SEGUIN, Texas >> More than 400 trailers packed with water, food, tarps and generators line a vacant airstrip in the farmland just northeast of San Antonio that has been transformed into a bustling logistics hub. Crews from the Department of Defense and the Federal Emergency Management Agency are working to dispatch aid to storm victims.

But the difficulty of responding to a major natural disaster was apparent Aug. 29 as more trucks of supplies rolled in, and almost none rolled out. Roads were tied up, needs were still not known. Four semis sent to supply a massive shelter at NRG Field in Houston, where NFL games and rodeos are usually held, were idling at a roadblock, unable to deliver food and water.

“It’s been a constant stream of trucks in,” Steven Bouie, a FEMA employee in an orange vest, said as he checked in a long line of trucks arriving. “Now we’re working on a big push to get it all out to people who need them.”

Disaster planners have been preparing for years for a storm like Hurricane Harvey, and repeated hurricanes on the Gulf Coast have given them plenty of practice, but the scale of this storm has pushed many emergency workers beyond their limits. Operators at the 911 system were overwhelmed, sending trapped residents to turn to social media. Police and firefighters got help from an armada of citizen bass boats and Jet Skis.

More than 30,000 people are in 230 shelters across Texas, but FEMA cautioned that the number would likely rise sharply. More than 50 counties in Texas and Louisiana have been impacted in some way by flooding, FEMA said. The Coast Guard continues to receive more than 1,000 calls an hour for help. More than 200,000 people have registered for FEMA assistance.

The military has sent in helicopters, cargo planes, trucks, amphibious vehicles, even special operations Marines in inflatable rafts, and were mobilizing hundreds of other troops.

Federal authorities say lessons learned from the often glaring missteps in the response to Katrina in 2005 have helped them to better prepare for the disaster unfolding in Texas. But many were reluctant to tout the accomplishment with the storm still swirling off the coast.

“I think we don’t know what we don’t know.” said Lt. Gen. Jeffrey Buchanan of the Army, as he walked into the command briefing of Army North, the military command in charge of homeland defense. So far, he said, troops and federal aid workers were doing all they could.

At a long table surrounded by maps and video screens, an Army North team took turns briefing the general on the military response: 400 deep water trucks moving through Houston’s flooded neighborhoods; a fleet of Black Hawk helicopters running night rescues when civilian aircraft often cannot fly; satellite communications teams moving in to crucial locations.

Crews had whisked hundreds of stranded people to dry land. Air Force planes were getting ready to evacuate hospitals in storm-crippled neighborhoods. Looting remained low, but the National Guard was ready to step in to help police if necessary.

“We’ve got Ospreys,” a Marine officer said, referring to tilt-rotor aircraft that flies like an airplane but can land vertically. “We’ll stage them in Florida in case we need them when the storm hits Louisiana.”

The general nodded silently as he absorbed each fact, then looked up.

“It’s bad and is probably going to get worse. When the rain stops we’ll find out,” he said. “It’s not just rescue, it’s recovery. We need to be looking 10 days out to see what we are going to encounter.”

The storm presents a challenge for federal authorities on a scale rarely seen: The nation’s fourth-largest city paralyzed, an unknown number of houses destroyed, tens of thousands of people displaced, shelters running low on supplies, the storm still hovering.

Federal officials say they are poised to help where needed and are taking their lead from local leaders. In the disaster relief chain-of-command, mayors, governors, police chiefs and other local authorities have run the show in recent years. FEMA and the military stand by to provide resources to help. Federal officials say local officials know best what is needed and where.

“We don’t want to go running to the guns with everything we’ve got and just become part of the problem,” Buchanan said.

This is a marked departure from the era of Hurricane Katrina, when federal authorities were more likely to impose control from above, said Gary Webb, a professor of emergency management at the University of North Texas.

“Katrina’s failures were a wake up call that really changed how emergency response is done,” said Webb, who gave authorities high marks on their response so far. “It forced federal agencies to be more nimble, and to really follow the lead of local authorities.”

After Katrina, he said, federal and local authorities strengthened joint training to ensure smooth operations. Congress passed laws to dismantle bureaucratic road blocks that kept agencies from working together, and require administrators to have considerable emergency response experience.

Local authorities have shown that they are much more willing to ask for help from ordinary citizens, Webb said. “In the past the practice was to tell people to stay out of the way,” he said. “But in a disaster of this scale, local authorities could never be prepared for the needs.”

So far, he said, FEMA and other responders have done a much better job than during Katrina. Communication has improved. FEMA, which was seen as nonresponsive in New Orleans, now embeds someone with local emergency response teams that act as a go-between.

When a mayor or fire chief requests a communications truck, shipment of food or generator for a nursing home that’s lost power, FEMA sends the request to the air field in Seguin.

“We’re 24-7, what they need, we will get them,” said Wes Myers, a FEMA logistics specialist who oversees the shipments at the air field. “The hours are long, but it’s a job we’re happy to do.”

He said so far he had encountered few problems.

“Houston has plenty of experience dealing with flooding, so they might be getting pretty good,” said Kathleen Tierney, a professor at the University of Colorado and the former director of the school’s Natural Hazards Center, noting that repeated storms have flooded the area since 2001. “But it is also the poster child for what not to do. Over and over decisions have favored growth and development over sustainability and safety.”

As the sun started to break through in Houston on Aug. 29, the long-term reckoning of past decisions was eclipsed for emergency workers by the immediate needs of their neighbors.

Pulling into Port Aransas, Rocky Emmons, a truck driver delivering one of the first trailers of water for FEMA, said National Guard troops immediately started pulling down pallets and giving them to thirsty families waiting in a line two blocks long at a local school.

“It all happened so fast,” he said. “And people really needed it.”