i ta 



THE 1M TROY EVENT OF RIVERS. 



cubic feet per second, or 21 cubic feet per second per square mik-, which would indicate 

 for the entire watershed above the Arve, including that of Lake Geneva itself, 56,480 

 cubic feet per second. The storage of Lake Geneva accounts for the difference, and 

 actually reduces the flow of the upper Rhone by about 45,000 (56,480 11,472) cubic 

 feet per second. 



"Again, it will be seen that the discharge of the great tributary, the SaSne, is at a 

 rate of only 4 second-feet per square mile. Although there is no lake forming a reser- 

 voir in this valley, as in that just described, the slope of the lower portion of the valley 

 for 100 miles above Lyons is so slight that floods do not pass off rapidly, but fill up the 

 bottoms over 166 square miles to a depth of 10 feet or more, giving a storage of upward 

 of 50,000,000,000 cubic feet. If the flow of this stream had been as great per square 

 mile of watershed as that of the Rhone above Lyons, without the moderating effect 

 of Lake Geneva, it would have been about 363,000 cubic feet per second instead of its 

 actual flow of about 50,000 cubic feet. Without the storage effects of Lake Geneva 

 and of the Saone valley, the discharge of the Rhone at Lyons would have been about 

 600,000 cubic feet instead of its actual discharge of less than 250,000 cubic feet. The 

 great influence of these two natural reservoirs in moderating the flood discharge of the 

 Rhone at Lyons is thus clearly apparent, and it is evident that without them the range 

 between high and low water, or the ratio of minimum to maximum discharge, would t 

 much greater than it actually is. It would not, however, be correct to infer from this 

 that the destructive power of the great floods of the Rhone would, under the above 

 supposition, increase in the same proportion as the discharge itself. Nature adapts 

 the channels of streams to the work required of them, and if the flood flow of this river 

 were greatly increased undoubtedly it would carve out a deeper and wider bed, and 

 would carry away, within the limits of safety, "a much larger volume of water than it 

 does at present. Thus, while the absence of these natural reservoirs would, probably. 

 to some extent increase the destructive power of the floods of the Rhone, it would not 

 do so in anything like the same proportion in which it would augment the flood dis- 

 charge at Lyons. 



"When, in the course of their investigations, the French engineers undertook to 

 supplement the effect of these natural reservoirs by artificial ones, they were confronted 



