WSP02976

• File Number: 8271.300
• Description: Colorado River Basin Salinity Control Program - General Information and Publications-Reports
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 12/1/1979
• Title: An Economic Evaluation of the Salinity Impacts From Energy Development - The Case of the Upper Colorado River Basin
• Water Supply Pro - Doc Type: Report/Study

Equation 22 states that the percentage change
of concentration at any point equals the
percentage change of salt less the percentE.'ge
change of volume of flow. The importance of
releasing water for dilution as one means of
reducing concentration is easily seen. The
smaller the percentage of water depletion

elF
(p), the greater the flow remaining in the

W
N
N
~

river system,
concentration

and henaC the smaller
leve 1(_) .
C

change in

Specific Models

For determining the allocation of water
between agricultural and energy activities
maximizing net benefits and the consequent
impacts on water quality, 1974 serves as a
base year. From this allocation, the change
in the salinity level due to projected agri-
cultural and energy usage in 1985 and 2000
can be estimated. If the estimated salinity
level exceeds the EPA standard issued in
1974, some control techniques must be under-
taken. Control alternatives to reduce
salinity include improvemerlt of irrigation
efficiency and conveyance systems, irrigation
scheduling, desalting irrigation return
flows, containment of tail water, utilization
of saline flows, flow augmentation through
weather modification, and adjustments in
water resource allocation and management
procedures. Some of these opt ions are not
economically feasible, technologically
effective, nor politically or legal;y viable.

Several salinity control techniques have
been suggested by the U. S. Department of
the Interior (1977) as the most promising for
the Upper Colorado Bas in. The three impor...
tant techniques selected for this study are:
1) structural methods of controlling natural
sources, 2) irrigation system improvements,
and 3) adjustments in water allocation and
management of the river. The first option
involves construction of evaporation and/or
desalting plants at point sources. The
second opt ion req u ires improvement in i rr i-
ga t ion ef f ic iency through inves tment in more
water-efficient techniques such as sprinkler
systems and lining canals in order to reduce
salt loading from return flows. The third
op t ion var ies the amount of water used for
dilution of the salt load of the river. The
first two options fall in the category of
structural methods whereas the third one is
a nonstructural method. In order, to analyze
the relative effectiveness of structural and
nonstructural measures to control salinity,
the following four alternative analyses are
cons idered.

Alternative 1

Under this alternative, water is allowed
td be transferred freely between uses without
consideration of salinity impact. Water will
be allocated between agricultural and energy

uses such that the value of the marginal
physical product of water will be equal in
both uses. This allocation is p"iven by the
solution to,the problem

Max Z 1 = TIA + TIE

subject to Equations 8 through 20 and 22.

* * *
The values of Zll 1TA, and TIE obtained
from the optimal solution are of importance
for use in the analysis.

.

Altern-ative 2

This alternative considers improvement
of irrigation efficiency and conveyance
systems in addition to construction of evapo-'
ration ponds and/or desalting plants (struc-
tural alternatives proposed by USBR) for
natural point sources. as means of reducing
salt loading. The expected high salinity
levels from future water developments can
be reduced through this alternative.
The cost of this alternative is derived
as follows: Let C~p be the cost per acre of
converting to irrIgation with a sprinkler
system (Xr SP ) j C~ be the cost per mile of
canal lining and VB be the maximum canal
miles in Sj and let Ca be the cost per ton of
salts (Cs) xemoved tiy desalting plants and
evaporation ponds. The total investment cost
of irrigation improvement and construction
of ponding for the entire Upper Basin is:
8 8 3SB
TC Ees XS + E CsVs + ECGG
I s=1 SP i,SP s=1 v s=1 (23)
i=1, 2, . . ., H

Sprinkler system reduces deep percolation1
and canal 1 in ing reduces seepage losses.
Both methods reduce the amount of salt load
entering the river through return flow.
Crops can be grqwn with present irrigation
systems (Xi and Xp) or with sprinkler systems
(Xf SP and X~,Sp), The productivity ~f
i rrfga ted land under a s pr Inkler s ys tern IS
assumed to remain the same as under the
present system., Although this assumption
may not be strictly true, the productivity
increases reported are small and data by crop
were not available at this time. Hence, the
total net return to crops under sprinkler
8 H s s s s
E E 0.\ oi - Ci)Xi,SP
8=1 i=1
added to the agricultural net return, 7TA.

~

irrigation

is

The constraints are adjusted to be
compatible with the adopted policy by speci-
fying the following equations:

Equation 8 -is modified to

H-l
. s ) s
E (Xi + Xi SP ~ L
i=1 ' c

xB+XS ~LSp
p p,SP

.

(8) ,

26