The waters travelling through Grand Canyon don’t follow the traditional pattern of having high flows during rainy seasons or when heavy snow melt is feeding into the river and low flows when precipitation is down. Instead, the changes in the Grand Canyon portion of the Colorado River are dictated more by how much water is being released through Glen Canyon Dam at any given time. Multiple agencies work together to determine how much water should be allowed to flow and for how long in order to achieve different goals. Those goals range from meeting the area’s power needs to building beaches to studying how different flows can increase bug populations and balance the ecosystem by providing food for native fishes.
This March, The Department of the Interior will be implementing what they call a “spring disturbance flow.” The purpose of this flow is to simulate the kind of run off that would be typical in spring were the dam not present.
It is standard for March’s managed flows to fluctuate from a daily low of around 8,000 cubic feet per second (cfs) to a daily high of around 15,000 cfs. For this experiment, though, releases will be reduced to a mere 4,000 cfs from March 15th-19th. Then, on March 20, flows will be increased gradually until they peak at 20,150 cfs on March 22nd. That high flow rate will then be held steady through March 25th, after which time standard operations will resume.
According to a news release from the Bureau of Reclamation, some of the expected ecological results of the spring disturbance flow are as follows: “As the changing flows disturb river bottom habitats, ecosystem responses may include elevated algae and insect production resulting in increased aquatic insect prey for endangered humpback chub, non-native rainbow trout, and other wildlife. The flows also may affect the non-native brown trout in Glen Canyon by reducing survival of emerging young, which may help protect native fish in the river.”
The flow will also provide an opportunity for required maintenance to be conducted on the dam.
The Bureau of Reclamation’s Upper Colorado Basin Regional Director, Wayne Pullan, applauds the numerous groups (including governmental agencies, Colorado River stakeholders, and Native American tribes, among others) who have come together to implement and show their support for this experiment and the adaptive management of Glen Canyon Dam more generally. He notes, “Scientific studies like these are an important part of our obligation to effectively balance the need for water and power resources with responsible stewardship of the Colorado River ecosystem.”
If you’d like to learn more about the spring disturbance flow, the most up-to-date information will be available at the Bureau of Reclamation’s website: https://www.usbr.gov/uc/progact/amp/DisturbanceFlow.html