Lake Powell is a large arid reservoir that represents about 70% of the water storage capacity for the Upper Colorado River Basin. It is the second largest reservoir in the United States by capacity (second only to Lake Mead). Lake Powell is an oligotrophic reservoir, which means that nutrient concentrations and algal production are generally low. This often results in very clear-water conditions, with an average secchi (water transparency) depth of 9 meters at a long-term monitoring site near the dam (period of record 1985-2020).
Lake Powell Water Quality Monitoring Program
The Lake Powell water quality monitoring program began in 1965 over concerns that Colorado River basin-wide salinity levels were increasing. The monitoring program collects data on water-quality conditions at the forebay of the reservoir (2.4 km from the dam) on a monthly basis and at 25-30 sites during quarterly 4-5 day reservoir surveys. The data collected as part of this program represents a unique and valuable long-term record of water temperatures, dissolved oxygen concentrations, major ions and, more recently (beginning in 1990), nutrients and biological constituents (Vernieu, 2015). The program is an interagency collaboration between the Bureau of Reclamation, the National Park Service, and the U.S. Geological Survey.
Lake Powell and the 21st Century Mega-Drought
Lake Powell has experienced dramatic fluctuations in water levels, from full capacity at 3700 ft above sea level in 1983, to a historic low of 177 ft below its full elevation in May 2022. Under low water levels, large regions of shoreline sediment in the reservoir become exposed. Dried sediments can be re-mobilized during spring inflow and can cause low oxygen conditions in the middle of the reservoir water column that can then be transported towards the dam. These low oxygen conditions develop when remobilized sediment stimulates both biological and chemical processes that use up oxygen. These low oxygen regions, termed metalimnetic low dissolved events, are a cause of concern for dam managers for two main reasons. The low dissolved oxygen concentrations pose corrosion concerns in the dam and can be harmful to fish populations in the Glen Canyon reach of the river (before rapids are able to mix oxygen back into the river). Work led by the U.S. Geological Survey aims to better characterize sediment oxygen use to inform existing dissolved oxygen modeling.
Lake Powell Biogeochemistry
Like many human-made reservoirs, Lake Powell transforms key aspects of water quality, altering downstream physio-chemical conditions. Lake Powell retains large amounts of sediment in its inlet regions, with some areas estimated to accumulate 2 to 3 meters of sediment a year. With this sediment retention, large amounts of phosphorus are also retained—reducing the downstream transport of this biologically necessary element by anywhere between 95 and 99%. Phosphorus is an important nutrient that supports algae growth and overall foodbase productivity for the downstream ecosystem. Some of the same processes that cause phosphorus retention in Lake Powell also reduce salinity and alkalinity — these reductions help meet downstream Colorado River salinity water quality standards. A recent mass balance study using historical water quality data collected by this program and by the U.S. Geological Survey water science center estimated that Lake Powell reduces the total downstream transport of salt by ~10% (Deemer and others, 2020).
Southwest Reservoir Greenhouse Gas Survey
Lakes and reservoirs are a significant global source of methane, a potent greenhouse gas. Still, little is known about how to predict methane emissions from arid reservoirs. In 2021, the U.S. Geological Survey measured greenhouse gas fluxes from 10 reservoirs in AZ, UT, and CA as part of a national reservoir survey being led by the Environmental Protection Agency (https://www.epa.gov/air-research/research-emissions-us-reservoirs). They also conducted a one-time survey of greenhouse gas emissions in Lake Powell to compare measurements with existing models of emissions (Waldo and others, 2021).
Lake Powell by the Numbers
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Formed in 1963
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Took 17 years to fill
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Capacity >24 million acre-feet (MAF)
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1850 miles of shoreline when full
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557 feet deep when full
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Water residence time is about 2 years on average
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Has more than 95 tributary arms
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Water levels have varied over 175 feet since full capacity was reached
- Overview
Lake Powell is a large arid reservoir that represents about 70% of the water storage capacity for the Upper Colorado River Basin. It is the second largest reservoir in the United States by capacity (second only to Lake Mead). Lake Powell is an oligotrophic reservoir, which means that nutrient concentrations and algal production are generally low. This often results in very clear-water conditions, with an average secchi (water transparency) depth of 9 meters at a long-term monitoring site near the dam (period of record 1985-2020).
Lake Powell Water Quality Monitoring Program
Sources/Usage: Public Domain.Bridget Deemer labels samples during a Lake Powell water quality monitoring trip. Photo by SBSC, Grand Canyon Monitoring and Research Center. The Lake Powell water quality monitoring program began in 1965 over concerns that Colorado River basin-wide salinity levels were increasing. The monitoring program collects data on water-quality conditions at the forebay of the reservoir (2.4 km from the dam) on a monthly basis and at 25-30 sites during quarterly 4-5 day reservoir surveys. The data collected as part of this program represents a unique and valuable long-term record of water temperatures, dissolved oxygen concentrations, major ions and, more recently (beginning in 1990), nutrients and biological constituents (Vernieu, 2015). The program is an interagency collaboration between the Bureau of Reclamation, the National Park Service, and the U.S. Geological Survey.
Lake Powell and the 21st Century Mega-Drought
Sources/Usage: Public Domain.Bathtub rings on a rock face in Lake Powell where the water has dropped and left mineral deposits behind. Photo by SBSC, March 2022. Lake Powell has experienced dramatic fluctuations in water levels, from full capacity at 3700 ft above sea level in 1983, to a historic low of 177 ft below its full elevation in May 2022. Under low water levels, large regions of shoreline sediment in the reservoir become exposed. Dried sediments can be re-mobilized during spring inflow and can cause low oxygen conditions in the middle of the reservoir water column that can then be transported towards the dam. These low oxygen conditions develop when remobilized sediment stimulates both biological and chemical processes that use up oxygen. These low oxygen regions, termed metalimnetic low dissolved events, are a cause of concern for dam managers for two main reasons. The low dissolved oxygen concentrations pose corrosion concerns in the dam and can be harmful to fish populations in the Glen Canyon reach of the river (before rapids are able to mix oxygen back into the river). Work led by the U.S. Geological Survey aims to better characterize sediment oxygen use to inform existing dissolved oxygen modeling.
Lake Powell Biogeochemistry
Sources/Usage: Public Domain.Nick Voichick at the winch. SBSC monitors Lake Powell water quality in partnership with the Bureau of Reclamation Colorado River Salinity Control Program and the National Park Service Glen Canyon National Recreation Area. Photo by SBSC, Grand Canyon Monitoring and Research Center. Like many human-made reservoirs, Lake Powell transforms key aspects of water quality, altering downstream physio-chemical conditions. Lake Powell retains large amounts of sediment in its inlet regions, with some areas estimated to accumulate 2 to 3 meters of sediment a year. With this sediment retention, large amounts of phosphorus are also retained—reducing the downstream transport of this biologically necessary element by anywhere between 95 and 99%. Phosphorus is an important nutrient that supports algae growth and overall foodbase productivity for the downstream ecosystem. Some of the same processes that cause phosphorus retention in Lake Powell also reduce salinity and alkalinity — these reductions help meet downstream Colorado River salinity water quality standards. A recent mass balance study using historical water quality data collected by this program and by the U.S. Geological Survey water science center estimated that Lake Powell reduces the total downstream transport of salt by ~10% (Deemer and others, 2020).
Southwest Reservoir Greenhouse Gas Survey
Sources/Usage: Public Domain.Sarah Waldo conducts greenhouse gas analysis with analyzer and floating chamber on Lake Powell as part of an SBSC, Grand Canyon Monitoring and Research Center study. Photo taken in 2017. Lakes and reservoirs are a significant global source of methane, a potent greenhouse gas. Still, little is known about how to predict methane emissions from arid reservoirs. In 2021, the U.S. Geological Survey measured greenhouse gas fluxes from 10 reservoirs in AZ, UT, and CA as part of a national reservoir survey being led by the Environmental Protection Agency (https://www.epa.gov/air-research/research-emissions-us-reservoirs). They also conducted a one-time survey of greenhouse gas emissions in Lake Powell to compare measurements with existing models of emissions (Waldo and others, 2021).
Lake Powell by the Numbers
-
Formed in 1963
-
Took 17 years to fill
-
Capacity >24 million acre-feet (MAF)
-
1850 miles of shoreline when full
-
557 feet deep when full
-
Water residence time is about 2 years on average
-
Has more than 95 tributary arms
-
Water levels have varied over 175 feet since full capacity was reached
Sources/Usage: Public Domain.A Seabird water quality profiling instrument, Lake Powell. This instrument is used to collect temperature, conductivity, dissolved oxygen, pH, turbidity, and chlorophyll a data from the reservoir. Water is pumped across the water quality sensors as the instrument is lowered through the water column on a winch. The result is binned estimates of different water quality parameters every 0.5 m throughout the entire depth of the reservoir. Photo by Robert Radtke, U.S. Bureau of Reclamation, 2012.
Sources/Usage: Public Domain.U.S. Bureau of Reclamation works with USGS SBSC Grand Canyon Monitoring and Research Center on water quality monitoring in Lake Powell. Robert Radtke checks a line of temperature loggers deployed in Lake Powell near the dam. Temperature loggers provide continuous (30-minute) temperature data for ~18 depths spanning the surface to the bottom of the reservoir.
Sources/Usage: Public Domain.A discrete water sample is collected from one of Lake Powell's Reservoir's main inflows. The Van Dorn water sampler pictured here is lowered to the desired depth and then triggered to close using a small metal weight. Photo by Robert Radtke, U.S. Bureau of Reclamation, 2005. -
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