The only thing in this aerial view of Houston (before flying machines) is a flood plain: https://en.wikipedia.org/wiki/File:Old_map-Houston-1873.jpg https://en

The only thing in this aerial view of Houston (before flying machines) is a flood plain: https://en.wikipedia.org/wiki/File:Old_map-Houston-1873.jpg https://en.wikipedia.org/wiki/File:Old_map-Houston-1873.jpg Where Houston was founded as a real estate venture to be the new center of government, business & industry for a newly independent nation, the land had been shaped by thousands of years of occasional overflow of these narrow bayous by miles beyond their normal banks. As the water from events like Hurricane Harvey always accumulates from all the upstream watersheds at this low point before moseying into the bay and the gulf. Or as a hurricane making a direct hit pushes the storm surge up the bay so the low point is not so low by comparison, and lesser rain than Harvey can be just as bad for some people. The purpose of Houston is to sell false estate (a flood plain) as if it was real estate, so a bigger fool has always been necessary. The 100-year and 500-year flood probabilities were likely gamed since the first flood of Houston. The capital moved upstream ending up in Austin. 100-year means one chance in 100 each year, if you're above the 500-year line it means you only have one chance in 500 every year. Note; where the big buildings were then is about where the big ones downtown are now.