7983

• UCREFRP Catalog Number: 7983
• Author: U.S. Department of the Interior.
• Title: Quality of Water, Colorado River Basin.
• USFW Year: 1993.
• USFW - Doc Type: Progress Report No. 16,
• Copyright Material: NO

6 Chapter 2 -Description of Basin

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 dividing point for the
upper and lower portions of the Basin.

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 about 15 maf at
Lee Ferry. Of this flow, more than 5 maf 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 a relatively arid
basin. Compared to others, such as the
Columbia River Basin, which drains
approximately the same area, it carries a much
smaller flow. Table 1 shows that while the
Colorado River Basin is one of the major
drainage basins in the continental United
States, its runoff is about equal to that of the
Delaware River which drains a much smaller
area.

River basin

Table 1.-Gomparison of river basin
drainage and runoff

Area
(1,000
square
miles)

Runoff
(inches
per year)

1.2
6.7
13.1
20.9

Runoff
(maf
per year)

Colorado
Mississippi
Columbia
Delaware

244
1,234
258
12

15
440
180
14

The flows at various points in the Colorado
River Basin for the 1941-91 period are given in
appendix A. The records of flow depict wide
fluctuations from month to month and
considerable variations from year to year.

RESERVOIR STORAGE

Wet and dry cycles have played a significant role
in bringing about the development of the
Colorado River reservoir complex (refer to
figure 1). Historic records show that the annual
flow of the river has varied from less than
6 million to more than 20 mafper year. The
reservoir system allows sufficient storage water
to maintain the flows of the river to meet
downstream needs during dry periods.

In addition to the major reservoirs, numerous
smaller reservoirs have been built on many of
the tributaries. Major storage began with Lake
Mead in 1935 and concluded with the filling of
Lake Powell in 1980. The Colorado River Basin
reservoirs now have a combined storage capacity
equal to approximately four times the total
average annual virgin (undepleted) flow of the
Colorado River.

The flow of the San Juan River is controlled by
the Navajo Dam, the Green River by Fontenelle
and Flaming Gorge Dams, and the Gunnison
River by the Wayne N. Aspinall Unit Dams.
Glen Canyon Dam is the only major dam on the
main stem ofthe Colorado River above Lee
Ferry, but it controls almost all the flow leaving
the Upper Basin.

Lake Mead, formed by Hoover Dam, supplies
most of the storage and regulation in the Lower
Colorado River Basin. Lake Mead provides
water for irrigation, municipal and industrial
uses, power generation, flood control, recreation,
and many other beneficial uses.

Lake Mohave, the reservoir formed by Davis
Dam, backs water upstream at high stages
about 67 miles to the tailrace of Hoover
Powerplant. Storage in Lake Mohave is used for
some reregulation of releases from Hoover Dam,
for meeting treaty requirements with Mexico,
and for developing power head for the
production of electrical energy at
Davis Powerplant. The river flows through a