WSP04095

• File Number: 8270.100
• Description: Colorado River Basin Water Quality/Salinity -- Misc Water Quality
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1987
• Author: USDOI
• Title: Quality of Water - Colorado River Basin - Progress Report No. 13 - January 1987
• Water Supply Pro - Doc Type: Report/Study

responsible for the last major additional depletion (approximately 1.5 million
acre-feetcper year) in the Lower Basin. Depletions in the Upper Colorado
Basin were estimated at 4.1 million acre-feet in 1985.

Consumptive use of water for irrigation within the Basin is
~ responsible for the largest depletions of the Colorado River. Exports,
~ reservoir evaporation, and municipal and industrial uses also account for
~ lesser but significant depletions. The following table summarizes both the
(11 Upper and Lower Colorado River Basin uses, including tributaries to the
Colorado River in the Lower Basin [4].

Table IV-i. Average water use in the Colorado River Basin
for 1976-80 (in 1,000 acre-feet)

Type of use
Reservoir evaporation
and channel losses
Irrigated agriculture
Municipal and industrial
Fish, wildlife, and recreation
Transbasin exports

Upper Basin

Lower Basin

758
1,984
178
o
3,647

1,682
5,180
453
50
11,604

The major part of the transbasin depletions in the Upper Basin is
made at higher elevations where the salinity concentrations are very low.
This removal of high quality water results in the remaining flows downstream
becoming more concentrated even though some salts are removed by the water
delivered to another basin. Many transbasin diversions have been made over
the years, and an additional number are projected to occur in the future.

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, and Roberts Tunnel and more
recent projects such as the San Juan-Chama, Fryingpan-Arkansas, and Homestake
resulted in increased exports to about 726,000 acre-feet per year for 1976-80,
with a peak in 1978 of 852,000 acre-feet.

B. Effects of Water Quality on Water Users

1. Recreation, Esthetics, and Fisheries

The major instream uses in the Colorado River include hydroelectric
power, propagation of fish and aquatic life, recreation (including swimming,
waterskiing, boating, rafting, etc.), and esthetics. A number of conflicts
between water uses have become prominent issues in recent years.

There can be many tradeoffs in water quality, eutrophication, and
esthetics both in the reservoir and downstream, depending on the depth of
reservoir withdrawal and the flushing rate. The depth of withdrawal
influences the temperature and nutrient releases from a reservoir. These
releases can now be controlled to some degree by the use of selective
withdrawal structures; however, conflicts have occurred in the operation of

IV-3