The Idaho Republican. [volume] (Blackfoot, Idaho) 1904-1932, 1924-02-21
THE IMPORTANCE OF RETURN
FLOW WATER IN IRRIGATION


and other variations and erosive eff
fects were undoubtedly much les
than at present. The natural and pro
fuse carpet of vegetation retarded
run-Off, increased absorption in tran
sit and delayed immediate appearance
in main river channels. Over-graz
ing of the grass cover in plain
plateau and mountain areas is placed
first in Importance as a cause of the
change in stream flow and erosion
with forest denudation by axe and
fire second. Two phases of irriga
ton offset these destructive tenden-
cies: Cd Reduced flood flows from
canal diversions and reservoir i'm
pounding, and CD return flow from
underground soil reservoirs of the
irrigated areas. The general net re-
suit to the lower portions of river
basins, where irrigation is extensive,
is a better equalized river and re-
duced food flows. The streams of
the more arid southwest are gen.
orally EXCEPTIONS to the above state
ment because irrigated areas are
small nd reservoir capacity negligi-
BILE. On such streams peak or food
flows are more acute and more fire.
quent than formerly.
Economic Value
Irrigation history is replete with
optimism of human nature as ex-
tpresSed in the construction of
bitches, whose available water sup
ply was doubtful in character or
undetermined. Early prediction was
that such bitches would have a poor
water supply, an increasingly infer
ior water supply, or ultimately no
water supply. The compensation eff
feet of return flow has saved many
wild or ill-advised effort in ditch
construction from failure and turned
it to success. The extension of the
irrigated area and its depth of
penetration into the surrounding
arid land has been the surprise of
pioneer engineers, and the results
have exceeded the anticipation of the
most sanguine residents in several
irrigated valleys. Several commun-
tiles, whose former water status was
uncertain and precarious have be-
come prosperous and their water
rights are now rated first class. See
page water has been a big factor in
the development of the South Platte
valley. Perhaps no area is more
typical or better illustrative of the
beneficial and healing effects of re-
turn waters from irrigation, than the
lower South Platte river area in
Colorado between the towns of Fort
Morgan and Julesburg, distance OF
100 miles. The present assessed
valuation of the irrigated land of the |
lower South Platte valley is over
$40, 100000, the area irrigated be-
ing 100000 acres. The average re-
turn flow of the river section is 500 |
sec.-ft. or 100000 acre-ft. annually |
Without seepage water this area
would have only a dOodwater sup
ply and it's economic Importance
would shrink at least one-half or
probably from $40,000,0O0 to $780,
100000. -
Seepage or return waters have at
tanned such volume on the U. 5.
reclamation service projects that the
federal government now makes
specific claim for such waters on the
various projects. On the North
Platte project in Wyoming and
Nebraska, the Shoshone project in
and others, the volume
and value of such waters is so great
hat litigation has resulted.
Source of Return Flow
In the process of conveying water
% land in unlined canals and its ap-
1lication to crop production, there
ire excessive losses. Roughly they
nay be as follows:
Conveyance or seepage losses by
1eep percolation from unlined canals
and Iaterals, range 1880 per cent;
average $50 per cent.
Field losses by deep percolation
and surface waste in application,
.ange 1920 per cent; average ID
Der cent.
Evaporation losses from canal
water, saturated ground surfaces
md irrigated fields, range 1890 per
,ent; average 20 per cent
Plant evaporation or Transportation
actual water consumption range
,O-4O per cent; average 80 per cent
Mean of FL U. S. reclamation
service projects, seven years record,
1912 to 1919, inclusive.
From the foregoing it Is evident
hat the plant consumption of water
s. roughly, only from one-fifth to ,
,ne-third of the water diverted at ,
he river headgate; also it is evil
lent that Excluding lined canals)
leep percolation losses in canal
ateral and field, amount to SO per /
,ent of the water diverted. Prob
IDLY SO per cent is general figure ,
or large areas and varied cond1-
ions. Where water is scare and ap- {
,lication is made with good hus- {
,andry these figures are reduced, i
ind where water is plentiful and
,sed lavishly they should be in !
,reased. 1t should also be under t
TODD that soil texture is a large I
actor in changing the above-men- {
toned percentage. 1t is, therefore. f
,vident that SO per cent or more OF f
he water diverted at the river Is
,vailable as a source to return flow. /
Underground Soil Reserves ,
Ordinarily soil is porous, the
roids ranging from 80 to SO per g
ent. Each acre of saturated soil In 6
irrigated areas will, therefore, reser- |
,oir one acre-ft. of underground I
water for each three feet Of depth. t
Untitled underground soil reservoirs t