7806

• UCREFRP Catalog Number: 7806
• Author: U.S. Department of the Interior.
• Title: Quality of Water, Colorado River Basin.
• USFW Year: 1997.
• USFW - Doc Type: Progress Report No. 18,
• Copyright Material: NO

Causes and Impacts of Salinity

population increase, M&I sources will be increasing salinity by approximately 133,000 tons per
year by the year 2010. However, most municipal wastes are relatively low in salt concentration in
comparison with natural, industrial, and agricultural sources. Complete elimination of such waste
discharges would be expensive when compared to other salinity control methods.

Consumptive Use of Water IRcreases Salinity

Addition of salts to the river system is not the only cause of increased salinity in the Colorado
River Basin. The consumption (depletion) of water reduces the dilution of saline inflows to the
river system, increasing the concentration of salinity. Water use is evaluated as part of
Reclamation's responsibilities in managing the river system. The Colorado River Basin,
Consumptive Uses and Losses Report[4] summarizes water use in the Basin. Table 2 summarizes
the Basin uses for 1981-85, including tributaries to the Colorado River in the Lower Basin. Work
is underway to update these estimates.

Table 2.-Water use in the Colorado River Basin (1981-85 average)

Total

Upper Basin use Lower Basin use
(1,000 af/yr)' (1,000 af/yr)
812 1,255
2,312 5,101
203 841
0 30
669 4,063
3,996 11,290

Type of use

Reservoir evaporation and channel losses
Agriculture (within basin)
M&I

Fish, wildlife, and recreational
Transbasin exports

1 Acre-feet per year.

With the exception of the Central Arizona Project, the Lower Basin has already developed most of
its water supply. CAP is the last major development to deplete water from the Lower Colorado
River (approximately 1.5 million acre-feet per year). Agriculture use is the single largest source of
depletions to the Colorado River. Exports, reservoir evaporation, and M&I uses also account for
lesser but significant depletions.

Most of the exports from the Upper Basin are made at higher elevations where the salinity
concentrations are very low. This loss of high quality water results in the remaining flows
downstream becoming more concentrated. Water exported from the Upper Basin during the period
1941-72 averaged about 360,000 acre-feet per year. Completion of such large projects as the
Colorado-Big Thompson, Duchesne Tunnel, Roberts Tunnel, and more recent projects increased
exports to about 669,000 acre-feet per year.

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