WSP11706

• File Number: 8271.300
• Description: Colorado River Basin Salinity Control Program - General Information and Publications-Reports
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1980
• Title: Development of Procedures to Evaluate Salinity Management Strategies in Irrigation Return Flows
• Water Supply Pro - Doc Type: Report/Study

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accountable" sources, both ungaged point
and nonpolnt sources in a model successfully
applied to four agricultural basins, namely,
Grand Valley and Arkansas River in Colorado,
Palo Verde Irrigation district in Cslifornia
and Yakima Valley in Washington.

Method 2: Improved estimation of salt
pickup was attempted by using separate
estimations of loadings by salt source and
summation in the form:

Tload = tinstr + tost + tag + tpa + tups

(2.2)

in which

Tload

total salt loading between
any two points of 8 stream.

Tinstr

incremental salt loading due
to instream salt dissolution
and precipitation phenomena.

tost

Incremental salt loading due
to natural (diffuse) sources.

tag

Incremental BaIt loadinE due
to agricultural (diff-use)
sources.

tps

Incremental salt loading due
to known point sources.

tups

Incremental salt loading due
to unknown poInt sources.

Salt loading by instream processes is
important for storm or other short-period
flows, but loading and deposition balance
out over longer periods. If one wishes to
model over long periods and can identify all
the significant point sources, Equation 2.2
r educes to

Tload - tnat + tag + tps ' . . . (2,3)
Of the three terms on the right side of
Equation 2.3, the diffuse agricultural
loading can be summed from its sources:

tag - SSRT + SART + SGEF + SSPL + STW

- SCNL

. . , (2,4)

in which

SSRT
SART

Salt in seepage returns.

Salt
flow

in agricultural return
from deep percolation.

SGEF
SSPL

Salt in effluent groundwater.

Salt returned to stream through
administrative and operational
spills.

STW

Salt returned to stream through
tail water runoff from irri-
gated fields,

SCNL

Salt taken from the stream in
canal diversions.

Known point source loadings can be estimated
from data on the sources. Riley and Jurinak
(1979) postulated that the total salt load
added within a subbasin could be apportioned
between natural and agricultural sources on
the basis of average quantity of water that
was estimated to flow through the soils of
each area;

Sn Wn
Sa Wa

~Q + ETag
Wd - ETag

, " , , (2,5)

in which
Sn = rate of salt loading from natu-
ral sources.
Sa tag.
Wn rate of drainage from natural
lands.
Wa rate of drainage from irrigated
lands.
~Q change in measured water flow,
Wd rate of water diversions for
irrigation within subbasin.
ETag evapotranspiration of water di-
verted for agriculture.

The salt loading from natural sources can
then be estimated from Equation 2.3 since all
terms but Tnat are now known.

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