By Philip Reed

Since August 1991, the Environment team from the Colorado River Storage Project Management Center has provided input on flow experiments being conducted by the Department of the Interior at Glen Canyon Dam. These experiments are coordinated through the Glen Canyon Dam Adaptive Management Program, a public-private partnership committed to improving the health of the Colorado River below the dam and into Grand Canyon National Park.

Experiments are conducted in order to determine the effects that varying releases have on rivers, populations of aquatic creatures and food sources for fish. This helps the biologists to better understand potential impacts of hydropower production and help ensure a healthy ecosystem.

In March, researchers from the U.S. Geological Survey’s Grand Canyon Monitoring and Research Center had a rare opportunity to study how spring floods affect the production of bugs and fish as well as other conditions that they are interested in improving below Glen Canyon Dam.

The best part? They didn’t even need an actual flood.

The importance of disturbance

The term disturbance can carry negative connotations but, in natural systems, disturbance is a critical part of the life history of many organisms.

Disturbances in rivers and streams, for instance, help maintain biological diversity by making new substrates and resources available. Of course, not all disturbances are created equal, nor are they equally beneficial.

The magnitude of the disturbance plays an important role; flows that are higher or lower than usual lead to different results in terms of the ability of algae and aquatic insects to flourish. The frequency of the disturbance and the timing – such as whether it occurs during spring or autumn – are also important factors.

Flow experiments qualify as disturbances, though they are obviously controlled and planned far ahead of time. With “disturbances” such as these, researchers can observe the specific impact they had and tailor future releases and experiments to meet resource goals of the Glen Canyon Dam Adaptive Management Program for the maximum benefit of river health.

Hydropower releases can impact the lifecycles of fish, as well as the insects and algae upon which they depend. Maintaining the health of the ecosystem is crucial and of high concern to WAPA in terms of its hydroelectric power operations.

The 2016 Long-Term Experimental and Management Plan established High-Flow Experiments as the principal type of disturbance for aquatic species. Previous HFEs suggested that spring would be the best time for a disturbance flow on bugs and algae, which are important food items for fish. 

Some necessary repair work to an apron – or the footing of the dam – at Glen Canyon Dam provided the opportunity to study the effects of a low flow, followed by a higher flow with the water that was held back during the repair.

“The Bureau of Reclamation would have had to drop the flows to perform the apron repair anyway,” said Fish Biologist Craig Ellsworth. “Since we were able to get the timing worked out, we were able to put a little bit of a spin on this particular event to follow with a high flow, which we termed a Spring Disturbance Flow, and collect some valuable data in a way that had very little impact to hydropower production.”

Because the Spring Disturbance Flow occurred in March when power prices were relatively low, and because there wasn’t any water bypassed around the turbines at Glen Canyon Dam, the cost to hydropower production was estimated to be only a couple thousand dollars. This is significantly lower than traditional HFEs, which incur costs between $1 million and
$3 million.

A flood of information

Traditionally, flow experiments originate through the DOI. In this case, the proposal came from stakeholders in the Glen Canyon Dam Adaptive Management Program, particularly the angling groups who use the rainbow trout fishery in the Glen Canyon Dam tailwater.

“We as a program developed this one and are advocating for it,” said Ellsworth. “It’s kind of a bottom-up approach this time around, and we’ve been working on it as a group, collaboratively, for around a year and a half.”

The experiment was intended to replicate a spring flood.

“A spring flood is something we really haven’t seen at Glen Canyon since 2008,” Ellsworth explained. “We are interested in learning about how spring floods affect the production of bugs and fish and all these other things we are trying to improve below the dam.”

In coordinating the details with other stakeholders and the GCMRC, Ellsworth was pleased with how well the idea came together.

“We’ve been pleasantly surprised about the amount of traction that we’ve gotten,” he said.

The plan, in brief, was to draw the river down significantly on March 15, with flows only around 4,000 cubic feet per second. This would allow divers to perform the necessary repair work on the apron. Then, between March 20 – 22, flows would be ramped up to around 20,150 cfs. They would continue at this rate until March 25.

“We could get a huge amount of valuable data about spring flooding, and we could do it as a program, with careful planning and being fully prepared to monitor its effect with the GCMRC,” said Ellsworth.

Low-flow river trip, high-quality data

Several days before the flow experiment began, researchers from the USGS embarked on a river trip to monitor the effects of the Spring Disturbance Flow on the aquatic insects in Grand Canyon.

They departed from Lees Ferry in Arizona, positioning themselves in the western part of the Grand Canyon prior to the flow reduction.

This part of the canyon was of particular interest to the researchers, due to recent increases in the population of endangered humpback chub. Departing ahead of the experiment allowed them to raft the nearly 200 miles downstream to be in position to collect their low-flow samples.

“Efforts are being made to better understand why populations of the endangered humpback chub are increasing in this part of the canyon, including trying to figure out if recent changes in the insect community might be fueling this change,” Ellsworth explained.

He described the sight of the Colorado River at such a low flow as an exceptional experience.

“The river hadn’t been held so low for so long since the 1980s,” he said. “The low water made for an exciting trip through the big rapids on the river.”

It may have been an exciting trip, but it was also a safe one, completed without incident. Ellsworth credits the professionalism of their river guides, who also had not seen the Colorado River as low as it was during this trip.

“Everything was different,” he continued. “Some of the big rapids were smaller and some of the smaller rapids were bigger than anyone expected.”

Through the summer, the team will study and continue to monitor the river below Glen Canyon Dam and through the Grand Canyon. The resulting data will be reported back to the Glen Canyon Dam Adaptative Management Program in January 2022.

The team is confident that their data and observations will prove to be extremely valuable.

“It was quite remarkable to be able to see the river this low,” said Ellsworth. “It provided us a great opportunity to understand how the riverbed is structured. We look forward to sharing what we find. Everything we learn during this experiment is one more step CRSP is taking toward keeping the Colorado River healthy.”

Note: Reed is a public affairs specialist.

A chart depicting Glen Canyon Dam Hourly Release Pattern: March 2021
An image of a worker in Glen Canyon dam taking samples near mossy rocks

Grand Canyon Monitoring and Research Center scientists collect aquatic macrophyte samples during the low-flow experiment below Glen Canyon Dam. (Photo courtesy of the Bureau of Reclamation).

Last modified on September 12th, 2023