WMOD00575

• Title: Suitability of the Upper Colorado River Basin for Precipitation Management
• Date: 10/1/1969
• Weather Modification - Doc Type: Report

where

o 2
Q
lIQ

is the increase in runoff.

is the standard deviation of runoff, and

One of the purposes of this study is to determine
the relative suitability of individual basins within
the Upper Colorado River Basin by calculating the ex-
pected increase in runoff for each, i.e., lIQ , from
equation (1) and the number of years needed for evalua-
tion, i.e., N , from equation (Z).

On the other hand, the pilot program involves many
sub-basins within major ones. In this case, it is
advisable to choose a favorable combination of sub-
basins for evaluation. For this purpose, a new varia-
ble, Q*, is constructed by a linear combination of n
runoff variables, Qi (i=l, Z, ..., n), i.e.,

Q*

alQl + aZQZ + ... + anQn

n
L aiQi
i=l

where Qi is the runoff from an individual sub-basin.

Much freedom is gained from a combination of runoff
variables from various basins such as (3) compared to
the use of a single basin runoff. The freedom gained
is twofold. First, there is freedom gained in the
process of selection of n basins among many. For
example, where there are 15 ways of selecting one basin
out of 15, there are 3003 ways of selecting five basins
out of 15. Second, there is freedom gained in the
process of selection of the parameters a. once n sub-
basins have been chosen. 1

However, for hydrologic reasons, two restrictions
were imposed on the choice of the parameters a:

(a) The mean of Q*, Q*, must be equal to the sum
of the means of the Qi' Qi' symbolically:

n n
Q*= 1: "'iQi 1: Q.
i=l i=l 1

and

(b) The expected increase of Q*, lIQ*, must be
equal to the sum of the expected increases in Qi'

lIQi' i.e., symbolically:

IIQ*

n
L aillQi
i=l

n
L lIQi
i=l

The hydrologic interpretation of equation (4) is that
the expectation of the random variable Q* is the mean
of the total runoff for the group of n basins. The
interpretation of equation (5) is that the expected in-
crease of the mean of Q* is that of the total runoff
for the group of n basins.

As for a single basin the number of years, N*,
needed for evaluation of grouped basins is given by:

N*

3.84 0Q/
(lIQ*)2

(6)

Another purpose of this study is to develop systematic
methods to obtain the most favorable combinations of
sub-basins in the pilot areas by determining the Ct. 's
1
such that the number of years, N*, in equation (6), is
kept to a minimum.

(3)

4. General plan of paper. In Chapter II, the
hydrologic characteristics of the Upper Colorado River
Basin are reviewed. In the same chapter, the potential
for weather modification in this region is also dis-
cussed. Chapter III treats the question of definition of
a criterion of suitability and its calculations. Chap-
ters IV and V discuss the data used in the study, the
techniques of data processing, and most importantly,
the results. Chapter VI concludes the study.

5. Select basic terms used in this study.

(a) Water Year

"Water year" begins October 1 and ends September
30 of the calendar year. The term, "annual," refers to
water year. In the text the words "year" and "water
year" are used synonymously.

(b) Precipitation

"Precipi tation" refers to rainfall and the water
content of snow. Winter precipitation includes precipi-
tation from September 1 through April 30 and spring
precipitation from May 1 through July 31. Winter pre-
cipitation generally falls in the form of snow in the
high mountain watersheds. Precipitation is measured
in inches.

(c) Runoff

(4)

"Runoff" refers to the river flow measured at a
gaging station. In this study, unit yield is used, i.
e., the depth, in inches, of the cumulative volume of
flow during a given period, when volume is spread
uniformly over the whole watershed. Spring runoff
includes runoff from April 1 through July 31.

(d) Upper Colorado River Basin

(5)

By this expression the drainage basin of the
Colorado River above Lee's Ferry is meant (see Figure
1) .

(e) Upper Basin of the Colorado River

A much smaller drainage basin is meant by this
expression. The Upper Basin of the Colorado River is
defined in this study as the drainage basin of the main
stern of the Colorado, close to its source, and of a
few tributaries. The limits of this basin are shown on
Figure 6 (b) .

i
~i
I

2