WSP00978

• File Number: 8271.300
• Description: Colorado River Basin Salinity Control Program - General Information and Publications-Reports
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1982
• Title: Optimizing Salinity Control Strategies for the Upper Colorado River Basin
• Water Supply Pro - Doc Type: Report/Study

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force a linear ralationship between the amount of c1eep percolation and the
corresponding salt reduction by imposing an upper limit on the groundwater
concentrations. In other worcls, the recluction in salts is directly propor-
tional to the reduction in subsurface flow volumes.

Increasing seasonal farm application efficiencies of an area to at least
65 percent will be a very difficult task almost anywhere in the Upper Colorado
River Basin. Most of the fields are small with irregular shapes ancl variable
slopes. Improvements in irrigation practices will be locally motivatecl and
justifiecl by increasing procluction ancl/or lower labor and other operational
costs, and not by concerns for improvecl water quality.

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The variety of structural improvements that might be effective in increas-
iri~irrigation efficiency inclucles lining or piping heacl and tailwater ditches
to eliminate seepage conversion to alternative irrigation systems which applies
. ... 'wlitl!r more uniformly with better control of the application c1epth. Moclifica-
tion of exist:l.ng systems such as aclding flow measurement devices, lallcl level.:....;:.:.
in6 ancl automation should also be incluclecl. It is assumed in the analyses
that all structural improvements also include sufficient technical assistanca..
from federal agency and extension personnel so that the systems will operate .
as designecl.

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The improvement of irrigation efficiencies through on-farm seepage con-
trol can be evaluated with the methocls outlinecl by Walker et al. (1977, 1979)
for conveyance linings. On these small systems, the parameter, K , woulcl
normally be zero end K would be reducecl to a value which is about one-third
of Kl for lergecanal linings since construction specifications are less rigid'
and fhe ditches contain fewer control structures. The use of pipe rather than
concrete linings, particularly gated pipe, can also be included in this
manner_

The effectiveness of amending existing systems or converting to other
methods of irrigation depends on the c1ifference in application efficiency that
can be achieved. Specifically, the change in deep percolation can be written
as:

~D = (1 - ~E ) D (22)
P a a
in which,
~D = reducecl c1epth of deep percolation in centimeters;
P
D = average depth of appliecl water in centimeters.
a

By assuming that the soil chemical reactions can be considerecl in equilibrium,
the precliction in salt pickup associated "With a change in c1eep percolation is
c1evelopecl from:

ME

(\: Qp\
= ASc~Dp \ - /

(23)

x 10-4

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