(26 Jun 2017) LEADIN:
Water experts in the United States are using a sophisticated dam replica to pinpoint what repairs will work best at Oroville Dam in California, the tallest dam in the U.S.
The dam's spillway was torn apart in February, triggering the evacuation of 200,000 people living downstream.
STORYLINE:
Inside this cavernous northern Utah warehouse, hydraulic engineers are sending water rushing down a replica of a dam built with wood, concrete and steel.
They're trying to pinpoint what repairs will work best for a spillway that was torn apart in February during heavy rains, causing 200,000 people living downstream to be evacuated.
Utah State University hydraulics engineering professor Michael Johnson kneels in front of the Oroville Dam replica to examine one of two channels that run the width of the spillway.
These channels 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 a proposed 300 million US dollar spillway reconstruction set to be completed by November.
That's 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 try to solve the mystery of why the spillway crumbled last February, hydrologists who built the replica are using it to guide California authorities on how they should build a new spillway so it can withstand rushing waters.
The Utah testing has confirmed that the channels to aerate water going down the spillway would ease pressure.
It's also shown that an adjustment to the curve proposed for about halfway down the steep spillway to decrease the force of rushing water would not help improve its effectiveness.
The idea was to make the curve more gradual near a steep part of the spillway where it caved in, leaving a gaping hole the size of a football field in the concrete chute.
Though computer modeling is being used extensively to plan the spillway repairs, California officials and hydrologists say high-tech testing is no replacement for dam replica research.
Johnson's team has a 277,000 US dollar contract for the work and will issue its final report in early fall.
The 100-foot (30-metre) long replica took 40 days to build.
Each simulation begins when a crew member slowly opens a large steering wheel like valve that sends water 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.
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, according to the dam engineering consultant leading the California investigation.
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.
Find out more about AP Archive: [ Ссылка ]
Twitter: [ Ссылка ]
Facebook: [ Ссылка ]
Instagram: [ Ссылка ]
You can license this story through AP Archive: [ Ссылка ]
