STORAGE RESERVOIRS. in 



situated along the stream. The total damages on French soil in the Rhone valley were 

 estimated at not less than $6,000,000. 



"So great a disaster in one of the most populous sections of France naturally led 

 to inquiries into the possibility of preventing a recurrence of it. Napoleon III., who 

 had taken a great interest in public works and favored a liberal extension of them, 

 ordered an elaborate investigation of the subject; first, as to the immediate protection 

 of great centers of population, and second, as to the practicability of 'modifying the 

 regime of great watercourses for the protection of the bottom lands by a diminution 

 of floods by means of reservoirs established near the head waters of the tributary 

 streams.' 



"The first part of the programme, viz., the protection of the river towns by works 

 intended to confine the floods to proper limits, was reported practicable at a total cost 

 of about $4,000,000. The second part of the programme, viz., the question of reservoir 

 construction, was considered in great detail and with a thoroughness of study which 

 makes it the best existing example of what may be expected from similar works in 

 other localities. 



"The river Rhone has a total length of about 447 miles and a watershed of about 

 36,670 square miles. Three hundred and thirty-six miles above its mouth is Lake 

 Geneva, an immense natural reservoir, with an area of 223 square miles. Below Lake 

 Geneva, at the distances given, the main stream receives the following important 

 tributaries : 



" The Arve, i^ miles below the outlet of the lake, drainage area 2422 square miles; 

 the Ain, no miles, drainage area 1355 square miles; the Saone, 131 miles, drainage 

 area 11,019 square miles; the Isere, 179 miles, drainage area 4360 square miles; the 

 Ardeche, 225 miles, drainage area 938 square miles; the Durance, 272 miles, drainage area 

 5716 square miles. The drainage area of all the other tributaries is about 7200 square 

 miles. The drainage area tributary to Lake Geneva is 2663 square miles, of which 

 2078 square miles pertains to the Rhone above the lake. 



"The flood of 1856 in the valley of the Rhone was practically a simultaneous affair 

 in all parts of the valley. Only in the upper portions was there any apparent progres- 

 sion. The maximum occurred at the mouth of the Arve thirty-six hours before it 

 reached the mouth of the Ain, 108 miles below; but for the entire remainder of the river 

 the maximum occurred on the same day, with a variation of only a few hours. The 

 causes that led to the flood were therefore operating throughout the entire valley, 

 swelling all the tributaries at once, and in consequence causing a simultaneous elevation 

 of all portions of the main stream. 



"The following table shows some of the characteristics of this flood, and 

 gives an admirable illustration of the effect of natural reservoirs in moderating 

 the flow of a stream. It will be observed that the flow of the Rhone just above the 

 Arve indicates a run-off of only 4.3 cubic feet per second per square mile. As a 

 matter of fact, the upper course of the Rhone was discharging into the lake 42,360 



