More Bank for your Brook: Competing Resources Influence Water Releases at Glen Canyon Dam

What do air conditioners, white water rafters, and humpback chub have in common? Each influences when and how much water is released through the Glen Canyon Dam.

Unique Commodity

Hydropower is most valuable when highest in demand. If dam operators in Arizona were only concerned with economically efficient hydropower production, the decision of when and how much water to release would correspond to the dials on air conditioners. That’s how the Glen Canyon Dam operated in its first few decades of use. Its energy production largely reflected electricity market conditions: high water releases during peak energy-use months countered by lower flows during off-peak months, with similar fluctuations for time of day. This operational system worked well for hydro energy production, but was at odds with the dam’s other purposes such as preserving a healthy ecosystem, promoting recreation, and protecting cultural sites.

Creating Science-based Policy: Glen Canyon Dam Adaptive Management Program

In response to the public’s concern about the negative impacts of its operation, Glen Canyon Dam adjusted its operational regime to better balance competing water uses through a series of studies and programs. In 1982, the U.S. Bureau of Reclamation (“Reclamation”) initiated the Glen Canyon Environmental Studies (“GCES”), an interdisciplinary research study identifying the adverse impacts of dam operation on the Colorado River and Grand Canyon ecosystems. Seven years later, Reclamation evaluated Glen Canyon dam operation strategies through an Environmental Impact Study (“EIS”), identifying several operation techniques that could reduce the negative environmental impact of dam operation. Reclamation considered nine alternative operational regimes. To hasten completion of the study, the US Congress passed the Grand Canyon Protection Act of 1992 (“Act”), which directed the Secretary of the Interior (“Secretary”) to mitigate adverse environmental impacts caused by Glen Canyon Dam operation in a timely manner. In 1996, the Secretary and Reclamation released a Record of Decision (“ROD”) selecting modified low fluctuating flow (“MLLF”) as the new operating regime for Glen Canyon Dam. The Secretary and Reclamation selected the MLLF regime because it had the potential to mitigate environmental and cultural impacts of dam operation while allowing flexibility for consistent hydropower production through reduced daily flow fluctuation and periodic “controlled floods.”

Today, a federal advisory committee called the Adaptive Management Work Group (“AMWG” or “Work Group”) implements the MLLF regime through the Glen Canyon Dam Adaptive Management Program (“GCDAMP”). The AMWG includes representatives from Native American Tribes, Federal and State resource agencies, Colorado River Basin States, and nongovernmental groups. The Work Group evaluates and revises dam management strategies in order to maximize hydropower production and mitigate negative impacts on the natural, cultural, and recreational resources in Grand Canyon National Park and Glen Canyon National Recreation Area.

What “natural, cultural, and recreational resources” are affected by the operation of Glen Canyon Dam?

The Secretary and Reclamation established the MLLF operating criteria to mitigate negative impacts of dam operation on endangered native fish populations, sacred prehistoric and Native American sites, sandbars, and camping beaches.

The humpback chub is the most notable endangered fish impacted by dam operations on the Colorado River. Dam operations affect water temperature, the amount of sediment in the river, and the health of the aquatic food base — all impacting the livelihood of the humpback chub. The MLLF regime aims to establish a new population of humpback chub in the main stem of the Grand Canyon through reduced daily flow fluctuation and the removal of nonnative fish. The MLLF regime limits the difference between daily maximum and minimum water flows through the dam to 6,500 cfs, as compared to the 25,000 cfs fluctuation in the former operational regime. These “habitat maintenance flows” reduce disruption of backwater and nearshore habitats essential to recently spawned humpback chub, increase the temperature of the water in these habitats, and support an aquatic food base. Mechanical removal of nonnative fish near the Little Colorado River reduces predation for humpback chub.

The MLLF regime also includes a long-term monitoring program to gauge any erosion to prehistoric and sacred Native American sites, such as the Rainbow Bridge National Monument. Though an established program is still in the works, GCMRC scientists have experimented with the following methods to monitor cultural resource conditions: (1) the development of baseline geomorphic data to compare with future changes, (2) new methods for tracking changes in site condition, such as light detection, laser-based topographic mapping, and weather monitoring stations, and (3) data compilation for creating a geomorphic model to explain the effects on site conditions. Concurrently, several Native American Tribes in GCDAMP have explored resource-monitoring methods that incorporate traditional ecological knowledge and western science.

A third major goal of the MLLF regime is to restore sandbars and camping beaches through periodic controlled floods. The volume of water that must be released annually from the Glen Canyon Dam is determined by the “Law of the River” — a collection of laws and agreements that manage the use of the Colorado River among the seven basin states and Mexico. However, AMWG determines the frequency and quantity of water releases. In the right conditions, high flow experimental releases (“HFEs”) redistribute sand from the main river channel farther downstream to restore riparian vegetation, provide key wildlife habitat, reduce erosion, and improve conditions for recreation like rafting and fishing.

Progress to Date

The Department of the Interior reports that GCDAMP has already had a positive impact. The humpback chub fish population nearly doubled from 2001 to 2008. The efforts of GCDAMP at Glen Canyon Dam have likely contributed to the rebound. The Department also reported general benefit resulted from the 2008 HFE including temporary increases in sandbars, stifling nonnative seedling germination, and an 80 percent reduction in an unwanted nonnative snail population.

In May 2012, the Department approved a protocol for GCDAMP to conduct HFEs any time trigger conditions are met until 2020. So far, one HFE was conducted in 2012.

Limited hydropower production is better for the health of the Colorado River, right?

As dams like Glen Canyon move away from market-based hydropower production to protect riparian habitat, other resources like natural gas and coal must compensate for the lost energy. If that is the case, what is the net environmental benefit?

This conversation is relatively new. There are more questions than answers about how management practices at Glen Canyon Dam impact ecological, recreational, and cultural resources, and how best to mitigate that impact. GCDAMP, with the help of scientists, economists, and the public, will continue to balance community needs for hydropower with other competing resources.


The title image features Glen Canyon Dam and is licensed under the Creative Commons Attribution 2.5 Generic License. The owner of this image does not endorse this blog.



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