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What's in a watershed? How Houston's landscape played a role in Harvey

Each of Harris County's 22 watersheds flooded during the storm

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HOUSTONHurricane Harvey was a storm felt along the length of the Texas coast and changed lives from Rockport to Refugio, and then east all the way to Beaumont.

While many Texas communities saw destructive flooding, some of the most shocking scenes came out of the greater Houston-area. And to understand why Hurricane Harvey was so destructive in Houston, you've got to start from the ground up.

Jeff Lindner, a meteorologist and hydrologist at the Harris County Flood Control District, said Houston's land isn't much different than a portion of Louisiana.

"We have a very urban area pretty much that has been built over the top of a marsh," Lindner said. "What I mean by marsh is it's not really different here than say southern Louisiana. It's very low-lying. It's very coastal."

Aside from being so close to sea level, the Houston area also has a lot of watersheds. 

A watershed is an area with defined boundaries that houses a body of water that drains to a certain point. These bodies of water can include creeks, bayous, rivers and reservoirs. 

Harris County -- which houses Houston -- has 22 watersheds. If the number seems a lot, that's because it is. In comparison, Bexar County has five watersheds, Travis County has seven, and Dallas County has nine. All of Harris County's watersheds drain to Galveston Bay on the southeast side of the county. 

Lindner said the watersheds could keep up with the rain from Harvey for a time, but it soon became too much. Rain began to pile up on top of the watersheds and wasn't moving downstream to drain fast enough.

The Saturday night and Sunday morning after Harvey made landfall was when things started to take a turn for the worse. 

"Water was everywhere. By Sunday mid-day, about 75 percent of our county was underwater, that had water above the ground. In the end, we had about 154,000 homes flood. That's just homes, " Lindner said. 

He added, "We've never faced a situation before where we had every single one of our 22 watersheds flooded, and I'm talking major, record flooding." 

That's what Harvey was: a record-smashing, life-changing storm. And while Houston's land did play a role in why the water didn't clear out fast enough, there's also the tremendous amount of rainfall to consider.

Lindner said some rainfall rates like those seen during Harvey is too much for any city to handle.

"So, it's more so the topography, the flat topography we have, but even more important it's the rainfall. How fast does the rain fall from the sky? If you get 30 inches over five or six days, your systems can sort of keep up with that," Lindner said.

"But, when you get 25-30 inches of rain in a 24-hour period, there's just no way your drainage systems are going to be able to keep up with that." 

(SCROLL BELOW TO VIEW A BEFORE & AFTER HARVEY ANIMATION)

While Harvey was first and foremost a deadly, destructive force, Lindner said it's also taught residents a lot. 

"I would probably say the residents of Southeast Texas, especially Harris County and Houston, know the most about their hydrology than any place in the nation because of Harvey. Because, it forced people to learn, 'What watershed do I live by? Where does my water come from? What elevation am I at?'"

While they may not have known as much about their hydrology before Harvey, Texans sure knew one thing -- when to start putting their communities back together. 

"What I always tell people: Things are a little bit different in Texas. We’re not gonna sit here and not do something. We kind of have this mentality, and I know you see it in Rockport and Port Aransas and any of the places you go, they start immediately," he said. 

"People around here, we start immediately. As soon as the wind, as soon as the rain stops, as soon as the water starts to go down, we’re out there helping each other recover. That’s something really special that we have."

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