METHODS 



This report is based on observations made on 92 plots on granitic soils at eleva- 

 tions between 5,500 and 9,500 feet in the Carson Range east and northeast of Lake Tahoe . 

 Most of the study sites were in the Jeffrey pine type, and ranged from fully stocked 

 stands of small sawtimber to open brushfields no longer supporting timber. The remain- 

 der were in an open lodgepole (P. contorta) and western white pine (P. montioola) stand 

 on the west face of Slide Mountain. 



Zn.£iltz*ozn.etex* 



Preliminary investigations revealed that water repellency was usually most severe 

 at the soil surface and that any disturbance of the surface soil (e.g., that caused by 

 driving a plot frame or inf iltrometer ring into the soil) could rupture the repellent 

 layer and allow water to bypass it. 



To minimize errors due to soil disturbance, we developed a special inf iltrometer . 

 (See appendix for construction details.) This inf iltrometer consists of a rainfall 

 simulator, similar to the raindrop-producing unit developed by Chow and Harbaugh (1965), 

 and a runoff-collecting trough. The rainfall simulator applies water uniformly to a 

 fixed area (3.7 square feet) at a controlled rate. No plot frame is used; the bounda- 

 ries of the plot are determined by the area of water application. Plot runoff is caught 

 by a trough at the downhill edge of the area of application. This runoff collector is 

 installed slightly below the soil surface and (when necessary) sealed with caulking 

 compound . 



3 



