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Principal Investigators: Topping, Wright, Melis, Rubin and Wiele, U.S. Geological Survey National Research Program, GCMRC, Marine Geology Team and Arizona District of Water Resources Discipline, respectively. . Statement of Problcm: Glen Canyon Dam has altered the character of the water that is released downstream into the Colorado River. The supply of fine sediment has been reduced to nearly zero, which has impacted fine sediment deposits and turbidity in Glen, Marble, and Grand Canyons. The thermal regime of the releases has changed from seasonal variations that followed air temperatures to nearly constant release temperatures throughout the year which are colder in the slimmer and warmer in the winter than pre-dam temperatures. These changes, as well as changes in the downstream delivery of minerals, nutrients, and carbon have altered the ecosystem of the Colorado River downstream from Glen Canyon Dam. The Lake Powell Project characterizes the water quality of the lake and downstream releases. This project monitors how the releases affect the downstream ecosystem and develops tools to assist decision-makers in the management of Glen Canyon Dam. Summary Project Description: The downstream IQWP has two major components. The first component is focused on monitoring and modeling the mass-balance of fine sediment in the CRE. The second component ofIQWP is focused on characterizing other water quality components of the ecosystem, such as water temperature, oxygen, nutrients, and carbon. Each component has monitoring and research' elements as described below. Downstream Monitoring Components: 1. Fine sediment mass balance: Use oflaser-acoustic system and conventional suspended-sediment samples to monitor t~ansport at several locations along the mainstem Colorado River and on key tributaries. Monitoring data are used to provide a continuous accounting of the mass-balance (input minus export) of sand and fine sediment in Marble and Grand Canyons and to assess the.impacts of experimental flows on the mass-balance. 2. Continuous water quality monitoring: Temperature, conductivity, dissolved oxygen, and pH are monitored at several locations along the mainstem Colorado River and key tributaries. Most sites are coincident with the mass-balance monitoring locations. Temperature monitoring in selected backwater habitat areas. Data are used to characterize the thermal regime and longitudinal gradient in mineral and oxygen content of the river, and to calibrate and validate numerical models. GCMRC FY2006 Annual Work Plan (Draft, June 10,2005) 25 . ,. .