480 NATURAL BASINS OF EECEPTION. 



never have become anytMng but a vast expanse of river-beds and 

 marshes ; for the annual floods would always have prevented the 

 possibihty of its improvement by man.* 



Lake Bourget in Savoy, once much more extensive that it is at 

 present, served, and indeed still serves, a similar purpose in the 

 economy of nature. In a flood of the Rhone, in 1863, this lake 

 received from the overflow of that river, which does not pass 

 through it, T2,000,000 cubic yards of water, and of course moder- 

 ated, to that extent, the effects of the inundation below.f 



In fact, the alluvial plains which border the course of most 

 considerable streams, and are overflowed in their inundations, 

 either by the rise of the water to a higher level than that of their 

 banks, or by the bursting of their dikes, serve as safety-valves for 

 the escape of their superfluous waters. The current of the Po, 

 spreading over the whole space between its widely separated 

 embankments, takes up so much water in its inundations, that, 

 while a little below the outlet of the Ticino the discharge of the 

 channel is sometimes not less than 19,500 cubic yards to the 

 second, it has never exceeded 6,T30 yards at Ponte Lagoscuro, 

 near Ferrara. The currents of the Mississippi, the Rhone, and 

 of many other large rivers, are modified in the same way. In 

 the flood of 1858, the dehvery of the Mississippi, a little below 

 the mouth of the Ohio, was 52,000 cubic yards to the second ; 

 but at Baton Rouge, though of course increased by the waters of 

 the Arkansas, the Yazoo and other smaller tributaries, the discharge 

 was reduced to 46,Y60 cubic yards. We rarely err when we 

 cautiously imitate the processes of nature, and there are doubtless 

 many cases where artificial basins of reception and lateral expan- 

 sions of river-beds might be employed with advantage. Many 

 upland streams present points where none of the objections usu- 

 ally urged against artificial reservoirs, except those of expense 

 and of danger from the breaking of dams, coxdd have any apph- 

 cation. Reservoirs may be so constructed as to retain the entire 

 precipitation of the heaviest thaws and rains, leaving only the 

 ordinary quantity to flow along the channel ; they may be raised 



* See, as to the probable effects of certain proposed hydraulic works at the 

 outlet of Lake Maggiore on the action of the lake as a regulating reservoir, 

 Tagliasecchi, Notizie sui Canali dell' Alia Lombardia, MUano, 1869. 



f Elisee Reclus, La Terre, i., p. 460. 



