

STORAGE RESERVOIRS. 115 



in the mountainous regions, faf removed from the bottom lands to be protected, it may 

 readily be seen how slight must be their influence on the flood heights in the valleys far 

 below. ... To reduce such a flood [as that of 1855] to the height required in order 

 to contain it within the proposed system of dikes would require a storage capacity 

 exceeding 33,000,000,000 cubic feet, and would cost $24,000,000. . . . 



"Other objections of a fundamental character as to all reservoirs have already 

 been stated. 



'The conclusion arrived at, therefore, is that the idea of 'reducing the floods of 

 the Garonne by means of artificial reservoirs must be abandoned.' 



" Loire River. The studies devoted to this question in the case of the river Loire 

 were more favorable to the use of reservoirs. This was owing to the more favorable 

 conditions which prevail on that stream. The main stream is formed by the union of 

 the upper Loire and the Allier near the city of Nevers at the Bee d'Allier. The Loire 

 is subject to the most extreme variations in the matter of flow. At the junction of the 

 two streams, for instance, it varies from about 10,000 cubic feet per second to 350,000 

 cubic feet. The floods in the lower river are ordinarily rendered harmless by the arrival, 

 at different times, of the floods from the various affluents ; but when the conditions cause 

 the simultaneous arrival of flood-crests from several tributaries the results are liable to 

 be of the most serious character. 



" The floods of the Loire River have always been a matter of great moment to the 

 interests of the valley, and have led to extensive works for their control. In the studies 

 above referred to the use of reservoirs on certain portions of the streams was recom- 

 mended, viz., upon the upper Loire and the Allier. These two streams, heading in 

 the south-central part of France, flow north nearly parallel to each other at distances 

 scarcely ever 50 miles apart. Their drainage areas are 7000 square miles and 4500 

 square miles, respectively. The geographical, geological, and meteorological condi- 

 tions are essentially the same for the two streams. They rise in high land some 4500 

 feet above the level of the sea. The mountain slopes are steep and the soil of a very 

 impervious character. The result is that the run-off responds quickly to the rainfall; 

 floods are quick and of short duration, and the curve of the flood-wave at any point is 

 sharp in character, i.e., very high compared with its length. The conditions in the two 

 valleys are so similar that the crests of floods reach the junction very nearly at the same 

 time, being only two or three hours apart in the great flood of 1856. The curves of 

 discharge of the two streams, both accentuated in character, are superimposed upon 

 each other, producing a curve of relatively the same relief, but absolutely nearly twice 

 as pronounced, as in the case of either tributary. 



"The union of two such considerable tributaries with floods of the nature above 

 described gives character to the flood-wave of the united stream for a great distance 

 below, or until the accession- of tributaries reaches an extent that may exert a marked 

 modifying influence. But it is stated that the sharp form of the wave does not entirely 

 disappear even to the mouth of the river. 



