398 
BASINS OF RECEPTION. 
mended by very strong considerations, such as tbe meteoro¬ 
logical effects of increased evaporable surface, tbe furnishing 
of a constant supply of water for agricultural and mechanical 
purposes, and, finally, their value as ponds for breeding and 
rearing fish, and, perhaps, for cultivating aquatic vegetables. 
The objections to the general adoption of the system of 
reservoirs are these: the expense of their construction and 
maintenance; the reduction of cultivable area by the amount 
of surface they must cover ; the interruption they would occa¬ 
sion to free communication; the probability that they would 
soon be filled up with sediment, and the obvious fact that 
when full of earth or even water, they would no longer serve 
their principal purpose; the great danger to which they would 
expose the country below them in case of the bursting of their 
barriers ; * the evil consequences they would occasion by pro¬ 
longing the flow of inundations in proportion as they dimin¬ 
ished their height; the injurious effects it is supposed they 
would produce upon the salubrity of the neighboring districts ; 
and, lastly, the alleged impossibility of constructing artificial 
basins sufficient in capacity to prevent, or in any considerable 
measure to mitigate, the evils they are intended to guard 
against. 
The last argument is more easily reduced to a numerical 
question than the others. The mean and extreme annual pre¬ 
cipitation of all the basins where the construction of such 
works would be seriously proposed is already approximately 
known by meteorological tables, and the quantity of water, 
delivered by the greatest floods which have occurred within 
the memory of man, may be roughly estimated from their 
visible traces. From these elements, or from recorded ob¬ 
servations, the capacity of the necessary reservoirs can be cal¬ 
culated. Let us take the case of the Ard&che. In the inun¬ 
dation of 1857, that river poured into the Rhone 1,305,000,000 
cubic yards of water in three days. If we suppose that half 
* For accounts of damage from the bursting of reservoirs, see Vallee, 
Memoire sur les Reservoirs <PAlimentation des Canaux , Annalcs dcs Fonts et 
Chaussees , 1833, ler s£mestre, p. 261. 
