WMOD00392

• Contract/Permit #: 14-06-D-7659
• Title: Weather Modification Design Study for Streamflow Augmentation in the Northern Sierra Nevada
• Date: 7/1/1976
• Weather Modification - Doc Type: Report

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is desirable or would be detrimental. Suspension rules governing seeding
operations are given in Volume III.

The reservoirs serve a multitude of purposes, two of
which are to provide flood control and to ameliorate the year-to-year
pi'ecipitation variability. In this latter capacity; they hold excess
run-off from one year to be used in the next. Thus, the effect of
seeding to increase run-off in one year can, through the reservoir, be
extended to alleviate deficits in a subsequent dry year, but not a previous

one.

Withholding seeding ope rations early in the season
results in the risk of missing early opportunities with the possibility
of inadequate opportunities being available in the later season. However,
this ri?k is relatively small. In fact, model results and data analysis
indicate that the m.iddle part of the winter (January and February) are
the months of highest potential in most years. This is due both to the
frequency of storms over the year and the fact that mid-winter storms
are more likely to be snowstorms rather than rain storms.

3.3

Hydrologic Considerations

The re we re four rec omrnendations in the San Diego State
report conce rning hyd rology. These recommendations are listed below
with a discussion of the study results relating to them presented in the
following paragraphs.

. An analys is, based on existing hydrologic models,
should be made of anticipated changes in flow regim.e of several repre-
sentative snlaller streams in the Sierra Nevada under alternative snow
augmentation strategies. Similar analyses should be made for
representative high-elevation lakes and reservoirs.

. A careful analysis, perhaps extending and elaborating
the work of Elliott, et al. (1973) should be made of the anticipated
effect on streamflow hydrographs and reservoir sto'rage outside the
snowpack zone of snow augmentation under a variety of plausible seeding
strategies. This shoul~ explic itly include cons ide ration of flood pos s ibilities,
which were not dealt with by Elliott, et al.

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