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<br /> <br />. " <br /> <br />-40- <br /> <br />Ilespite limitat.ions in the curl1ent techniques for measuring snow, <br />results have been highly useful in forecasting streamflow in western <br />States. Accuracy of the forecasts may be expected to improve as more <br />comprehensive methods are devised for combining the measurements'of snow <br />with data on related factors--clima1;ic, hydrologic, topographic, and <br />botanic. <br /> <br />Recent innovations in instrumentation <br /> <br />To obtain data on water equivalent of snowpack at unattended remote <br />stations, the Corps of Engineers has developed a gage in which a beam of <br />gamma radiation attenuates in passing vertically through the pack, and <br />the attenuated intensity of radiation is telemetered by radio. The advan- <br />tage isobvious--water equivalent may be determined as frequently as <br />desired, from locations of critical hydrologic significance even though <br />they may be inaccessible to personnel during the winter. Disadvantages <br />include the relatively large first Qost, difficulty in calibrating ade- <br />quately. some radiation hazard, the limitation that only a, single sampling <br />point is reported, and occasional failure of the unattended instruments. <br />Only a few of these gages have been installed as of 1964, in certain major <br />river basins; more may be expected as management of water sources becomes <br />more intensive. A general description of the gage and its operation <br />fOllows. <br /> <br />, As presegSly developed, the eq~ipment includes (1) a gamma-ray source, <br />cobalt-60 (Co ), enclosed in a lead collimating cylinder that is mounted <br />15 feet above the land surface and ('2) a scintillation detector and' photo- <br />multiplier that is mounted flush with the land surface directly below the <br />C060 source, and that measures intensity of the beam of radiation ema- <br />nating from that source. A snowpack attenuates the intensity of radiation <br />reaching the detector, and the amount of this attenuation measures water <br />equivalent in the snowpack. The intensity of radiation measured by the <br />scintillation detector is converted 'into electrical pulses suitable for <br />transmission by FM radio to a receiver and decoder. The system operates <br />on suitable storage batteries and the FM transmitter is a special low- <br />drain type. A reading of wa,ter equivalent is obtained in from 10 to 60 <br />seconds. Transmission time being so short, readings can be obtained daily <br />or more frequently over an e.ight-month period of unattended operation. <br /> <br />A second and promising i,nnovation is the "snow pressure pillow" with <br />accessory telemetric equipment, first suggested by Beaumont in 1957 and <br />under development in the Northwest (Warnick and Penton, 1963). Heart of <br />this device is a butyl-rubber pillow placed on level grcund before the <br />onset of winter, and filled with a rion-freezing fluid. The pillow is 10 <br />to 12 feet in diameter and 3 to 4 iriches thick. Snow accumUlating above <br />this pillow imparts increasing pressure to the confined fluid, and that <br />pressure is II sensed" by a transducer or by a float in a manometer tube. <br />~sponse of the sensing component is coded and reported by low_drain <br />radio. The pressure pillow can measure accurately the water equivalent <br />of snow over a very wide range of depth. Calibration is simple and cost <br />:j..s substantially less thlln that of ths ll;amma-ray gage. <br />