WSP12637

• File Number: 8282.300
• Description: Colorado River Operations and Accounting - Lower Basin Administrative Procedures
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 8/1/1996
• Author: DOI-BOR
• Title: Description and Assessment of Operations-Maintenance and Sensitive Species of the Lower Colorado River - Volume I - Report - 08-01-96
• Water Supply Pro - Doc Type: Report/Study

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OJ2321

ll. DESCRIPTION OF ACTION

A. Introduction

This chapter of the assessment provides a descriptive overview of Reclamation's role on the
lower Colorado River. Four specific areas are addressed: 1) an overview of the river and
its operational facilities, 2) Reclamation's discretionary role, acting on behalf of the
Secretary, in implementing the Law of the River, 3) an overview of current river operation
and maintenance activities employed by Reclamation to implement the Law of the River,
4) Reclamation activities under section 7(a)(1) of the ESA conserving threatened and
endangered species, and 5) a summary. '

Most of the lower Colorado River's water, or about 96 percent of the annual supply, flows
into the lower basin at Lees Ferry from the upper basin. The mean annual flow at
Lees Ferry between 1935 and 1990 was about 10,165,000 acre-feet. The remaining
4 percent came from side flows during rainstorms and tributary rivers in the lower basin.
Colorado River water flows are highly variable from year to year and the mean annual
inflow is about 472,700 acre-feet. Figure 4 illustrates the quantities of lower Colorado River
water released and diverted yearly.

The Law of the River requires the United States to operate the lower Colorado River with
the following three main priorities: 1) for river regulation, improvement of navigation, and
flood control, 2) for irrigation and domestic uses, including the satisfaction of present
perfected rights, and 3) for power. Water cannot be released unless there is a valid
beneficial use for the water, and it is then released at a time and in a way to meet the water
delivery need, and to maximize other benefits including power production. Beyond these
requirements, the United States takes into consideration such other needs on the river as
recreation, wildlife, water quality, and species conservation. The facilities which were built
to enable meeting these requirements are shown in Figure 5. More-detailed descriptions of
these structures and others are provided in "Appendix D - Major Facilities on the lower
Colorado River".

Hoover Dam is the northernmost Reclamation facility on the lower Colorado River and is
located 68 miles downstream from Pierce Ferry. The dam provides flood control protection
and the reservoir it forms provides the majority of the storage capacity for the lower basin.
The dam's four intake towers draw water from reservoir elevations above 895 feet and drive
17 generators within the dam's powerplant. Maximum water flow rate through the
generators is approximately 49,000 cubic feet per second (cfs). Lake Mead, the name of the
reservoir behind Hoover Dam, can store 31,250,000 acre-feet of water up to an elevation of
1,221 feet at the top of the dam's spillway gates. Lake Mead's surface area is 162,700 acres
when full. Water is diverted from, and some water is returned to, Lake Mead for use in
southern Nevada for domestic purposes by the Southern Nevada Water Authority and other
users.

Davis Dam is located 67 miles below Hoover Dam and operates as a re-regulation facility

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