Water-Temperature Data for the Colorado River and Tributaries Between Glen Canyon Dam and Spencer Canyon, Northern Arizona, 1988-2005

Abstract

The regulation of flow of the Colorado River by Glen Canyon Dam began in 1963. This resulted in significant changes to the downstream ecosystem of the Colorado River in Grand Canyon, contributing to the initiation of the Glen Canyon Environmental Studies program in 1982, followed by establishment of the Glen Canyon Dam Adaptive Management Program in 1996. This report describes a water-temperature dataset collected through these programs for the reach of the Colorado River and selected tributaries between Glen Canyon Dam and Spencer Canyon (approximately 261 river miles) in northern Arizona from 1988 to 2005. The primary purposes of the report are to summarize the methods of data collection, processing, and editing; to present summary statistics; and to make the data described in the report available. Introduction The regulation of the Colorado River by Glen Canyon Dam, which began in 1963, resulted in a significant change in the physical and biological environments of the Colorado River downstream from the dam in northern Arizona (fig. 1). Flow regulation by the dam reduced annual peak flows, raised minimum flows, and increased daily fluctuations in flows according to hydropower demand (Topping and others, 2003). As a result of the construction and operation of the dam, sandbars and other fine-grained deposits have been eroded (Topping and others, 2000; Wright and others, 2005). Additionally, the presence of the dam has led to a change in the water temperature below the dam (fig. 2). Before flow regulation by the dam, the temperature of the river at Lees Ferry, located approximately 25 km downstream, fluctuated from near freezing in the winter to nearly 30oC in the summer. During and after the filling of Lake Powell, which occurred in June 1980, the temperature range and average temperature of the river have both decreased, because the penstock intakes withdraw water from approximately 70 m below the full-conservation pool elevation of 1,128 m. The water withdrawn from the penstocks and released below the dam is significantly cooler during most of the year than the water at the surface of Lake Powell. In concert with these changes to the downstream physical environment, Glen Canyon Dam has affected the aquatic and terrestrial ecosystems, including the aquatic food base (Kennedy and Gloss, 2005), fish community (Gloss and Coggins, 2005), and terrestrial vegetation (Ralston, 2005). Also, cultural and recreational resources within Grand Canyon have been affected (Fairley, 2005; Kaplinski and others, 2005). Recognition of these changes contributed to the initiation of the Glen Canyon Environmental Studies (GCES) program in 1982, followed by establishment of the