Flash floods that crippled the Chicago area on Aug. 2 caused about $1 million in damage to Northwestern’s Evanston campus and might have ruined Welsh-Ryan Arena’s basketball floor, NU officials said.

Director of Risk Management Christopher Johnson said the downpour, which dumped as much as 4 inches of rain in one hour, ruined carpets, walls, papers and computers in 78 of the campus’ 160 buildings.

Risk management officials are still assessing the damage to the Welsh-Ryan basketball floor, Johnson said. He said his office is aiming to complete final damage totals in about a month.

NU’s insurance should cover most of the damage, said Eugene Sunshine, vice president for business and finance.

The Technological Institute was hardest hit by the flood, Johnson said. In addition to soaked walls and carpets, some scientific equipment, including an electron microscope, was damaged.

As Weinberg junior John Rhyner tried to get to a 9 a.m. final for a summer physics class, he waded through knee-deep water on Orrington Avenue to get to his car. He drove to North Campus and walked to Tech, where he saw a manhole cover floating on a fountain of water.

“There was so much flooding that the sewers were pushing water back up, and the manhole cover was spinning around, levitated on a column of water,” Rhyner said. “So I stood on top of it, and it spun me around. It was a great way to unwind before a final.”

The flooding became worse throughout the day, and NU shut down its campus and evacuated some buildings at about 11 a.m. The university notified students and employees about the shutdown by sending e-mails and voice mails and putting a breaking news link on its Web site, said Alan Cubbage, vice president for university relations.

The university evacuated the buildings that had standing water, such as University Library. The library’s basement flooded, but no books were damaged, Johnson said.

Most of the campus was empty by noon, and no one was injured, Cubbage said.

Floodwater contaminated an area in the Sports Pavilion and Aquatics Center where chlorine for the pool was stored, and several nearby fire departments sent their hazardous materials teams to clear the area, Cubbage said.

Facilities management employees cleaned the flooded buildings after the waters subsided, and risk management crews checked fire prevention systems, Johnson said.

The campus reopened the next day, and university employees began assessing damage and repairing walls and carpets.

Johnson said mold inside walls became a problem in the following weeks. Maintenance workers had to cut out portions of drywall to access the mold and spray chemicals to kill it.