‘Significant’ sinking ground discovered in Houston suburbs

HOUSTON — A troubling analysis of thousands of local water and oil wells in the Houston metro area has revealed significant rates of subsidence — or gradual sinking — in some of the area’s fastest-growing suburbs. Even worse, researchers from the University of Houston say up until now these developments haven’t been covered or reported at all.

This research was led by Shuhab Khan, professor of geology at the University of Houston. His team found substantial subsidence in the Houston neighborhoods of Katy, Spring, The Woodlands, Fresno, and Mont Belvieu. They identified groundwater, oil, and gas withdrawal as the primary causes of this sinking.

“Subsidence used to be a rare phenomenon. Now, it is all over the world,” Khan says in a university release. “There are 200 locations in 34 countries where there’s known subsidence. Cities in the northern Gulf of Mexico, such as Houston, have experienced one of the fastest rates of subsidence.”

Sinking ground, of course, means a higher risk of flooding for local homes and businesses. Besides that, study authors add that it also creates a negative feedback loop. The weight of floodwater from severe flooding compresses the sediments in the subsurface, potentially exacerbating the already compacted soil, driving subsidence even further.

Houston sinking by an inch each year

The team used interferometric synthetic aperture radar (InSAR) data obtained from a European Space Agency satellite for this study. That dataset showed a total subsidence of up to nine centimeters (3.5 in) to the north, northwest, and west of Houston from 2016 to 2020. The subsidence rate was two centimeters (0.8 in) annually.

The research team also applied a statistical tool called applied optimized hot spot analysis to groundwater level data collected over the past 31 years from more than 71,000 water wells. This helped the team investigate how much groundwater pumping has contributed to subsidence. Similarly, they used the same analysis on over 5,000 oil and gas wells to estimate subsidence impact.

“It is thanks to the latest advances in geospatial analysis that we were able to investigate subsidence across the Houston area in unprecedented detail,” explains Otto Gadea, a graduate student from Khan’s team. “By analyzing comprehensive datasets from recent years, we determined for the suburbs, excessive groundwater extraction appears to be the primary driver of subsidence. Meanwhile for other areas such as Mont Belvieu, subsidence can be attributed to the heavy withdrawal of local oil and natural gas reserves.”

Houston
Fence deformation due to Long Point fault in Spring Branch. (University of Houston)

Could an earthquake rock Houston?

Due to population growth, groundwater extraction has become much more prevalent in the Houston area. More specifically, Prof. Khan notes downtown Houston, suburbs to Houston’s southeast, and parts of Spring Branch have all experienced subsidence in the past, but because of groundwater regulations, the subsidence is no longer significant.

Prof. Khan’s team also looked into the possible natural causes for the sinking, such as the expansion and shrinking of Houston’s clay, silty, and sandy soil sediments, or flooding repercussions. It’s possible sinking may also be causing fault movement in the area.

“If current ground pumping trends continue, faults in Katy and The Woodlands will likely become reactivated and increase in activity over time,” the study concludes.

The study is published in the journal Remote Sensing.

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