General Motors continues to assess flood damage today at its R&D operations outside Detroit after record rainfall in the region earlier this week closed the facility, which serves as the global hub for work on some of the automaker’s most important projects.

The 704-acre (285-ha) facility in Warren, MI, closed Tuesday after 4.6 ins. (11.7 cm)  of rain moved through southeast Michigan on Monday. A major drainage system for the city runs directly through the campus.

“Unfortunately we had some serious problems over the past few days,” GM product development chief Mark Reuss says during an event Thursday outside of Detroit. “There’s a lot of damage.”

While 15,200 of the GM Tech Center’s 19,000 employees are back to work today, two of the most critical buildings on the campus, design and R&D, remain closed. Employees at GM Design tell WardsAuto their main building was “devastated” and it could be “months” before the facility is fully operational again.

Water damage was extensive, they say, and historical archives and a photo lab in the building’s basement were destroyed.

According to GM documents, 1.1 miles (1.76 km) of tunnels connect various buildings on the campus, and the network has served as a storage and holding area over the years for items such as concept cars.

GM spokeswoman Katie McBride says the extent of the damage remains unclear. “They are in the midst of discovery,” she says.

Flooded basements in the buildings cut off electrical power, McBride says.

The 3,800 employees yet to return to campus work mainly in design and R&D. Sources tell WardsAuto some employees were issued safety equipment – hard hats, glasses and masks – to retrieve work-related items and carry out their responsibilities elsewhere.

McBride says the automaker’s “focus is on safety” until the buildings can be repaired.

Crews plan to work through the weekend, and progress updates are being issued every four hours.

Within 24 hours of the shutdown, customer-facing operations such as OnStar, call centers and IT centers reopened, McBride says.

The 58-year-old GM Tech Center appears on the National Register of Historic Places. It was designed by architect Eero Saarinen and boasts many futuristic and noteworthy exterior and interior design elements.

When the facility opened in 1956, the celebration was broadcast on national television, and then-President Dwight Eisenhower delivered a radio address before a crowd of 5,000 people.

Reuss acknowledged the unique nature of the tech center.

“A lot of these historic old buildings there,” he says. “There’s a lot of water in those places.”

– with Tom Murphy in Royal Oak, MI