496 NATURAL BASINS OF RECEPTION. 
of the channel is sometimes not less than 19,500 cubic yards to 
the second, it has never exceeded 6,730 yards at Ponte Lago- 
scuro, 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 delivery of the Missis- 
sippi, a little below the mouth of the Ohio, was 52,000 cubic 
yards to the second, but at Baton Rouge, though of course in- 
creased by the waters of the Arkansas, the Yazoo, and other 
smaller tributaries, the discharge was reduced to 46,760 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 expansions of river-beds might 
be employed with advantage. Many upland streams present 
points where none of the objections usually urged against arti- 
ficial reservoirs, except those of expense and of danger from 
the breaking of dams, could have any application. Reser- 
yoirs may be so constructed as to retain the entire precipitation 
of the heaviest thaws and rains, leaving only the ordinary quan- 
tity to flow along the channel; they may be raised to such a 
height as only partially to obstruct the surface drainage; or 
they may be provided with sluices by means of which their 
whole contents can be discharged in the dry season and a sum- 
mer crop be grown upon the ground they cover at high water. 
The expediency of employing them and the mode of construc- 
tion depend on local conditions, and no rules of universal appli- 
cability can be laid down on the subject.* 
It is remarkable that nations which we, in the inflated pride 
of our modern civilization, so generally regard as little less 
than barbarian, should have long preceded Christian Europe in 
the systematic employment of great artificial basins for the 
various purposes they are calculated to subserve. The ancient 
Peruvians built strong walls, of excellent workmanship, across 
* The insufficiency of artificial basins of reception as a means of averting 
the evils resulting from the floods of great rivers has been conclusively shown, 
in reference to a most important particular case—that of the Mississippi—by 
Humphreys and Abbot, in their admirable monograph of that river. 
