286 



YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 



At the beginning of the rainy season, in early December, the soil on 

 all four of these basins was very dry as a result of the long dry 

 season. The accumulation of litter, duff, humus, and soil on the 

 forest-covered catchment areas absorbed 95 per cent of the unusually 

 large precipitation. On the nonforested area only 60 per cent of the 

 precipitation was absorbed, although the rainfall was much less. 



Rainfall and run-off during January, February, and March, 1900. 



Area of 



catchment 



basin. 



Condition as to 

 cover. 



Precipita- 

 tion. 



Run-off 



per square 



mile. 



Run-off in 

 percent- 

 age of pre- 

 cipitation. 



Sq. miles. 



0.70 



1.05 



1.47 



.53 



Forested 



Inches. 

 24 

 24 

 24 

 16 



Acre-feet. 



452+ 

 428+ 

 ,557+ 

 828+ 



Per cent. 

 35 

 33 

 43 

 95 



do 



do 



Nonforested 



The most striking feature of this table as compared with the previ- 

 ous one is the uniformly large run-off as compared with the rainfall. 

 This clearly shows the enormous amount of water taken up by a dry 

 soil, either forested or nonforested, as compared with one already 

 nearly filled to saturation. During the three months here noted, on 

 the forested basins about three-eighths of the rainfall appeared in the 

 run-off, while on the nonforested area nineteen-twentieths appeared in 

 the run-off. 



Rapidity of decrease in run-off after the close of the rainy season. 



Area of 



catchment 



basin. 



Sq. miles. 



0.70 



1.05 



1.47 



.53 



Condition as to 

 cover. 



Forested 



do 



do 



Nonforested 



Precipita- 

 tion. 



April run- 

 off per 

 square 

 mile. 



May run- 

 off per 

 square 

 mile. 



June run- 

 off per 

 square 

 mile. 



Inches. 



Acre-feet. 



Acre-feet. 



Acre-feet. 



1.6 



153- 



66- 



25- 



1.6 



146- 



70+ 



30- 



1.6 



166+ 



74+ 



30+ 



1 



56+ 



2- 







The above table clearly shows the importance of forests in sustain- 

 ing the flow of mountain streams. The three forested catchment 

 areas, which, during December, experienced a run-off' of but 5 per 

 cent of the heavy precipitation for that month, and which during Jan- 

 uary, February, and March of the following year had a run-off of 

 approximately 37 per cent of the total precipitation, experienced a 

 well-sustained stream flow three months after the close of the rainy 

 season. The nonforested catchment area, which, during December, 

 experienced a run-off of 40 per cent of the rainfall, and which during 

 the three following months had a run-off of 95 per cent of the precip- 

 itation, experienced a run-off' in April (per square mile) of less than 



