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9 (which included streams in Colorado, Wyoming, and Utah) correlations of 0.9 or better were found in eight cases and 50 record(3 sho.ved correlation coefficients of 0.8 or better. Although snovr course observations are intended to provide only an index of overall basin snowfall experience, and generally have only limited applica- tion to the evaluation of precipitation enhancement efforts, they may offer the best practical means in situations where access to a basin is restricted and resources for instrwnantation lind ted. 41. Anyone seriously interested in applying sno"\" survey techniques Viill benefit from reading "Snow Survey and Vlater Supply Forecasting" published bJ' the SO.il Conservation Service of the United States Department of Agriculture as Section 22 of i ts National Engineering Handbook. It is available from the Superi.ntendl?nt of Documents, U,S. Government Printine Office, as Stock No. 0107-0667. The following paragraphs present information dI'a"\m from that document. 42. SnOH courses are lines of sampling points with overall lengths ranging betVieen 300 feet (90 m) to 1,000 feet (300 m) or more, ..rith the end points well max'ked for identification in deep snow. Sampling intervals range from 25 feet (8 m) to 100 feet (30 m). The sampling procedure involves recovery of a complete column of the accumulated snoi,'pack by driving a calibrated duraluminum tube equipped .,rith a cutting head down to the ground surface. Weighing the sampler and the sno..: sample it contains leads to a ,va ter-equi valent reading. 43. Since the snow course observations are intended to be representative of large areas, care in selection of the sampling site is important. The elevation chosen should.be high enouglJ to avoid melting of snow dUTing the snow accumulation season. A gently sloping terrain will minimize biasing the readings due to ponding of meltwater under the snowpack, vri thou:~ making access for sampling too dLfficul t, Small protected mOUl1tain meadovrs, ",here drifting of sno'i:fall is reduced by surround- ing forest, are considered ideal snoVi course sites. 44. ""here "\'linter access is difficult, snow pressure pillows have proven useful as sensors in radio telemetry systems. These are flat, antifreeze-filled fluid containers made of corrosion-resistant metal or 'butyl rubber, covering areas ranging from 20 to 120 square feet (2 to 12m2), Pressur,? transd.ucers, electronic signal converters, and float-activated devices provide the means for both local x'eeording and radio transmission. They work well on level land and slopes of up to ;~O per cent. 45. Although much attention has been paid to the gross errors of measux'ement that can result vrhen precil)itation gauges are used to catch snoVifall, particularly in windy circwnstances (Rostad, 1925), networks of gauges equipped with shields (Alter, 1937) designed to reduce the effect of wind across the gauge opening have proven useful in precipitation enhancement evaluations carried out in Colorado (Grand and Kahan, 1974). Al though shielded prec:Lpi tati<lll gauges kave lltlt pr(Jv8e. par'Ucularly effective in improving the catch of rainfall, their usefulness where the precipi ta. tion falls as snow has been wel1-docwnented. (Rechard and Law~lOn, 1971). 46. Where access for observation after each snowstol:m is possible, snoVlboards have proven useful. '1'hes8 are simple, easily manufactured devices consisting of a squa.re board vri th a (lo"\'lel or steel rod to facili ta te finding after snow has covered the board. The board i.s pla.ced on top of the snoHpack after each storm and provi.des a means of measuring the amount of snOH that has been deposited since the previous reading. The boa:nl should. be large enough to provide a stable base for the vex,tical rod, but light enough to stay on the surface of the previous sn01". Squa:ees 16 inches (0.4 m) on a. side have been popular but the size is not critical.