Houston's Flood Problem
According to the Harris County Flood Control District, flooding is Harris County's number one natural disaster.
As anyone who has lived in Houston for a few years knows, Houston has a flood problem. The reasons are many.
Man-made factors play a leading role. Explosive suburban growth, the proliferation of impermeable concrete, asphalt, and brick, and Houston’s aging drainage system—all contribute to Houston's frequent street flooding.
The area’s natural topography discourages runoff. The flat ground rises only about 1 foot per mile, and the indigenous clay soil repels rainwater.
The weather gets most of the blame—whether global warming, long-term climate cycles, random weather patterns, or simply intense downpours that overpower drainage systems. For example, in 2001, Tropical Storm Allison delivered up to 80% of Harris County’s average annual rainfall in less than a week. And in 2017, Hurricane Harvey dumped 40 inches of rain over Houston in just 4 days.
When a waterway floods the adjacent land because of heavy rainfall, the flooded area is called a floodplain. The floodplain is identified by its frequency of occurrence. FEMA Flood Insurance Rate Maps show 1% (100-year) and 0.2% (500-year) floodplains. A 100-year floodplain has a 1% chance of being flooded by the same amount or more in any given year. A 500-year floodplain has a 0.2% chance.
Unfortunately, Houston’s sprawl shows no real signs of containment, despite new policies regarding developments and water detention—and climate models predict even larger, more frequent storms. And unfortunately, because the funding allocated by government entities and taxpayers for long-term flood mitigation will probably never be enough, dealing with storms and floods may always be a factor of life in Houston.
Houston's 21st Century Floods
Houston has an unsettling habit of flooding on national holidays.
June 2001 Tropical Storm Allison
June 2006 Torrential rain
Sep. 2008 Hurricane Ike
May 2015 Memorial Day flood
Oct. 2015 Halloween Day flood
April 2016 Tax Day flood
May 2016 Memorial Day flood
Aug.-Sep. 2017 Hurricane Harvey
July 2018 Fourth of July flood
Sep. 2018 Labor Day flood
Oct. 2018 Halloween Day flood
Dec. 2018 Willow Waterhole basin complex completed
Sep. 2019 Tropical Storm Imelda
Sep. 2020 Tropical Storm Beta
Hurricane Harvey’s
Massive Span
Hurricane Harvey dumped almost a year’s worth of rain on Harris County in just a few days, flooding more than 120,000 structures. (Harris County Flood Control District).
Hurricane Harvey occurred in 2017, before the Willow Waterhole basin was completed. More than 24 inches of rain fell in Houston in just the first 24 hours—overwhelming most flood mitigation structures. If the basin had been finished, the surrounding area would still have flooded, but to a significantly lesser degree.