TEMPERATURE

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Water Temperature below Glen Canyon Dam Prior to completion of Glen Canyon Dam in 1963, the temperature of water flowing through the Grand Canyon each year was highly variable, ranging from the icy, spring run-off to the warm, 85-degree summer-heated flows. However, once the dam was constructed, the temperature of the water released from the dam - drawn from the depths of Lake Powell and released through the dam's penstock intakes - ranged for many years between 45 and 50 F (7 to 10 C). With the lowering of Lake Powell, release temperatures have been increased to as high as 59 F (15 C) which has likely led to an increase in the humpback chub and other native fish populations in Grand Canyon. These increases in temperature, however, also increase the risk of expanding the distribution and abundance of cool/warm-water nonnative fish like brown trout, green sunfish, smallmouth bass, and walleye which could have a devastating impact on the humpback chub population in Grand Canyon like they have on humpback chub and other native fish populations in the Upper Basin.

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Thermoclines Warm water is less dense and essentially "floats" on top of cold water. This creates a stratification of water temperatures in a reservoir with warm water at the surface and cold water near the bottom. The point in the water column where the water changes from warm to cold is called the thermocline. Forebay Temperatures Forebay temperature 2000-2016; https://www.usbr.gov/uc/rm/amp/twg/mtgs/17jan26/AR4_Radtke.pdf As reservoir elevations change, the thermocline gets closer or farther away from the penstocks at Glen Canyon Dam. Thermoclines, Penstock Depths, and Release Temperatures December 2018 Operations Call As the penstocks begin to draw from above the thermocline, release temperatures can increase drastically. December 2018 Operations Call Downstream Warming The timing of seasonally warm release temperatures and high summer air temperatures have a large influence on downstream river temperatures. The warmest release temperatures occur in late October/early November but the greatest potential of warming the river in Grand Canyon occurs in July and September when air temperatures are the hottest. The reason is that it takes a lot longer to warm all the water in Lake Powell vs the water in the river as it flows downstream through the canyon. Another thing to note that during the winter, river temperatures actually cool with distance downstream because releases are actually warmer than ambient air temperatures. June 2016 Operations Call

Links and Information Temperature Learning Page TCD Learning Page Nonnative Fish Page Bioenergetics Page Near Shore Ecology (NSE) Study of the fall steady flow test The Low Summer Flow Experiment (LSF) Page Temperature Gages Glen Canyon Dam Site: Hourly Averages Glen Canyon Dam near Page, AZ Paria River at Lees Ferry, AZ Colorado River at Lees Ferry Colorado River near river mile 30 Colorado River above Little Colorado River near Desert View, AZ Little Colorado River above the mouth near Desert View, AZ Colorado River near Grand Canyon, AZ Bright Angel Creek near Grand Canyon, AZ Colorado River abv Lava Canyon rm66 Colorado River bl rm127 Kanab Creek above the mouth near Supai, AZ Havasu Creek above the mouth near Supai, AZ Colorado River above National Canyon near Supai, AZ Colorado River above Diamond Creek near Peach Springs, AZ Colorado River above Spencer Creek at river mile 246 Papers and presentations 2022 Low water levels at Lake Powell impact the fish downstream FY 2022 Drought Funding: Infrastructure Alternatives Basin Hydrology, Operations and Water Quality 2021 Glen Canyon Dam Release Temperatures Temperature Control and Fish Passage at Glen Canyon Dam – Recent Progress 2020 Mihalevich eta al, 2020, Water temperature controls for regulated canyon‐bound rivers: Water Resources Research GCMRC 2019 Annual Reporting Meeting Overview – Part 2b Potential implications of a warmer future for the Colorado River ecosystem 2018 Temperature Control Device Update PPT Dibble et al., 2018, Warm water temperatures and shifts in seasonality increase trout recruitment but only moderately decrease adult size in western North American tailwaters: Environmental Biology of Fishes Temperature and nutrients as ecosystem drivers in the Colorado River PPT, Lake Powell as a regulator of temperature and Lake Powell as a regulator of nutrients PPT 2017 Water Quality in Lake Powell and Its Influence on the Colorado River Below Glen Canyon Dam PPT Pine et al. 2017. Growth of Endangered Humpback Chub in Relation to Temperature and Discharge in the Lower Colorado River. USU Watershed Sciences Faculty Publications 2015 Benefits and Risks of Temperature Modification at Glen Canyon Dam to Fishes of the Colorado River through the Grand Canyon ppt 2013 Valdez et al. 2013. Benefits and risks of temperature modification at Glen Canyon Dam to aquatic resources of the Colorado River in Grand Canyon. U.S. Bureau of Reclamation, Upper Colorado Region, Salt Lake City, UT. Ross et al., 2013, Nearshore thermal gradients of the Colorado River near the Little Colorado River confluence, Grand Canyon National Park, Arizona, 2010: U.S. Geological Survey Open-File Report Nearshore Temperature Findings for the Colorado River in Grand Canyon, Arizona—Possible Implications for Native Fish Results of Early Temperature Analyses of the Long-Term Experimental and Management Plan EIS Effects of Water Temperature on Predation Vulnerability of Humpback Chub 2012 Temperature Considerations in the RTCD alternative for LTEMP Flow Temp Turbidity Effects of Temperature on Native Fish 2010 Incorporating thermal regimes into environmental flows assessments: modifying dam operations to restore freshwater ecosystem integrity by Julian D. Olden and Robert J. Naiman (University of Washington, Seattle) Selective withdrawal and sediment augmentation update Temperature Control Device and Sediment Augmentation Report TWG Chair Temperature Control Device/Sediment Augmentation Sediment and Temperature Modeling Update PPT as presented at January 2010 Annual Reporting Meeting Temperature Control Device and Sediment Augmentation and PPT 2009 Selective Withdrawal and Sediment Augmentation Update PPT Grand Canyon Monitoring and Research Center Updates Grand Canyon Monitoring and Research Center (GCMRC) Update 2008 The Glen Canyon Dam temperature control device: restoring downstream habitat for endangered fish recovery Anderson and Wright. 2007. Development and application of a water temperature model for the Colorado River below Glen Canyon Dam, Arizona. Hydrological Science and Technology, V 23, No 1-4. 2007 Valdez and Speas. 2007. A Risk Assessment Model To Evaluate Risks and Benefits to Aquatic Resources From A Selective Withdrawal Structure On Glen Canyon Dam 1999 Glen Canyon Dam Modifications to Control Downstream Temperatures, Plan and Draft Environmental Assessment Other Stuff Fish occupying warmer water have higher metabolic demands than individuals in cooler water, and if these demands increase concurrently with a seasonal decline in prey availability, then growth rates and condition may be reduced. [1] Water Temperatures at the Little Colorado River Confluence (RM 61), 1990-2015