no THE IMPROVEMENT OF RIVERS. 



for these joint purposes cannot be counted on for flood protection. It would probably 

 be unsafe to allow a higher effick-nry in this resjHTt than 50 per cent. 



"For reasons to be fully considered further on, very few, if any, reservoirs have 

 been built for the exclusive purpose of protecting against floods the valleys below them; 

 but there are numerous examples where this has been an important consideration in 

 their construction. Two cases may be cited in France. The celebrated dam at the 

 Gouffre d'Enfer. on the river Furens, near St. Etienne, was built largely to protect St. 

 Etienne from the destructive freshets of the Furens. It was of course expected to 

 make use of the stored water for industrial purposes, which in a thickly populated dis- 

 trict could not but be important. As to the results obtained, the expectations in regard 

 to flood protection have been fully realized. 



"The Ternay Dam likewise had as an important motive for its construction the 

 protection of the town of Annonay from the floods of the Ternay, although in this case, 

 as in that just cited, industrial uses of the stored water were considerations of great 

 weight. The result of this work, as to flood protection, has been a success. 



"There are certain reservoirs in Germany, as that at Dahlhausen, on the Wappen, 

 and another in the valley of the Bever, which serve very much the same purpose as do 

 those at Furens and Ternay in France, and exercise an important influence upon the 

 floods in their respective valleys. Various similar works have been constructed in other 

 parts of Europe, but all have other motives in addition to that of flood protection to 

 justify their 'construction. 



" The systematic creation of a comprehensive system of reservoirs on any river 

 for the sole purpose of mitigating the severity of floods has never been undertaken. 

 The subject has, however, received exhaustive study, and some examples of such studies 

 will therefore be of imix)rtance in this connection. By far the most important of these 

 studies, as might have been expected, is to be found in France. It took place during the 

 reign of Emperor Napoleon III., as a result of the floods of 1856. These floods were 

 among the greatest and most destructive that had ever visited France, and aroused a 

 great deal of interest in the question of their future prevention. Among the various 

 proposals which were brought forward at the time was that of constructing reservoirs 

 at the head waters or on the tributaries of the various streams, among which particular 

 attention was given to the Rhone, Garonne, and Loire. These investigations were 

 ordered by the Emperor under date of July 19, 1856, and resulted in the most exhaus- 

 tive analysis of the whole subject and in reports of great scientific value. They embraced 

 the three streams above mentioned, and the result was adverse to the project so far 

 as the Rhone and Garonne were concerned and favorable as to the Loire. A brk't" 

 r6sum6 of the reports will here be given. 



"Phone River. The damages wrought by the flood of 1856 in the Rhone Valley 

 were extraordinary. Over 540,000 acres of rich valley lands were submerged and the 

 newly started crops were destroyed. The injury to bridges, dikes, revetments, and 

 other ri"er works was very great, as was also the destruction to the towns and cities 



