DISCUSSION: FORESTS, RESERVOIRS, AND STREAM FLOW 459 
and of replenishing the great underground reservoir from which the mr. Pinchot. 
springs and streams are fed. 
What is the importance of ground storage, which is so lightly 
passed over? Professor King has found that ordinary soils have a 
capacity of from 4 to 5 in. of water per foot of depth, or even more.* 
Ground-water extends to a considerable depth. Considering the earth 
masses which lie above the stream levels in mountainous regions, one 
may form an idea of what ground storage means to the permanency of 
stream flow. The ground-water is constantly in motion, is replenished 
entirely from the surface, and is easily disturbed by any change in 
surface conditions. 
In certain regions where there is a very thick humus, reaching 
oceasionally, as in the Adirondacks, a depth of 8 ft. it has an im- 
portant storage capacity; but the capacity of the humus is always 
insignificant compared with that of the ground. The mountains them- 
selves are the chief reservoirs, and the principal function of the 
forest, so far as water is concerned, is to keep the surface soil 
permeable, so that these reservoirs of ground-water may be regularly 
and bountifully replenished. When the importance of the forest to 
ground storage is once realized, a very large part of Colonel Chit- 
tenden’s argument is.seen to rest on a fundamental misconception. 
While admitting that for average conditions the forest bed has 
some retentive influence, the author hastens to say emphatically that 
“it is not true for extreme conditions—great floods and excessively low 
waters.”+ He further says:t 
“When a period of heavy storms occurs, spreading over a great 
area, continually increasing in intensity, the forests, by retaining some 
portions of the earlier showers and paying them out afterward, do 
produce a general high condition of the river which may greatly 
aggravate a sudden flood arising later from some portion of the water- 
shed.” 
This curious conception seems to have taken root: Assuming, for 
example, that the humus is able to hold 1 in. of rainfall; then, when a 
later storm of 4 or 5 in. comes on, not only the 4 or 5 in. of the 
storm runs into the streams, but also the 1 in. which was there before. 
Thus the storm itself would have destroyed the storage capacity of 
the forest floor; an assumption which doubtless Colonel Chittenden 
will repudiate at once, when his attention is called to it. 
The speaker was quoted as saying that the increase of rainfall 
due to the forest is about 10 per cent. That figure was taken from 
the estimate of Dr. Ebermeyer who, perhaps, has studied the influence 
of mountain forests on precipitation as carefully as any one else. 
*¥F, H. King, Nineteenth Annual Report, U. 8. Geological Survey, Part II. 
+ Page 247. 
t Page 249. 
