Lake Hefner is where OKC stores about 40% of its drinking water. Oklahoma City Water Utilities Trust requests to draw from Canton Lake whenever Hefner gets too low. The U.S. Army Corps of Engineers manages and executes approved releases.
This water began its approximately 100-mile journey from Canton last Tuesday. City officials say the water has made its way down the North Canadian River and should be arriving in Oklahoma City now.
Engineer Larry Hare has been working with Oklahoma City for more than three decades and was involved with planning this release.
“The whole summer, everybody has said, you know, Hefner is getting pretty low,” Hare said. “I said, yeah, yeah, it is. But it's okay.”
When lake levels reached about five feet below normal, conversations began in earnest about pulling water from Canton Lake.
The goal of a release like this is to even out water levels between the two lakes. Canton has been faring better than many lakes across the state after a summer of abnormally high rainfall in northwest Oklahoma.
“We don't want one lake to be drastically low and one to be very, very full,” Hare said. “I was surprised to see how full Canton was due to this summer. And I was like, wow, okay. Let's see what kind of releases we can make and see how they can level out between each other.”
Hare said this draw is expected to bring Hefner and Canton to around 4 feet below their respective normal levels.
When planning a release like this, OKC Utilities staff consult with the Oklahoma Water Resources Board, the Oklahoma Department of Wildlife Conservation, the Army Corps of Engineers (which operates the dam at Canton Lake) and community representatives from the Canton Lake area.
“The Oklahoma Department of Wildlife Conservation and the residents at Canton were very concerned about how the release will affect their tourism and fishing,” Hare said. “One thing that we do not want to do is to adversely affect their fishery if we can at all possibly avoid it.”
One of the ways they work to avoid it is with careful timing. Hare said as the weather cools down, fish gather in the deeper water near the dam to stay warm. If water levels at Canton were to get lower as Oklahoma’s drought continues, fish would be corralled into a smaller space where they’d be more likely to get pulled through the dam’s low sluice gates.
“So we decided, if we were going to do it, now would be the time to unfortunately lose a little bit of fish, but not a vast majority of fish,” Hare said.
It’s not just fish that come down the river with the water released from Canton. As river levels rise, the water can pick up trash and limbs along the way to OKC.
Hare said the city deals with that by doing a “first pass flush” at the Overholser Dam. That’s where they can close the gates to divert the North Canadian River up the Hefner Canal towards Lake Hefner.
“But before we do that, we allow as much junk and loose particles and all that good stuff flow through the river dam downstream, before we close the gates there and then allow the water to back up and then flow into the Hefner canal,” Hare said.
The Army Corps of Engineers controls the release of the water from Canton Lake. They start slow and ramp up the flow of water coming from the dam. Hare said that easing into the release prevents the rushing water from doing unnecessary damage to the riverbanks.
Still, as that water pours into Lake Hefner, it kicks up material from the bottom of the lake.
“You'll see kind of like a stirring action in this great big bowl called Hefner,” Hare said. “So as the water goes in, it'll stir up the sediment there.”
Officials with the OKC Utilities Water Quality Division said the sediment settles before it reaches the intake for the water treatment plant, so the treatment process is business as usual.
