WSP09842

• File Number: 8273.600.30
• Description: Colorado River Basin Salinity Control - Federal Agencies - USDA
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1991
• Title: The Economics and Management of Water and Drainage in Agriculture
• Water Supply Pro - Doc Type: Report/Study

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106

APPROACHES TO DRAINAGE PROBLEMS

Table 4. Comparison of simulation resu~s for the three different strate-
gies of irrigation and drainage management (I, II, III).

Yield Loss'
~v,.: Project3 Project4 v~. ECJ

Strate~

~V'
,.

~v.
~

!
II
III

417.6
417.6
417.6

495.5
427.8
427.8

77.9
10.2
o

2
4
o

20
45
o

82.4
82.4
72.2

3.0
3.0
0.5

.RV C1 = cumulalive volume (units) or water used by crops in evapotranspinuion in all four
projects.
bRViw = cumulativc"w'Olumc (units) oCwalcrdivc:rted (pumped) from river (or irrigation in
aU four projects.
CRV ~ ... cumu:ative volume (units) of drainage waler discharged (pumped) back to river.
dCumulative :05$ of crop yield within Projects 3 and 4.
r:v rw::l VolJmc (units) of river remaining in stream below Project 4.
rECrw = EC of river below Project 4, dS/m.

for by the cotton grown in Projects 3 and 4 with drainage water. With Strategy
III the volume of water diverted from the river is lower than with Strategy I and
no drainage water is returned to it. As a result, the river salinity is low and
constant throughout its entire length, the volume of the river is somewhat
reduced compared to Strategj!, and no losses in Clopyie\d occur anywhere in
any project of the entire river basin. The percentage losses in crop yield
predicted under the lhree strategies are 22, 49, and 0 for Strategies!, II, and Ill,
respectively.
While the implementation of Strategy III is technically and agronomically
feasible, economic considerations must also be favorable before such practices
can be advocated. The analysis was therefore extended to include economic
, considerations and certain related externalities resulting from the diversion of
irrigation water and the discharge and disposal of drainage.
Several general assumptions were made in the analysis. First it was assumed
that the on-farm practices and behaviors of the individual farmers which
innuence profits are not appreciably changed as a result of implementing
Strategy II or III. Since the agronomic analysis assumed steady state with regard
to the soil salinity buildup, it was also assumed in the economic analysis. Third,
it was implicitly assumed that the leaching fractions used for water application
rates were achieved. No deficit irrigation was considered. Fourth, no techno-
logical change was considered in this analysis. The same agricultural and
irrigation practices and technologies are assumed to be applied under aU
strategies presented.