402 DISCUSSION: FORESTS, RESERVOIRS, AND STREAM FLOW 
Mr. Leighton, fanciful presentation of a light and fleecy snow, two-thirds of which 
' is held aloft for the greedy melting of the spring rains, finds no 
justification in actual experience. What proportion, for example, of a 
total snowfall could the trees sustain, when the layer on the ground 
is from 10 to 15 ft. deep ? 
_ The author’s comparison of the run-off from Puta Oreek and 
American River is unfortunate, for he has given a total mis-statement 
of relative rainfall and run-off on the two areas, as is shown un- 
mistakably in Mr. Pinchot’s discussion and diagram, Fig: 16. 
In the author’s discussion of practical effects, it will be of interest 
to consider the hypothesis that records of 200 years are necessary to 
establish the trend of run-off as affected by forest cover and deforesta- 
tion. It has been demonstrated by the work of the Geological Survey 
that, in a period of 10 years, run-off conditions, in practically all parts 
of the country, are comprehended, from one extreme to the other. It 
may. be that, here and there, an extreme low. or an extreme high water 
may occur in one decade which is not reached in another; but this 
is of no consequence in summing up the tendencies of the river to 
floods and to low waters. These extreme conditions are mere sports, 
due to unusual occurrences, and it is as illogical to consider them as 
representative of general tendencies, as it would be to accept the 
physiological and anatomical freaks in a museum as representative of 
the human race: The comparison of run-off conditions in 10-year 
periods has been well set forth in an article* by John C. Hoyt, Assoc. 
M. Am. Soc. C. E. Therefore one need not despair because the 
records do not comprehend the 200 years which have been prescribed 
by certain engineers. : 
The claim that a 200-year record is necessary arises from the fact 
that the investigators are looking for -freak conditions, in order to 
endeavor to substantiate certain hypotheses. If the details leading 
up to the floods and low waters be examined, the whole matter resolves 
itself into the task of ascertaining cause and effect. The real question 
to be solved is: Does a rainfall of a certain depth, at a certain season 
of the year, cause a greater flood since deforestation than it did 
formerly under well forested conditions? Now, the answer to this 
question can be ascertained from recent records. Cyclical changes, so- 
called, in precipitation do not enter into the question, because the whole 
record is reduced to a common basis, irrespective of cycles, but de- 
pending solely on actual depth of rainfall and comparative conditions 
of ground surface. The author, in presenting Table 1—extreme gauge 
records on various streams-—merely reveals a fundamental miscon- 
ception. It is not the contention of well-informed persons, as far as 
the speaker is aware, that deforestation produces higher floods. The 
real effect is to cause more frequent and more prolonged floods. 
* Engineering News, April 23d, 1908. 
