9302

• UCREFRP Catalog Number: 9302
• Author: Tyus, H.
• Title: Aquatic Ecosystem Recovery Plan for Mainstream Rivers of the Colorado River Basin.
• USFW Year: 1996.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

PART I: INTRODUCTION
General
The Colorado River drains about 244,000 mi' of the southwestern United
States and Mexico (Figure 1). Originating in the Never Summer and Wind River
ranges of Colorado, Utah, and Wyoming, it flows about 1,500 mi. through four
other western States (Arizona, California, Nevada and New Mexico) as it
travels toward its historic outfall into the Gulf of California in Mexico
(Carlson and Muth 1989). Most of the water in the system is snowmelt that
originates in high mountain streams generally above 10,000 ft amsl. Tributary
streams at lower elevations add comparatively little water. The natural
hydrograph reflects the regular and prominent influence of spring runoff in
May and June (Maddux et al. 1993; Stanford 1994). Peak flows produce
extensive seasonal flooding of overbank areas. Although the magnitude of the
peak runoff is variable, the timing of the event is predictable. Migh
discharge and erodible substrate produce very turbid water for much of the
year. Smaller tributaries are prone to flash flooding after unpredictable
summer storms. Storm events contribute to turbidity in the main river during
the base flow period.
The ancient Colorado River watershed was a much wetter environment than
now exists (Smith, M. 1981), and portions of the river system were dominated
by lacustrine habitat (Minckley et al. 1986). The basin is now much more
arid, and the river is more constrained within its banks, except for seasonal
flooding. Seasonal inundation is significant in part because wetland areas
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