HR: 0800h
AN: H41A-0135    [Abstracts]
TI: Modeling Water Temperatures in the Colorado River Below Glen Canyon Dam, Arizona to Assess the Influence of Operational and Environmental Factors on Downstream Thermal Dynamics
AU: * Anderson, C R
EM: canderson@usgs.gov
AF: USGS, 2255 N. Gemini Dr., Flagstaff, AZ 86001, United States
AU: Wright, S A
EM: sawright@usgs.gov
AF: USGS, 6000 J St., Sacramento, CA 95819, United States
AB: The closure of Glen Canyon Dam in 1963 transformed the seasonally warm Colorado River into a consistently cold river owing to the hypolimnetic releases associated with deep penstock withdrawal structures within Lake Powell. This regulation effect has substantially altered the thermal regime of the downstream riverine environment which, in turn, has greatly impacted the biota of the river corridor, particularly native fishes and the aquatic food base. Given the significance of water temperature as one of the primary controls on many biological processes in aquatic ecosystems, the capability to predict downstream water temperatures allows resource managers the ability to assess potential future impacts of environmental and operational factors. To support adaptive management below the dam, we developed a suite of water temperature models for the mainstem and nearshore environments. The modeling suite consists of a one-dimensional temperature model for the mainstem, completely mixed "pond" models for nearshore, low-velocity "backwater" environments that are thought to be important rearing habitat for juvenile native fish, and multi-dimensional models for kilometer scale reaches in order to evaluate water temperatures in backwaters as well as other less defined shoreline habitats. The calibrated mainstem model has been used to evaluate water temperatures under a variety of scenarios for water releases from Glen Canyon Dam, such as flows with daily fluctuations (i.e. electricity load-following) compared to steady flow releases, and across a range of annual release volumes and temperatures associated with variability of basin hydrology and reservoir storage. Simulation results suggest that daily dam operations result in negligible differences in mainstem water temperature throughout the river corridor (average difference < 0.1°C). However, storage conditions in the upstream reservoir, which are controlled by decadal-scale upper Colorado River basin climate, can have a significant influence on mainstem temperatures. For example, simulated average temperature differences between low and high release volumes for a two week period with typical, mid-summer meteorological conditions ranged from 0.5°C approximately 24 kilometers below the dam to 2.6°C approximately 386 kilometers below the dam. Similar simulation efforts are currently underway with the nearshore temperature models to assess the effects of dam operations and environmental factors on thermal dynamics in backwaters and other nearshore environments.
DE: 1808 Dams
DE: 1847 Modeling
DE: 1871 Surface water quality
DE: 1880 Water management (6334)
SC: Hydrology [H]
MN: 2007 Fall Meeting