DISCUSSION: FORESTS, RESERVOIRS, AND STREAM FLOW 441 
per unit of area in that part of the water-shed would have reached ur. Labelle. 
the figures given for the Octoraro Basin. The foregoing statement 
would corroborate the author’s 7th proposition.* 
The Bureau of Forestry has investigated different water-sheds, from 
time to time, for the purpose of ascertaining the effect of forests on 
stream flow. These investigations can be divided into two classes: (1) 
Those carried out in adjoining water-sheds, both forested and de- 
forested; (2) those carried out in a given water-shed before and after 
deforestation. 
The investigations carried out in the San Bernardino Mountains, 
California, belong to the first type. Mr. James W. Toumey,t in 
recording the results of the above, prefaces his tabulation as follows: 
“There are so many complex conditions influencing the flow of 
streams that it is extremely difficult to determine the effect of forests 
on run-off by the comparison of the discharge of streams on forested 
and nonforested catchment areas. It is believed by many that stream 
flow is so largely influenced by the amount, intensity, and character 
of the precipitation, the configuration and area of the catchment basin, 
the character of the absorbing medium and the underlying rocks, and 
the general climate, as well as the forest itself, that we shall probably 
never be able to measure quantitatively the influence of forests on 
the flow of streams by the comparison of forested and nonforested 
regions. Catchment areas differ so greatly in the features mentioned 
above that our most conservative and able investigators have been: 
forced to the conclusion that ‘in respect to run-off, each stream 1s a 
law unto itself, ” 
The results of his investigations are summarized in Table 16. 
TABLE 16. 
Apeacot RUN-oFF IN PERCENTAGE OF PRECIPITATION: Run-off 
catchment ae ind Une. ; 
basin, as to In J. in acre-fee 
in square cover. In December, |. vanuary, per square 
miles. 1899. ee ie ene Annual. mile, 
: Forested. 3 85 28 25 — 
08 Be 6 33 30 30 — 
1.47 ee 6 43 36 80 + 
0.53 Non-forested. 40 95 69 0 
The rainy season begins in December and ends in March. The 
precipitation is 46 in. for the forested and 33 in. for the non-forested 
areas. At first sight the results are all in favor of forests, except as 
to the total annual run-off, which is 69% for the non-forested and 
* Page 281. 
+ ‘The Relation of Forests to Stream Flow,” by James W. Toumey; a reprint from the 
Yearbook of the Dept. of Agriculture, 1903. 
