WSP08403 - Laserfiche WebLink

Home Browse Search

Chapter I Purpose and Need 2 LOCATION This assessment focuses on the Colorado River corridor from Lake Powell, formed by Glen Canyon Dam in northwestern Arizona, southward through Glen and Marble Canyons and westward through the Grand Canyon to Lake Mead. The docwnent will disclose all significant impacts of the alternatives wherever they may occur and plans to avoid or mitigate adverse impacts. Lake Powell and the 15 miles of the river below Glen Canyon Dam are part of the Glen Canyon National Recreation Area. The remaining 278 miles of the river flow through the Grand Canyon National Park. Regional impacts that may occur outside of the immediate geographic area are also evaluated. PURPOSE AND NEED FOR ACTION The purpose of the proposed action is to carry out the FWS's recommendation to implement a selective withdrawal program and determine the feasibility of providing wanner water to remove jeopardy and help recover endangered fish below Glen Canyon Dam. This would include modification of the existing penstocks to allow wannwater releases and a monitoring and adaptive management program to refine operations. Cold-water releases from Glen Canyon Dam limit recruitment of native and endangered (wannwater) fish in the mainstem of the Colorado River in the Grand Canyon. Deep, hypolimnetic releases from Glen Canyon Dam have cooled the temperature of the river in the Grand Canyon. Because its penstocks draw on water from deep in the reservoir, spring, summer, and fall releases are much colder than before the dam. This has created an excellent cold-water (trout) fishery below the dam, but prevents native, wannwater fish from thriving and spawning in Temperature Controls et Glen Canyon Dam the river. The population ofhwnpback chub in the Grand Canyon is the largest of six in existence. For the most part. the hwnpback chub only spawn in the Little Colorado River, a wannwater tributary to the Colorado River about 60 miles below Glen Canyon Dam. The fish thrive in the wannwaters of the Little Colorado River, but may be vulnerable to catastrophes because the range of their habitat is extremely limited. Some spawning may occur in the mainstem (near hot springs) and in other small tributaries, but only to a limited extent. Exioting Oeep .. 'Jr- Wann Surf1IIce Water Water Intake "'-- /~\ ~ CoIdOaapWatar / /,:..' '" __jjf Gala . - Figure 2 - Schematic of Intake Modifications.