Chapter 3 Affected Environment
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Chapter Three Chapter 3 Affected Environment 3.1 Introduction Chapter 3 describes environmental resources (e.g., hydrologic, biologic, and socioeconomic) of the Colorado River Basin that could be affected by the proposed federal action and the range of alternatives for implementing the proposed federal action described in Chapter 1 and Chapter 2, respectively. The extent to which each specific resource may be impacted is discussed in Chapter 4. Section 3.2 presents a general discussion of the geographic scope within which potential effects of the alternatives are analyzed, and describes each of the potentially affected Colorado River reaches and water service areas. Subsequent sections in this chapter describe specific resources that may be potentially affected, such as water deliveries, recreation and biologic resources. Each resource section contains a discussion of one or more specific issues identified for consideration through scoping, public review and comment, and internal review (Chapter 1, Table 1.5-1). Final EIS – Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for 3-1 October 2007 Lake Powell and Lake Mead Affected Environment Chapter 3 This page intentionally left blank. Final EIS – Colorado River Interim Guidelines for October 2007 3-2 Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead Chapter 3 Affected Environment 3.2 Geographic Scope The proposed federal action considers modified operations of Lake Powell and Lake Mead over a wide range of reservoir elevations as addressed by the four operational elements discussed in Section 1.2, i.e., shortage conditions, coordinated operations of Lake Powell and Lake Mead, storage and delivery of Colorado River system and non-system water, and the modified ISG. Such operational changes may affect reservoir storage levels of, and releases from, Lake Powell and Lake Mead, which in turn may subsequently affect river flows, available water supplies, and other resources. This section describes the geographic scope of specific issues and potential effects associated with changes in the operations of Lake Powell and Lake Mead, as discussed and analyzed under the alternatives considered in this Final EIS (Chapter 2). Reservoirs located upstream of Lake Powell and operated independently of Lake Powell would not be affected by the proposed federal action. However, the releases from Lake Powell and Lake Mead and downstream river flows could be affected by these changes. As such, the upstream limit of the potentially affected environment for the purposes of this Final EIS is the full pool elevation of Lake Powell, and the downstream limit is the SIB (Figure 3.2-1). In addition to the potential impacts that may occur within the Colorado river corridor, the alternatives may also affect the water supply that is available to specific Colorado River water users in the Lower Basin due to the shortage guidelines element of the proposed federal action. The following water agency service areas are included in the affected environment discussions: ♦ Arizona water users, particularly the lower priority water users located in the CAP service area; ♦ The SNWA service area; and ♦ The MWD service area. 3.2.1 Definition of Colorado River Reaches The section of the Colorado River extending from Lake Powell to the SIB consists of river reaches, two large reservoirs (Lake Powell and Lake Mead) and two smaller reservoirs located downstream of Lake Mead (Lake Mohave and Lake Havasu, Figure 3.2-2). The Colorado River and adjacent areas (i.e., backwaters and marshes) comprise heterogeneous geographic and hydrologic regimes, which differ in their resource composition and resource management administration. Final EIS – Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for 3-3 October 2007 Lake Powell and Lake Mead Affected Environment Chapter 3 Figure 3.2-1 Geographic Scope Final EIS – Colorado River Interim Guidelines for October 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 Final EIS – Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for 3-5 October 2007 Lake Powell and Lake Mead Affected Environment Chapter 3 For ease of discussion with respect to affected areas and potential effects, the Colorado River has been divided into the following reaches (Table 3.2-1). Table 3.2-1 Colorado River Reaches and Reach Limits Reach Reach Limits2 Lake Powell and Glen Canyon Dam Gypsum Canyon to Glen Canyon Dam (RM 712.9) Glen Canyon Dam to Separation Canyon (RM 450.6), including Grand Glen Canyon Dam to Lake Mead Canyon National Park Separation Canyon (RM 450.6) to Hoover Dam (RM 342.2), including Lake Mead and Hoover Dam1 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 (RM 192.3) to Adobe Ruin and Reclamation’s Cibola Gage Parker Dam to Cibola Gage (Adobe Ruin) 1 (RM 87.3) 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 (Reclamation 2004a-e). 2 For purposes of this Final 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. These reaches and their associated issues are discussed briefly below and in more detail in Section 3.3, Hydrologic Resources. Each of the resource discussions is generally organized by river reaches and in some instances the river reaches are combined to better focus the discussion of issues. 3.2.1.1 Lake Powell and Glen Canyon Dam Lake Powell is the second largest reservoir on the Colorado River and has a total storage capacity of 24.32 maf. It is formed by waters of the Colorado River impounded by Glen Canyon Dam. The reservoir is narrow, over 180 miles in length, and has a shoreline that is over 1,900 miles long. Lake Powell primarily provides water storage for use in meeting the delivery requirements to the Lower Basin consistent with the Law of the River. At the full pool elevation of Lake Powell, this reach includes approximately 25 miles of Cataract Canyon, 50 miles of the San Juan River, and approximately 170 miles of Glen Canyon. Lake Powell is located within the GCNRA which is administered by NPS. Reclamation retains authority and discretion for the operation of Glen Canyon Dam and Lake Powell. The Navajo Indian Reservation also borders a segment of this river reach. The City of Page, Arizona is also located within this reach and diverts water from Lake Powell. Final EIS – Colorado River Interim Guidelines for October 2007 3-6 Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead Chapter 3 Affected Environment 3.2.1.2 Glen Canyon Dam to Lake Mead This reach of the Colorado River extends from Glen Canyon Dam to the upper limits of Lake Mead. It is comprised of a narrow river corridor through the last 15 miles of Glen Canyon, Marble Canyon, and Grand Canyon. These canyons are in the GCNRA and Grand Canyon National Park which are administered by NPS. Navajo Indian Reservation and Hualapai Indian Reservation also border segments of this river reach. 3.2.1.3 Lake Mead and Hoover Dam Lake Mead, formed by Hoover Dam, is the largest reservoir on the Colorado River and has a total storage capacity of 27.38 maf. The reservoir is approximately 115 miles in length and has a shoreline that is over 550 miles long. The reservoir provides water storage to regulate the water supply and meet the delivery requirements of the Lower Division states and Mexico. The reservoir is located within the LMNRA which is administered by NPS. Reclamation retains authority and discretion for the operation of Hoover Dam and Lake Mead. 3.2.1.4 Hoover Dam to SIB The Colorado River reach from Hoover Dam to the SIB is contained within the shallow Colorado River Valley in which Lake Mohave, Lake Havasu and other smaller diversion reservoirs are located. Under the BCPA and the Consolidated Decree (Chapter 1), releases from Hoover Dam are generally made to meet the downstream water delivery requirements for Arizona, California, Nevada, and Mexico. The northern segment of this river reach, which includes Lake Mohave, lies within the LMNRA, which is administered by NPS. The lower reach is bordered by a combination of federal, Tribal and private land. Lake Havasu State Park is administered by the State of Arizona. Picacho State Recreation Area is administered by the State of California. Refuges managed by FWS include Havasu National Wildlife Refuge (NWR), Bill Williams River NWR, Cibola NWR, and Imperial NWR. Fort Mojave, Chemehuevi, Colorado River Indian, Fort Yuma Indian, and Cocopah Indian Reservations are located along this river reach. The 23.7 mile long reach that extends between the NIB to the SIB also forms part of the international boundary with Mexico. The individual reaches included between Hoover Dam and the SIB are: ♦ Hoover Dam to Davis Dam. This reach extends from Hoover Dam to Davis Dam and includes Lake Mohave up to its full pool elevation. The approximately 67-mile length of this reach generally comprises Lake Mohave.