WSP02180

• File Number: 8051.500
• Description: Section D General Statewide Issues - Basin of Origin Legislation - Transbasin Diversions
• State: CO
• Basin: Statewide
• Date: 4/14/1944
• Author: C L Patterson
• Title: Opportunities for Trans-Mountain Diversion in Colorado
• Water Supply Pro - Doc Type: Report/Study

0008GS

2,000,000 A,F, in Colorado, Of the estimated Colo-
rado total, more than half consists of importations to
the South Platte river basin. In fact the two proj-
ects, later to be described, together are estimated
to have a combined yield of about 960,000 A,F,
annually, or nearly half the contemplated total expor-
tations of Colorado river water for use in Colorado
east of the Continental Divide,

Production Estimates
In connection with trans-mountain diversion de-
velopments, and with other water projects in Colo-
rado intended for streamflow regulation, water
conservation, flood control, hydro-electric power gen-
eration, and combinations thereof, for municipal,
agricultural, industrial and related beneficial pur-
poses, the engineering department of the Colorado
Water Conservation Board makes determinations,
where possible, and estimations, when necessary, of
the production, use and disposal of the water re-
sources of the State, And, since all the natural
streams arising in Colorado are interstate in char-
acter, such investigations lead into adjoining States
and competitive territories, But for the moment our
attention may be restricted to Colorado,
The original source of all of Colorado's water
resources is natural precipitation, the inadequacy of
which, at the same time, creates the need for and
value of the water resources, As might be expected
from Colorado's inland location and varied topog-
raphy, there are wide differences in the amounts of
precipitation, as recorded at Weather Bureau sta-
tions scattered over the State, ranging from less
than 10 inches annually in sheltered valleys, to more
than 50 inches on the exposed crests and slopes of
some mountain ranges, The reported long-time aver-
age precipitation for all observation stations in Colo-
rado is 16,5 inches,
Bearing that average rate in mind, .it is appar-
ent that the high-mountain areas receiving more
than 30 inches annually involve relatively small areas
as compared with the more extensive lower plains
regions receiving less than 15 inches annually, These
high mountain areas, themselves, are too cold and
commonly too steep and rocky to be valuable for
agricultural purposes, other than summer grazing
of livestock. But they are valuable in another way,
The large precipitation, mostly at such altitudes in
the form of snow, melts in late spring and early
summer months, and affords life-giving waters for
the thirsty valley lands and arid plains below, As
distinguished from the infrequent and occasionally
violent floods in foothills and plains regions, the
mountain runoff, which is perennial in character
and not subject to cloudburst types of floods, con-
stitutes the water-supply basis for a large share of
Colorado's irrigation development, which in turn is
today the State's most important industry,
. Average Precipitation .
Total precipitation in Colorado, over the 66,-
500,000 acres of State area, at the reported average
rate of 16.5 inches, is equivalent to 93,000,000 acre
feet of water annually, What an empire could be
created in Colorado if that amount of water, flowing
in the streams of the State, were available for diver-
sion and needed as at present for beneficial use, But
before the rains and snows find their way, on the
surface and underground, into tributary and main
river channels, some 13.5 inches of the precipitation,
or about 82 per cent of the total precipitated water,
is returned by the processes of evaporation and
transpiration to the atmosphere from whence it
came,

In humid regions the rates of precipitation are
generally equal to and frequently greater than the
rates of evaporation, This relation probably prevails
in the high mountain areas of Colorado, as indicated
by the evaporation rate of 25 inches at Leadville.
But in general and for most of Colorado" evapora-
tion rates are several times greater than rates of
precipitation-such evaporation rates in agricul-
tural areas ranging from 45 to 55 inches in western
Colorado, from 35 to 50 inches along the eastern
foothill regions, and from 50 to 60 inches along the
eastern boundary of the State,

16,600,000 Acre Feet
Colorado's water resources, with which we are
here concerned, consist of the unevaporated 3 inches
of precipitation, or the remaining 18 per cent of the
precipitated water. Measured as streamflow and
estimated as original runoff, the State's water re-
sources aggregate 16,600,000 A,F, in a year of normal
climatic conditions. Out of this original supply
nature takes another toll in the form of channel con-
veyance losses, and the supply is further depleted
through its storage diversion and utilization, prin-
cipally in connection with irrigation, Without at-
tempting to submit details, our investigations indi-.
cate that up to the present time, and after some 80
years of irrigation and related developments in Colo-
rado, we are collectively and consumptively using
not more than one-third of the State's water re-
sources, or less than ,5,500,000 A,F, annually; and
that the remaining unconsumed outflows from Colo-
rado, approximating two-thirds of the original water
production, equal or exceed 11,000,000 A,F, of water
in an average year,
What are the reasons for this indicated non-use
or fractional development of Colorado's water re-
sources? Manifestly, one reason is that some of the
total water production occurs at locations so near
each of the State's four borders as to preclude its
control, diversion and utilization in Colorado, And
there are other, though less apparent, reasons which
will briefly be discussed. Among these are the prob-
lems created by variable climatic conditions, involv-
ing reservoirs for equalizing the widely fluctuating
streamflows and water supplies; problems resulting
from the distorted distribution and unbalanced rela-
tions between the locations of the State's water and
land resources; and problems arising from the claims
by other States of rights and interests in the waters
of streams arising in Colorado.
Natural precipitation is variable from day to day,
from one month, season and year to another, and by
non-periodic and non-predictable cycles of years. For
example, as compared with normal precipitation in
Colorado averaging 16,50 inches annually, Weather
Bureau records disclose variations ranging from 6(\
per cent to 136 per cent of normal, by individual
years, and from 89 per cent to 111 per cent of normal,
by lO-year periods, Assembled by stream basins, the
precipitation records disclose greater departures, and
still greater fluctuations, above and below normal
values, may be noted by consulting individual sta-
tion records,

Production Varies

From streamflow records and comparisons it is
known that water production in Colorado, averaging
16,600,00 A,F. in a normal climatic year, varies
from year to year from about 6,600,000 A,F" or 40
per cent of normal to about 26,000,000 A.F.. or about
160 per cent of normal: and \'aries by ten-.year peri<'d