Growth of Impervious Cover Across Political Boundaries, Watersheds Complicates Flooding
In December, the New York Times published a story about a company called Descartes Labs, which had trained computers to scan satellite images to detect changes in impervious cover. Descartes found that Texas had 9 of the top 20 counties in the US when ranked by the growth of impervious cover. So I contacted them to learn more.
A Better Understanding of the Planet
Descartes positions itself as a data refinery for satellite imagery. They process images from the major NASA and ESA satellite constellations at scale, creating a digital data twin of the entire planet that monitors the whole earth, in near real-time. Their mission: to better understand the planet.
The red dots in the map below show land that is newly covered in concrete or rooftops. It is a form of “heat map” that shows the hottest areas for growth. Studying this map, we can learn several things:
- Stories about the demise of suburbs and exurbs after the real estate crash in 2008 proved short-lived. From the numerous rings around major metropolitan centers, you can see that growth outside of major metropolitan areas continues.
- Texas appears to have the greatest increase in density of any state.
- Far more growth happened in the East than the West.
A Closer Look at Texas
This next map, also courtesy of Descartes, zooms in on Texas and surrounding states. The yellow dots simply correspond to the names of metropolitan centers.
Growth around Houston seems fairly uniform, though my eye does detect slightly more weight to the north, west and south than the east. This will likely change in the next decade with the extension of the Grand Parkway toward the east.
Factors Contributing to Flooding
Several factors contribute to Houston’s reputation for flooding:
- Rapid population growth and corresponding growth of impervious cover, as Descarte showed. The impervious cover causes floodwaters to concentrate/accumulate faster.
- Loss of wetlands And flood plain storage
- Flat, poorly drained landscape
- Gulf moisture that regularly brings hurricanes, tropical storms and torrential rains
- Fierce dedication to individual freedom, property rights, and local authority (Hey, this IS TEXAS after all.)
- Political fragmentation
- Widely varying flood control regulations
- Upstream development that overwhelms the capacity of downstream drainage channels
In the last century, Houston has exploded from a sleepy city of less than 200,000 to a 9-county metropolitan statistical area with a population of about 7 million covering more than 9 thousand square miles.
Now, superimpose watersheds over those counties and you can see how difficult the flood control situation becomes.
Solutions Will Require Cooperation
Rivers and streams cross political boundaries throughout this region. So solutions to flooding problems are, by definition, regional. Yet development regulations and guidelines are anything but.
Most regulations pay lip service to “no adverse impact” on downstream neighbors. But in many areas, the regulations may be based on ancient maps and antiquated data. Moreover, they may have little to no oversight or enforcement.
Retain Your Rain
The region’s growth depends on its reputation for quality of life. If we are to continue growing, we must work together to solve flooding problems.
If every developer did one simple thing, we could eliminate most of our flooding problems. Just be responsible for the rain that falls on your property. Detain it long enough to avoid adding to flood peaks.
It’s that simple and that difficult. Especially considering that Texans don’t like having other people tell them what to do.
Posted by Bob Rehak, with thanks to Descartes Labs
863 Days since Hurricane Harvey and 112 since Imelda
