Why did Houston neighborhoods continue to flood under sunny skies?

For days, Houston-area residents living in the San Jacinto River watershed watched their cars fill with mud and the windows of their homes give way to brown floodwaters, even after the sky cleared. is illuminated. While many fled before the floods, local authorities rescued more than 230 people and 180 pets when the local emergency subsided on Monday.

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The urgent and dramatic rescue effort disconcerted many residents south of the river, who watched emergency services shift into high gear while their own sidewalks were barely damp.

“It makes our messaging difficult when we’re outside on a blue sky and a sunny day,” said Mark Sloan, Harris County emergency management coordinator.

The trajectory of the floods, sometimes surprising, is an oddity of the region’s geography and an almost imperceptible slope towards the Gulf of Mexico.

Sloan said Harris County’s creeks, creeks, bayous and rivers typically fill up when rain falls within its boundaries. In this case, most of the muddy water that swept through local neighborhoods fell farther north in Houston before flowing into the San Jacinto River to its eventual exit point into the Gulf of Mexico.

“It’s like a giant pipe. It fills this pipe, and all of a sudden it’s all coming towards us,” he said.

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Floodwaters, some of which flowed through the San Jacinto River Authority’s Lake Conroe Reservoir, did not peak all at once. The East Fork of the river near River Terrace peaked at 77.75 feet Friday afternoon, while the West Fork near Humble peaked at 58.8 feet Saturday. Water then flowed from each fork into Lake Houston, a municipal reservoir managed by the Coastal Water Authority, before passing Channelview and exiting at Morgan’s Point.

National Oceanic and Atmospheric Administration gauges at both forks were still recording moderate to major flooding Monday afternoon, as was another gauge station near Highway 90.

“It takes a while for precipitation to move downstream. And there are different lakes and reservoirs that release the water level there,” said Cameron Batiste, a meteorologist with the National Weather Service. “Many rivers and streams are expected to remain high for days or even weeks.”

Batiste said the flooding actually began with heavy rains on April 28, which saturated the ground to the north. The rain resumed midweek, as Huntsville recorded 15 to 20 inches and southeast Montgomery County recorded 20 to 25 inches. The runoff accelerated the pace of three rivers: Trinity, Navasota and San Jacinto.

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Officials have talked for years about controlling the impact of the overflowing San Jacinto River, which occurs during most storms. The two reservoirs dug into its canals have valves that can release water before heavy rains to reduce the impact of flooding. Not this time either. The move requires advance notice, and the forecast for the Houston area called for only a few inches of rain, which is below the city’s usual release threshold. No one expected a historic deluge, forecasters say.

Once flooding began, the San Jacinto River Authority controlling Lake Conroe began raising and closing its floodgates to minimize flooding on its sides. Its largest release, Thursday afternoon, saw a volume of water equal to nearly 72,000 cubic feet per second flow into the waterway. As its own levels fell, these releases diminished, pushing less water into the system.

“There are about 3,000 square miles of land where every drop of water that doesn’t get absorbed into the ground or stay in a pond or lake will eventually flow into Lake Houston,” Matt said Barrett of the San Jacinto River Authority. head of flood management division.

“We’re a place that floods frequently and it’s a healthy part of the ecosystem,” said Jill Bouillon, executive director of the Bayou Land Conservancy, which works to preserve floodplains. She said that while wetlands in the area would hold water and release it more gradually, it would flow directly from homes or paved surfaces.

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“Our creeks, our bayous, our creeks, our rivers, they all go to the Gulf of Mexico,” she said. “We live in a flooded place and so we have to learn to coexist with water, to leave room for rivers.”

Dustin Hodges, chief of staff to Houston City Council member Fred Flickinger, whose Kingwood district flooded in neighborhoods like Forest Cove and North Shore, said many people who lost their homes had already been flooded and rebuilt after Hurricane Harvey in 2017.

“A lot of them have raised their homes since Harvey, or are living there in anticipation of what might happen, so they were pretty prepared,” Hodges said.