WMOD00569

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

SNOWPACK, RUNOFF, AND STREAMFLOW
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COLORADO RIVER
BASIN
Fig. 7. Possible augmented runoff from the target areas In average snowfal
year (Milllon-Acre-Feet). Total out-of-basln a'ugmented runoff Is 1.15 mllllon-
acre-feet.
Water Quality in the Southwest
In the Colorado River Basin, water quality is a more urgent
~ problem than projected shortages. The water flowing out of the
(. Upper Basin already exceeds the U.S. Public He.alth Service
Drinking Water Standards for the concentration of dissolved
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SNOWP ACK, CLOUD-SEEDING, AND THE COLORADO RIVER

The runoff from the snowpack occurs mainly during the
late spring and early summer. As the air starts to warm up,
melting begins at the lower elevations and progresses up the
mountains. These conditions tend to produce a more or less
constant melting during the runoff period. However, unusually
warm periods or strong warm winds can cause rapid melting up
to very high elevations. These high melting periods can speed
evaporation losses, but they also cause rapid increases in stream
flow and longer periods of high water flows in streams. WOSA
would not influ~nce how often unseasonably early hot spells
might occur, but by increasing the snowpack depth and the
length of time Show could be on the ground, WOSA would
increase the probability of rapid meltoff situations.
The water yield is the runoff that results from the seasonal
snowfall. This figure averages the losses throughout the season
from the snowpack and during the snowmelt season, as well as
the variations from one part of the basin to another. We can
only estimate water yield, because there are few measurements
of the snowfall at high altitudes. We estimate that in an average
year in which cloud-seeding has been conducted at every oppor-
tunity, about 48 % of the augmented winter season precipitation
would reach the streams. If snowfall were a third higher than
average, the augmented runoff yield would be 52 % , but if it
were a third lower than the average, the augmented yield
would be 45 % (Figure 7).
These yields were used to compute the addition to water
supply that a full-scale WOS1\could produce. In an average
year, 2.3 million acre-feet could be produced within the Upper
Colorado River Basin. One year out of three, it might be either
lower than 1.1 or higher than 3.6 million acre-feet. Because of
the snow that WOSA brings to mountain slopes where the run-
off flows out of the basin, about 1.2 million acre-feet of addi-
tional water would be produced outside the Upper Colorado
River Basin, mostly east of the Continental Divide.

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