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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~8 0-2'33-1

I. OVERVIEW

A. Introduction

This biological assessment (BA) 1) describes the U.S. Bureau of Reclamation's (Reclamation)
current and projected routine lower Colorado River operations and maintenance, 2) describes
the environmental baseline, 3) discusses critical habitat and the biology and distribution of
species along the lower Colorado River that have protected status, or may be subject to such
status under the Endangered Species Act of 1973, as amended (ESA), and 4) determines the
potential effect of such operations and maintenance on such species. The ESA section 7
consultation resulting from this BA focuses on those actions in which there is discretionary
Federal (Reclamation) involvement or control.

The geographic area included in this BA is within the lower Colorado River basin (Figure 1)
and is focused on the mainstream lower Colorado River and its loo-year flood plain, from
the upper end of Lake Mead at Pierce Ferry to the Southerly International Boundary with
Mexico (SIB) (Figure 2). The BA addresses Reclamation's discretionary operations of lower
Colorado River dam facilities, maintenance of river control features, and other activities such
as endangered species conservation.

In the United States, the Colorado River drains about 250,000 square miles from portions of
seven States - Wyoming, Colorado, Utah, New Mexico, Nevada, Arizona, and California.
Over 170,000 square miles of the watershed are above Hoover Dam. The headwaters of the
Colorado River are located in central Colorado, about 1,440 river-miles upstream from its
mouth and 1,000 river-miles upstream from Hoover Dam.

The upper Colorado River basin ranges from 3,000 to over 14,000 feet in elevation and
supplies most of the water discharge which occurs in the entire basin. Most water discharge
occurs during the months of April through July when the winter snowpack melts. The area
of the lower Colorado River basin is generally arid, with very little tributary runoff reaching
the mainstream of the Colorado River, except during occasional storms. Lee Ferry,
15.5 miles downstream of Glen Canyon Dam, is cited in the Colorado River Compact as the
boundary between the upper basin and the lower basin of the Colorado River.

Management of Colorado River water resources is a complex undertaking involving physical,
biological, socioeconomic, and legal considerations. Management of the river is governed by
an international treaty with Mexico and several minutes of the International Boundary and
Water Commission (IBWC), two major interstate compacts, a Decree of the U.S. Supreme
Court, various statutes, and contracts between the United States and water and power
customers. These collectively are known as the "Law of the River" (Table 1).

The Federal role in managing the lower Colorado River differs in many respects, sometimes
significantly, from its role in the upper basin. In the lower basin of the Colorado River,

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