494 NATURAL BASINS OF RECEPTION. 
construction of reservoirs of such magnitude for such a pur- 
pose is financially, if not physically, impracticable, and when 
we take into account a point I have just suggested, namely, 
that the reservoirs must be empty at all times of apprehended 
flood, and, of course, their utility limited almost solely to the 
single object of preventing inundations, the total inapplicability 
of such a measure in this particular case becomes still more 
glaringly manifest. 
Another not less conclusive fact is, that the valleys of all the 
upland tributaries of the Ardéche descend so rapidly, and have 
so little lateral expansion, as to render the construction of 
capacious reservoirs in them quite impracticable. Indeed, engi- 
neers have found but two points in the whole basin suitable for 
that purpose, and the reservoirs admissible at these would have 
only a joint capacity of about 70,000,000 cubic yards, or less 
than one-ninth part of what I suppose to be required. The 
ease of the Ardéche is no doubt an extreme one, both in the 
topographical character of its basin and in its exposure to 
excessive rains; but all destructive inundations are, in a 
certain sense, extreme cases also, and this of the Ardéche 
serves to show that the construction of reservoirs is not by 
any means to be regarded as a universal panacea against 
floods. 
Nor, on the other hand, is this measure to be summarily 
rejected. Nature has adopted it on a great scale, on both 
flanks of the Alps, and ona smaller, on those of the Adiron- 
dacks and of many lower chains. The quantity of water which, 
in great rains or sudden thaws, rushes down the steep declivi- 
ties of the Alps, is so vast that the channels of the Swiss and 
Italian rivers would be totally incompetent to carry it off as 
rapidly as it would pour into them, were it not absorbed by the 
capacious basins which nature has scooped out for its reception, 
freed from the transported material which adds immensely both 
to the volume and to the force of its current, and then, after 
some reduction by evaporation and infiltration, gradually dis- 
charged into the beds of the rivers. In the inundation of 1829, 
