STUDY METHODS 



The study area lies between 4,000 and 5,000 feet elevation in the rugged, upper 

 portion of the Priest River Experimental Forest. The area is divided into north and 

 south aspects by a sharp-crested ridge, which extends 1,200 feet higher to the summit of 

 the Selkirk Mountain range. The forest ecosystem is comprised predominantly of western 

 hemlock {Tsuga heterophylla (Raf . ) Sarq.), western white pine [Pinus monticola Dougl.), 

 and western redcedar {Thuja pliaata Donn.), undisturbed by man and mature in age 

 (fig. 13. Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco), western larch {Larix 

 occidentalis Nutt.) and Engelmann spruce {Fiaea engelmannii Parry) are intermingled but 

 subordinate in volume on the moist north aspect. On the drier south aspect, western 

 hemlock and western redcedar are usually missing from the mixture and Douglas-fir 

 assumes a dominant role. The general canopy is 120 to 140 feet tall and very dense on 

 the north aspect; it is 20 to 30 feet shorter and more open on the drier south aspect. 



Influenced by the Pacific Ocean, the winters are cool and wet and the summers dry. 

 Winter temperatures are less severe than in the higher elevations of the Rocky Mountains. 

 Storm-bearing winds usually sweep in from the southwest. Occasionally, during the winter 

 a continental storm will come from the east and northeast. Year-long precipitation 

 averages over 40 inches. 



Instrumentation. --Qxiring the planning stage, we were confronted with the lack of 

 a suitable instrument to measure directly the outflow from beneath a snowpack. The 

 problem was solved by designing a snow lysimeter based on a concept used earlier by the 

 Corps of Engineers at the Central Sierra Snow Laboratory (9) . 



The snow lysimeter collects outflow in a ground- level pan (fig. 2) from an undis- 

 turbed, finite column of snow deposited in place (fig. 3). A thin layer of polyethylene 

 encloses the column of snow and prevents lateral flow from entering the lysimeter. (The 

 cross-sectional area of the column and pan is 2.7 sq. ft.) As the effluent drains into 

 a catchment tank it is monitored continuously by a water level recorder. The outflow, 

 depending upon the nature of the storm or thawing condition, represents an' integrated 

 measure of rain, throughfall-drip, and snowmelt percolate. The installation and routine 

 operation of the lysimeter are more fully described elsewhere (2,3). 



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