The Idaho Republican. [volume] (Blackfoot, Idaho) 1904-1932, 1924-02-21

years OF irrigation history In the
valley there has been a gradual with
: drawal of at least 100000 acre-f
r of water from river circulation. Thi
8 vast underground reservoir natural
: fiuctuates slightly from year to veal
3 and in dry cycles is depleted, servin
: as an equalizer to river flow, but re
covering during years of heav
: stream flow and application.
, When irrigation Is first practice,
in a community the water demand
/, (per acre irrigated) on river suppl.
is at maximum, and practically al
} water diverted, except surface waste
lis temporarily lost to the stream
Gradually there is a building up o.
an underground reservoir in from
five to twenty years with return flow
in increasing volume until eventually
the return flow may approximate OF
exceed one-third Of the total yearly
diversion. 1t is apparent that dur
ing the irrigation history of river
there occurs a period of years when
| irrigation demands indicate that the
limit of water supply has been
reached. This condition is only tenn
pOrary and later on return flow en-
riches river flow and permits an ex-
tension of the irrigated acreage.
Investigations of the Poudre river
in Colorado show a return of close
to 35 per cent of the annual average
original water supply of that stream
measured at entry to the plains. On
the South Platte in Colorado the per-
centage is about so. On the Salt and
ella rivers in Arizona returns of 35
to IS per cent have been measured.
History of Return Flow
Return waters from irrigation
were first observed in Colorado forty
years ago, irrigation having COM
menced in a small way in 1860. The
first known published return-flow
measurements were made in 1885 on
the Cache la Poudre river in Colo
RADIO between Fort Collins and
Greeley. They confirmed the obser-
vations of irrigators for several
years to the effect that there was an
increase in river flow. Commencing
in 1889 and continuing until 1915,
covering a period of thirty-two years,
seepage measurements were made
annually on the Cache la Poudre
river from Poudre canyon to the
mouth, forty-seven miles, and on
the South Platte river from Platte
canyon to the Nebraska line, dis
lance of 235 miles. During that
period seepage or return flow meas
urements were also extended to the
important streams in the principal
irrigated valleys in Colorado. Other
states have conducted similar in
vestigations. In Arizona early re-
turn-fow measurements were made
on the Salt river and the ella (see U.
S. department of agriculture expert
ment station bulletin 104,) and in !
1910 amounted to 100000 acre-ft. |
During the past five years the U. S.
reclamation service has made special |
Investigations on some of the mod |
ern irrigation projects in connection |
with drainage return flow from ir-
rigation. The conclusion from these |
studies and from comparisons with |
the natural return flow from large
older irrigated areas is that the
amount of water actually consumed |
by crops is relatively small compared |
with the amount diverted, and
further that the efficient drainage on
an irrigated project, the actual plant
has decidedly low limits
regardless of the water applied.
Method of Measurements
The first return-hOw measurements
we're determined by dividing river
INTO sections five, ten or twenty miles
IN length and measuring with cur
rent meters the section inflow Tin
,ec.-ft.) section outflow and all in ;
.ervening tributary infiows and ditch
)r canal diversions; the total inflow
minus the total outflow gives the 1
gain or loss. The work was con-
lucted more as determination OF |
liver gains or losses than total return /;
low of a specific irrigated area.
Where pronounced returns were OBJ
served in side channels the work was
extended to them. Work has usually
been confined to main stream chan
lels.
Such investigations were formerly {
conducted in the late summer or fall
when stream flow was low or at
minimum and river measurements
could be made by wading. September {
md October were the usual months |
lltho few measurements have been
made in the spring; rainfall was
neager in the fall months, and con- {
litions generally were more favor
lble to accuracy. At first 1t was as
;umed that seepage returns were
more or less constant turnout the J
vear, and the fall records were fire. ;
luently taken at face value for the
1ear. In recent years investigators l
IN the main South Platte river by &
he state engineer of Colorado were t
made during every month of the t
ear to determine seasonal varia- l
ions and their character. More re-
med methods were used and greater
.ccuracy secured than during the I
Investigations In 1920 on a 150-
nile stretch of the main South Platte Y
liver continuous records by automa- |
ic waterstage registers were secured
or eighteen months of all section in
low, section outflow, tributary in t
low and canal diversions. Some '
fifty recording cages were required. {
The seasonal variation is compare
lively small and approximates the t
'ariations found in the North Platte
n Nebraska, where soil conditions f
re similar (viz., porous, sandy soil g