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<br />were dispersed. An unknown proportion of it was de-
<br />posited on the ground or on vegetation near the gener-
<br />ator sites; a further unknown proportion was carried
<br />to one side or the other of the study area or deposited
<br />with precipitation either upwind or downwind from the
<br />study area, or escaped precipitation processes and
<br />remained suspended in the atmosphere. An estimate that
<br />70 kg of silver actually accumulated within the 340,000
<br />hectares of the study area appears reasonable, an accu-
<br />mulation of 0.04 grams per hectare season. The current
<br />preliminary estimate of average snow accumulation in
<br />the study area for the five years amounts to 65 cm
<br />water-equivalent per season. If 25 percent of this
<br />fell from seeded storms, this amounts to about 0.003
<br />gm of silver per hectare per centimeter of seeded pre-
<br />cipitation.
<br />
<br />During the five years of the Colorado River Basin Pilot
<br />project, there was a midwinter dip in the frequency of
<br />storms suitable for seeding, corresponding to mean
<br />upper-air temperatures too cold for "seedability." The
<br />experiments did not establish with a reasonable degree
<br />of confidence whether precipitation increases would
<br />appear as prolongation of snowfall durations or as in-
<br />creases of intensity, or both. Many such questions
<br />can be answered only by further experimentation.
<br />
<br />However, the results suggest strongly that the snowfall
<br />climate under seeding will differ from the natural cli-
<br />mate only in very subtle ways that can be distinguished,
<br />if at all, only by sophisticated statistical analysis.
<br />That seeded snowfall will be in any way strange, either
<br />as perceived or as it interacts with the natural en-
<br />vironment, is now considered extremely unlikely.
<br />
<br />LITERATURE CITED
<br />
<br />Armstrong, R. L., and Ives, J. D. 1976.
<br />Avalanche release and snow characteristics.
<br />Institute of Alpine and Arctic Research.
<br />University of Colorado Occasional Paper.
<br />Bould er .
<br />Cooper, C.F., and W.C. Jolley. 1969. Ecological
<br />effects of weather modification: a problem analysis.
<br />School of Nat. Resour., Univ. Michigan, Ann Arbor
<br />160 pp.
<br />Cross, C.W., and E.S. Larsen. 1935. A brief review
<br />of the San Juan region of southwestern Colorado.
<br />U.S. Geol. Survey Prof. Paper No. 843. 138 pp.
<br />Division of Atmospheric Water Resources Management.
<br />1970. Colorado River basin pilot project: Cloud
<br />seeding research in the San Juan Mountains. Bureau
<br />of Reclamation, U.S.D.I., Washington, D.C.
<br />Grant, L.O., C.F. Chappell, and P.W. Mielke, Jr. 1968.
<br />The recognition of cloud-seeding opportunity. Proc.
<br />National Conf. on Weather Mat. 1:372-385.
<br />Grant, L.O. (ed). 1969. Weather modification: An
<br />operational adaptation program for the Colorado
<br />River Basin. Dept. Atmospheric Sci., Colroado State
<br />Univ. Mimeo, 98 pp.
<br />Kuo, M. and K. Cox. 1975. Analysis of Colorado
<br />precipitation. Environmental Res. Center, Colorado
<br />State Univ., Fort Collins. Completion Rep. Series
<br />No. 63. 36 pp.
<br />Mather, K.F. 1957. Geomorphology of the San Juan
<br />Mountains. In Guidebook of southwestern San Juan
<br />Mountains, Colorado. Eighth Field Conf., New
<br />Mexico Geol. Soc. p. 102-107.
<br />Morel-Seytoux, H.J. 1968. Suitability of basins to
<br />weather modification and statistical evaluation of
<br />attainment. Hydrology Program, Colroado State Univ.,
<br />Fort Collins. 4 part report.
<br />
<br />National Academy of Science. 1964. Sciehtific pro-
<br />blems of weather modification. Nat. Acad. Sci.-Nat.
<br />Res. Coun. Publ. 1236. 56 pp.
<br />Teller, H.L., J.D. Ives, H.E. Owen, and H.W. Steinhoff.
<br />1970. The San Juan ecology project - phase I. Dept.
<br />Watershed Sci:, Colorado State Univ., Fort Collins.
<br />150 pp.
<br />U.S. Department of Commerce. 1961. Precipitation
<br />distribution maps of Colorado, 1931-1960.
<br />U.S. Forest Service. 1961-1963. Township maps of
<br />forest and range'types. San Juan National Forest,
<br />Durango, Colorado.
<br />1965. Tentative descriptive soils legend,
<br />Piedra Soil Survey Area, San Juan National Forest.
<br />U.S. Forest Service, Rocky Mountain Region, Denver,
<br />Co. Mimeo, 71 pp.
<br />1968. Pacific southwest hydrologic analysis,
<br />---phase I. Summary of analysis procedures. U.S.
<br />Forest Service, Rocky Mountain Region, Denver, Co.
<br />Mimeo, 68 pp.
<br />
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