Under the threat of more rain and flooding this week, the regional hub that is Houston faced the daunting prospect of clearing mud-swept roadways, opening two of the nation’s busiest airports and resuming operations at the country’s second-
busiest port.

Many streets remained impassable, with water more than waist-high. Those highways not flooded too often led to others that were. And officials said it was too soon to say when the transit system would resume operations.

Houston is a city that for the past eight years led the nation in growth, and although transit was considered to have its place, the city’s backbone is the oil industry, which relies heavily on new highways to get around town. When the city spread out into Harris County — which has 6.5 million people to the city’s 2 million — the connections were roadways. The state maintains more than 1,200 miles of them, including four interstates, three of which crisscross the downtown area.

Even though the worst of the storm appeared to be over, transportation officials continued to urge people to stay off the roads.

“We’re expecting more rain,” Houston Fire Chief Samuel Peña said. “The roads are dangerous. Stay off the roads.”

Once the water clears, it may take weeks or months before roads are fully ready for travel, said Dave Newcomb, a senior research engineer at the Texas A&M Transportation Institute. He said the primary concern will be local streets and roadways, not the freeway system.

“The freeways are probably going to be okay,” Newcomb said. “They’re built with lots of support underneath them. They’re built for heavy loads and adverse conditions.”

But local roads built on rain-saturated soil may be left in a weakened state, he said, taking a month or two before they stabilize. Bridges that had swift-
moving floodwaters around them must be checked for scouring around their supports, he said.

The sheer scale of the immediate recovery is daunting.

“It is really difficult because we’re so spread out and highway- dependent,” said Kyle Shelton, ­director of strategic partnerships at the Kinder Institute, an urban- research think tank at Houston’s Rice University. “We just have so many streets and so many roads and so much other infrastructure to make sure is okay and bring back online. That’s going to take weeks and months.”

Houston’s two big airports — George Bush Intercontinental Airport and the William P. Hobby Airport — will begin to see traffic on their runways even as the rest of the region struggles to find its footing. Officials said Hobby will remain closed until Wednesday; Bush until Thursday.

The magnitude of the backup to the national aviation system caused when Houston shuts down was evident Monday: 772 flights had been set to depart from the two airports, carrying close to 94,000 passengers. The two airports had a record 1.9 million passengers pass through security last month.

A truck driving on a Houston highway near Rice University cruises through floodwaters on Aug. 27 after Tropical Storm Harvey dropped record-level rainfall in the area. (Dylan Baddour)

“You may not even be heading to Houston and still run into
this,” said Anne McDermott of ­Farecompare.com. She said that late Sunday a flight to Dallas landed in Memphis because so many ­Houston-bound flights had been diverted to Dallas. “It’s going to continue to be a fluid situation.”

The Houston Metro’s bus system, three light-rail lines and paratransit services were shut down Monday, with no word on when they would resume service. In a statement, Metro officials said they will monitor the situation to determine when it would be safe to resume service.

If history is precedent, it may be a while before those buses are back on the road. After Hurricane Katrina in 2005, it took weeks to restore bus service in New Orleans — partly because of the condition of flooded roadways, but also because hundreds of buses were underwater after the storm. With the city’s bus fleet unusable, the Federal Emergency Management Agency had to scramble to bring in more than a thousand private coaches to help with evacuation efforts.

The Houston Metro tried to prevent a similar outcome for this storm, parking more than 100 buses in the HOV lane on an elevated section of Interstate 59.

“This is a city that was built, in large part, in defiance of nature,” said Christof Spieler, an urban planner who is on the board of Metro.

“Basically, developers just treated this as a big empty canvas and just spread out across it. We tend to sort of ignore the natural underpinnings of the city. When this amount of rain falls, suddenly that natural geography reasserts itself.”

And in the long run, Houston — like the rest of the country — has to wrestle with how to become more resilient in an era when weather hazards are increasing. Over the past three years, there have been three floods that have “all been labeled unprecedented,” Shelton said.

While freeways and many local streets have major sections that are underwater, many other areas are not submerged, depending on their elevation and how much rain there was in that particular place.

“Houston is used to flooding. We’re not used to anything on the scale of what just happened,” Spieler said.

Rapid development over the past two decades — and the sprawling networks of accompanying roadways, subdivisions and parking lots — have left Houston especially susceptible to major flooding, said Samuel Brody, a Texas A&M University urban planning professor who leads the Center for Texas Beaches and Shores.

Such surfaces leave little return path for floodwaters to go into the ground or drainage channels.

“You’ve got a smearing of pavement all over a flood-prone region,” he said. “You’re putting more impervious surfaces over a large area that is dominated by flood-prone, low-lying landscapes, so when it rains, there’s all this impervious surface. It increases the volume and velocity of water going into the bayous which Houston uses as their primary drain system.”

Between 1996 and 2011, as development boomed, the percentage of impervious surfaces in Houston grew by 25 percent, Brody said, citing a report he led that examined the effect of development on flood damage in the Gulf of Mexico region. And although the extreme rainfall totals from Harvey probably would have caused flooding no matter what, Brody said the presence of pavement increases the amount of damage on the ground.

The 25-mile-long complex of docks and warehouses that make up the Port of Houston planned to remain closed Tuesday.

Kurt Nagle, chief executive of the American Association of Port Authorities, said that early indications show there is “light to moderate” infrastructure damage along the Houston Ship Channel — 150 business facilities that generate $617 billion in economic activity per year. At least three vessels originally headed for Houston have been diverted to New Orleans, and more may be detoured in coming days from Houston and other affected ports in Galveston, Victoria, Beaumont, Port Lavaca and others.

The continuing severe weather may have further effects on the ports in the region, Nagle said. But even once things clear up, significant work will need to be done before shipping channels in the area can reopen. The Coast Guard will need to perform surveys of the area to determine whether buoys and navigation aids have been moved or lost, and the Army Corps of Engineers will need to perform a channel assessment to ensure that no debris is blocking the shipping channels under the surface.

Benny Rousselle witnessed the ravages of water during Katrina from his perch as president of Plaquemines Parish, south of New Orleans. The priorities for leaders in Houston are clear, for now: help those who are stranded.

“The pressure is on the local elected officials to get this community up and running as quick as possible, so they can come home and help with the recovery,” said Rousselle, who is now on the parish council. “But you cannot do that until you have enough utilities and roadways cleared so they can come in,” Rousselle said.

Faiz Siddiqui contributed to this report.