Three Instruments Used in Avalanche Hazard Forecasting: 1. Snow Settlement, Temperature; 2. Snow Collector for Recording Rain Gauge; 3. Temperature Telemeter (Classic Reprint)

Edward R. LaChapelle

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Excerpt from Three Instruments Used in Avalanche Hazard Forecasting: 1. Snow Settlement, Temperature; 2. Snow Collector for Recording Rain Gauge; 3. Temperature Telemeter

Further details may be obtained from the Alta Avalanche Study Center.

This instrument has been in use for a number of years at Alta, Stevens Pass and Squaw Valley. It provides a simple and reliable means of measuring snow cover settlement throughout the winter without disturbing the snow cover. A simple adaptation, shown in the schematic diagram, permits observation of snow tempera tures as well.

The settlement gauge is nothing more than a Wheatstone bridge, the vertical resistance wire forming one side of the bridge and the helix potentiometer the other. The resistance wire, #20 to #2h-gauge nichrome, is suspended vertically in the center of a smooth, level area in the study plot, and is long enough to clear the maximum winter snow depth. Following each snowfall, a wooden lattice supporting a crocodile clip connector is placed on the snow surface and the clip attached to the resistance wire. A connecting lead runs from the slip to junction box. The lattice may be constructed of stripes of lath, l8 to 2b inches long, nailed together and painted white. As the lattice becomes buried under subsequent snowfalls, settlement carries it downward and the clip slides along the resistance wire. Its buried position at any time may be determined by connecting the test set and balancing the bridge, as indicated by zero-reading on the galvanometer . Comparison of the helix potentiometer dial reading with a previously determined calibration chart locates the height of the clip and lattice above the ground in terms of inches or centimeters.

A modification at Stevens Pass uses sliding contacts permanently attached to the resistance wire. The clips are connected to these instead of to the wire itself.

The lattice with clip and lead wire may be stored inside until required. The lead wire is then uncoiled and attached to a terminal strip in the junction box.

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