NATURAL BASINS OF RECEPTION. 495 
the water discharged into Lake Como from the 15th to the 20th 
of September amounted to 2,600 cubic yards the second, while 
the outflow from the lake during the same period was only at 
the rate of about 1,050 cubie yards to the second. In those 
five days, then, the lake accumulated 670,000,000 cubic yards 
of superfluous water, and of course diminished by so much the 
quantity to be disposed of by the Po.* In the flood of October, 
1868, the surface of Lago Maggiore was raised twenty-five 
feet above low-water mark in the course of a few hours.+ 
There can be no doubt that without such detention of water by 
the Lakes Como, Maggiore, Garda, and other subalpine basins, 
almost the whole of Lombardy would have been irrecoverably 
desolated, or rather, its great plain would never have become 
anything but a vast expanse of river-beds and marshes; for the 
annual floods would always have prevented the possibility of its 
improvement by man.{ 
Lake Bourget in Savoy, once much more extensive than 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, 72,000,000 cubic yards of water, and of course 
moderated, to that extent, the effects of the inundation below.§ 
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 sepa- 
rated embankments, takes up so much water in its inundations, 
that, while a little below the outlet of the Ticino the discharge 
*Barrp Samira, Italian Irrigation, i., p. 176. 
+ Bollettino della Societa Geog. Italiana, iii., p. 466. 
t 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’ Alta Lombardia, Milano, 1869. 
§ ELISEEE RecLusE, La Terre, i., p. 460. 
