128 



Kepoi;t S.A. a. Ad\ axckmknt of Scir.xoi-:. 



saturation. Another feature is tlie enormous percentai^e of lun-off 

 from a saturated treeless area. 



Kapiihtv of Decrease in Ri x-off aftek the IIaixv Season. 



Area of 



Catchment 



Basin. 



Sq. Mile^ 

 0-70 



Condition as 

 to Cover. 



Forested 



T^ . ., April Run 

 Frecipita- ^ ™ 

 ,. ^ oil per 



^^^"- Sq. Mile. 



Inches. 

 1-6 



Acre-feet. 

 153 



May Run- 'June Run- 

 off per off per 

 Stj. Mile. Sq. Mile. 



Acre-feet. Acre-feet 

 66 25 



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

 ing; thip flow of mountain streams. The three forested catchment areas, 

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

 the hea\'y precipitation for that month, and which during January, 

 February and March of the following 3'ear had a run-off of approxi- 

 mately 37 per cent, of the total precipitation, experienced a well-sus- 

 tained stream-flow three months after the close of the rainy season. 

 The non-forested catchment area, which during December experienced 

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

 following nionths had a run-off of 95 per cent, of the precipitation, ex- 

 perienced a run-off in April (per square mile) of less than one-third of 

 that from the forested catchment areas, and in June the flow from the 

 non-forested area had ceased altogether. 



Annual Rainfall axd Rux-off on Forested axd Nox-Forested 

 Catchmext Areas in the San Bernardino Mountains, Cali- 

 fornia. 



Ai'ea of Catch- Condition as 

 ment Basin. to Cover. 



Precipita- 

 tion. 



Sq. miles. 



0-70 



1-05 



1-47 



•53 



Forested 



Non-forested 



Inches 

 40 

 46 

 46 

 33 



Run-off Run-off in Per- 

 per S(|uare centage of Pre- 

 cipitation. 



Mile. 



Acre feet. 



731 



756 



904 



1192 



Per cent. 



2S 

 30 

 36 

 69 



According to M. Mahc', experiments were made many years ago 

 in the Montagne-Noii-e on two valleys, one wooded and the other 

 denuded. It was found that the ft)nner gave less run-ott' immediately 

 after rain : the flow continued all the year, while the latter rapidly 

 became dry. 



