WSP09641

• File Number: 8200.750
• Description: San Juan River General
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 3/9/1976
• Author: Steinhoff and Ives
• Title: Ecological Impacts of Snowpack Augmentation in the San Juan Mountains - Colorado - March 9 1976
• Water Supply Pro - Doc Type: Report/Study

were dIspersed. An unknown proportion of it was de-
posited on the ground or on vegetation near the gener-
ator sites; a further unknown proportIon was carrIed
to one side or the other of che study area or deposited
~ith precipitation either upwind or downwind from the
study area, or escaped precipitation processes and
remained suspended in the atmosphere. An estimate that
70 kg of silver actually accumulated within the 340,000
hectares of the study area appears reasonable, an accu-
mulation of 0.04 grams per hectare season. The current
preliminary estimate of average Bno~ accumulation in
the study area for the five years amounts to 65 cm
water-equivalent per season. If 25 percent of this
fell from seeded storms, this amounts to about 0.003
gm of silver per hectare per centimeter of seeded pre-
cipitation.

During the five years of the Colorado River Basin Pilot
project. there was a midwinter dip In the frequency of
storms suitable for seeding, corresponding to mean
upper-air temperatures too cold for "seedability." The
experiments did not establish with a reasonable degree
of confidence whether precipitBtion 1ncreases would
appear as prolongation of snowfall durations or as in-
creases of intensity, or both. Many such questions
can be answered only by further experimentation.

Ho~ever, the results suggest strongly that the snowfall
climate under seeding will differ from the natural cli-
mate only in very subtle ways that can be d1stinguished.
if at all, only by sophisticated statistical analysis.
That seeded snowfall will be in any way strange. either
as perceived or as it interacts with the natural en-
vironment, is now considered extremely unlikely.

LITERATURE CITED

Armstrong. R. L., and Ives. J. D. 1976.
Avalanche release and snow characteristics.
Institute of Alpine and Arctic Research.
University of Colorado Occasional Paper.
Bould er .
Cooper, C.F., and W.C. Jolley. 1969. Ecolog1cal
effects of weather modification: a problem analysis.
School of Nat. Resour., Univ. Michigan, Ann Arbor
160 pp.
Cross. C.W., and E.S. Larsen. 1935. A brief review
of the San Juan region of southwestern Colorado.
U.S. Geal. Survey Prof. Paper No. 843. 138 pp.
Division of Atmospheric Water Resources Management.
1970. Colorado River basin pilot project: Cloud
seeding research in the San Juan Mountains. Bureau
of Reclamation, U.S.D.I., Washington. D.C.
Grant, L.O., C.F. Chappell, and P.W. Mielke, Jr.
The recognition of cloud seeding opportunity.
National Conf. on Weather Mat. 1:372-385.
Grant, L.O. (ed). 1969. Weather modiFication: An
operational adaptation program for the Colorado
River Basin. Dept. Atmospheric Sci., Colroado State
Oniv. Mimeo, 98 pp.
Kuo, M. and K. Cox. 1975. Analysis of Colorado
precipitation. Environmental Res. Center. Colorado
State Vniv., Fort Collins. Completion Rep. Series
No. 63. 36 pp.
Mather, K.F. 1957. Geomorphology of the San Juan
Mountains. In Guidebook of southwestern San Juan
Mountains, COlorado. Eighth Field Conf., New
Mexico Geol. Soc. p. 102-107.
Morel-Seytoux, H.J. 1968. Suitabil1ty of basins to
weather modification and statistical evaluation o(
attainment. Hydrology Program, Colroado State Univ.,
Fort Collins. 4 part report.

1968.
Proc.

National Academy of Science. 1964. Scientific pro-
blems of weather modification. Nat. Acad. Sci.-Nat.
Res. Coun. Publ. 1236. 56 pp.
Teller, H.t., J.D. Ives. H.E. Owen, and H.W. Steinhoff.
1970. The San Juan ecology project - phase I. Dept.
Watershed Sc1" Colorado State Univ., Fort Collins.
150 pp.
U.S. Department of Commerce. 1961. Precipitation
distribution maps of Colorado. 1931-1960.
U.S. Forest Service. 19&1-1963. Township maps of
forest and range'types. San Juan National Forest,
Durango, Colorado.
_____ 1965. Tentative descriptive soils legend.
Piedra Soil Survey Area, San Juan National Forest.
U.S. Forest Service. Rocky Mountain Region. Denver,
Co. Mimeo. 71 pp.
1968. Pacific southwest hydrologic analysis,
---phase 1. Summary of analysis procedures. U.S.
Forest Service, Rocky Mountain Region, Denver, Co.
Mimeo. 68 pp.

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