WMOD00283 ‎(3)‎

• Title: Application of the Colorado River Simulation System in Evaluation of Weather Modification Activity
• Prepared By: Edward M. Novak
• Date: 7/1/1980
• Weather Modification - Doc Type: Report

In the Lower Basin, each demand generally represents a particular user, such
as the MWD (Metropolitan Water District), CAP (Central Arizona Project),
etc.

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The CRSS node di agram or network, fi gure 3, was used to interface the incre-
ment increase from weather modification with historic generated inputted
flows. Yearly natural flows and total dissolved solids at Lees Ferry arE~
depicted in table 1. Table 2 represents stations on the network which are
input points and correspond to those areas affected by incremental increiises
from weather modification depicted on figure 1. These specific stations were
adjusted for precipitation enhancement (table 3). Regression analysis
techniques were used to provide values in table 3. Flow intercept and slope
were determined from comparison of 1952-1971 virgin flow at a particular
station with incremental flow at that station as listed in the Twelve Basin
Investigation 6/. The salt loading coefficient was determined in a similar
manner by comparing the 1952-1971 virgin flow with salinity values set up in
the CRSS model. The mean flow multiplied by 140 percent at each station was
utilized for establishing suspension criteria. The data were arranged by
water year in the computer program. The majority of the runoff for a water
year occurs in the May-August period of each year.

Virgin flow values for the input points shown in figure 3 were compared to
precipitation enhancement increases as listed in the Twelve Basin Investiga-
tion 6/. The 1952-1971 historical period was used in this analysis because
this was the span of years covered by the Twelve Basin Investigation in
establishing precipitation increases due to weather modification.

Suspension criteria for the study was developed by using the specific limits
stipulated for the Colorado River Basin Pilot Project 8/ and those proposed
for the Sierra Cooperative Pilot Project 9/. These suspension period values
were tested against historical snow course data, and a single critedon of
1.4 times the 1952-1971 mean was used.

The results of the CRSS runs provide a realistic analysis of operational
weather modification activity in the Upper Colorado River Basin from 1991 to
2020.

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