104 



THE IMPROVEMENT OF RIVERS. 



except when ice closes the way; and the river and harbor engineer has little to do with 

 low-water problems or protection against floods, but rather with the deepening of liar 

 bors and connecting channels for an ever-increasing size of vessels and volume of com- 

 merce. 



"The vital function which the fluctuation of levels, both annual and cyclic, plays 

 in the economy of the Great Lakes is doubtless not generally appreciated even by the 

 engineering profession. Only recently distinguished engineers have boldly asserted 

 that this fluctuation of levels is an evil which must not be suffered to continue, and they 

 have proposed plans by which it may be corrected. Yet nothing is more certain than 

 that any curtailment of these fluctuations, either annual or cyclic, can be accomplished 

 only by a corresponding curtailment at certain seasons of the discharge of the lake 

 outlets. 



" Besides the Great Lakes of the St. Lawrence basin there are many other natural 

 reservoirs in various parts of the world. In order to convey some idea of their geo- 

 graphical distribution, magnitude, and regulating influence upon stream-flow, the fol- 

 lowing list of the more prominent examples is presented: 



LIST OF PROMINENT EXAMPLES OF NATURAL RESERVOIRS. 



"The moderating influence of any of these lakes upon the streams below them is, 

 of course, very great. Lake Geneva, for example, in the great flood of 1856 discharged 

 only 11,400 cubic feet per second at the maximum, as against 56,480 cubic feet which 

 it was receiving from its watershed. 



" In Italy the lakes on several of the northern tributaries of the Po have long been 

 noted for the control which they exercise over the streams flowing through them. The 



