WMOD00569

• Title: Snowpack, Cloud Seeding and the Colorado River
• Date: 1/1/1974
• Weather Modification - Doc Type: Report

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STREAMFLOW

STOP CLOUD SEEDING
ABOVE THIS LINE

50

00

50

MAY

DATE OF SNOWPACK MEASUREMENT

it did before WOSA, more water must be handled by the streams
in the same time. If the snowmelt season is a few weeks longer
because of WOSA, the possibility of a high temperature or warm
wind is increased. Thus, WOSA will increase the probability
of flooding. .
The natural stream channels in the Upper Basin can gen-
erally handle more water than the average seasonal snowpack
yields. By comparing historical flooding records with snowpack
accumulations, we can determine how large a runoff the streams
can handle. This has been done for the target area of the Colo-
rado River Basin Pilot Project in the San Juan Mountains. The
results show that if the accumulated snowpack can be held to
150% of the average on April 1, the probability of more than
minor flood damage will increase only slightly. WOSA could
stay within these limits and reduce the WOSA-created precipi-
tation by only about 10%. This is the same limitation that
would be desired to reduce the probability of creating new
avalanche runs (Figure 10)

mlts for flood control

10. Seeding

Fig.

SNOWPACK, RUNOFF, AND

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SNOWPACK, CLOUD-SEEDING, AND THE COLORADO RIVER

The natural level of aval~mche risk is. accepted by residents
as part of life in the region. A program that combines all of the
possible control procedures could hold the risk below the nat-
ural level, even with WOSA, at a relatively small cost. With such
a program

Roads should be closed on the worst storm days. Such days
occur naturally two to three times in an average winter in the
Ouray-Silverton area of Colorado, for example, and with
WOSA the roads might be closed on five days in an average
winter. The costs are inconvenience to travelers and to workers
in the area, and loss of revenue to local business and industry.

APR

MAR.

FEB

Passive control structures should be built at the small number
of runs where avalanches are extremely frequent. One control
structure should be built (at an estimated cost of $150,000) at
Blue Point, near Silverton, Colorado. It would be desirable to
build at least one more structure along the Ouray-Silverton
road for a cost of $500,000.

Active avalanche control should be extended to provide for all
the expected increases brought about by WOSA, and also to
provide control on nonpublicroads. The expected increases in
cost would be $24,000 per year in Colorado and less than
$10,000 per year in Wyoming.

Cloud-seeding should be limited so that the seasonal snowfall
does not exceed that of high years such as 1957, 1962, and
1965. If this were done, no new avalanche runs should result
from the WOSA program, but average WOSA water produc-
tion would be reduced by about 10% in those years.

Ii

Flooding occurs when a stream channel cannot hold the
volume of water flowing into it. A summer cloudburst can cause
flooding, and so can an early thaw, or a warm spring rain. High
temperatures or warm winds can happen at any time during the
snowmelt season. They are unrelated to the amount of snow on
the ground, so that flooding has occurred in years of light snow-
pack as well as heavy. .
WOSA will increase the amount of runoff water to be
handled by the streams. If the snowmelt season lasts as long as

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