A hot-spot analysis of subsidence in the Houston metro area during the period from 2016 to 2020 revealed total subsidence of up to 9 centimeters in some areas. Rates of subsidence approached 2 cm per year. (Two centimeters equals 0.8 inches. Nine centimeters = 3.54 inches.)
The scientific study, named “Surface Deformation Analysis of the Houston Area Using Time Series Interferometry and Emerging Hot Spot Analysis” appeared in a scientific journal called Remote Sensing. Authors included Shuhab D. Khan, Otto C. A. Gadea, Alyssa Tello Alvarado and Osman A. Tirmizi from the Department of Earth and Atmospheric Sciences at the University of Houston.
Correlating InSAR Data with Well Data
The authors correlated observations of surface deformation using interferometric synthetic aperture radar (InSAR) data with an analysis of 71,000 water and and 5,000 oil-and-gas wells in the Houston area. They collected the InSAR data over 5 years and the well data going back 31 years.
USGS calls InSAR an effective way to measure changes in land-surface altitude. The images are compiled by using radar signals with a very high degree of resolution bounced off Earth from orbiting satellites. By measuring the time for the signals to travel to earth and back, researches can measure altitude. And by superimposing images taken at different times, researchers can measure changes in altitude over time.
Documenting Link between Subsidence and Groundwater Pumping
Khan and his team sought to determine how much groundwater pumping contributed to subsidence (sinking ground). They performed the same analysis for oil and gas pumping.
The researchers found the greatest subsidence – which had not been previously reported – in some of the region’s fast-growing suburbs – Katy, Spring, The Woodlands, Fresno and Mont Belvieu. They identified groundwater pumping as the primary cause in the first four, and oil and gas pumping as the primary cause in Mont Belvieu.
Otto Gadea, a graduate student from Khan’s team is quoted in Phys.org as saying, “We determined for the suburbs that excessive groundwater extraction appears to be the primary driver of subsidence.”
Population Growth Drives Groundwater Pumping
With population growth, groundwater extraction has become more prevalent in the Houston area. But subsidence is no longer substantial in areas that regulate it through entities such as the Harris-Galveston Subsidence District.
The Appearance of Regulation as Cover for Private Interests
Other counties have set up entities to regulate ground water withdrawal, such as the Lone Star Groundwater Conservation District (LSGCD) in Montgomery County. However, the elected board chose not to include a subsidence limit in its desired future conditions. Many of the board members were backed by money from Quadvest, the area’s largest private groundwater pumper.
Website’s such as StopOurSinking.com have long linked excessive groundwater pumping in Montgomery County with a host of issues ranging from subsidence, flooding, pavement breaks, and foundation shifting to pipeline problems. However, the LSGCD Board has cherry-picked scientific evidence that supports unlimited groundwater pumping.
This latest study by the UH team will make that harder. It validates many of the claims StopOurSinking has made for years. Khan’s team even concluded that subsidence may even cause fault movement in the area.
Link to Fault Movement, Too
“If current ground pumping trends continue, faults in Katy and The Woodlands will likely become reactivated and increase in activity over time,” the authors write. No seismic activity is reported along these faults yet they say. They believe the movement is happening by “aseismic creep.” However, Khan and his team found evidence of fault activity in “damages to roads, buildings and other infrastructure in the vicinity of these faults. Displacement along some is measured by up to 3 cm/year.”
Posted by Bob Rehak on 10/12/22
1870 Days since Hurricane Harvey
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