Canals, Tunnels and Penstocks

Reclamation begins relining of Glen Canyon Dam river outlet works

The project will reline all four outlets and take about one year to complete, and is meant to ensure efficient and reliable water deliveries for future generations.
,
Tags
Reclamation begins relining of Glen Canyon Dam river outlet works

The Bureau of Reclamation announced that relining of the river outlet works at Glen Canyon Dam is under way, funded through a $8.9 million investment from the Bipartisan Infrastructure Law.

The project will reline all four outlets and take about one year to complete, and this work is meant to ensure efficient and reliable water deliveries for future generations. However, Reclamation said the dam’s infrastructure and its ability to deliver water downstream are not at risk.

Through the Bipartisan Infrastructure Law, Reclamation is investing $8.3 billion over five years for water infrastructure projects, including rural water, water storage, conservation and conveyance, nature-based solutions, dam safety, water purification and reuse, and desalination. Since President Biden signed the law in November 2021, Reclamation has announced $4.2 billion for 575 projects.

The outlets, also referred to as bypass tubes, consist of four steel pipes that move water from Lake Powell directly downstream into the Colorado River, bypassing the hydropower generating units. Glen Canyon Dam impounds Lake Powell, the largest storage unit of the Colorado River Storage Project, and provides water for a 1,320 MW hydroelectric powerhouse.

The original coal-tar coating that covers the inside of the outlets is more than 60 years old, is showing normal signs of wear and tear, and is due for replacement, Reclamation said. The original lining was brushed on by hand, with spot repairs completed as needed over the years. The project includes removing the old lining and replacing it with an epoxy primer and polysiloxane topcoat, which will be applied using a robotic sprayer. This lining system has been extensively studied in laboratory tests and successfully applied to numerous pieces of infrastructure, including Fontana (North Carolina), Pineview (Utah) and Grand Coulee (Washington) dams.

Historically, Glen Canyon Dam’s outlets have been used sparingly; water is almost always conveyed through the penstocks to produce hydropower before it is released downstream, Reclamation said. The outlets are intended to be used when the power plant is unavailable to release water or when required releases exceed the capacity of the power plant. But with lower lake levels, the outlets could be used more frequently, as experienced with the recent implementation of cool-mix flows, which release water from both the penstocks and river outlet works to send cooler water downstream and disrupt the spawning of nonnative fish below the dam.

Reclamation argues that the potential for increased use of the outlets during low reservoir levels has made this planned maintenance, which was recommended in 2017, a priority.

Reclamation recently found new and minor cavitation damage after operating the outlets at low reservoir levels during a high-flow experiment in April 2023. While relining the outlets won’t prevent the risk of additional cavitation when operating at low reservoir levels, Reclamation is working on reducing that risk through the recent development of interim operating guidance for the outlets and additional analyses.

Earlier this summer, Reclamation began releasing deeper, and therefore colder, water from Lake Powell through Glen Canyon Dam to disrupt the establishment of smallmouth bass, which could negatively affect populations of threatened humpback chub, below the dam. The need for these flows was triggered after the average observed daily water temperatures reached smallmouth bass reproduction thresholds above 15.5 degrees Celsius (60 degrees Fahrenheit) at the confluence of the Colorado River with the Little Colorado River.

The declining elevation of Lake Powell has led to the release of warmer water from Glen Canyon Dam. Invasive fish, such as smallmouth bass, residing in the upper layer of Lake Powell are more likely to pass through the dam and spawn downstream. If left unchecked, they could continue to expand their population. Smallmouth bass are known to prey on native fish species in the Grand Canyon that are protected by the Endangered Species Act.

Earlier this year, Reclamation established interim guidelines on Glen Canyon Dam, addressing reduced capacities for the river outlets when the reservoir level is low, due to the increased risk of cavitation at elevations of 3,550 feet or below. With Lake Powell’s elevation above this threshold, the river outlets will operate safely and under normal conditions, with no elevated cavitation risk. Additionally, scheduled recoating work will proceed as planned, as only one of the four river outlets can be recoated at a time and only two river outlets will be in use at any given time for the cool mix flows.

Reclamation said it will continue to work with the Western Area Power Administration to minimize the impacts of reduced power generation to customers by adjusting the timing of these releases. Reclamation will also continue to work with its partners to develop and implement additional preventative actions to combat non-native species in the Colorado River.