7409

• UCREFRP Catalog Number: 7409
• Author: U.S. Department of the Interior.
• Title: Quality of Water, Colorado River Basin.
• USFW Year: 1991.
• USFW - Doc Type: Progress Report No. 15,
• Copyright Material: NO

Chapter 2

Description of Basin

The Colorado River Basin encompasses portions
of seven States: Wyoming, Utah, Colorado,
Nevada, New Mexico, Arizona, and California.
The river flows over 1,400 miles from its
headwaters in Wyoming and Colorado. It joins
with tributaries from Utah and New Mexico;
flows through the Grand Canyon; provides State
boundaries for Nevada, Arizona, and California;
flows through the Republic of Mexico; and
terminates in the Gulf of California. The
Colorado River provides municipal and
industrial water for more than 18 million people
and irrigation water to 1.7 million acres in the
United States.

CLIMATE

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Extremes of temperature in the Colorado River
Basin range from -50 to 130 OF. The northern
portion of the basin is characterized by short,
warm summers and long, cold winters; and
many mountain areas are blanketed by deep
snow all winter. Much of the area consists of
high basins or valleys with cold winters and hot,
dry summers. The southern desert portion of
the basin has long, hot summers, practically
continuous sunshine, and.almost complete
absence of freezing temperatures. Rainfall
averages 2.5 inches per year in the southern end
of the basin, while total precipitation in the
mountains reaches 40 to 60 inches annually.

HYDROLOGY

The Colorado River begins where peaks rise
more than 14,000 feet in the northwest portion
of Rocky Mountain National Park in Colorado,
70 miles northwest of Denver. It meanders
southwest for 640 miles through the Upper
Basin to Lee Ferry.

The Green River, the major tributary of the
Colorado River, rises in western Wyoming and
discharges into the river in southeastern

Utah-730 river miles south of its origin and
220 miles above Lee Ferry. The Green River
drains 70 percent more area than the Colorado
River above their junction, but produces only
about three-fourths as much water. The
Gunnison and San Juan Rivers are the other
principal tributaries of the Colorado River in the
Upper Basin.

The Colorado River Basin has a total area of
approximately 244,000 square miles, carrying an
average annual virgin flow of 13 to 15 million
acre-feet at Lee Ferry. Of this flow, more than
5 million acre-feet per year are exported to the
Arkansas and Missouri River basins, the Great
Basin, southern California, and the Rio Grande
basin.

The Colorado River Basin is an arid or semiarid
basin. Compared to others, such as the
Columbia River Basin, which drains
approximately the same area, it carries a
smaller flow, as shown in table 1. While the
Colorado River Basin is one of the major
drainage basins in the continental United
States, its runoffis about equal to that of the
Delaware River which drains a much smaller
area.

Table 1.-COmparison of
river basin drainage and runoff

Area Runoff Runoff per
(1.000 (million unit area
square acre-feet inches
River basin miles) per year per year
Colorado 244 15 1.2
Mississippi 1.234 440 6.7
Columbia 258 180 13.1
Delaware 12 14 20.9

The flow at various points in the Colorado River
Basin for the 1941-89 period is given in tables 1
through 20 at the end of this report. The records