A pair of 70-year-old reservoir dams that protect downtown Houston and a levee in a suburban subdivision began overflowing Tuesday, adding to the rising floodwaters from Harvey that have crippled the area after five consecutive days of rain.
Brazoria County authorities posted a message on Twitter warning that the levee at Columbia Lakes south of Houston had been breached and telling people to "GET OUT NOW!!!" Brazoria County Judge Matt Sebesta said residents were warned that the levee would be overtopped at some point, and a mandatory evacuation order was given Sunday.
Engineers began releasing water from the Addicks and Barker reservoirs Monday to ease the strain on the dams. But the releases were not enough to relieve the pressure after one of the heaviest downpours in U.S. history, Army Corps of Engineers officials said. Both reservoirs are at record highs.
The release of the water means that more homes and streets will flood, and some homes will be inundated for up to a month, said Jeff Lindner of the Harris County Flood Control District.
The county is trying to determine where the water will go, Lindner said.
Meanwhile, more than 17,000 people are seeking refuge in Texas shelters, the American Red Cross said. With rescues continuing, that number seemed certain to grow.
Calls for rescue have so overwhelmed emergency teams that they have had little time to search for bodies. And officials acknowledge that fatalities from Harvey could soar once the floodwaters start to recede from one of America's most sprawling metropolitan centers.
More than four days after the storm ravaged the Texas coastline as a Category 4 hurricane, authorities had confirmed only three deaths -- including a woman killed Monday when heavy rains dislodged a large oak tree onto her trailer home in the small town of Porter. But unconfirmed reports of others missing or presumed dead were growing.
"We know in these kinds of events that, sadly, the death toll goes up historically," Houston Police Chief Art Acevedo told The Associated Press. "I'm really worried about how many bodies we're going to find."
One Houston woman said Monday that she presumes six members of a family, including four of her grandchildren, died after their van sank into Greens Bayou in East Houston.
Virginia Saldivar told The Associated Press her brother-in-law was driving the van Sunday when a strong current took the vehicle over a bridge and into the bayou. The driver was able to get out and urged the children to escape through the back door, Saldivar said, but they could not.
"I'm just hoping we find the bodies," Saldivar said.
Houston emergency officials could not confirm the deaths.
A spokeswoman for a Houston hotel said one of its employees disappeared while helping about 100 guests and workers evacuate the building.
The disaster is unfolding on an epic scale, with the nation's fourth-largest city mostly paralyzed by the storm that parked itself over the Gulf Coast. With nearly 2 more feet (61 centimeters) of rain expected on top of the 30-plus inches (76 centimeters) in some places, authorities worried the worst might be yet to come.
Harvey kept drenching Houston and the surrounding area. Rain fell Tuesday at about half an inch (1 centimeter) per hour over Harris County -- home to Houston -- and up to 2 inches (5 centimeters) per hour to the east.
The Houston metro area covers about 10,000 square miles (25,900 square kilometers), an area slightly bigger than New Jersey. It's crisscrossed by about 1,700 miles (2,700 kilometers) of channels, creeks and bayous that drain into the Gulf of Mexico, about 50 miles (80 kilometers) to the southeast from downtown.
President Donald Trump was expected Tuesday in Corpus Christi and Austin for briefings on the first major natural disaster of his administration. Vice President Mike Pence said in an interview with Corpus Christi radio station KKTX that he will visit southeast Texas later this week.
Forecasters expect the storm to linger over the Gulf before heading back inland east of Houston sometime Wednesday. The system will then head north and lose its tropical strength.
It could creep as far east as Mississippi by Thursday, meaning New Orleans, where Hurricane Katrina unleashed its full wrath in 2005, is in Harvey's path. Foreboding images of Harvey were lighting up weather radar screens early Tuesday, the 12th anniversary of the day Katrina made landfall in Plaquemines Parish.
Rescuers meanwhile continued plucking people from inundated Houston neighborhoods. Mayor Sylvester Turner put the number by police at more than 3,000. The Coast Guard said it also had rescued more than 3,000 by boat and air and was taking more than 1,000 calls per hour.
Chris Thorn was among the many volunteers still helping with the mass evacuation that began Sunday. He drove with a buddy from the Dallas area with their flat-bottom hunting boat to pull strangers out of the water.
"I couldn't sit at home and watch it on TV and do nothing since I have a boat and all the tools to help," he said.
Nearly 6,000 inmates displaced by flooding have been moved from prisons in the Houston area to other facilities in South and East Texas, according to the state Department of Criminal Justice.
A mandatory evacuation was ordered for the low-lying Houston suburb of Dickinson, home to 20,000. Police cited the city's fragile infrastructure in the floods, limited working utilities and concern about the weather forecast.
In Houston, questions continued to swirl about why the mayor did not issue a similar evacuation order.
Turner has repeatedly defended the decision and did so again Monday, insisting that a mass evacuation of millions of people by car was a greater risk than enduring the storm.
"Both the county judge and I sat down together and decided that we were not in direct path of the storm, of the hurricane, and the safest thing to do was for people to stay put, make the necessary preparations. I have no doubt that the decision we made was the right decision."
He added, "Can you imagine if millions of people had left the city of Houston and then tried to come back in right now?"
By Tuesday morning, more than 9,000 people were at the city's largest shelter set up inside the George R. Brown Convention Center -- which originally had an estimated capacity of 5,000.
Red Cross spokesman Lloyd Ziel said that volunteers made more space inside the center, which also was used to house Hurricane Katrina refugees from New Orleans in 2005, in part by pushing some cots closer together. A shortage of cots means some people will have to sleep on chairs or the floor.
The center settled down at night, after an occasionally chaotic day that saw thousands of evacuees arrive in the pouring rain. Officers and volunteers at times rushed to attend to those with medical needs.
Before the storm is gone, up to 20 more inches (51 centimeters) of rain could fall, National Weather Service Director Louis Uccellini said Monday.
That means the flooding will get worse in the days ahead and the floodwaters will be slow to recede once Harvey finally moves on, the weather service said.
Sometime Tuesday or early Wednesday, parts of the Houston region will probably break the nearly 40-year-old U.S. record for the biggest rainfall from a tropical system -- 48 inches (120 centimeters) -- set by Tropical Storm Amelia in 1978 in Texas, meteorologists said.