WSP07784

• File Number: 8221.112.I
• Description: Central Arizona Project
• State: AZ
• Basin: Colorado Mainstem
• Date: 4/29/1983
• Title: Draft Environmental Impact Statement: Regulatory Storage Division - Central Arizona Project
• Water Supply Pro - Doc Type: EIS

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B.

Geographic Setting

The CAWCS study area encompasses approximately 13,400 square miles, or
8,576,000 acres, in central Arizona, including portions of Maricopa, Gila, and
Pinal Counties. The entire Phoenix metropolitan area is located within the
CAWCS boundaries. Figure 1 shows the CAWCS study area. The population of the
area is over 1.5 million people, almost 90 percent of whom live in Maricopa
County. There are five Indian Communities in the study area.

C. Purpose and Need

The alternative actions described in this EIS have three principal
purposes. These are:

1. To increase the operating efficiency of the CAP through the
conservation of Salt, Verde, and Agua Fria River flows, and
through regulation of Colorado River water deliveries from the
Granite Reef Aqueduct.

2. To provide facilities and means to meet the flood control needs
on the Salt and Gila Rivers through the Phoenix metropolitan
area.

3. To provide for the structural safety of existing Bureau of
Reclamation dams on the Salt and Verde Rivers.

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Construction of a regulatory storage unit for CAP water will improve
the operating flexibility and efficiency of the CAP and will allow the
importation of greater quantities of Colorado River water in years when it is
available. Without regulatory storage capacity the CAP system can be operated
only in direct response to demand, limiting the opportunity to effectively
manage the project's water and power resources.

A series of floods through the Phoenix metropolitan area between
February 1978 and February 1980 caused substantial damage in the fonn of
property damage, income losses, and emergency costs, and had severe impacts on
transportation and on people living in the flood zone. These floods heightened
public demands for flood control and flood protection.

Hydrologic analyses for the maximum probable flood (or Inflow Design
Flood - IDF) indicate that all six Salt River Project (SRP) storage dams on the
Salt and Verde Rivers have inadequate storage and/or spillway capacity to
contain and/or pass the IDF without overtopping. Such an occurrence could
jeopardize the safety of the dams. The potential overtopping or failure of any
of these dams is considered serious because of the potentially catastrophic
consequences which would result for Phoenix and other downstream communities.

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