Collection of atmospheric data for Project Skywater

Jack N. Washichek Soi2 Conservation Service, Denver, CoZorado, U. S. A.

ABSTRACT: lect snow data on three different atmospheric resources research projects in Colorado and New Mexico.

data collection and the design of this equipment.

This paper describes different techniques employed to col-

The report indicates equipment not normally employed in snow

It summarizes the operation and resultant data.

RESUME: obtenir les donndes de neige des plans de recherches des trois différentes ressources atmosphériques dans le Colorado et New Mexico.

utilisé dans les collections et modèles de ce matériel sur les données de neige.

Ce papier décrit les différentes techniques employées pour

I1 indique les demandes de matériel qui n’est pas normalement

I1 résume les données d’opération et de résultat.

The Snow Survey Unit of the Soil Conservation Service (U.S. De- partment of Agriculture) in Colorado has been involved in the collec- tion of atmospheric data since 1965. A considerable part of its effort has been directed toward the U.S. Bureau of Reclamation’s “Project Skywater“.

Mountain drainages to increase runoff and subsequently the available water supply. Measurements of the snowpack would have to be refined to the point where possibly a 2 or 3 per cent increase could be detect ed.

now playing in this program. Bureau asked the Snow Survey Unit to collect snow data for the proj- ect at three locations in Colorado and New Mexico. The resulting data would be used as an aid in evaluating the Bureau’s cloud seeding program - “Project Skywater”. As this was a new kind of project, the information needed and the way it should be collected had to be decided.

samples of snow are taken. Snow courses range from 68.6 to 304.8 metres in length, Courses may be in the form of an X, an L, or a straight line. Ten or more sample points are established along the line of a snow course. These points are designated by a measured distance and direction from a starting point. The distance between measurement points is usually 7.6 or 15.2 metres.

excellent snow versus elevation relationship can be established.

lee-side of the tree rows in larger parks. High winds or blizzard conditions are not typical of the area, but many drifts do occur in the areas adjacent to the bands of trees.

Project near Steamboat Springs, Colorado (Fig. 1). This area is char-

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This project is aimed at increasing the snowpack in key Rocky

This is the role the Soil Conservation Service has been and is At the program’s inception in 1964, the

For this study a snow course refers to a specific location where

Snow courses range in elevation from 1,980 to 3,250 metres so an

The ridge snow courses are established in small parks or on the

One of the locations selected for this effort was the Park Range

acterized by relatively high annual precipitation of which a major portion is snow. The ice nuclei process of precipitation formation predominates, and a major portion of the storms are associated with southwest to northwest winds over the area. The Park Range lies east of Steamboat Springs and provides the orographic effects. There is no major mountain range to the west for 280 kilometres.

The project area covers 32.18 by 38.62 kilometres. area ranges in elevation from 2,000 to 3,250 metres.

The Snow Survey Unit established 16 new snow courses to add to the six already existing in the area. Courses were checked every ten days to insure uniform measurements. Each sample point of each snow course was checked to make sure no drifts or blowouts were developing. If a sample point was found to be inconsistent, it was deleted or moved to a better location.

Overall the

DATA ANALYSIS

Each year since 1965 the data has been checked for completeness, accuracy, and coverage. Each year the snowpack varies as to depth, density, and time of deposit, but the precipitation characteristic continues. The Buffalo Pass snow course was used to normalize all other courses. It is interesting to note that although the snowpack varied as much as 70 per cent since 1965, the comparison between courses remains almost constant, Figure 2 shows a summary of all years since 1965. lents falls in such a narrow band. Correlation coefficients (r) between Buffalo Pass and the other snow courses were computed for years of record. These correlations are extremely high, ranging from a high of r = 0.992 for Little Lake-Buffalo relationship to r = 0.967 for Patrol Station-Buffalo Pass comparison. The correlation coeffi- cients provide only a measure of the degree of association between the compared snow courses. This is the only determination considered necessary. The measurement of the snow is only an index and probably not the true amount of snow in the area. Serial correlation is ex- pected and has no overall effect.

Snow pil- lows were 3.66 metres in diameter, and were made of butyl rubber. When filled with 1324.8 litres of methanol, the snow pillows were about 10.16 centimetres thick. The pillows were installed flush with the ground. Pressure transducers and on-site recorders completed the installation, A modified A-35 recorder that automatically up-dates itself each hour was used. Six sites were selected for automation.

Figure 3 shows a comparison between pillow re.adings and manual readings. It is possible that the snow pillow is more accurate than the snow tube. Careful manual readings produce a very small error. Here again we are interested only in a comparison of indices and the sensor most representative of the area.

another area was selected as a pilot project for the Colorado River. This area is located in southwestern Colorado. Primary source of water is the San Juan River, a tributary to the Colorado (Fig. 4). This area lies generally north and east of Durango. This area is characterized by high precipitation which falls in the form of snow much as in the Steamboat Springs area. Snow-laden winds are gener- ally from the south and southwest.

kilometres from north to south in its deepest part. Elevations range

It is amazing that all the data on water equiva-

Snow pressure pillows were used as sensors in 1966.

Cloud seeding in the Park Range area was suspended in 1969 and

The area is about 177 kilometres from east to west and about 97

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from the valley floor at 1,980 metres to ridge elevations in excess of 4,500 metres. The La Plata Mountains lie immediately to the west and present a barrier in excess of 4,850 metres in places. There is no barrier to the south.

metre metallic pillows were laid to form a 2.44 x 3.05 metre surface. This pillow (Fig. 5) seem less likely to develop leaks, but if leaks do occur they can be readily repaired in the field. of antifreeze are required to fill each pillow. comparatively easy to transport.

After two years of operation it is obvious that the excellent comparison between snow courses is not possible in this area as in the Park Range.

buildup as well as the recession of the pack. be identified and evaluated. this project. New Mexico, located immediately e a t of Cuba, New Mexico (Fig. 6).

The project area is characterized by elevations of 2,100 metres at Cuba to 3,200 metres on the San Pedro Peaks. 2,984 metres. Most of the area lies within the 2,500 to 2,900 metre level. The average annual precipitation at Cuba is 38.0 centimetres; at Jemez Springs, 44.9 centimetres. The average annual temperature is 8°C at Cuba and 11°C at Jemez Springs.

The snow pillow recorder chart for the 1968-69 and 1969-70 season gives some idea of the variation in snow water content. The maximum water content in 1968-69 was 38.86 centimetres (121.92 centi- metres of snow) ; in 1969-70 the peak was 18.3 centimetres (94.0 cen- timetres of snow). The Soil Conservation Service precipitation gauges indicated totals of 88.9 centimetres at Black Rock, 87.1 cen- timetres at Teakettle, and 79.0 centimetres at Resumidero for the calendar year 1969.

Because this is a relatively low precipitation area and melting can occur almost anytime during the winter , precipitation gauges were considered a necessity. To obtain data on all forms of precipitation, snow courses and/or pillows, precipitation gauges, and soil moisture units were employed.

A new fulcrum weighing precipitation gauge was developed for installation on the seven new snow courses. The fulcrum weighing device was designed to make the weighing procedure easier and faster while maintaining the accuracy of the direct weight measurement. The new gauge permits measurements to be made from the ground at all times.

plate, a standpipe 1.83 metres by 7.6 centimetres in diameter, a special self-contained fulcrum weighing device, a 106.68 centimetre precipitation bucket with a 20.3 centimetre orifice and a windshield 1.22 metres in diameter (Fig. 7). A petcock allows the can to be drained without being removed. Access to the upper structure is by means of a portable 1.91 centimetre steel U which fits into the steel stand. The fulcrum lever length was checked for accuracy during development. 2:l ratio gave the most reliable results.

manually lifting the bucket from the gauge and weighing directly. Data were analyzed by the computer after the first year to determine accuracy .

A new type pillow was used on these sites. Four 1.22 x 1.52

Only 15 litres The pillows are

The pillow sites provide daily indications of the snowpack Individual storms can

No major problems were encountered in This was not the case on the Jemez Mountain Project in

Nacimiento Peak is

The gauge consists of an anchor in concrete and a levelling base

Laboratory tests revealed that a lever length with a

Measurements were made using the fulcrum method as well as by

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The correlation coefficients comparing the manual to the fulcrum method are listed below:

Black Rocks .99747 Jarosa Canyon .99819 Re s umi der o .99870 Rio Puerco ,99787 Rito Cafe .99915 Rock Creek .99834 Te akett 1 e .99282

These coefficients indicate a high degree of association between the two methods of measurement. From readings it was determined that the fulcrum method overweighs more often than underweighs, indicating very little friction in the fulcrum.

A snow pillow and soil moisture unit were installed at the Teakettle snow course. The pillow operated only intermittently. It is believed that some bridging may be occurring due to the low snow and the possibility of ice layers within the snowpack. moisture analysis indicated that some moisture penetrates the upper two metres of soil mantle during most of the winter months.

The soil

SUMMARY

No absolute determinations can be made from these few years of analysis, a summary of ideas will be listed to assist other re- searchers in instrumentation for snowpack evaluation.

By carefully analyzing each area to be evaluated, it is possible to obtain extremely accurate measurements of precipitation. network of data collection points are needed at the start of each project. A number of these may be eliminated if correlations are good. Many times, depending upon the area, variations in precipita- tion of only 2 or 3 per cent can be determined.

The pillow by itself is not sufficient to determine total snow accumulation at low elevations, nor in areas subject to melt during the winter months. pillows provide an excellent index at some locations whereas precipi- tation gauges alone tend to measure less than actually falls.

Manual measurements are accurate, but time consuming and labori- ous in deep snow. It is necessary to keep close records of each point on each snow course to prevent measurement of drifts or hollows. Some manual measurements are needed to ascertain accuracy of pillows and precipitation gauges.

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Precipitation gauges used in conjunction with

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Fig. 1. Park Range Project - northwestern Colorado

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SNOW COURSES BY ELEVATION

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OSAGE L Fig. 2. Six years record of snow courses in per cent

of Buffalo Pass course

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Fig. 3. Comparison chart showing manual and pillow measurement of snow pack at Long Lake snow course (1966-67)

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Fig. 5. Four galvanized pillows are hooked up together to form effective surface 2.44 x 3.05 metres

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Fig. 6. Jemez Mountain Project in northwestern New Mexico

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BASE PLATE A Fig. 7. Fulcrum precipitation gauge assembly

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DISCUSSION

E.J. Langhum (Canada) - I am interested in the effect of snow pillows on the mass transfer that would normally take place across the snow-soil boundary. Interference with the natural evolution of the snowpack should have effects both on the total mass of snow upon the pillow and on the water retention properties during runoff periods. In either case, the difference between the characteristics of the snow over the pillows and over the surrounding terrain would lead to unrepresentative measurements.

profiles in the snowpack and compared them with the snow over a pillow or similar impermeable material.

And in such a case, 1 would also like to enquire as to the ac- curacy he obtained in his measurements because if the effect of the snow pillow which I have suggested is negligible in deep snowpacks, it may not be negligible in a shallow snowpack. In this respect, I would also be interested to have an opinion on the lower limit of the mean depth of snowpack for which snow pillows are useful as a measuring device.

I would like to ask Dr. Washichek, if he has looked at vertical

J.N. Wushichek (U.S.A.) - Several studies have been conducted on this subject such as buoying the snow pillow in the soil. This had no effect other than measuring the amount of water in the soil mantle above the pillow. Duff layers over the pillow produced no evident effect. Further, plastic sheets placed over the pillow for protection against pinhole leaks showed no effects other than to prevent the formation of depth hoar on the soil.

to 175 inches, hence, any interference at the soil-snow interface would be negligible. In New Mexico the depths encountered range from 2 to 4 ft so that there might be some interference at the soil- snow interface. Some bridging seems to occur at the New Mexico site as meltwater moves down through the pack. from the erratic hourly readings.

primarily for deeper snowpacks.

Snow depths in the Steamboat Springs area of the U.S. reach 150

This has been deduced

I would not recommend the pillow for the Prairie regions; it is

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