Engineers use replica to pinpoint California dam repairs

June 26, 2017 by Brady Mccombs
In this Friday, June 16, 2017, photo, hydraulic engineering professor Michael Johnson looks at the water flow on a replica of the Oroville Dam spillway at Utah State University's Water Research Laboratory, in Logan, Utah. California water officials are relying on key hydrology tests being performed on the replica of the spillway to pinpoint what repairs will work best at the tallest dam in the U.S for a spillway that was torn apart in February. (AP Photo/Rick Bowmer)

Inside a cavernous northern Utah warehouse, hydraulic engineers send water rushing down a replica of a section of a dam built out of wood, concrete and steel—trying to pinpoint what repairs will work best at the tallest dam in the U.S. for a spillway torn apart during heavy winter rains that triggered the evacuation of 200,000 people living downstream.

The sound of rushing water is deafening as Utah State University hydraulics engineering professor Michael Johnson kneels in front of a replica of an Oroville Dam spillway the size of a small house to examine one of two channels that run the width of the spillway to allow air into the water to prevent bubble formations that can damage the concrete spillway of the real dam.

The new channels, called aerators, are one of the key features in the proposed $300 million spillway reconstruction set to be completed by November—when winter rains and snow will once again increase the flow of water into the lake above the dam.

While a separate team of dam experts tries to solve the mystery of why the spillway crumbled last February, the hydrologists who built the replica are using it to guide California authorities on how they should build a new spillway so that it can withstand rushing waters.

Besides confirming that the channels to aerate water going down the spillway would ease pressure on the spillway, the Utah testing has determined that an adjustment to a curve about halfway down the spillway would only slightly improve its effectiveness. The idea was to make the curve more gradual near a steep part of the spillway where it caved in and left a gaping hole the size of a football field in the concrete chute.

In this Friday, June 16, 2017, photo, hydraulic engineering professor Michael Johnson looks at the water flow on a replica of the Oroville Dam spillway at Utah State University's Water Research Laboratory, in Logan, Utah. California water officials are relying on key hydrology tests being performed on the replica of the spillway to pinpoint what repairs will work best at the tallest dam in the U.S for a spillway that was torn apart in February. (AP Photo/Rick Bowmer)

Though computer modeling is being used extensively to plan the spillway repairs, California officials and the hydrologists say high tech testing is no replacement for dam replica research. Johnson's team has a $277,000 contract for the work and will issue its final report in the early fall.

Water flow patterns, pooling and waves can be different than computer models predict, said Ted Craddock of California's Department of Water Resources.

"This is an important validation process," Craddock said. "Water behaves very similar at a smaller scale as a larger scale."

Physical models to test proposed dams and dam repairs are necessary because "the flow of water is very complex and momentum is transferred at the molecular level," Johnson said.

In this Friday, June 16, 2017, photo, hydraulic engineering professor Michael Johnson talks to reporters about the replica of the Oroville Dam spillway at Utah State University's Water Research Laboratory, in Logan, Utah. California water officials are relying on key hydrology tests being performed on the replica of the spillway to pinpoint what repairs will work best at the tallest dam in the U.S for a spillway that was torn apart in February. (AP Photo/Rick Bowmer)

"We haven't got enough computer power to model that many molecules at once," he said.

Each simulation of the 100-foot (30-meter) long replica that took 40 days to build begins when a crew member slowly opens a large steering wheel like valve that sends water screaming down a chute modeled after the spillway and crashing into blocks that disperse it and send it in waves to a replica of the river. Johnson almost has to shout for his team to hear him above the noise of the water mimicking a flood.

The hydrologists calculate the velocity of the water, track how much air is being absorbed in the water and document what they see in weekly reports to California authorities.

To help with the design, the separate team investigating the spillway failure sent California water officials and Utah hydrologists a list of factors they've found that could have contributed to the failure—many focusing on the condition of the spillway's concrete, slab joints and foundation. But no one factor has been discovered yet to determine how the failure happened, said John France, a dam engineering consultant leading the California investigation.

In this Friday, June 16, 2017, photo, water flows from a replica of the Oroville Dam spillway at Utah State University's Water Research Laboratory, in Logan, Utah. California water officials are relying on key hydrology tests being performed on the replica of the spillway to pinpoint what repairs will work best at the tallest dam in the U.S for a spillway that was torn apart in February. (AP Photo/Rick Bowmer)

Dam experts say one of the most unsettling aspects of the events is that it occurred without warning after decades of maintenance and inspection reports showing no clues of the pending collapse.

California state officials have pointed to the torrents of runoff pouring into the dam at the time of the crisis. But the amount of water streaming down the two flood-release spillways when they began to collapse was relatively small.

The average age of the nearly 91,000 dams in the United States is 56-years-old, according to the American Society of Civil Engineers, and 2,170 of the taller dams are structurally deficient in one way or the other, according to the industry group. So the research in Utah may help improve dam safety elsewhere.

"We have folks across the world who are really looking at what's happening with Oroville," Johnson said

In this Friday, June 16, 2017, photo, water flows from a replica of the Oroville Dam spillway at Utah State University's Water Research Laboratory, in Logan, Utah. California water officials are relying on key hydrology tests being performed on the replica of the spillway to pinpoint what repairs will work best at the tallest dam in the U.S for a spillway that was torn apart in February. (AP Photo/Rick Bowmer)

Explore further: Miniaturizing America's tallest dam

Related Stories

Miniaturizing America's tallest dam

June 9, 2017

Engineers at Utah State University's Utah Water Research Laboratory have constructed a 1:50 scale model of the Oroville Dam spillway.

What we know so far about problems at the tallest US dam

February 16, 2017

It's been more than a week since engineers at the nation's tallest dam noticed damage to its emergency spillway, launching a series of events that culminated with the threat of catastrophic flooding and the two-day evacuation ...

Two dams illustrate challenge of maintaining older designs

February 19, 2017

Twelve years ago, widespread destruction from Hurricane Katrina on the Gulf Coast helped compel federal engineers 2,000 miles away in California to remake a 1950s-era dam by constructing a massive steel-and-concrete gutter ...

188,000 under evacuation orders near Northern California dam

February 13, 2017

At least 188,000 people remain under evacuation orders after Northern California authorities warned an emergency spillway in the country's tallest dam was in danger of failing Sunday and unleashing uncontrolled flood waters ...

Recommended for you

Enhancing solar power with diatoms

October 20, 2017

Diatoms, a kind of algae that reproduces prodigiously, have been called "the jewels of the sea" for their ability to manipulate light. Now, researchers hope to harness that property to boost solar technology.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.