible lands the depth of overflow would be reduced 

 from 2.2 to 3.2 feet. But this would not entirely prevent submersion, and the necessity 

 for dikes would exist as before. Through Lyons the flood height would be reduced possi- 

 bly 3 feet, but would save none of the special works of protection and would but slightly 

 diminish their cost. From Lyons down the diminution of height of flood would be 

 as follows: Below mouth of Saone, 1.3 feet; at Tournon, 0.8 foot; at Valence, 0.6 foot; 

 below Valence, inappreciable. The effect of the proposed reservoirs in the valley of 

 the Durance on the floods of the Rhone below the junction of the two streams would 

 be to diminish the flood height at Beaucaire 1.3 feet; at Aries, about 0.5 foot; below 

 Aries, not at all. 



"The effect of these reservoirs, therefore, although considerable in absolute mag- 

 nitude, would not be sufficient, in comparison with their great cost, to justify adoption 

 and the project was reported upon adversely by the engineers. 



"This report does not deal with the low-water flow of the Rhone at all, nor with 

 the effect which this storage would have upon the interests of navigation. Undoubtedly 

 it would be much greater than in the control of floods. For example, the 10,000,000,000 

 cubic feet of water that could be stored upon the upper Rhone and the Ain would pro- 

 vide a flow of about 4000 second-feet for one month, or 1300 second-feet for three months, 

 and could undoubtedly be so regulated as to be of considerable advantage to naviga- 

 tion. The increase for a period of one month only over the low-water flow at Lyons 

 would be nearly 50 per cent. 



" Garonne River. Similar studies to those just described were also made in the 

 case of the Garonne, which had likewise suffered severely from the floods of 1855 and 

 1856. Without reviewing these studies in detail, the following conclusions may be 

 stated in the language of the report: 



" ' Reservoirs, when their capacity is great enough, have a very powerful d'Uvt in 

 diminishing the flood discharge of the streams on which they are built, but thc-ir influence 

 diminishes enormously with distance; and inasmuch as suitable sites can be found only 



