WSP04876

• File Number: 8270.100
• Description: Colorado River Basin Water Quality/Salinity -- Misc Water Quality
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1983
• Author: USDOI
• Title: Quality of Water - Colorado River Basin - Progress Report No. 11 - January 1983
• Water Supply Pro - Doc Type: Report/Study

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PART IV. CAUSES OF SALINITY

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A.

Increased Concentration from Salt Additions

1.

Natural Sources of Salinity

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Flo.... and qual ity records reveal that along certain reaches of
the Colorado River there are lar~e increases in thf' dissolved-solids load
that cannot be attributed to irrigation or other man-related activity.
This increase is mainly due to natural diffused sources and saline
sprln}i;S.

Natural diffused sources are those sources of salt contribution
which occur gradually over long reaches of the river system. S.11t pickup
Occurs over large Breas of surface and underlying soils, from stream
channels and banks, and is difficult to identify, measure, or control.
This source contributes the largest overall share of the salts to thp
Colorado River. Natural point sources are mainly saline springs \otlere
the contribution of salt and water is easilv identified, issuinR from
single or concentrated sources.

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Very little information was obtained prior to irrigation,
making it difficult to identify the magnitude of specific natural sources
of salinity in the Colorado River Basin.

Previous reports have identified some of the natural sources
of salinity; however, a basinwide field review has not been made in the
recent past. The need for a review has been identified in the Probleml'l
~nd Needs section, Part X, and will be addressed in future reports.

2. Agricultural Sources of Salinity

lrrigation in the Colorado RivE"r Basin has increased the
total dissolved solids in the Colorado River. Return flows from the
irrigated lands pick up salts from the soils and under1yin~ shales and
transport them to the river. The development of future irrigation
projects will further increase the salt load to the river.

Studies prIor to irrigation would be helpful to determine con-
tribution from irrigation, but they have not been made in most areas.
The amount of salt from this source must therefore be estimated or
detennined by detailed investigations, possibly with the use of simula-
t Ion model s.

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Salt balance conditions exist ...nen the amOunt of dissolved
solids carried off the land is equal to that amount added. Pickup of
salt as used in this report represents an cnbalanced condition shown by
the incrf'as€' of total dissolved-SOlids load in the return flow over the
total load in the applied ...ater. Salt pickup char~eable to irrigation
would be only that additional amount Io'hich occurs as 3 result of irriga-
t ion .1.nd should not inc lude the a!!Iount resul t i:lR from natural sources.

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