Torrential rains that flooded downtown Oklahoma City on May 31 built up enough force to blow out the 5-inch-thick concrete slab in the basement of a city office building, an engineers' report says.
Amid the destruction, colorful paintings of shields, a spear with dangling feathers and other tribal symbols have been revealed on the basement walls of the 100 Building, which is thought to be 75 to 90 years old.
Repairing the damage to the seven-story building, at 100 N Walker Ave. just south of City Hall, is expected to cost $2.1 million to $2.3 million.
Insurance will cover most of the cost, with the state and federal governments reimbursing the city for much of the rest under terms of a disaster declaration.
The Friday night storms came on the tail end of nearly two weeks of violent weather that killed nearly 50 people, including seven schoolchildren who died in an EF5 tornado in Moore.
The report by White Engineering Associates of Oklahoma City says about 4.2 inches of rain fell the evening of May 31 between 7:15 and 11:15 p.m. It says 2 inches fell in the first hour.
Downtown streets flooded and water ran under the doors of numerous buildings.
During the storm, floodwater flowed into a pit on the Arts District parking garage construction site just east of the 100 Building.
Dug by the contractor to locate the 100 Building's foundation, the pit was adjacent to the building and reached a depth several feet below the basement floor.
When the pit filled, the basement floor blew upward and water poured in, reaching a depth of nearly 10 feet in 3 minutes, said Jim Lewellyn, a program manager in Public Works.
Mud filled the basement and everything was ruined, from furniture to electrical equipment. Once it was cleaned out, the paintings were revealed on the basement's east wall.
The engineers' report says the building's footings appear sound, with no evidence of cracks in the “cast-in-place” concrete structure that would indicate a foundation failure.
The engineers recommended filling in an area that washed out as the water poured in. They suggested removing the remains of the basement floor and installing a drainage system before pouring a new 5-inch concrete slab.
The two elevators were knocked out. They need to be running before city workers who have been in temporary quarters all summer can return to their offices. Engineers said the elevator pit, which reaches below the water table, should be waterproofed as part of the project.