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Chapter 3 – Affected Environment

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Chapter 3 – Affected Environment Glen Canyon Dam Long-Term Experimental and Management Plan October 2016 Final Environmental Impact Statement 3 AFFECTED ENVIRONMENT Chapter 3 describes the environmental resources (physical, biological, cultural, recreational, and socioeconomic) that could be affected by the range of alternatives for implementing the Glen Canyon Dam Long-Term Experimental and Management Plan (LTEMP), as described in Chapters 1 and 2. The extent to which each specific resource may be affected by each alternative is discussed in Chapter 4, Environmental Consequences.1 3.1 PROJECT AREA The project area includes the area potentially affected by implementation of the LTEMP (including normal management and experimental operations of Glen Canyon Dam and non-flow actions). This area includes Lake Powell, Glen Canyon Dam, and the river downstream to Lake Mead (Figure 3.1-1). More specifically, the scope primarily encompasses the Colorado River Ecosystem, which includes the Colorado River mainstream corridor and interacting resources in associated riparian and terrace zones, located primarily from the forebay of Glen Canyon Dam to the western boundary of Grand Canyon National Park (GCNP). It includes the area where dam operations impact physical, biological, recreational, cultural, and other resources. This section of the river runs through Glen, Marble, and Grand Canyons in Coconino and Mohave Counties in northwestern Arizona. Although this EIS focuses primarily on the Colorado River Ecosystem, the affected area varies by resources and extends outside of the immediate river corridor for some resources and cumulative impacts. Portions of Glen Canyon National Recreation Area (GCNRA), GCNP, and Lake Mead National Recreation Area (LMNRA) outside the Colorado River Ecosystem are also included in the affected region for certain resources due to the potential effects of LTEMP operations. For resources such as socioeconomics, air quality, and hydropower, the affected region was larger and included areas potentially affected by indirect impacts of the LTEMP. 3.1.1 Colorado River Setting The Colorado River rises in the Rocky Mountains of Colorado, flows southwesterly about 1,450 mi, and terminates in the Gulf of California. Its drainage area of 242,000 mi2 in the United States represents one-fifteenth of the area of the country. As presented in the Colorado River Basin Water Supply and Demand Study (Reclamation 2012h), almost 40 million people in the seven western states of Arizona, California, and Nevada (Lower Division States), and 1 Pre-dam conditions are discussed in this chapter to provide historical context on certain resources that exist in an already altered environment; however, such references are not intended to form the basis for comparison of the alternatives in this Environmental Impact Statement (EIS), or to provide goals for achieving resource conditions. The action alternatives are compared to the No Action Alternative (Alternative A), as is the standard practice for National Environmental Policy Act of 1969 as amended (NEPA), compliance. 3-1 Glen Canyon Dam Long-Term Experimental and Management Plan October 2016 Final Environmental Impact Statement FIGURE 3.1-1 LTEMP Project Area and Surrounding Lands (This map is for illustrative purposes, not for jurisdictional determinations; potential area of effects varies by resource as described in this chapter and in Chapter 4.) Colorado, New Mexico, Utah, and Wyoming (Upper Division States) rely on the Colorado River and its tributaries to provide some or all of their municipal water needs. Colorado River water is used to irrigate nearly 5.5 million ac of land in the Basin, which produces about 15% of the nation’s crops and about 13% of its livestock. The Colorado River is the lifeblood for at least 22 federally recognized American Indian Tribes , 7 National Wildlife Refuges, 4 National Recreation Areas, and 11 National Parks. Hydropower facilities along the Colorado River supply more than 4,200 megawatts (MW) of electrical capacity to help meet the power needs of the West and reduce the use of fossil fuels (Reclamation 2012h). The primary units of the Colorado River Storage Project (CRSP)—Glen Canyon, Flaming Gorge, Blue Mesa, Morrow Point, and Crystal—provide the majority of the hydroelectric power for the Upper Basin. CRSP has a combined installed capacity of more than 1,800 MW, with Glen Canyon accounting for approximately 73% of the CRSP facilities’ total generating capacity. Given the many and varied uses that depend on Colorado River water, as well as the significant public interest in the region, it is important yet difficult to achieve a suitable balance in the use of the Colorado River. Out of the 1,450-mi length of the Colorado River, it is the 3-2 Glen Canyon Dam Long-Term Experimental and Management Plan October 2016 Final Environmental Impact Statement 284-mi reach that flows through Glen Canyon Dam and the Grand Canyon that is the affected reach under discussion in this EIS. It is against this background that the resources of the Colorado River Ecosystem are discussed and evaluated. 3.1.2 Geologic Setting For more than 5 million years, the forces of geologic uplift, weathering, and downcutting of the Colorado River and its tributaries have carved the Grand Canyon. The canyon is about a mile deep and varies in width from a few hundred feet at river level to as much as 18 mi at the rim. The erosive forces of the river cut only a narrow gorge; other geologic forces, including flowing water over the canyon walls, freezing and thawing temperatures, and abrasion of rock against rock cut the wider canyon. The Colorado River acts like a huge conveyor belt transporting finer sediment particles to the ocean. In cutting the canyon, the river has exposed rocks of all geologic eras, covering a span of nearly 2 billion years. The rocks of the Grand Canyon are part of the Colorado Plateau, a 130,000-mi2 area covering most of the Colorado River Basin. The elevation of the canyon rim varies between about 5,000 and 8,000 ft above mean sea level (AMSL), with the North Rim being about 1,000 ft higher than the South Rim. Glen Canyon cuts through the massive Navajo Sandstone of the Mesozoic Era and is about 200 million years old. Downstream from Lees Ferry, a sequence of nearly horizontal sedimentary rocks of the Paleozoic Era appears at river level, beginning with the Kaibab Formation that caps much of the canyon rim. In Marble Canyon, the river passes through cavernous Redwall Limestone. The river is narrower here and in other places where the Paleozoic rocks are relatively hard, but becomes wider through the more easily eroded formations. The shelves of Tapeats Sandstone (more than 500 million years old) at the base of the Paleozoics appear near the mouth of the Little Colorado River. Farther downstream, the narrowest reaches are cut through the dense, dark-colored Vishnu Schist of the Proterozoic era (about 1.7 billion years old). In the Toroweap area, the youngest rocks in the canyon are exposed, which are remnants of lava flows that poured over the North Rim about 1 million years ago during the Cenozoic era. The hardened lava still clings to the canyon walls, and basalt boulders still affect river flow at Lava Falls Rapid. The Grand Wash Cliffs mark the southwestern edge of the Colorado Plateau and the mouth of the Grand Canyon at the headwaters of Lake Mead. 3.1.2.1 Tribal Perspectives on Geologic Setting2 The Colorado River, through the Glen Canyon, Marble Canyon, and Grand Canyon (Canyons), has a prominent place in the traditional cosmology of the Havasupai Tribe, Hopi 2 Sections in this EIS entitled “Tribal Perspectives” are intended to represent the viewpoints of the Tribes who participated as Cooperating Agencies based on their input. The text was provided by the Tribes, and only minor typographic modifications were made prior to insertion into the EIS. 3-3 Glen Canyon Dam Long-Term Experimental and Management Plan October 2016 Final Environmental Impact Statement Tribe, Hualapai Tribe, Navajo Nation, Pueblo of Zuni, and the Southern Paiute Tribes and continues to have an important place in their contemporary cultures and economies. For example, Navajo oral history concerning the Grand Canyon and its tributaries states that it was developed during the time of creation of this world. Water was everywhere, and the world was named Ni′ Hodisq―the Glittering World. The people were given this world to live in after a series of trials with the native inhabitants (Chiishta Dootl′ izh, Chiishta Litso, and Chiishta Ligaii). The people discussed ways to make the world habitable; after much talk, they decided that rivers, creeks, and streams would be created to drain the world, which in turn would become the veins of the earth. The Colorado River is one of those veins. Haashch′ eeh yalt′ i′ i, the Talking God, and Haasch′ eehoghaan, the Evening God, became the advisors to the people, and under their direction, the world was created as it is today. In other oral histories, people say that Ghaa′ ask′idii, the Humpback God, created the Grand Canyon. After this world was given to humans by the Holy People, they cleared the water away. The Humpback God stood in the center of the world and dragged his cane from east to west and created the canyon. The water drained and created the rivers, creeks, and streams, which became the veins of the earth. The essence of the Humpback God is manifested by bighorn sheep and mountain goats as seen in the Grand Canyon today (Roberts et al. 1995). 3.1.3 Climatic Setting Climatic conditions in the area vary considerably with elevation. At Bright Angel Campground (elevation 2,400 ft) near Phantom Ranch, the climate is characterized by mild winters, hot summers, and low rainfall.
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