U.S. Department of the Interior October 2022 

Technical Report No. ENV-2022-61

Low Dissolved Oxygen in Releases: 

Current State-of-Practice 

Colorado River Storage Project

Upper Colorado Basin Region
Mission Statements

The U.S. Department of the Interior protects and manages the 

Nation’s natural resources and cultural heritage; provides scientific 

and other information about those resources; honors its trust 

responsibilities or special commitments to American Indians, 

Alaska Natives, and affiliated Island Communities.

The mission of the Bureau of Reclamation is to manage, develop, 

and protect water and related resources in an environmentally and 

economically sound manner in the interest of the American public. 

Cover Photo – Night View of Glen Canyon Dam with bypass tunnels open during 2008 high flow 

experiment (Bureau of Reclamation).
U.S. Department of the Interior October 2022 

Technical Report No. ENV-2022-61

Low Dissolved Oxygen in Releases: 

Current State-of-Practice 

Colorado River Storage Project

Upper Colorado Basin Region

Prepared by:

Bureau of Reclamation

Technical Service Center

Denver, Colorado

Technical Report No. ENV-2022-61

Low Dissolved Oxygen in Releases: 

Current State-of-Practice

Colorado River Storage Project

Upper Colorado Basin Region

Prepared by: Steve Hollenback

Physical Scientist, 86-68240

Checked by: Michael Horn

Supervisory Biologist, 86-68290

Peer reviewed by: Clarence Fullard

Fish Biologist, UC-411

Acronyms and Abbreviations

DO dissolved oxygen 

FERC Federal Energy Regulatory Commission

ft3/s cubic feet per second

GCMRC U.S. Geological Survey Grand Canyon Monitoring and Research Center 

mg/L milligram(s) per liter

Reclamation Bureau of Reclamation

TMDL total maximum daily load

TVA Tennessee Valley Authority

USFWS U.S. Fish and Wildlife Service

USGS U.S. Geological Survey 

i 

Contents

Page

1.0 Introduction ..........................................................................................................................1

2.0 Low Dissolved Oxygen Issues at Reclamation Facilities ....................................................3

2.1 Indian Creek Reservoir ............................................................................................4

2.2 Klamath River ..........................................................................................................4

2.3 Malheur River ..........................................................................................................5

2.4 Yakima River Basin .................................................................................................5

3.0 Dissolved Oxygen Monitoring at Reclamation Sites of Concern ........................................6

3.1 Indian Creek Reservoir ............................................................................................6

3.2 Klamath River ..........................................................................................................7

3.3 Malheur River ..........................................................................................................7

3.4 Yakima River Basin .................................................................................................7

4.0 Management of Dissolved Oxygen at Reclamation Sites of Concern .................................7

5.0 Assessment of Current Monitoring and Modeling at Lake Powell......................................8

5.1 Current Method of Dissolved Oxygen Monitoring at Lake Powell .........................8

5.1.1 Assessment of Current Dissolved Oxygen Monitoring 

Effectiveness at Lake Powell .................................................................11

6.0 Consideration of Downstream Resources ..........................................................................11

6.1 Forecasting Ability.................................................................................................11

6.2 Ecosystem Impacts of Low Dissolved Oxygen Releases from 

Lake Powell ...........................................................................................................13

6.2.1 Risk of Low Dissolved Oxygen Releases from Lake Powell ....................13

6.2.2 Brown and Rainbow Trout Dissolved Oxygen Tolerance .........................14

7.0 Mitigation Tools for Low Dissolved Oxygen ....................................................................14

7.1 Aeration Mitigation ................................................................................................15

7.1.1 Aeration Weirs ...........................................................................................15

7.1.2 Artificial Destratification ...........................................................................17

7.1.3 Hypolimnetic Oxygenation ........................................................................17

7.1.4 Side Stream Oxygenation ...........................................................................17

7.1.5 Bubble Plume Oxygenation .......................................................................18

7.1.6 Speece Cones..............................................................................................20

7.1.7 Turbine Aeration ........................................................................................21

7.1.8 Penstock Intake Aeration ...........................................................................23

7.2 Management Mitigation .........................................................................................24

7.2.1 Selective Withdrawal Structures ................................................................24

7.2.2 High Flow Events .......................................................................................25

7.3 Feasibility of Using Dissolved Oxygen Mitigation Tools at 

Glen Canyon Dam..................................................................................................25

8.0 References ..........................................................................................................................29
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Tables

Table Page

1 List of the 27 primary monitoring stations for the water quality database 

(Vernieu 2015) .................................................................................................................9

Figures

Figure Page

1 Cartoon demonstrating (left to right) a simplified version of how eutrophication 

occurs due to nutrient loading in a waterbody (National Oceanic and 

Atmospheric Administration 2018). ................................................................................1

2 Typical seasonal thermal mixing and stratification that results in low DO in

natural lakes and man-made reservoirs; arrows represent the mixing of water 

(Bevelhimer 2006). ......................................................................................................... 2

3 Location of monitoring stations (ICR-1, ICR-2, and ICR-5), Speece cone, 

and equipment building where the air blowers are housed at Indian Creek 

Reservoir (Bergsohn 2015). ............................................................................................ 6

4 Yellow dots indicate sondes in the Glen Canyon Reach of the Colorado River 

and are labeled by river mile from Glen Canyon Dam (the red star indicates a 

thermistor string in Lake Powell, and the yellow star indicates the Wahweap 

sampling site (Deemer 2020). ....................................................................................... 10

5 Historical DO concentration in Lake Powell at Glen Canyon Dam from 1991 

to 2006 with elevation in feet on the x-axis and the penstock elevation displayed 

by the black box overlay.. ............................................................................................. 13

6 Picture of an aerating weir in the downstream channel of the regulating dam in the 

Nam Kathang River (Descloux 2015)........................................................................... 16

7 Schematic of a side stream oxygenation system showing hypolimnetic water 

drawn to the surface where it is oxygenated then redistributed at the reservoir 

bottom (Gerling 2014). ................................................................................................. 18

8 Schematic view of a bubble plume diffuser and turbine withdrawal 

(Mobley 2006). ............................................................................................................. 19

9 Schematic of a Speece cone oxygenation system (Brown & Caldwell, Inc. 1995). ......... 21

10 Schematic representing three methods for an auto-venting turbine, including 

central (blue), distributed (green), and peripheral (yellow) (Rholand 2009). ............... 22

11 Upstream face of Glen Canyon Dam circa 1964 showing the penstocks.. ....................... 23

12 Schematic of a selective withdrawal structure demonstrating the ability to

remove water from a targeted strata within the water column (Sherman 2001). .......... 24
1 

1.0 Introduction 

All natural lakes and man-made reservoirs undergo similar processes that result in seasonal 

inputs of organic matter and nutrients, algal growth periods, stratification, and the potential 

for decreases in dissolved oxygen (DO) at certain depths due to chemical and biological 

processes (Figure 1). The degree of DO depletion within a waterbody is impacted by how 

isolated the hypolimnion is from the upper layers, the temperature, and the amount of oxygen 

demand at certain depths (Figure 2). Both natural lakes and reservoirs can experience strong 

stratification, leading to low DO at certain depths, but in regard to downstream water quality, 

these low DO events are more concerning in man-made reservoirs than in natural lakes.

Figure 1.—Cartoon demonstrating (left to right) a simplified version of how eutrophication occurs due 

to nutrient loading in a waterbody (National Oceanic and Atmospheric Administration 2018). 
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Low Dissolved Oxygen in Releases: Current State-of-Practice 

2 

Figure 2.—Typical seasonal thermal mixing and stratification that results in low DO 

in natural lakes and man-made reservoirs; arrows represent the mixing of water 

(Bevelhimer 2006). 

A key difference in water quality downstream from natural lakes and man-made reservoirs is due 

to the difference in depth from which water is released. In natural lakes, water typically flows 

downstream from the relatively well-oxygenated surface waters, whereas many man-made 

reservoirs release water from a depth that tends to have significantly lower DO (Beutel 1999). 

Low DO releases have a well-documented potential to cause significant negative impacts to 

downstream ecosystems (Bevelhimer 2006). However, not all water from reservoirs is released 

from below the thermocline (the hypolimnion), and not all releases from below the thermocline 

are bad for downstream habitats. Depending on the reservoir purpose, dam design, and 

operational requirements, releases can occur at a wide range of depths, and water from many 

dams is purposefully released from below the thermocline to help route sediment-heavy 

inflows through a reservoir, draw higher DO water from further upstream to the deeper parts 

of a reservoir, and to pass colder water downstream to overheated habitats. Although there are 

some potential benefits to releasing water from below the thermocline, these benefits have 

largely been outweighed by the intermittent lack of oxygen in the outflow at Glen Canyon Dam, 

which has caused concern for ecosystem health between Glen Canyon Dam and Lees Ferry in 

2003, 2005, 2014, and 2019 (Deemer 2020). Further, as the climate changes, these low 

DO events are predicted to increase in both frequency and magnitude at Glen Canyon Dam 

(U.S. Fish and Wildlife Service [USFWS] 2016). 
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Water impairments caused by low DO dam releases are not unique to Glen Canyon Dam. 

Monitoring and/or mitigating for low DO in dam tailraces is a requirement of an estimated 

40 percent of Federal Energy Regulatory Commission (FERC) licenses (Bevelhimer 2006). 

Because low DO is a historical concern at a wide range of reservoir sites, a number of case 

studies and other summary documents have been developed for a large suite of projects in 

the United States and throughout the world. While focused on studies in the United States, this 

report used sources from other areas of the world as well. Technologies in use are not unique to 

any particular area but are instead related more to the problem at hand and local conditions. 

When determining the best method to mitigate low DO dam releases, these case studies can 

provide valuable lessons and guidance when designing a system intended to overcome the 

unique challenges inherent to every dam site while operating within a reasonable budget 

(Higgins 1999). 

Increasing DO in dam releases not only has an added expense associated with buildout or 

equipment installation, it also typically incurs considerable operational costs that must 

be factored into any successful mitigation plan: Low DO mitigation projects often entail 

significant operational costs related to losses in hydropower revenue through reduced power 

generation, ongoing operations and maintenance costs, the cost of monitoring and modeling DO 

conditions, and the costs of necessary consumables such as liquid oxygen (U.S. Geological 

Survey [USGS] 2020). To plan for and develop a cost-effective DO mitigation system, a basic 

understanding of DO mitigation history, methods, and applicability is essential. 

In this report, case studies of select Bureau of Reclamation (Reclamation) installations with DO 

issues and project mitigation success are presented. Monitoring and modeling of DO upstream 

of and downstream from Lake Powell are discussed, as low DO releases from Lake Powell are 

threatening the downstream ecosystem. Successful DO mitigation methods at other reservoir 

locations are also presented to inform managers of mitigation systems that should be considered

for use at Glen Canyon Dam. 

Note: This is not an engineering report or feasibility study. This report presents mitigation 

alternatives and options to improve DO on a general level. 

2.0 Low Dissolved Oxygen Issues at 

Reclamation Facilities

Many FERC-licensed projects include requirements to mitigate and/or monitor downstream DO, 

and many have minimum DO requirements (Mobley 1997). Water releases with low DO are a 

common problem at many existing hydropower facilities because the turbine intakes are often far 

below the water surface, where DO may be as low as 0 milligrams per liter (mg/L) (United States

Department of Energy 2016). 
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Below, we briefly present a selection of waterways downstream from Reclamation facilities for 

which there are reports and studies focusing on low DO: Indian Creek Reservoir, the Klamath 

River, the Malheur River, and the Yakima River Basin. The general overview presents the 

different DO issues at Reclamation sites as well as possible solutions. 

2.1 Indian Creek Reservoir

Indian Creek Reservoir has been on California’s 303(d) pollutant list (a State’s list of impaired 

and threatened waters) for low DO since 1998. After studying the DO, sediment load, water 

temperature, and anthropogenic influences on the water entering the reservoir, oxygen 

consumption by plants, stimulated by high phosphorous in the water, and sediment oxygen 

demand were determined to be the two most viable causes of eutrophication (Idaho Department 

of Environmental Quality 2001). Phosphorous can reduce DO by stimulating nuisance aquatic 

algae growth. As the biomass of algae increases, its nighttime respiration increases, thereby 

reducing oxygen in the water. When the biomass dies, its decomposition further reduces DO as 

shown on Figure 2 (Bolke 1979). In 2008, a hypolimnetic oxygenation system was constructed in 

Indian Creek Reservoir that uses Speece cones connected to an onsite oxygen generation system. 

This system was operated from 2009 to 2014, for an average of 3,252 hours each year, and liquid 

oxygen was injected at an average rate of 517 pounds per day across those six years. Steps were 

also taken to mitigate phosphorus loads so as to not exceed the maximum total allowable levels 

for water inflows into the reservoir. Following operation of the hypolimnetic oxygenation system

and measures to limit phosphorus inputs upstream, target DO levels within and downstream from 

Indian Creek Reservoir have consistently been met or exceeded (Bergsohn 2015). 

2.2 Klamath River

Reclamation DO concerns are not limited to a single reservoir; there have been concerns about 

the DO levels throughout much of the Klamath River Basin for many years (McCaughey 2020). 

Reclamation began monitoring Klamath Basin water quality in the early 1990s and found the 

Klamath River main stem regularly experienced impairments due to low DO levels (California 

Water Board [CAWB] CAWB-R1 2010). During a fishkill in 1999, the DO concentrations 

within monitored portions of the lower Klamath River ranged from 3.1 to 7.6 parts per million 

(Zedonis 2001), and it was reported that throughout the basin, DO concentrations were regularly 

too low to meet the Action and Basin Plan objectives (CAWB-R1 2010). In 2009, as a mitigation 

measure, a blower and turbine venting system were installed at Iron Gate Dam. The system has 

been used on an ongoing basis beginning in 2013and has demonstrated the ability to consistently 

increase oxygen levels in the portion of the river near the downstream outlet at Iron Gate Dam to 

acceptable levels (PacificCorp 2018). To assist with DO issues in other areas of the Klamath 

Basin, beginning December 2010, the North Coast Regional Board began implementing an 

Action Plan for the Klamath River. The plan included dam management and control of total 

maximum daily loads (TMDLs), such as nitrogen and phosphate, to control water quality issues 

such as low DO (Klamath Basin Restoration Agreement 2010). Unfortunately, this plan only 

moderately helped to relieve impairments caused by low DO levels in the Klamath River Basin 

(USGS 2018). 
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2.3 Malheur River

Similar to the widespread DO concerns in the Klamath River Basin, the Malheur River was listed 

on Oregon’s 303(d) pollutant list for low DO throughout its length (Oregon Department of 

Environmental Quality 2010). Reclamation has interests in this basin through the Vale Project, 

which includes Warm Springs Dam, Agency Valley Dam, and Bully Creek Dam, as well as other 

diversion works and drainage systems. Low DO releases from Warm Springs Dam were the 

biggest concern of the system (Warm Springs Hydro, LLC 2013). A turbine aeration system 

was constructed at this location to ensure water discharged during power production met State 

water quality standards, and a bypass structure was installed to route water with higher DO 

downstream when not needed for power production. Operation of the turbine aeration system and 

installation of the bypass structure alleviated low DO concerns downstream from Warm Springs 

Dam (Dadoly 2010). At the Bully Creek and Agency Valley Dams, low DO remains a concern 

primarily due to orthophosphate loading. To help mitigate this issue, TMDLs were established 

and have largely been met; however, impairments due to low DO conditions downstream from 

these two dams have still been recorded, though they tend to not be as severe as they were before 

TMDLs were established (Malheur Watershed Council 2019; Rose 2006). 

2.4 Yakima River Basin

While reservoirs often exacerbate low DO conditions in a basin, some Reclamation DO issues 

have little to do with a reservoir; they are caused by conditions in the waterway. The Yakima 

Basin Project is a complex system with a number of dams, diversions, dikes, and irrigation 

projects (Reclamation 2022) that has experienced issues in some reaches such as degrading water 

quality associated with excessive plant growth, which can result in low DO concentrations 

especially in summer (Wise 2009). Within the basin there were nine 303(d) DO listings: low DO 

levels observed in some reaches were largely attributed to high agricultural return flows with 

high levels of nutrients (Hiebert 1999). In addition to high nutrient loading, low water levels in 

the river reaches were also identified as a contributing factor to the low DO levels. Low water 

levels in river reaches can accelerate the heating of waterbodies, and it can also increase 

macrophyte and phytoplankton growth which, in turn, tends to further reduce DO concentrations 

(Reclamation 2002). The strong link between DO and primary productivity in the Yakima basin 

produces cyclical DO impairments: during the day, plants and algae typically generate oxygen, 

but at night and during decomposition, they reduce DO below its acceptable criterion level 

(Pickett 2016). Fortunately, the Yakima River is one of the more intensely studied rivers in 

Washington State, and plenty of historical water quality data has been recorded to develop a 

one-dimensional steady-state model with QUAL2E modeling software that helps predict DO 

by forecasting water temperatures and considering primary productivity (Carroll 2001). This

forecasting tool has helped to create TMDLs for the basin which, in turn, have helped to control 

DO. However, it has not completely alleviated low DO concerns because water levels in the 

Yakima River cannot be increased to a sufficient depth to reduce water temperature which, in 

turn, reduces primary productivity (Urmos-Berry 2019). 
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3.0 Dissolved Oxygen Monitoring at 

Reclamation Sites of Concern

Strategies for monitoring water quality vary significantly among Indian Creek Reservoir, the 

Klamath River, the Malheur River, and the Yakima River Basin so as to allow each system and 

facility to achieve their monitoring goals without using excessive financial or personnel resources.

To provide more detailed information on the Reclamation sites of concern mentioned above in 

section 2.0, below we will briefly describe the monitoring strategies used at each site along with 

a discussion of mitigation steps. 

3.1 Indian Creek Reservoir

Monitoring Indian Creek Reservoir 2012 TMDLs required water quality tracking at three

monitoring stations. One of the stations (ICR-1) is located near the dam, another (ICR-3) is 

located near the center of the reservoir, and the third (ICR-5) is located near the upstream end 

of the reservoir at a relatively shallow depth. Each month, water quality samples are collected 

along with vertical profiles of water temperature and DO concentration (Figure 3). Water quality 

samples were collected around pre-dawn to ensure the day’s lowest DO measurement was

captured (Idaho Department of Environmental Quality 2001). After installation of the 

hypolimnetic oxygenation system, the reported annual cost of operation was approximately 

$9,800 from 2010 to 2014 (Bergsohn 2015). 

Figure 3.—Location of monitoring stations (ICR-1, ICR-2, and ICR-5), Speece 

cone, and equipment building where the air blowers are housed at Indian 

Creek Reservoir (Bergsohn 2015). 
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3.2 Klamath River

Reclamation has been collecting hourly water quality data, including DO, at most sites 

throughout the Klamath River Basin since 1990. The USGS Klamath River Basin Water-Quality 

Mapper (https://or.water.usgs.gov/projs_dir/klamath_wq_mapper) displays current and 

historical monitoring sites (USGS 2018). As part of this monitoring system, three monitoring 

stations are associated with Iron Gate Reservoir: One is below Iron Gate Dam, another is at the 

Camp Creek Campground in the upstream northern branch of the reservoir, and the third is at 

the Jay Williams Boat Ramp in the upstream eastern branch of the reservoir. The frequency of 

monitoring varies: once in May, at least twice a month in June through November, and not at 

all in December through April, as DO is not a big concern during these months (PacificCorp 

2018). 

3.3 Malheur River

In the Malheur Basin, the Oregon Department of Environmental Quality maintains four water 

quality monitoring stations (information is available at: https://orwater.deq.state.or.us/Login.aspx.) 

In addition, Reclamation monitors approximately 80 locations throughout the basin; data are

available through the Environmental Protection Agency’s STOrage and RETrieval (STORET) 

database (https://www.epa.gov/waterdata/water-quality-data). Reclamation monitors two 

locations in each reservoir created by the Warm Springs: Agency Valley and Bully Creek Dams. 

In each reservoir, one monitoring site is downstream from the dam, and the other is in a far 

upstream location. The frequency of monitoring at these sites varies between sites and between 

years, but regardless of the monitoring regime, low DO conditions are typically found to occur in 

summer throughout much of the Malheur River (Dadoly 2010). 

3.4 Yakima River Basin

In the Yakima River Basin, much of the data gathered on water quality has been from water 

quality projects or studies, not a long-established monitoring regime. There are three permanent 

continuous ambient monitoring stations in the Yakima River Watershed: One is located in the 

Yakima River downstream from Cle Elum, another is located in the Yakima River at Nob Hill, 

and the third is in the Yakima River at Kiona (Urmos-Berry 2019). The frequency of water 

quality monitoring varies between sites and between years. 

4.0 Management of Dissolved Oxygen at 

Reclamation Sites of Concern

Management of DO levels at Reclamation sites of concern varies widely depending on, but not 

limited to, the severity of the issue, impacts on the ecosystem, and funding. At Indian Creek 
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8 

Reservoir, a hypolimnetic oxygenation system, which uses Speece cones connected to an onsite 

oxygen generation system, functions to resolve low DO issues in tailwaters through dispersing 

oxygen at certain depths upstream of the dam (Bergsohn 2015). At Warm Springs and Iron Gate 

Reservoirs, an oxygenation system oxygenates water as it passes through turbines inside of 

the dam (Dadoly 2010; PacificCorp 2018). Both systems have been notably successful partly 

due to implementation of TMDL limits upstream of the dams. 

5.0 Assessment of Current Monitoring and 

Modeling at Lake Powell

5.1 Current Method of Dissolved Oxygen Monitoring at 

Lake Powell

The Grand Canyon Monitoring and Research Center (GCMRC) has monitored Lake Powell and 

the releases from Glen Canyon Dam since 1997 to determine not only the status and trends of 

water quality but also to determine the effects dam management has on water quality (USGS 

2020). 

Two continuously logging water quality sondes are used to monitor DO from dam releases: One 

is connected to an active penstock, and one is directly below the dam. Monthly water quality 

monitoring consists of sampling at three locations: (1) in the forebay area immediately upstream 

of Glenn Canyon Dam, (2) in the dam draft tubes, and (3) 25 km downstream from Glen Canyon 

Dam at Lees Ferry (USGS 2020). During this monthly sampling, a vertical profile of various 

water quality constituents, including DO, is collected from the forebay area. In addition, 

another ± 27 stations (at full reservoir pool) are monitored quarterly, as these sites (Table 1) 

mostly represent major areas of the reservoir and are typically located in the thalweg (Vernieu 

2015). 

Water quality data are entered into a SQL-based data platform the GCMRC developed to house 

existing data and to provide more streamlined processes for newly generated Lake Powell water 

quality data. This database provides easier access than the previous Microsoft Access database, 

but at last report, there were still some portions under testing and development; it is anticipated 

to be complete in 2022. 

In 2021, the sonde directly below Glen Canyon Dam was set up to transmit near real-time data 

to the GCMRC’s Amazon Web Services platform. The data have been linked to an online data 

visualization platform, which is currently being shared with stakeholders and colleagues at 

Reclamation (USGS 2020). Data from the sonde from 2015 to the present are currently available 

at https://www.gcmrc.gov/discharge_qw_sediment/. Data for years before 2015 will be available 

on the site in the future (Deemer 2020). 
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Table 1.—List of the 27 primary monitoring stations for the water quality database (Vernieu 2015)

The GCMRC conducts discharge monitoring and additional water quality monitoring 

downstream from Lake Powell at 8 mainstem and 16 tributary gage sites for a variety of 

parameters including DO, turbidity, and suspended sediment concentrations (Figure 4 shows 

sites for Lees Ferry and those upstream). From the data collected, it has been determined 

that seasonal variations of DO at the penstocks of Lake Powell can impact the downstream 

Glen Canyon reach of the Colorado River (USGS 2020). 

CE-QUAL-W2 modeling to assist in the prediction of low DO events at Glen Canyon Dam is 

done through a DO module, which has been shown able to predict low DO events, but it does 

not consistently predict DO concentrations at penstock intake elevations accurately (Deemer 

2020). 
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Figure 4.—Yellow dots indicate sondes in the Glen Canyon Reach of the Colorado 

River and are labeled by river mile from Glen Canyon Dam (the red star indicates a 

thermistor string in Lake Powell, and the yellow star indicates the Wahweap sampling 

site (Deemer 2020). 
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5.1.1 Assessment of Current Dissolved Oxygen Monitoring Effectiveness 

at Lake Powell

CE-QUAL-W2 modeling to assist in the prediction of low DO events at Glen Canyon Dam is 

done through a DO module that has been shown able to predict low DO events with a mean 

accuracy of 1.15 mg/L, but it does not consistently predict DO concentrations at penstock intake 

elevations accurately (frequently in the metalimnion). This model is useful for long-term 

planning of dam management, but it currently lacks the resolution to accurately predict the 

length and magnitude of a DO event (Williams 2007). To increase the resolution of the current 

CE-QUAL-W2 model, a number of factors could be monitored better, including meteorological 

data (hourly is best):

• Shading influence on the reservoir

• Improved vertical monitoring resolution at the penstocks

• Improved records

• Predictive ability of incoming flows

• Any other modeled inputs for phosphorous or DO (Cole 2015)

6.0 Consideration of Downstream Resources

6.1 Forecasting Ability

The ability to forecast DO levels within a waterbody is directly tied to the ability to monitor and 

model the net processes that contribute and consume oxygen. The ability to mitigate low DO at 

the outlet of any reservoir is directly linked to the ability to predict when and to what magnitude 

low DO will occur. In Lake Powell, like other waterbodies, the primary sources of DO are 

photosynthesis of algae during the day, wind mixing of surface waters, and the inflow of oxygenrich waters. The primary processes that consume oxygen are biochemical oxygen demand, 

sediment oxygen demand, and respiration by algae at night. In turn, primary production, 

biochemical oxygen demand, and sediment oxygen demand are directly impacted by inflow 

volume, water temperature, nutrient availability, reservoir stratification, and circulation (Johnson 

1981). With a well-developed forecasting tool, the management of dam operations and any 

mitigation system can be optimized to ensure downstream water quality criteria are met without 

incurring excessive costs (Cooke 1989).

Generalized seasonal variation of DO is well documented at Lake Powell. The DO levels are 

highest in spring and early summer chiefly because, at this time of year, inflows are at their 

highest, bringing well-oxygenated water deep into the reservoir; primary productivity generates

oxygen during the day; mass algal die-offs have not begun; temperatures are moderate; and 

wind-induced mixing tends to be higher. During the late summer into fall, DO concentrations 

tend to be at their lowest mostly due to increased biological oxygen demand from mass algal dieoffs, lower inflows, higher temperatures, and stratification. Throughout the rest of the year into 
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spring, DO concentrations tend to increase as a result of the higher DO capacity of cold water 

and the natural mixing process created by the cold-water underflow and cooling of surface 

waters (Vernieu 2009).

Generalized daily variations have also been documented. In the tailwater of Glen Canyon Dam,

daily DO oscillations show a notable increase during the day and a decrease at night due to 

photosynthesis and respiration of the algal community (Vernieu 2009). The amplitude of daily 

DO changes at Lees Ferry, downstream from the dam, ranges from 0.5 to over 3 mg/L depending 

on the season, with the lowest fluctuations in winter when the algal community is least active 

(USGS 2017).

Beyond general seasonal and daily variations at Lake Powell, more specific DO variations occur 

under different conditions. For example, when reservoir elevations are low in years of high 

inflow, the inflows cut through delta sediments and resuspend organic matter and nutrients,

contributing to increased biochemical oxygen demand, which results in lower DO within the 

reservoir (Hering 2009). Similarly, in years of low inflows, the incoming water is typically 

warmer, which may increase primary production, leading to lower DO within the reservoir. 

These variables, among others, need to be monitored and modeled to accurately forecast low DO 

events at Lake Powell (USGS 2020). Data and the modeled predictions, with the exception of 

elevated water temperatures and nutrient concentrations at the penstock inlets, have not been 

in close agreement, particularly for DO (Williams 2007). Low DO events have also occurred

in Lake Powell near the Colorado River inflow through mechanisms that are still not fully 

understood. These events are suspected to be tied to elevated water temperatures in the river

(USGS 2020). 

Antecedent conditions may be used to predict low DO events in Glen Canyon Dam tailwaters

if a model cannot forecast precise DO concentrations at the outlet works. In fiscal year 2020,

monitoring capabilities were limited, reducing our ability to forecast low DO events through 

the CE-QUAL-W2 model. During this time, data from a subset of monitoring stations were

compared to previous low DO events, and the risk of a low DO event was determined to be low. 

This prediction was correct; the minimum DO recorded at the tailwaters was well above 6 mg/L 

(USGS 2020). However, this process only worked to predict general risk. Many low DO events 

have occurred during years when the reservoir water elevation was low and spring inflow high 

(Vernieu 2010). Low DO in Glen Canyon Dam tailwaters can also occur during years of low 

inflows or higher reservoir water elevations (Reclamation 2016). Additionally, even if low DO 

events at Glen Canyon Dam tailwaters only occurred during years of low reservoir elevation and 

high spring inflows, using only antecedent conditions would not be sufficient to predict the 

magnitude of a low DO event.

In the future, low DO events are predicted to become more frequent, highlighting the need to 

continue improving the forecasting ability of the predictive models. Climate-change driven 

variation in inflow, evapotranspiration, evaporation, and increased temperatures are all 

anticipated to increase the rate and magnitude of low DO events at Lake Powell (Reclamation 

2016). Additionally, reservoir elevations are also anticipated to be regularly below historical 

norms, which will increase the frequency and magnitude of low DO events (USGS 2020).
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6.2 Ecosystem Impacts of Low Dissolved Oxygen Releases 

from Lake Powell

Managing flows to avoid low DO events at Glen Canyon Dam is limited due to the 

implementation of the Modified Low Fluctuating Flows established in 1996 for Rainbow Trout 

recruitment and general ecosystem health downstream from the reservoir (USFWS 2016) 

and because the bypass tubes may only be used to avoid anticipated spills from Lake Powell 

(Reclamation 2016). To date, DO levels downstream from the reservoir have usually been below 

saturation, but the oxygen levels in the water typically do not drop low enough to significantly 

impact the aquatic ecosystem. There have been negative impacts at Glen Canyon Dam due to 

low DO events in the past, and climate change is anticipated to increase the frequency and 

magnitude of these events (USFWS 2016) partially because, as water temperatures increase 

due to climate change, biological oxygen demand will also increase, further reducing DO in 

Lake Powell waters (Runge 2011). 

6.2.1 Risk of Low Dissolved Oxygen Releases from Lake Powell

Low DO releases from Lake Powell are a risk to the ecosystem downstream from Glen Canyon 

Dam depending on how low the DO level is and how long the DO remains depressed in the 

waterway. Ideally, DO levels for fishes should remain from between 7 and 9 mg/L; levels below 

5 mg/L can cause chronic stress to fish species, and most fishes cannot survive when the DO 

level falls below 3 mg/L. The level of DO at the Glen Canyon Dam tailraces typically remains 

above 5 mg/L, but unintentional fishkills due to short periods of DO levels below 3.5 mg/L have 

been documented. While these events do not regularly occur downstream from the dam, the 

intensity, duration, and frequency of low DO in Lake Powell at Glen Canyon Dam have 

increased in recent years (Figure 5) (USGS 2020). 

Figure 5.—Historical DO concentration in Lake Powell at Glen Canyon Dam from 1991 to 2006 with 

elevation in feet on the x-axis and the penstock elevation displayed by the black box overlay. Below the 

DO concentration plot is a plot of the inflow from the Colorado River to Lake Powell as the red line and 

outflows through Glen Canyon Dam as the blue lines. As displayed here, low DO passing through the dam 

has not historically been an issue, but it is becoming more of a concern (Vernieu 2006). 
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The impact of low DO levels in waterways can affect the entire food chain. Benthic organisms 

are a significant food source for the fish community; when the benthic community is reduced 

by low DO events, fishes can become stressed if they do not find an alternate food source. 

Organisms that comprise the benthic community typically can tolerate a much lower DO level 

than fishes, but they have much less mobility to leave a low DO environment; this results in them 

being more susceptible to die-offs from localized areas of very low DO levels (McCormick 

1995).

6.2.2 Brown and Rainbow Trout Dissolved Oxygen Tolerance

Management and water quality released from Glen Canyon Dam can have a direct impact on 

fish communities downstream. The Rainbow Trout population increased from 1991 to 1997 

following the implementation of a steadier flow regime that resulted from the Modified Low 

Fluctuating Flows guidance established in 1996. However, populations declined from about the 

year 2000 to 2007 likely due to increased water temperatures, decreased DO, and lower flows. 

Following habitat improvement efforts at Glen Canyon Dam in 2008, Rainbow Trout 

populations improved through 2010 (Makinster 2011).

While DO levels at around 6.0 to 7.0 mg/L downstream from Glen Canyon Dam during 

lower DO months are typically acceptable for fish populations (USFWS 2016), even a small 

decrease in DO can significantly reduce habitat quality. Declines in Rainbow Trout downstream 

from Lake Powell in 2001 and 2007 have been attributed to a combination of elevated water 

temperatures and periodic DO deficiencies (Makinster 2011).

Recent declines in the abundance of fishes below Glen Canyon Dam have largely been attributed 

to both low DO and increased water temperatures (Makinster 2011). In 2005, a low DO/high 

temperature event coincided with much lower recruitment and growth in the Glen Canyon 

Rainbow Trout fishery (Korman 2012). In 2019, a plume of low DO water with elevated 

temperatures moved through Lake Powell and contributed to historically low concentrations 

of DO in the Grand Canyon Dam tailwaters. Low DO events tend to coincide with high 

temperature events, so it is difficult to separate the negative impacts of one from the other;

however, improving DO conditions during elevated temperature events would reduce one source 

of stress on fishes and benthic communities which, if mitigated, would likely increase fish 

abundance.

7.0 Mitigation Tools for Low Dissolved 

Oxygen

Mitigation methods for low DO releases from dams can widely be classified as either aeration 

or management solutions. Aeration is a process that increases the DO concentration in water, 

typically for the purpose of increasing water quality. This can be accomplished through 
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entraining a large amount of air in the form of bubbles to increase the air-water contact surface 

area for maximum oxygen transfer. This surface area may then be increased through either 

hydraulic or mechanical methods. 

Hydraulic methods of aeration use the potential energy of the hydraulic head to mix water. 

Common structures used for aeration include weirs, spillways, water jets, and closed conduit 

flow arrangements. Through these structures, similar amounts of air transfer that would typically 

occur over kilometers in a river can occur at a single site.

Mechanical methods of aeration may include the use of pumps, aeration lines, turbines, or other 

structures that use energy to actively mix oxygen into water (Tennessee Valley Authority [TVA] 

2021). Some of these methods include aeration weirs, artificial destratification, hypolimnetic 

oxygenation, and turbine aeration. Aeration weirs create a waterfall scenario, greatly increasing 

the uptake of oxygen by the water. Artificial destratification refers to the process of moving 

compressed air through perforated pipes located at the bottom of a water column to help to mix 

oxygen into the lower water strata. Hypolimnetic oxygenation increases DO in water with a pure 

oxygen distribution system that aerates water in the hypolimnion while preserving a lake’s 

thermal stratification. Turbine aeration mixes air with water inside of a hydropower dam at the 

turbines. Each of these methods have advantages and drawbacks. 

Dam management solutions include adjustments such as releasing varying amounts of water 

downstream at different times or releasing water from various water supply intakes and 

outlets (an example of adjusting the water supply intake could include releasing water 

from different strata of the water column, such as through a selective withdrawal intake) 

(Gelda 2007). 

DO mitigation methods are discussed below individually; however, they can also be used

in combination, which may increase the overall effectiveness and reduce collective

drawbacks. 

7.1 Aeration Mitigation

7.1.1 Aeration Weirs

Aeration weirs are hydraulic aeration structures that are placed downstream from a dam to 

aerate reservoir outlet waters. Similar to a much smaller dam being placed downstream from a 

larger dam, they increase water oxygenation and can help maintain a minimum tailwater flow 

(Figure 6). Although there are other methods to hydraulically aerate water, such as using a 

hydraulic jump, labyrinth weirs, and shuts, the low-head aeration weirs are typically better, and

they cost less to operate (Jaiswal 2019). Weir aeration is commonly used at fish hatcheries and 

water treatment plants to aerate large volumes of water, as the hydraulic head used for aeration is 

not as costly as using pumps (TVA 2021). 
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Figure 6.—Picture of an aerating weir in the downstream channel of the regulating dam in the 

Nam Kathang River (Descloux 2015). 

In general, weir aeration occurs as the water drops over it and forms a free jet, similar to a 

natural waterfall. Most of the oxygen transfer occurs during the breakup of the jet at the water 

pool’s surface and when the jets impact with the bottom of the pool. As such, the shape, size, 

and general structure of the weir itself, as well as the water pool, heavily factor into design 

considerations, as the design of a weir can significantly impact oxygen absorption efficiencies. 

For example, the shape of a weir defines the water jet shape, which strongly influences oxygen 

transfer efficiency. Efficiency is strongest with a triangular shape and lowest with a rectangular 

shape. Additionally, the idyllic tailwater depth at which the jet impacts it is dependent on the 

drop height and water discharge, wherein ideally air bubbles will penetrate to slightly less than 

the approximate maximum depth (Baylar 1999). Design standards for aeration of water at 

Reclamation facilities can be found in the guidance for constructing spillways and other outlet 

works (LaBoon 2014). These design standards consider the aeration needs of water passed 

downstream and inform development. Modeling of the aeration that occurs in the spillway of 

a dam may help predict aeration efficiency of a weir (Urban 2008). 

To date, there has been more success of reaerating water from a dam due to installing aeration 

weirs than with nearly any other aeration method (Long 1997). Continued design refinements 

have increased aeration efficiency. For example, in Laos, a weir made of hexagonal metallic 

structures with two consecutive falls has been highly efficient (Descloux 2015). Increases in 
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aeration have also been accomplished through other methods, such as modifying the weirs to 

resemble piano keys (Sangsefidi 2021). In addition to improvements that can be made to the 

structures themselves, improvements in DO monitoring methods and refinements in hydraulic 

modeling capabilities should also be pursued.

Although aeration weirs have been successful at reaerating water from a dam, installation and 

maintenance of an aeration weir at Glen Canyon Dam may be problematic. The steep walls of 

the canyon hinder access, and the design of the dam itself does not allow for easy installation 

of the large-scale aeration weirs required to be effective. If these challenges were overcome, 

aeration weirs could effectively increase downstream DO with minimal operating costs at this 

dam.

7.1.2 Artificial Destratification

Artificial destratification is typically used in smaller reservoirs with a strong and undesired 

stratification to help “turn” the manmade lake. While this method can effectively increase DO in 

the hypolimnion, mixing of the reservoir brings higher nutrient loads and temperatures into the 

epilimnion. This may have detrimental impacts on large, older reservoirs, such as Lake Powell,

which pass water downstream from lower in the water column strata (Brown & Caldwell, Inc. 

1995).

7.1.3 Hypolimnetic Oxygenation

Hypolimnetic oxygenation aerates the hypolimnion while preserving thermal stratification by 

oxygenating the hypolimnion using pure oxygen gas. The reduced thermal mixing reduces 

not only cyanobacteria growth but also other issues related to mixing a reservoir. Hypolimnetic 

oxygenation may be accomplished through side stream oxygenation, bubble plume oxygenation, 

and/or submerged contact chamber systems.

7.1.4 Side Stream Oxygenation

Side stream oxygenation systems (Figure 7) pump hypolimnetic water to the surface, inject the 

water with oxygen, then discharge the water back into the hypolimnion. This system has high 

energy costs associated with the continued pumping of water and maintaining a pressurized 

chamber; as such, it is not often used in deep reservoirs. Side stream oxygenation has more 

benefits for shallow lakes and streams, and it does not require significant structure installation at 

the reservoir bottom (Gerling 2014).
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Figure 7.—Schematic of a side stream oxygenation system showing hypolimnetic water drawn to the 

surface where it is oxygenated then redistributed at the reservoir bottom (Gerling 2014). 

7.1.5 Bubble Plume Oxygenation

While a side stream oxygenation system introduces oxygen to water above the surface, bubble 

plume oxygenation systems use a group of oxygen diffusers located at a lake’s bottom and an 

oxygen source located above the water’s surface. This system is designed so the oxygen plume 

disperses below the thermocline (Figure 8). Bubble plume oxygenation was developed in the 

1980s and has been successfully used in several large reservoirs since its development (Brown & 

Caldwell, Inc. 1995). Advancements have included using a more spread-out diffuser system and 

finer oxygen bubbles to ensure the bubbles remain below the thermocline to encourage better 

dissolution of oxygen into the water.

Of the many options for mechanical aeration, bubble plume oxygenation through air diffusion 

lines on the bottom of a reservoir has proven to be one of the most popular methods. Like 

aeration weirs, bubble plume oxygenation systems can be found at fisheries and water treatment 

plants, as they provide a reliable and cost-effective method of oxygenating large volumes of 

water (Al-Ahmady 2006). 

The modern technology of aerating the hypolimnion of waterbodies is based on what was 

developed in the early 1980s in Switzerland in an attempt to inhibit phosphorous loading in deep 

lakes (Gachter 1998). It has been employed at many locations ever since for many different 

aeration purposes. One drawback of the bubble plume oxygenation system is that it has trouble 

maintaining a well-oxygenated sediment water interface because, in some waterbodies, most of 

the oxygen is concentrated in the upper levels of the hypolimnion (Mobley 2006). This may not 

be a negative at Lake Powell, where the penstock intakes are at an elevation typically near the 

upper level of the hypolimnion. 
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Figure 8.—Schematic view of a bubble plume diffuser and turbine withdrawal (Mobley 2006). 

At Douglas Dam in Tennessee, a diffuse deep-water oxygenation system that uses liquid oxygen 

and an array of 16 diffuser frames to aerate almost 4.5 acres of water directly upstream of the 

dam is used. The water depth at the dam where the water is being aerated is about 125 feet, and 

the total impoundment of the dam is approximately 1,408,000 acre-feet of water. This system has 

effectively improved the downstream DO of water released from Douglas Dam, with minimal 

upswelling or mixing of the metalimnion. The system’s average daily use of pure oxygen 

exceeds 5 tons/day during the highest use time of year, as it was designed as a “topping off” 

system to increase DO. A surface water pump is used to provide a baseline for DO improvement 

(Mobley 1995). 

Another bubble plume oxygenation system is operated at Amisk Lake in Canada to increase DO 

in the hypolimnion and to remediate conditions caused by high internal phosphorous loading. 

The system is operated year round, with average oxygen injection rates up to 1.4 tons/day during 

the summer months and up to 0.8 tons/day in winter. These injection rates have improved 

summer DO concentrations in the hypolimnion from an average of 1.0 to 4.6 mg/L, and they 

have also reduced phosphorous concentrations in the waterbody near the bubblers (Prepas 1997). 

Even though aeration systems are relatively well established as a method to enhance DO in the 

hypolimnion of waterbodies, they are not always a suitable solution. For example, in 2004, the 

U.S. Army Corps of Engineers deployed an aeration system at Willow Creek Lake to increase 
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hypolimnetic DO. When the system was installed and tested, it destratified the reservoir,

resulting in an increased density and duration of harmful algal blooms. Due to these issues, 

use of the system was discontinued in 2008 (U.S. Army Corps of Engineers 2019).

There are plentiful case studies on bubble plume aeration, as it is one of the more established 

methods to aerate a waterbody upstream of a dam. The TVA has been one of the leaders in this 

field for decades. Initially, they employed bubble plume aeration to supplement other DO 

enhancement methods, then it was used as a stand-alone enhancement method when less 

expensive options were not viable. The TVA came to use bubble plume aeration as a stand-alone 

enhancement exclusively more often, as its advantages became more apparent and justified the 

higher costs (Moore 2015). The TVA developed an early set of case studies on aeration lines

used to increase DO in reservoirs, including an analysis of their performance at six TVA Dams.

Although dated, this analysis is a valuable reference; it helps us understand the details of design 

challenges associated with this aeration method, as it details the basics of system functioning 

(Mobley 1997).

7.1.6 Speece Cones

The term “Speece cone” is a common name given to a low-pressure downflow bubble contact 

chamber that functions to saturate water with air (Figure 9). Speece cones can be deployed 

above water, similar to side stream oxygenation systems, but with low pressure. However, for 

the purposes of hypolimnetic aeration of large waterbodies, they are typically employed at the 

bottom of the reservoir as submerged contact chamber oxygenation systems, which reduces 

pumping expenses (Horne 2019). The conical chamber functions as a downflow bubble contact 

chamber used for high-efficiency, low-pressure oxygen transfer. The chamber itself has no 

moving parts; maintenance is limited to pumps, diffusers, and intakes (CH2M Hill 2013).

Through deploying a Speece cone mounted to the bottom of a lake, a submerged pump draws 

water from the hypolimnion to the top of the cone, where it mixes with oxygen supplied from an 

onshore facility. A common variation of this type of system is often referred to as a Speece cone 

oxygenation system. This type of system has been successful in aerating water in large reservoirs,

with less chance of turning the thermocline than bubble plume systems, and the oxygenated water 

has a greater chance of remaining toward the bottom of the hypolimnion (Horne 2019).

Speece cones have been used at a wide range of locations for both wastewater treatment as well 

as hypolimnetic oxygenation, and a wide range of case studies have been developed on their 

design. In addition to Indian Creek Reservoir discussed above, one well documented location is 

the Camanche Reservoir wherein a large, submerged contact chamber oxygenation system was 

employed successfully long-term as the only oxygenating system in the reservoir. The reservoir 

impounds up to 417,000 acre-feet and has an approximate depth at dam of up to 60 feet. The 

system is designed to provide up to 8 tons/day of oxygen and has successfully maintained DO 

levels above 5 mg/L at the dam (Brown & Caldwell, Inc. 1995).
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Figure 9.—Schematic of a Speece cone oxygenation system (Brown & Caldwell, Inc. 1995). 

7.1.7 Turbine Aeration 

Turbines can be modified with air injection systems to mix oxygen with water inside a 

hydropower dam. These systems can be an appealing option to increase DO in waters 

downstream from a hydropower dam, as maintenance costs are low, the amount of oxygen 

used is less (if injecting pure oxygen) than in hypolimnetic oxygenation systems, and the 

aeration effects can be more controllable than with other methods (Key 2009). 

Turbine aeration systems can be designed in a variety of ways. For example, large-scale 

design considerations include where aeration occurs within turbines (central, peripheral, and 

distributed) (Figure 10). Each of these locations of air injection impact the efficiency of the 

aeration system at different portions of the turbine’s operational range (Rohland 2010). In 

addition to air injection location within the turbine itself, there are a significant number of other 

design considerations that can impact the efficiency of turbine aeration. Fortunately, there are 

plentiful case studies: in 2017, 178 aerating turbines at 58 hydropower plants existed in the 

United States, with 137 of these being vertical francis turbines with a capacity over 5 megawatts, 

similar to those at Glen Canyon Dam (March 2017). 

An alternative method to air injection in turbines involves using a draft tube to encourage air 

mixing in the turbines through a passive air intake. This method uses the pressure change as 

water flows over the turbine blades to draw air through the draft tube to mix with the water. 

This has been attempted at Canyon Ferry Reservoir, with multiple modifications, initially 

without success. With initial modifications, sufficient air was not drawn into the draft tube 

passively. However, after installing a blower to force air through the draft tube, acceptable DO 

levels were reached, but only when the turbines were running at a reduced load (Reclamation 

2007). 
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Figure 10.—Schematic representing three methods for an auto-venting turbine, including central 

(blue), distributed (green), and peripheral (yellow) (Rholand 2009). 

Other experiments have been successful in increasing the DO of water passed through a turbine 

without requiring forced air. For example, at Deer Creek Reservoir in 1992 through 1994, 

passive aeration was able to improve DO levels from about 1.7 to 2.7 mg/L. The primary cost 

was the loss of power generated due to running the turbines less efficiently and an increased 

tailwater level (Wahl 1995). 

In addition to the above methods of passive turbine aeration, “rough zone” operation may be 

conducted wherein a turbine is operated to produce an increased vacuum in order to draw more 

air through draft tubes, vacuum breaker systems, or snorkel tubes. Operating a turbine in the 

rough zone induces cavitation which, in turn, increases the vacuum inside a turbine. During 

cavitation, air is mixed with water, which increases DO levels, but it may damage turbines, 

decreasing power grid reliability and increasing maintenance costs. In theory, rough zone 

operation is possible without damaging turbines, but it does require operation at reduced 

efficiency, which decreases the power generated, and it may not be consistent within a dam 

managers statutory authority. 
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7.1.8 Penstock Intake Aeration

A penstock aeration system injects either pure oxygen or natural air at point sources near 

the penstock inlet (Figure 11) so bubbles are swept along through the penstock, which 

oxygenates water released from the dam. These systems are best applied to dams with long, 

deep penstocks that can provide sufficient time to increase oxygen transfer and have a 

minimum number of penstock inlet locations that need to be outfitted with aeration equipment 

(Reservoir Environmental Management, Inc., and HDR, Inc. 2010). The penstocks at Glen 

Canyon Dam are 500-foot long, 15-foot-diameter steel tubes that carry water from the reservoir 

to the turbines. They should provide sufficient surface area and length for aeration (Vernieu 

2009). 

Figure 11.—Upstream face of Glen Canyon Dam circa 1964 showing the penstocks. 

Here the water level is below the penstocks but above the dam outlets (Bureau of 

Reclamation/A.E. Turner). 

Similar to turbine aeration systems, one disadvantage is that penstock aeration systems can only 

increase oxygen during hydropower operation. An additional disadvantage is that, compared 

to hypolimnetic aeration and turbine aeration, controlling the system can be more difficult 

because, at lower penstock flows or at higher volumes of air injection, much of the air may 

not be captured by the penstock intake. This limits how many low DO events can be mitigated 

(Reservoir Environmental Management, Inc., and HDR, Inc. 2010). 
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7.2 Management Mitigation

7.2.1 Selective Withdrawal Structures

Selective withdrawal structures allow project operators to release water from several levels 

(Figure 12) within a reservoir. They may release warmer water, which carries more oxygen, or 

colder, less oxygen-rich waters (Sherman 2001). Reclamation has multiple case studies for

reference to assist in understanding the benefits and limitations of a selective withdrawal system. 

These structures were developed primarily to control temperature releases, but they also have a 

documented ability to help control DO concentrations of released waters (Svodoba 2019). 

Figure 12.—Schematic of a selective withdrawal structure demonstrating the ability 

to remove water from a targeted strata within the water column (Sherman 2001). 

The powerplant penstock intakes at Glen Canyon Dam provide little option for controlling 

the water level that is passed through the penstocks. The penstocks have an average 100-footthick withdrawal zone and a near-field acceleration zone of about 100 feet from the dam face 

depending on stratification, the wind, the withdrawal rate, and other factors (Vermeyen 2011). 

Reclamation has modeled a multilevel intake that withdraws water through an opening cut into 

the top of an existing trash-rack structure to allow warmer, higher oxygen water to flow into the 

turbines and downstream, which could help improve downstream water quality. However, due 

to cost restrictions and few anticipated benefits, the project has not moved forward (Vermeyen 

1999). 
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7.2.2 High Flow Events

Water management solutions at Glen Canyon Dam for increasing downstream DO at 

Lake Powell are currently limited to high flow events through the outlet works, which bypass 

the power turbines. While high flow events do effectively increase oxygen levels below the dam, 

the benefits quickly diminish at the return to normal flows (Reclamation 2016). Another limit to 

this management option is that the bypass tubes may only be used to avoid anticipated spills 

from Lake Powell, and the costs associated with any release that bypasses the powerplant for 

reasons other than to avoid a spill must be paid for by the Glen Canyon Dam Adaptive 

Management Program (Reclamation 2016) partially because, at Glen Canyon Dam, the 

electricity sales are the only direct form of revenue; the reservoir’s waters are not sold 

(Thompson 2022).

An additional limitation of management solutions to low DO events at Glen Canyon Dam is that 

the outlets and spillways were never designed to be used long term. The intent was for all of the 

water routinely flowing from Glen Canyon Dam to go through the eight penstocks to generate 

electricity. If the dam’s outlet works were to be used regularly to bypass water around the 

penstocks, significant redesign of the bypass outlet works would likely be necessary to ensure 

they could safely handle the increased use. For now, the water quality of Lake Powell at its 

penstocks typically defines the water quality of Glen Canyon Dam releases (USGS 2020).

7.3 Feasibility of Using Dissolved Oxygen Mitigation Tools 

at Glen Canyon Dam

Regardless of the method used to mitigate low DO events downstream from Glen Canyon Dam,

it will take significant engineering analyses to determine what process is the most feasible and 

economical. While it is beyond the scope of this report to recommend a specific technology for 

increasing DO, it is our aim to provide a brief overview of the state of technology and how it 

may be applied at the dam. Below we provide a summary of the overall feasibility of using 

various DO mitigation tools at Glen Canyon Dam.

Upstream changes that might reduce organic loads have had relatively little success because,

unless contaminant sources are point sources, such as effluent streams, manufacturing plants,

or something similar, it is difficult to reduce the amount of organic matter entering a reservoir. 

Much of the organic matter that flows downstream into Lake Powell comes from sources that are 

spread over a very wide area; it may be from anywhere in the very large upstream watershed. 

With an increasing watershed size, the problem of limiting inputs grows exponentially.

Of the methods discussed above to increase DO below Glen Canyon Dam, two methods have 

a high potential to effectively mitigate low DO events with minimum drawbacks: turbine 

aeration and hypolimnetic aeration. Both have a reasonably well-developed design and are 

efficient at controlling the DO in waters passed through large dams.
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Turbine aeration is an appealing option to increase DO levels. It allows for significant control 

over the oxygenation of released waters, as oxygen input to water passing through the dam 

can be immediately controlled. Turbine aeration also uses less oxygen, if pure oxygen injection 

is used, than in hypolimnetic oxygenation, as only the water passing through the dam is 

oxygenated. Additionally, the components of this system are easy to access and maintain 

because they are not at the bottom of the reservoir. However, this method can require significant 

alteration to the turbines at a high expense, and some variations of turbine aeration systems 

decrease turbine efficiency. Alternatively, some variation of rough zone operation can be easily 

implemented, though at a cost to hydropower generation. Running in the rough zone may or 

may not produce much benefit, as the amount of air used will depend on how well balanced the 

turbines can remain under this scenario.

Hypolimnetic aeration consists of a broad class of methods, as discussed above, but the most 

applicable to increasing downstream water quality at Glen Canyon Dam are bubble plume 

aeration and Speece cones. The primary difference between the two is where water oxygenation 

occurs. In Speece cones, oxygenation occurs in a chamber, and in bubble plume aeration, 

oxygenation occurs in an open waterbody. Both systems have proven to be effective at aerating a 

reservoir’s hypolimnion upstream of a dam and, in turn, have increased the DO of water passed 

through the dam. One advantage of hypolimnetic aeration is that it does not require any direct 

modification to the dam or any of its facilities, although it does use more oxygen than turbine 

aeration. It also increases DO within the reservoir near the dam, which may benefit the aquatic 

ecosystem.

The cost of using pure oxygen can be high in either turbine or hypolimnetic aeration systems, but 

neither should not be discounted. In order to use pure oxygen for aeration, either an oxygen 

generator must be installed onsite, or oxygen must be delivered, both of which are associated 

with a significant cost. Many hypolimnetic aeration systems in use today have moved toward 

onsite oxygen generators for both reliability and ensuring availability of oxygen when needed. 

The advantages of using pure oxygen instead of atmospheric air include higher solubility, higher 

system transfer efficiencies, reduced size of mechanical devices due to lower volumes needed,

and lower recirculation rates, all of which allow for maintenance of higher DO levels in 

oxygenated waters and help to not disturb the metalimnion during hypolimnetic aeration.

In regard to oxygen transfer efficiency alone, pure oxygen has significant advantages: transfer 

efficiencies of 10 percent for air and 20–30 percent for oxygen inline diffusers. Turbine aeration 

has transfer efficiencies of 20–40 percent for air and 60–90 percent for oxygen (Herrmann-Heber 

2021). These differences in efficiencies arise because air itself is only 21 percent oxygen; 

therefore, a much higher volume is needed to achieve the same results. The transfer efficiency 

of oxygen is partially driven from the saturation deficit, meaning the higher the target DO 

concentration, the more oxygen will be required. As the saturation limit is approached, there are 

diminishing returns of adding more oxygen the closer we get to saturation. The DO saturation 

limit of water is also regulated by water temperature, salt content, and depth. Colder, deeper 

fresh water has a higher saturation limit than warmer, saltier, shallow water (Al-Ahmady 2006).
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Assuming that a 100-percent transfer efficiency is attainable, and given that Glen Canyon

typically releases at a rate of 8–10,000 cubic feet per second (ft3/s) on average during months

low DO is likely to occur within the reservoir, there would be approximately 22 tons of pure 

oxygen/day required to achieve a 2 mg/L increase of DO at a discharge of 8,000 ft3/s. As

100-percent oxygen transfer is not possible, the real amount of oxygen used would be higher, 

and that amount of oxygen should serve as a starting point for any feasibility study at a facility 

the size of Glen Canyon Dam under normal flow conditions.

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8.0 References

Al-Ahmady, K. 2006. Analysis of Oxygen Transfer Performance on Sub-Surface Aeration 

Systems. International Journal of Environmental Research and Public Health 3(3):301–

308.

Baylar, A.B. 1999. Study of Aeration Efficiency at Weirs. Turkish Journal of Engineering 

Environmental Science 24:255–264.

Bergsohn, P. 2015. Indian Creek Reservoir TMDL Progress Report for 2014. South Tahoe 

Public Utility District.

Beutel, M.H. 1999. A Review of the Effects of Hypolimnetic Oxygenation on Lake and 

Reservoir Water Quality. Jounral of Lake and Reservoir Management 15(4):285–297.

Bevelhimer, M C. 2006. Assessment of Dissolved Oxygen Mitigation at Hydropower Dams 

Using an Integrated Hydrodynamic/Water Quality/Fish Growth Model. Oak Ridge, 

Tennessee: Department of Energy.

Bolke, E. 1979. Dissolved-Oxygen Depletion and Other Effects of Storing Water in Flaming 

Gorge Reservoir, Wyoming and Utah. Washington, D.C.: U.S. Geological Survey.

Brown & Caldwell, Inc. 1995. Camanche Reservoir Oxygenation Demonstration System: Report 

on Operation, 1993/94. Oakland, California: Alex Horne Associates & Biosystems 

Analysis, Inc. for East Bay Municipal Utility District.

Bureau of Reclamation. 2002. Interim Comprehensive Basin Operating Plan. U.S. Department of 

the Interior, Bureau of Reclamation.

_____. 2007. Canyon Ferry Dissolved Oxygen System Presentation. Bureau of Reclamation, 

Denver, Colorado.

_____. 2016. Glen Canyon Dam Long-Term Experimental and Management Plan. Bureau of 

Reclamation, Salt Lake City, Utah.

_____. 2016. Record of Decision for the Glen Canyon Dam Long-Term Experimental and 

Management Plan Final Environmental Impact Statement. U.S. Department of the 

Interior, Bureau of Reclamation.

_____. 2022. Yakima Project. Bureau of Reclamation Projects and Facilities.

https://www.usbr.gov/projects/index.php?id=400
Technical Report No. ENV-2022-61

Low Dissolved Oxygen in Releases: Current State-of-Practice

30

Carroll, J.J. 2001. Bureau of Reclamation Columbia River Pump Exchange Project: Potential 

Water Quality Impacts on the Lower Yakima River. Olympia, WA: Washington State 

Department of Ecology.

California Water Board (CAWB) CAWB-R1. 2010. Action Plan for the Klamath River Total 

Maximum Daily Loads. Final Klamath River TMDL Action Plan and Basin 

Plan.California Water Boards North Coast - R1. September.

CH2M Hill. 2013. Assessment of Technologies for Dissolved Oxygen Improvement in 

J.C. Boyle Reservoir, Final Report. Portland, Oregon: PacifiCorp Energy.

Cole, T.W. 2015. CE-QUAL-W2: A Two-Dimensional, Laterally Averaged, Hydrodynamic and 

Water Quality Model, Version 3.72. Portland State University, Department of Civil and 

Environmental Engineering.

Cooke, D.K. 1989. Water Quality Management for Reservoirs and Tailwaters, Report 1: InReservoir Water Quality Management Techniques. Vicksburg, Mississippi: U.S. Army 

Corps of Engineers, Waterways Experiment Station.

Dadoly, J.M. 2010. Malheur River Basin Total Maximum Daily Load (TMDL) and Water 

Quality Management Plan (WQMP). DEQ 10-WQ-023, State of Oregon Department of 

Envrionmental Quality, Portland.

Deemer, B. 2020. Metalimnion Low Dissolved Oxygen Events in Lake Powell and Their 

Transport Downstream from Glen Canyon Dam. U.S. Geological Survey, Grand Canyon 

Monitoring and Research Center, Southwest Biological Center, Flagstaff, Arizona.

pp. 1–21.

Descloux, S.C. 2015. Efficiency of the Nam Theun 2 hydraulic structures on water aeration and 

methane degassing. Hydroecological Applications, 24.

Gachter, R.W. 1998. Ten years of artificial mixing and oxygenation: no effect on the 

internal phosphorous loading of two eutrophic lakes. Environmental Science and 

Technology 32:3659–3665.

Gelda, R.K. and S.W. Effler. 2007. Simulation of operations and water quality performance of 

reservoir multilevel intake configurations. Journal of Water Resources Planning and 

Management 133(1). January.

Gerling, A.B. 2014. First report of the successful operation of a side stream supersaturation 

hypolimnetic oxygenation system in a eutrophic, shallow reservoir. Water 

Research 67:129–143.
Technical Report No. ENV-2022-61

Low Dissolved Oxygen in Releases: Current State-of-Practice

31

Hering, J.W. and R.A. Wildman, Jr. 2009. A Study of the Dynamincs of Phosphorous Associated 

with Suspended and Deposited Sediments in the Colorado River Delta, Lake Powell, 

Utah. Bureau of Reclamation, Salt Lake City, Utah.

Herrmann-Heber, R. R. 2021. Experimental Oxygen Mass Transfer Study of Micro-Perforated 

Diffusers. Energies 14:7268.

Hiebert, S. 1999. Limnological Surveys of Five Reservoirs in the Upper Yakima Basin, 

Washington. Bureau of Reclamation, Denver, Colorado.

Higgins, J.B. 1999. Overview of Reservoir Release Improvements at 20 TVA Dams. Tennessee 

Valley Authority, Knoxville, Tennessee.

Horne, A.J. 2019. Hypolimnetic oxygenation 2: oxygen dynamics in a large reservoir with 

submerged down-flow contact oxygenation (Speece cone). Lake and Reservoir 

Management 35:3:323–337.

Idaho Department of Environmental Quality. 2001. Indian Creek Subbasin Assessment. Idaho 

Department of Environmental Quality, December.

Jaiswal, A.G. 2019. Aeration Through WeirsA Critical Review. In: A. Agnihotri, K. Reddy, and 

A. Bansal (editors). Sustainable Engineering. Lecture Notes in Civil Engineering, Vol 30. 

pp. 187–200.Springer, Singapore.

https://doi.org/10.1007/978-981-13-6717-5_19

Johnson, N.P. 1981. Oxygen Depleted Waters: Origin and Distribution in Lake Powell, Utah.

New York: American Society of Civil Engineers.

Klamath Basin Restoration Agreement. 2010. Klamath Basin Restoration Agreement for the 

Sustainability of Public and Trust Resources and Affected Communities. February 18.

https://klamathrenewal.org/wp-content/uploads/2020/07/Klamath-Basin-RestorationAgreement-2-18-10.pdf

Key, T. 2009. Hydropower Technology Roundup Report, Technology on Aerating Turbines, 

1017966 Technical Update. Electric Power Research Institute, Palo Alto, California.

Korman, J.M. 2012. Estimating Recruitment Dynamics and Movement of Rainbow Trout 

(Oncorhynchus mykiss) in the Colorado River in Grand Canyon using an Integrated 

Assessment Model. Canadian Journal of Fisheries and Aquatic Sciences 69(11):1827–

1849.

LaBoon, J.M. 2014. Design Standards No.14, “Appurtant Structures for Dams (Spillways and 

Outlet Works).” Bureau of Reclamation, Denver, Colorado.
Technical Report No. ENV-2022-61

Low Dissolved Oxygen in Releases: Current State-of-Practice

32

Long, K.N., J.M. Nestler, and J.C. Fischenich. 1997. Survey of Habitat-Related Channel 

Features and Structures in Tailwaters, EL-97-6. U.S. Army Corps of Engineers,

Vicksburk, Mississippi.

Makinster, A.P. 2011. Status and Trends of the Rainbow Trout Population in the Lees Ferry 

Reach of the Colorado River Downstream from Glen Canyon Dam, Arizona, 1991–2009.

Scientific Investigations Report 2011-5015. U.S. Geological Survey, Reston, Virginia.

Malheur Watershed Council. 2019. Final Report for Oregon Watershed Enhancement Board 

Grant #216-5043, Monitoring the Malheur. Oregon State University, Ontario.

March, P.J. 2017. Industry Experience with Aerating Turbines. Doylestown, Pennsylvania: 

Hydro Performance Processes, Inc.

McCaughey, B.C. 2020. Water Quality Monitoring, Hoopa Valley Tribe WY, 2019. Hoopa 

Valley Land Management Tribal Enivronmental Protection Agency, Hoopa, California.

McCormick, M. 1995. Fish feeding on mobile benthic invertebrates: influence of spatial 

variability in habitat sssociations. Marine Biology 121:627–637.

Mobley, M. 1997. TVA Reservoir Aeration Diffuser System. Tennessee Valley Authority, 

Norris, Tennessee.

Mobley, M.B. 1995. Widespread oxygen bubbles to improve reservoir releases. Lake and 

Reservoir Management 11(3):231–234.

Mobley, M.H. 2006. Diffuser System Modeling and Design for Dissolved Oxygen Enhancement 

of Reservoirs and Releases. Mobley Engineering, Inc., Norris, Tennessee.

Moore, B.M., M. Mobley, J. Little, B. Kortmann, and P. Gantzer. 2015. Aeration and 

Oxygenation Methods for Stratified Lakes and Reservoirs. North American Lake 

Management Society, Lakeline Vol 29.

National Oceanic and Atmospheric Administration. 2018. What is eutrophication? Retrieved 

from National Ocean Service, National Oceanic and Atmospheric Admisitration, 

U.S. Department of Commerce.

https://oceanservice.noaa.gov/facts/eutrophication.html

Oregon Department of Environmental Quality. 2010. Fact Sheet: Reducing Water Pollution in 

the Malheur River Basin and Middle Snake-Payete Subbasin. State of Oregon 

Department of Environmental Quality, Pendleton.

PacificCorp. 2018. Klamath Hydroelectric Settlement Agreement Implementation Report.

Portland, Oregon: PacifiCorp.
Technical Report No. ENV-2022-61

Low Dissolved Oxygen in Releases: Current State-of-Practice

33

Pickett, P. 2016. Yakima River Preliminary Assessment of Temperature, Dissolved Oxygen, and 

PH. Washington State Department of Ecology, Olympia.

Prepas, E.B. 1997. Effects of hypolimnetic oxygenation on water quality in Amisk Lake, 

Alberta, a deep, eutrophic lake with high internal phosphorous loading rates. Canadian 

Journal of Fisheries and Aquatic Sciences 54(9).

Reclamation (see Bureau of Reclamation).

Reservoir Environmental Management, Inc., and HDR, Inc. 2010. Long Lake HED Phase II 

Aeration Modeling Assessment of Alternatives. Prepared for Avista Corporation by 

Reservoir Environmental Management, Inc., Chattanooga, Tennessee, and HDR, Inc., 

Bellevue, Washington. July.

Rholand, K.F. 2009. Aerating turbines for Duke Energy’s new bridgewater powerhouse.

Hydro Review 29:58–64.

Rohland, K.M. and J.C. Sigmon. 2008. “Aeration Solutions for New Hydro — The Bridgewater 

Project,” HydroVision 2008 Technical Papers CD-Rom, HCI Publications, Kansas City, 

Missouri.

Rose, B.P. and M.G. Mesa. 2006. Bull Trout Forage Investigations in Beulah Reservoir 

Oregon – Annual Report for 2006. Open-File Report 2009-1036. U.S. Geological Survey.

38 p.

Runge, M.B. 2011. Non-Native Fish Control below Glen Canyon Dam – Report from a 

Structured Decision-Making Project. U.S. Geological Survey, Laurel, Maryland.

Sangsefidi, Y.T.-D. 2021. Hydrodynamics and Free-Flow Characteristics of Piano Key Weirs 

with Different Plan Shapes. Water (13)15.

Sherman, B. 2001. Scoping Options for Mitigating Cold Water Discharges from Dams.

Agriculture, Fisheries and Forestry – Australia.

Svodoba, C. 2019. Review of Temperature Control Options for Reservoir Release Flows. Bureau 

of Reclamation, Denver, Colorado.

Thompson, J. 2022. Challenge at Glen Canyon, What’s at Stake in a Shrinking Lake Powell. The 

Land Desk. 10 p. April 20.

Tennessee Valley Authority (TVA). 2021. Boosting Oxygen in the Tennessee Valley Tailwaters.

Tennessee Valley Authority, Knoxville, Tennessee.

TVA (see Tennesee Valley Authority).
Technical Report No. ENV-2022-61

Low Dissolved Oxygen in Releases: Current State-of-Practice

34

Urban, A.G. 2008. Modeling total dissolved gas concentration downstream from spillways.

Journal of Hydraulic Engineering 134(5):550–561.

Urmos-Berry, E.N. 2019. Quality Assurance Project Plan – Upper Yakima Basin Water Quality 

Monitoring for Aquatic Life Parameters: Water Temperature, Dissolved Oxygen, and pH.

Washington State Department of Ecology, Olympia.

U.S. Army Corps of Engineers. 2019. Long-Term Release of Additional 1,000 Acre-Feet 

(Totaling 3,500 Acre-Feet) Supplemental Environmental Assessment to the Long-Term 

Withdrawal of Irrigation Water Willow Creek Lake, Morrow County, Oregon, 

Environmental Assessment, March 2008. U.S. Army Corps of Engineers.

United States Department of Energy. 2016. Hydropower Vision – A New Chapter for America’s 

1st Renewable Electricity Source. U.S. Department of Energy, Springfield, Virginia.

U.S. Fish and Wildlife Service (USFWS). 2016. Biological Opinion for the Glen Canyon 

Canyon Dam Long-Term Experimental and Management Plan, Coconino County, 

Arizona. U.S. Fish and Wildlife Service. November 28.

U.S. Geological Survey (USGS). 2017. Glen Canyon Dam Adaptive Management Program 

Triennial Budget and Work Plan – Fiscal Years 2018–2020. U.S. Geological Survey, 

Bureau of Reclamation.

_____. 2018. Klamath River Basin Water-Quality Data. U.S. Geological Survey, Portland, 

Oregon.

_____. 2020. Fiscal Year 2020 Annual Project Report to the Glen Canyon Dam Adaptive 

Management Program. U.S. Geological Survey-Grand Canyon Monitoring and Research 

Center, Flagstaff, Arizona.

USFWS (see U.S. Fish and Wildlife Service).

USGS (see U.S. Geological Survey).

Vermeyen, T. 1999. Glen Canyon Dam Multi-Level Intake Structure Hydraulic Model Study.

Bureau of Reclamation, Denver, Colorado.

_____. 2011. Glen Canyon Dam Penstock Withdrawal Characteristics, 2007–2008, HL-2011-02. 

Bureau of Reclamation, Denver, Colorado.

Vernieu. 2006. Update on Water Quality of Lake Powell and Glen Canyon Dam Releases.

U.S. Geological Survey, Southwest Biological Science Center-Grand Canyon Monitoring 

and Research Center, Flagstaff, Arizona.
Technical Report No. ENV-2022-61

Low Dissolved Oxygen in Releases: Current State-of-Practice

35

Vernieu, W. 2009. Historical Physical and Chemical Data for Water in Lake Powell and from 

Glen Canyon Dam Releases, Utah-Arizona, 1964–2013. U.S. Geological Survey, Reston, 

Virgina.

_____. 2010. Effects of Drought on Water Quality of Lake Powell and Glen Canyon Dam 

Releases. Colorado River Commissions of Nevada Implications of Lower Lake Levels. 

U.S. Geological Survey, Reston, Virgina. 40 p.

_____. 2015. Biological Data for Water in Lake Powell and From Glen Canyon Dam Releases, 

Utah and Arizona, 1990–2009. U.S. Geological Survey Data Series 959. U.S. Geological 

Survey, Reston, Virgina.

Wahl, T. 1995. Aerating Powerplant Flows to Improve Water Quality. Bureau of Reclamation, 

Denver, Colorado.

Warm Springs Hydro, LLC. 2013. Warm Springs Dam Fish Passage Waiver Application.

Warmsprings Irrigation District, Vale, Oregon.

Williams, N. 2007. Modeling Dissolved Oxygen in Lake Powell using CE-QUAL-W2. Brigham 

Young University, Provo, Utah.

Wise, D.Z. 2009. Assessment of Eutrophication in the Lower Yakima River Basin, Washington, 

2004–07. U.S. Geological Survey. Reston, Virginia.

Zedonis, P. 2001. Empirical and Theoretical Influences of Pulse Flow from Lewiston Dam on 

Water Temperature and Dissolved Oxygen of the Lower Klamath River. U.S. Fish and 

Wildlife Service, Arcata, California.