Mr. Leighton. 
396 DISCUSSION: FORESTS, RESERVOIRS, AND STREAM FLOW 
greater than that of the soil beneath the forest, provided, of course, 
the two soils are of the same character? With physical conditions 
identical, the retentive capacity must be the same; but, when one 
recalls that the forest mulch must assist in this absorption by retard- 
ing the water that would otherwise run over the ground, the superiority 
of forest-covered soil for modifying run-off would secm hardly to be 
susceptible of more complete demonstration. It is readily admitted 
that there are some soils which, even under forest cover, will not retain 
as much of the precipitation as some others which are kept bare; but, 
in making comparisons of this kind, one is assuming, of course, that 
the conditions are comparable. It is assumed that the soils are the 
same in point of texture and retentive capacity. In the beginning of 
his paper Colonel Chittenden implies that the soil beneath the forest 
must be impervious. Later, in the paragraph quoted, he implies that 
it may be somewhat pervious, but not to as great a degree as the 
soil unprotected by forests; all of which indicates that the original 
conception, as well as the deductions, are unfortunate, from his point 
of view. 
In the pursuit of his argument, a contradiction is presented.* The 
regulative effect of the forest bed in moderate storms is clearly ad- 
mitted. It is then stated that, by reason of later and heavier storms, 
this forest bed gives up what it had originally retained. Of course, 
the forest bed does not store the floods, as the author claims, and 
equally, of course, it does not prolong the run-off after the storms 
have passed, this being the function of the great ground-storage reser- 
voir; but, assuming for purposes of illustration that his contentions 
are true, how can it be possible that this forest mulch may contribute 
to a later flood, and produce a devastation greater than would occur 
if the area had been bare? Assume that a rainfall has occurred, 
which has just saturated the forest mulch, and that it can store 
no more. Let a later and heavier rain follow. Is not this forest mulch 
going to retain its retentive capacity, irrespective of later rains? If so, 
how is it possible that merely by reason of a later rain the forest 
mulch is going to shed all that later rain and, in addition, the water 
which it had received from the previous rain? Under such a conception, 
the second rain must have an effect of desiccation on the mulch. If 
the contention were that the forest mulch would have no effect on the 
run-off from the second rain, admitting for the moment that the 
author had not misconceived the fundamental idea, then his conclu- 
sions would be justified; but, in order to contend that this forest mulch 
is going to increase the flood, the assumption must be made that it 
will give up gratuitously that which it had previously collected. It is 
hardly likely that so able a man as Colonel Chittenden will, on taking 
thought, subscribe to such an assumption. 
* Page 249. 
