PUB00068

• Year: 1952
• Title: A Hundred Years of Irrigatioin in Colorado, 100 Years of Organized and Continuous Irrigation
• Author: CWCB
• Description: Irrigation history of Colorado
• Publications - Doc Type: Historical

.-60....

these years was 1,20.0.,0.0.0. acre-feet of wh1ch about two-th1rds "as return
flO1, to the r1ver. an th1s bas1s ,for every three RecMld'.feet di.verted
from the r1ver and app11ed as i.rrigation, two secwnd-feet returns for
reuse in canals on dovmstream. The one secnncl..f()ot unaccounted for is
assumed to be consumptive use. ',villi.s .u0lwludes that increase in diver-
sion is a major contribution to l..,turll flow.

About 190.9 the area irrigated in the valley west of Bridgeport
approximated 50. 00.0. acres and not until after 1912 did the return flow.
become perceptible. Additional lands were put under irrigation and by'
1919 had reached a total of 2"..0.0.0. acres ill the valley between Whalen
and Bridgeport. III 1.9~7 t,he irrigated area approximated 350.,0.0.0.
acres. \'/illi.s found that the mean monthly flow of the river, after the
Pathfinder Rescl'Voir began storing flood water in 1910., was about 50.
;pet'oenc less for Nay and June than the mean prior to that time. For
.1uly it was about 30. percent less; August,95 percent more; September,
22.' percent more; and for o.ctober, 215 percent more. This increase in
river flow during these mo~ths being the result of the application of
water to irrigated lands between Whalen and North Platte, Nebraska. It
is to be noted that the very large increase in the return flow occurs
during September and o.ctober.

I

.

The increased. diversions from the river are believed to be the
major contribution to the return flow. Most of the water returning to
the river is through deep percolation and is designated as "invisible
return flow." It is believed that the extent of return flow to the
North Platte is the greatest for any of our western streams. Because
of this substantial increase in the available water supply for irriga-
tion the stability of agriculture in this valley is definitely assured.

During recent years many western streams that provide water for
irrigation, have been studied to determine the extent of return flow.
The Sacramento River between Red Bluff and Sacramento during July for
the years 1924 to 1928 inclusive had an average return flow of 36 per-
cent of the river flow. However, streams having wide valleys and of
flat grade may show losses instead of gains in discharge. (The San Luis
Valley along the Rio Grande is an example, according to Dr. Wm. p.
Headden.)

In the Poudre River Valley, in northern Colorado, during the
period of irrigation development, about 1 second-foot was considered
to be required per 80. acres of land. At that time the general water
table was at a considerable depth and the area irrigated was not large.
From 1870. to 1880. the irrigated acreage in the valley was .increased to
about 15,00.0. acres and at the time the first return flow measurements
were taken in 1885 the total irrigated area had reached about 70.,0.0.0.
acres. The return flow from the mouth. of the Canyon to Greeley in 1885
was less than 50. second-feet. The irrigated area in the valley in-
Creased with the years and for the period 190.6 to 1910. the return flow
to the river had increased to more than 20.0. second-feet during the fall
months. This can only be accounted for through the substantial amount
of return flow, and reuse of the water supply. (434 acres per second-
foot is high efficiency.) ,