HOUSTON (AP) — As the human toll and the strain on flood defenses mounted yesterday, the rain from Harvey officially became the heaviest tropical downpour in US history.

A pair of 70-year-old reservoir dams that protect downtown Houston and a levee in a suburban subdivision began overflowing yesterday, adding to the rising floodwaters from Harvey that have crippled the area after five consecutive days of rain that set a new continental US record for rainfall for a tropical system.

The rains in Cedar Bayou, near Mont Belvieu, Texas, reached 51.88 inches (132 centimeters) as of 3:30 pm CDT. That’s a record for both Texas and the continental United States, but it does not quite pass the 52 inches (133 centimeters) from Tropical Cyclone Hiki in Kauai, Hawaii, in 1950 (before Hawaii became a state).

The previous record was 48 inches set in 1978 in Medina, Texas, by Tropical Storm Amelia. A weather station southeast of Houston reported 49.32 inches of rain as of yesterday morning.

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 the relentless downpours, 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 Linder of the Harris County Flood Control District.

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.

The levee was later fortified, but officials said they did not know how long the work would hold.

Officials in Houston were also keeping an eye on infrastructure such as bridges, roads and pipelines that are in the path of the floodwaters.

Water in the Houston Ship Channel, one of the nation’s busiest waterways, which serves the Port of Houston and Houston’s petrochemical complex, is at levels never seen before, said Linder.

The San Jacinto River, which empties into the channel, has pipelines and roads and bridges not designed for the current deluge, Linder said, and the chance of infrastructure failures will increase the “longer we keep the water in place”.

Among the worries is debris coming down the river and crashing into structures and the possibility that pipelines in the riverbed will be scoured by swift currents.

In 1994, a pipeline ruptured on the river near Interstate 10 and caught fire.

Although forecasters had feared that another 2 feet could fall in some places, it appeared that the outlook had improved somewhat. The weather service said two to three more inches was expected to fall, perhaps a little less in Houston proper, as the storm moved east.

But south-eastern Texas and south-western Louisiana are still likely to see “relentless torrential rains”, with another six to 12 inches of rain across the upper Texas coast through Friday as Harvey moves slowly east over the Gulf of Mexico, the National Hurricane Center said.

It is expected to make landfall again this morning, probably in south-western Louisiana.

The system 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 lit up weather radar screens early yesterday, the 12th anniversary of the day Katrina made landfall in Plaquemines Parish.

The disaster is unfolding on an epic scale, with the nation’s fourth-largest city mostly paralyzed by the storm that arrived as a Category 4 hurricane and then parked over the Gulf Coast. The Houston metro area covers about 10,000 square miles (25,900 square kilometers), an area slightly bigger than New Jersey.