Chapter 3 Affected Environment
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1 Chapter Three 2 Affected Environment This page intentionally left blank. Chapter 3 Affected Environment 1 3.1 Introduction 2 Chapter 3 describes environmental resources (i.e., hydrologic, biologic, and socioeconomic) of 3 the Colorado River Basin that could be affected by the proposed federal action described in 4 Chapter 1and Chapter 2. The extent to which each specific resource may be impacted is 5 discussed in Chapter 4. 6 Section 3.2 presents a general discussion of the geographic scope within which potential effects 7 of the alternatives are analyzed and describes each of the Colorado River reaches and affected 8 water service areas. Subsequent sections in this chapter describe specific resources that may be 9 potentially affected, such as water deliveries, recreation and biologic resources. Each resource 10 section contains a discussion of one or more specific issues identified for consideration through 11 scoping, public review and comment, and internal review (Chapter 1, Table 1.5-1). Draft EIS – Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations 3-1 February 2007 for Lake Powell and Lake Mead Affected Environment Chapter 3 1 This page intentionally left blank. Draft EIS – Colorado River Interim Guidelines for February 2007 3-2 Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead Chapter 3 Affected Environment 1 3.2 Geographic Scope 2 The proposed federal action considers modified operations of Lake Powell and Lake Mead over 3 a wide range of reservoir elevations as addressed by the four operational elements discussed in 4 Section 1.2: shortage conditions; coordinated operation of Lake Powell and Lake Mead; storage 5 and delivery of Colorado River system and non-system water; and the modified ISG. Such 6 operational changes may affect reservoir storage levels of, and releases from, Lake Powell and 7 Lake Mead, which in turn may subsequently affect river flows, available water supplies, and 8 other resources. 9 This section describes the geographic scope of specific issues and potential effects associated 10 with changes in the operations of Lake Powell and Lake Mead, as discussed and analyzed under 11 the alternatives considered in this Draft EIS (Chapter 2). Reservoirs located upstream of Lake 12 Powell and operated independently of Lake Powell would not be affected by changes in the 13 operations of Lake Powell and Lake Mead, but the releases from reservoirs located downstream 14 of Lake Mead could be affected by these changes. As such, the upstream limit of the potentially 15 affected environment for the purposes of this Draft EIS is the full pool elevation of Lake Powell, 16 and the downstream limit is the SIB (Figure 3.2-1). 17 In addition to the potential impacts that may occur within the river corridor, the alternatives may 18 also affect the water supply that is available to specific Colorado River water users in the Lower 19 Basin due to the shortage guidelines element. The following water agency service areas are 20 included in the affected environment discussions: 21 ♦ Arizona water users, particularly the lower priority water users located in the CAP 22 service area; 23 ♦ The SNWA service area; and 24 ♦ The MWD service area. 25 3.2.1 Definition of Colorado River Reaches 26 The section of the Colorado River extending from Lake Powell to the SIB consists of river 27 reaches, two large reservoirs (Lake Powell and Lake Mead) and two smaller reservoirs 28 downstream of Lake Mead (Lake Mohave and Lake Havasu, Figure 3.2-2). The Colorado 29 River and adjacent areas (e.g., backwaters and marshes) comprise heterogeneous geographic 30 and hydrologic regimes, which differ in their resource composition and resource management 31 administration. Draft EIS – Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations 3-3 February 2007 for Lake Powell and Lake Mead Affected Environment Chapter 3 Figure 3.2-1 Geographic Scope 1 Draft EIS – Colorado River Interim Guidelines for February 2007 3-4 Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead Chapter 3 Affected Environment Figure 3.2-2 Colorado River Reaches Draft EIS – Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations 3-5 February 2007 for Lake Powell and Lake Mead Affected Environment Chapter 3 1 For the ease of discussion with respect to affected areas and potential effects, the Colorado 2 River has been divided into the following reaches (Table 3.2-1). Table 3.2-1 Colorado River Reaches and Reach Limits Reach Reach Limits Lake Powell and Glen Canyon Dam Gypsum Canyon to Glen Canyon Dam (RM 712.9) Glen Canyon Dam to Lake Mead Glen Canyon Dam to Separation Canyon (RM 450.6) 2, including Grand Canyon National Park Lake Mead and Hoover Dam1 Separation Canyon (RM 450.6) to Hoover Dam (RM 342.2), including Lake Mead Hoover Dam to Davis Dam1 Hoover Dam (RM 342.2) to Davis Dam (RM 276), including Lake Mohave Davis Dam to Parker Dam1 Davis Dam (RM 276) to Parker Dam (RM 192.3), including Lake Havasu Parker Dam to Cibola Gage (Adobe Ruin) 1 Parker Dam (RM 192.3) to Adobe Ruin and Reclamation’s Cibola Gage Cibola Gage to Imperial Dam1 Reclamation’s Cibola Gage (RM 87.3) to Imperial Dam (RM 49.2) Imperial Dam to Northerly International Boundary (NIB) 1 Imperial Dam (RM 49.2) to the NIB (RM 23.1) NIB to SIB1 NIB (RM 23.1) to SIB (RM 0.0) 1 These reaches are identical to those described in the LCR MSCP. 2 For purposes of this Draft EIS, river miles are numbered along the length of the Colorado River channel south to north starting with RM 0.0 at the SIB with Mexico. Dam locations, other features and reach limits are identified and noted at their respective river miles. 3 4 These reaches and their associated issues are discussed briefly below and in more detail in 5 Section 3.3, Hydrologic Resources. Each of the resource discussions is generally organized 6 by river reaches and in some instances the river reaches are combined to better focus the 7 discussion of issues. 8 3.2.1.1 Lake Powell and Glen Canyon Dam 9 Lake Powell is the second largest reservoir on the Colorado River and has a total storage 10 capacity of 24.32 maf. It is formed by waters of the Colorado River impounded by Glen 11 Canyon Dam. The reservoir is narrow, over 180 miles in length, and has a shoreline that 12 is over 1,900 miles long. Lake Powell primarily provides water storage for use in meeting 13 the delivery requirements to the Lower Basin consistent with the Law of the River. At the 14 full pool elevation of Lake Powell, this reach includes approximately 25 miles of Cataract 15 Canyon, 50 miles of the San Juan River and approximately 170 miles of Glen Canyon. 16 Lake Powell is located within the GCNRA which is administered by the NPS. 17 Reclamation retains authority and discretion for the operation of Glen Canyon Dam and 18 Lake Powell. The Navajo Indian Reservation also borders a segment of this river reach. 19 The City of Page, Arizona is also located within this reach and diverts water from 20 Lake Powell. Draft EIS – Colorado River Interim Guidelines for February 2007 3-6 Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead Chapter 3 Affected Environment 1 3.2.1.2 Glen Canyon Dam to Lake Mead 2 This reach of the Colorado River extends from Glen Canyon Dam to the upper limits of 3 Lake Mead. It is comprised of a narrow river corridor through the last 15 miles of Glen 4 Canyon, Marble Canyon, and the Grand Canyon. These canyons are in the GCNRA and 5 Grand Canyon National Park which are administered by the NPS. The Navajo Indian 6 Reservation and Hualapai Indian Reservation also border segments of this river reach. 7 3.2.1.3 Lake Mead and Hoover Dam 8 Lake Mead, formed by Hoover Dam, is the largest reservoir on the Colorado River and 9 has a total storage capacity of 27.38 maf. The reservoir is approximately 115 miles in 10 length and has a shoreline that is over 550 miles long. The reservoir provides water 11 storage to regulate the water supply and meet the delivery requirements of the Lower 12 Division states and Mexico. The reservoir is located within the LMNRA which is 13 administered by the NPS. Reclamation retains authority and discretion for the operation 14 of Hoover Dam and Lake Mead. 15 3.2.1.4 Hoover Dam to SIB 16 The Colorado River from Hoover Dam to the SIB is contained within the shallow 17 Colorado River Valley in which Lake Mohave, Lake Havasu and other smaller diversion 18 reservoirs are located. Under the BCPA and the Consolidated Decree (Chapter 1), 19 releases from Hoover Dam are generally made to meet the downstream water delivery 20 requirements for Arizona, California, Nevada and Mexico. The northern segment of this 21 river reach, which includes Lake Mohave, lies within the LMNRA, which is administered 22 by the NPS. The lower reach is bordered by a combination of federal, Tribal and private 23 land. Lake Havasu State Park and Picacho State Recreation Area are administered by the 24 state of Arizona. Refuges managed by the FWS include Havasu National Wildlife Refuge 25 (NWR), Bill Williams River NWR, Cibola NWR, and Imperial NWR. Indian 26 reservations which are located along this river reach include the Fort Mojave, 27 Chemehuevi, Colorado River Indian, Fort Yuma Indian, and Cocopah Indian 28 reservations.