FLOODS OF THE ARDFCHE. 
387 
surface—tlie water being sufficient only to supply the subter¬ 
ranean channels of infiltration—and the Ardeche itself is 
almost everywhere fordable, even below the mouth of the 
Chassezac. But in floods, the river has sometimes risen more 
than sixty feet at the Pont d’Arc, a natural arch of two hun¬ 
dred feet chord, which spans the stream below its junction 
with all its important affluents. At the height of the inunda¬ 
tion of 1827, the quantity of water passing this point—after 
deducting thirty per cent, for material transported with the 
current and for irregularity of flow—was estimated at 8,845 
cubic yards to the second, and between twelve o’clock on the 
10th of September of that year and ten o’clock the next 
morning, the water discharged through the passage in question 
amounted to more than 450,000,000 cubic yards. This quan¬ 
tity, distributed equally through the basin of the river, would 
cover its entire area to a depth of more than five inches. 
The Ardeche rises so suddenly that, in the inundation of 
1846, the women who were washing in the bed of the river 
had not time to save their linen, and barely escaped with their 
lives, though they instantly fled upon hearing the roar of the 
approaching flood. Its waters and those of its affluents fall 
almost as rapidly, for in less than twenty-four hours after the 
rain has ceased in the Cevennes, where it rises, the Ardeche 
returns within its ordinary channel, even at its junction with 
the Phone. In the flood of 1772, the water at La Beaume de 
Buoms, on the Beaume, a tributary of the Ardeche, rose thirty- 
five feet above low water, but the stream was again fordable 
on the evening of the same day. The inundation of 1827 was, 
in this respect, exceptional, for it continued three days, during 
which period the Ardeche poured into the Phone 1,305,000,000 
cubic yards of water. 
The Pile delivers into the sea 101,000 cubic feet or 3,741 
cubic yards per second, on an average of the whole year.* 
* Sir John F. W. Herschel, citing Talabot as his authority, Physical 
Geography (24). 
In an elaborate paper on “Irrigation,” printed in the United States 
Patent Report for 1860, p. 169, it is stated that the volume of water poured 
