7997

• UCREFRP Catalog Number: 7997
• Author: Nash, L. L. and P. H. Gleick.
• Title: The Colorado River Basin and Climatic Change, The Sensitivity of Streamflow and Water Supply to Variations in Temperature and Precipitation.
• USFW Year: 1993.
• USFW - Doc Type: EPA 230-R-93-009,
• Copyright Material: NO

quality using the Colorado River Simulation System (CRSS), a reservoir-simulation model developed and

operated by the U.S. Bureau of Reclamation (Figure 1).

The Colorado River is one of the most important river systems in the United States. Although

not a large river, even in comparison to other rivers in the US, the Colorado flows through some of the most

arid regions of the country and is the primary source of water for a region with extensive agriculture, large

cities, and a diverse ecosystem. The Colorado River Basin covers approximately 243,000 square miles, parts

of seven states, and reaches Into Mexico. Annual unimpaired runoff of the Colorado River at Lee Ferry has

ranged from 5.6 (million acre-feet) maf to 24.0 mat since regular streamflow recording was initiated in the

early part of this century.2 Over the same period, mean annual unimpaired runoff has been about 15.1 maf;

however, tree-ring analyses dating back to 1512 have suggested that the long-term mean may be closer to

13.5 maf (Stockton and Jacoby, 1976).

The apportionment of the Colorado River has been more complete than that of the waters of
any other river through many hard-tought lawsuits, negotiations, political battles, and an International treaty.
The Colorado River Compact of 1922 divided the basin Into two sections. The upper basin, In which most

of the region's runoff originates, Includes those parts of Wyoming, Colorado, Utah, New Mexico, and Arizona
that drain into the Colorado River above Lee Ferry, Arizona? The more arid lower basin encompasses most

of Arizona, southeastern Nevada,. southeastern Utah, western New Mexico and portions of southern

California. The lower basin states were guaranteed that the upper basin states would deliver an annual

average of 7.5 maf of water (over a ten year period) to Lee Ferry, a point on the river approximately on the

Arizona-Utah border. The upper basin states received a right to use an equivalent amount of water (if It was

2For convenience to US water managers, water volumes are presented here In acre-feet, the standard
unit of measurement in the western United States. One acre-foot is equivalent to 1,233 cubic meters. A flow
of one cubic meter per second (ems) is equal to 70.02 acre-feet per day.

3Lee Ferry, Arizona, also known as the .compact point" Is the point at which the Colorado River passes
from the upper to the lower basins as established by the Colorado River Compact of 1922. It Is located
approximately 16 miles downstream of Lake Powell and one mile downstream of the Parla River. It should
not be confused with ~ Ferry, which is a point further upstream on the river, near Glen Canyon Dam.

2