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

-!.ower So11 Te1lll'erature

A noticeable decline 1n forest populations of small
lIlallllMls occurred follo..ing winters of heavy anowfall.
This was most ev1dent in the numbers of deer mice
(PeromyscuH maniculatus) but 1t was also found 1n
chipmunka (Eutamias minimua) and tn MicrotuS app.
The basic reason for the population decline derives
from the delayed growth of esaential apring fooda and
results primarily from a delay in breeding so that
fewer litters 5re produced. The delayed grOYth of
plants was a function of lower soil temperatures and
the longer snow cover. ~o Similar effect was found
on the toad (Bufo boreas). or pocket gopher (Tho~mys
talpoides) populations.

_Deeper Snowpack

As anow depth increaaed. elk (Cervus candensis) moved
to areaa where snow was shallower than 40 Cm. They
avoided regions with GOre than 70 Cm of penetrable
snow depth. A 15 percent increase in snowpack ~y
decrease available elk winter range by 8 percent.
Spring movement of elk was more strongly associated
with the start nf new growth in mountain meadows than
directly with the receding snowline. Ample habitat
waS available for elk calving below the anowline and
without regard to anow depth.

MicrObes

Plant litter in the tundra decreased in areaa of
deeper anowpack. This preaumably reflect~ removal by
the additional flux of water through the sy~tem rather
than an incrsase in decomposition rates.

Abiotic factors

The effects of the snowpack on soil eroaion resulted
from the greater area of bare aol1 left by the decrease
in vegetative cover around snowbanks. Those predicted
for the tundra area of the San Juan Mountains derive
from either the additional snow depth or the additional
II1eltwater produced by cloud seeding.

~eper Snowpack

If the area of long-laating anowbanks expand after an
increase in snowfall, local changes In the ratea of
soil erosion on the bare surface around them may in-
crease by a factor of 10. Thia effect ahould not
extend beyond the immediate vic1nity of already ex-
isting sn~w drifts and sO should nOt be important re-
gionally.

-Addittonal Meltwater

Theoretical conaideratlona suggest that an increased
streamflow generated by cloud seeding should be
associated with an increase in the t~tal amount of
dissolved material r~ved from the tarKet area. This
is supported by empirical observations of rock weather-
ing rates and stream water quality in the tundra
environment. However. this effect will be aliKht and
should not be concentrated spatially.

-HIstorical CllAatologv

Temperature fluctuations oVer the laat 120 years In-
dicate s cooling trend from the late 1560's to about
1930 when a reveraal occurred; pr..cipitation trend..
are inversely related to tewperature trends. These
trends are quite different from thosenoted In ..any
parts of the sorthern Hemisphere. Seasonal preciplta-

tlon fluctuations ahow rapid transitions from relative-
ly dry to relatively wet _d....

-Silver

So aignificsnt increase in silver cOncentration were
found in the target area. except in small areas near
generator aitea, after four winters of seeding. So
deleterious effects af silver iadide additions have
been noted at concentrations which could be expected
due to cloud seeding.

HISTORY ~~D DES1GS

The San Juan Ecology Project waa established as OnS of
a co~lex of investigations arisIng trom the need to
explore the posaibiliti~s of increasing the availabil-
its of water 1n the Cnited Statea Southwest. In 1968
Congresa authorized the Bureau of Recla158tion to
inltiate weather .ndific8tton pilot project6 to teat
the feasibility of large scale ~Inter cloud seeding
which showed promise of being an economical technique
for au~nting the flow of the Colorado River (Division
oi Atmospheric Water Resources Management 1970).
Analyats of previous research findings indicated that
the most likely chance of success would come from
winter seeding of orographic storms over aome of the
high mountain areas aituated in the tpper Colorado
River Basin. Grant et a1. (1968) tested thia approach
on a limited scale at Climax, Colorado. and found
significant increases 1n snowfall when s<,edlng e'qler-
i~nts were performed under apectfic weather situatiOna,
Knowledge accruing from thla study. snd from tWO otbers
in CoI~rado (Steamboat Springs and Wolf Creek Pasa).
and from a Satlenal Academy of Sciences Report (1964).
led to the concluaion that carefully managed winter
cloud-seeding technique\! could produce a 10 tll 30
percent incr..asl!' in IllOUntaln snowfall. The Bureau of
Reclamation designed the Colorado River Basin Pilot
Project (part of Project Skywater) to teat this
possibility On a sub-operstiona1 acale. The most re-
cent statement On the elfectlveneas of this deaign is
given In sUlIIIIIiIry fOrlll by flow..ll (thill Chapter).

\
I

The San Juan Mountains of southwestern Colorado were
chosen as the site of the cloud seedin~ pIlot project
becauae of their atrategic locatIon for intercepting
winter orographic stOrma deriving from the south..est
which would also ensure relatively frequent occurrence
of a cloud-top temperature condition calculated to be
within the lIIOat effective s..eding range of above -26 C.
The or1ginal area deatined ~o receIve 2he cloud-seed-
ing experiment was 8.550 km (3.300 mi ) on the west-
ern side of the Continental 01vide. and above 2.900 .
(9.500 ftl elevation (rig. 1).

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ri~ure 1. San Juan cloud seeding target ar~a. and
int...nsh'e study ..U.,".

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