Arizona Game and Fish Department

Major Conclusions from Research to Date

Humpback chub

 e USGS has developed and used a computer model 

to assess the Grand Canyon humpback chub population 

status and trends from 1989 to 2008. Reproductively 

mature humpback chub (4 years old and older) appear 

to have decreased from 1989 to about 2001, when 

the population stabilized around 5,000 adults. From 

2001 to 2008, the adult population increased by 

approximately 50 percent to an estimated 

7,650 individuals. Uncertainty in the model 

estimate means the current adult population 

is likely between 6,000 and 

10,000 individuals.  e 

observed increasing trend 

could be the result of 

drought-induced warming, 

removal of nonnative  sh, or 

a combination of these and 

other factors.

Sandbars

Sandbars and camping beaches continue to erode 

under typical Glen Canyon Dam operations. Substantial 

increases in canyon sandbars are only possible with shortduration high- ow releases timed to take advantage of 

sand provided by tributaries downstream of the dam 

following seasonal  ooding.  e sustainability of newly 

created sandbars depends on the pattern of releases from 

the dam between these high- ow releases.
U.S. Geological Survey

Dave Walsh, Bureau of Reclamation

Jeff Sorensen, Arizona Game and Fish Department

Paul Alley, U.S. Geological Survey

Federal E orts to Protect Grand Canyon

 e Grand Canyon of the Colorado River, one of 

the world’s most spectacular gorges, is a premier U.S. 

National Park and a World Heritage Site.  e canyon 

supports a diverse array of distinctive plants and animals 

and contains cultural resources signi cant to the region’s 

Native Americans.

About 15 miles upstream of Grand Canyon National 

Park sits Glen Canyon Dam, completed in 1963, which 

created Lake Powell.  e dam provides hydroelectric 

power for 200 wholesale customers in six western 

States, but it has also altered 

the Colorado River’s  ow, 

temperature, and sedimentcarrying capacity. Over 

time this has resulted in 

beach erosion, invasion and 

expansion of nonnative species, 

and losses of native  sh. 

Public concern about the 

e ects of Glen Canyon Dam 

operations prompted the 

passage of the Grand Canyon 

Protection Act of 1992, which 

directs the Secretary of the 

Interior to operate the dam 

“to protect, mitigate adverse impacts to, and improve 

values for which Grand Canyon National Park and Glen 

Canyon National Recreation Area were established...” 

 is legislation also required the creation of a long-term 

monitoring and research program to provide information 

that could inform decisions related to dam operations and 

protection of downstream resources.

Glen Canyon Dam

Adaptive Management Program

To mitigate the impacts of dam operations on downstream 

resources, the Secretary of the Interior signed a formal 

decision in 1996 that altered historical  ows from the 

dam and established the Glen Canyon Dam Adaptive 

Management Program. Adaptive management, also 

known as “learning by doing,” 

is a way to evaluate and revise 

management actions as new 

information becomes available. 

Science—in the context of 

adaptive management—is the 

“compass” used to chart such 

changes in course.

 e adaptive management program is 

facilitated by the 25-member Adaptive 

Management Work Group, a Federal 

Advisory Committee that provides 

recommendations on the operation of 

Glen Canyon Dam to the Secretary 

of the Interior.  e group includes 

representatives from Native American 

Tribes, Federal and State resource 

agencies, Colorado River Basin States, 

and nongovernmental groups.

Grand Canyon Monitoring 

and Research Center

Established in 1995 to meet the 

mandates of the 1992 legislation, 

the Grand Canyon Monitoring and Research Center 

(GCMRC) of the U.S. Geological Survey (USGS)

is today the science provider to the Glen Canyon 

Dam Adaptive Management Program. In this role, 

the GCMRC provides relevant scienti c information 

about the status and recent trends of important natural, 

cultural, and recreational resources a ected by the 

operational regime in 

place at Glen Canyon 

Dam since 1996.

 e GCMRC focuses its e orts on 

three primary activities:

Monitoring

Consistent, long-term repeated 

measurements are undertaken using 

scienti cally accepted protocols to 

measure status and trends of key 

resources, including native and 

nonnative  shes, sandbars, water 

quality, aquatic food base, riparian 

vegetation, and cultural sites.

Research and Development

Research and development activities 

address speci c hypotheses related to 

key resources and develop and test new 

technologies or monitoring procedures

Experimentation

Experiments are conducted to determine how releases 

from Glen Canyon Dam and other management actions 

can be used to meet key resource goals.  e GCMRC is 

best known for a series of three high- ow experiments, 

or water releases designed to mimic natural seasonal 

 ooding, conducted in 1996, 

2004, and 2008, to learn if 

 ows can be used to restore 

sandbars and wildlife habitat.
“Let us raise science aloft as the 

olive branch of peace and the 

emblem of hope.”

John Wesley Powell, 1882

Second Director, USGS

Arizona Game and Fish Department

Major Conclusions from Research to Date

Humpback chub

 e USGS has developed and used a computer model 

to assess the Grand Canyon humpback chub population 

status and trends from 1989 to 2008. Reproductively 

mature humpback chub (4 years old and older) appear 

to have decreased from 1989 to about 2001, when 

the population stabilized around 5,000 adults. From 

2001 to 2008, the adult population increased by 

approximately 50 percent to an estimated 

7,650 individuals. Uncertainty in the model 

estimate means the current adult population 

is likely between 6,000 and 

10,000 individuals.  e 

observed increasing trend 

could be the result of 

drought-induced warming, 

removal of nonnative  sh, or 

a combination of these and 

other factors.

Sandbars

Sandbars and camping beaches continue to erode 

under typical Glen Canyon Dam operations. Substantial 

increases in canyon sandbars are only possible with shortduration high- ow releases timed to take advantage of 

sand provided by tributaries downstream of the dam 

following seasonal  ooding.  e sustainability of newly 

created sandbars depends on the pattern of releases from 

the dam between these high- ow releases.
Arizona Game and Fish Department

Major Conclusions from Research to Date

Humpback chub

 e USGS has developed and used a computer model 

to assess the Grand Canyon humpback chub population 

status and trends from 1989 to 2008. Reproductively 

mature humpback chub (4 years old and older) appear 

to have decreased from 1989 to about 2001, when 

the population stabilized around 5,000 adults. From 

2001 to 2008, the adult population increased by 

approximately 50 percent to an estimated 

7,650 individuals. Uncertainty in the model 

estimate means the current adult population 

is likely between 6,000 and 

10,000 individuals.  e 

observed increasing trend 

could be the result of 

drought-induced warming, 

removal of nonnative  sh, or 

a combination of these and 

other factors.

Sandbars

Sandbars and camping beaches continue to erode 

under typical Glen Canyon Dam operations. Substantial 

increases in canyon sandbars are only possible with short

duration high- ow releases timed to take advantage of 

sand provided by tributaries downstream of the dam 

following seasonal  ooding.  e sustainability of newly 

created sandbars depends on the pattern of releases from 

the dam between these high- ow releases.