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|Title:||Accuracy of field snow surveys, western United States, including Alaska|
|Authors:||United States. Soil Conservation Service.|
Work, Robert Archibald, 1904-
Stockwell, Homer J.
Freeman, T. G.
Beaumont, R. T.
Western United States
Snow water equivalent
|Publisher:||Cold Regions Research and Engineering Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Technical report (Cold Regions Research and Engineering Laboratory (U.S.)) ; 163.|
Summary: The popular Federal snow sampler tends to over-measure the water equivalent of snow. The error ranges from an average of about 7% in shallow, light-density Alaskan snow to as much as 10 to 12% in deep snow of higher density. These errors may be significant to stream forecasters who use quantitative forecast methods based on snow surveys. The errors are not significant in the Soil Conservation Service forecast system which uses snow cover as an index to resultant runoff. The observation, however, can be singularly important in comparative field studies with other devices to measure snow water equivalent, such as "talking" pillows or pressure platforms, or the radioactive isotope gage, where results from Federal samplers are accepted as representing more or less exactly the water equivalent of the snowpack. It appears that the over-measurement of snow water equivalent by Federal-type samplers (cutter point inner diameter 1.485 in.≠) is related to the shape and arrangement of the cutting teeth. Blunt tooth cutters (e. g. Federal) show the greatest over-measurement error, sharp tooth cutters (e. g. Bowman) the least over-measurement error. It is probable that a cutter for the highly portable Federal type sampler could be designed to reduce or eliminate this error, yet retain the present cutter's proven ability to cut and hold cores and penetrate dense snow of great depth. Wide differences in air temperature are not an appreciable source of error in Federal snow sampler scales. The scales themselves are individually very accurate at room temperature. The studies show no appreciable error attributable to erratic inner cutter point diameter, although there remains the theoretical possibility that snow tube accuracy might be, in part, an inverse function of cutter diameter. Experienced snow surveyors can read the tubular scales accurately more consistently than inexperienced observers. The error due to inconsistency in reading the scale is minor, except in very shallow snow. No evidence was found that slots in the tubes were a contributing source to over-measurement of water equivalent by Federal samplers. Of the samplers capable of deep snow sampling the Rosen tube consistently demonstrated the least over-measurement. This is believed due to the shape and sharpness of its cutter. The Rosen tube unquestionably is much easier to drive in deep dense snow, but it does not release its cores as well as the Federal sampler. If the clearance between the cores and the tube barrel inner face of the Rosen-sampler were increased it would unquestionably be a superior snow survey tool. However, since this sampler weighs twice as much as a standard Federal sampler, its use would not be popular with snow surveyors on long foot trips. The Adirondack sampler is very accurate. However, for snow in excess of 5 ft. deep, it is not considered practical under field conditions. If it were provided in lengths greater than 5 ft. while retaining its diameter, it would be extremely difficult to drive into dense frozen snow, and unhandy to transport on foot. It does not retain its cores with security when withdrawn from the snowpack. The Bowman sampler is very accurate and appears reasonably practical for field snow survey work where snow depths are generally less than 8 ft. In general, the authors conclude that the present Federal snow sampler equipment is as utilitarian as can be found for deep dense western snows, and even for shallow sub-Arctic snow. However design modification and further test work must be performed on the cutter point to reduce the over-measurement error of this equipment.
|Appears in Collections:||CRREL Technical Report|
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