NEW ORLEANS (AP) — Storms moving ahead of a cold front overwhelmed New Orleans’ aging drainage system Wednesday morning, flooding streets and prompting closure of a section of interstate highway.

Drainage of the flood waters was slowed when a main turbine that generates powers to the city’s drainage pumps tripped offline, Ghassan Korban, head of the Sewerage and Water Board of New Orleans, said at a news conference.

Korban said as much as 4 inches (10.16 centimeters) of rain fell in a short period of time in some parts of the city, more than the drainage system can handle. He said he believes, based on findings so far, that the more than two-hour loss of one generator did not cause the flooding. “I truly believe, and we will quantify that, that the street flooding would have occurred anyway,” Korban said.

The state highway department said a portion of westbound Interstate 610 in New Orleans was shut down for a time due to high water. Several underpasses in the flood-prone city were closed. Local news outlets showed pictures of cars swamped after drivers tried to get through flooded areas.