8/17/2025 – Three scientists have summarized more than 100 years of studies about the relationship of groundwater and land subsidence in the Houston region. The study’s title: “A Century (1906-2024) of Groundwater and Land Subsidence Studies in Greater Houston Region: A Review.” The review revealed some stunning facts about past groundwater management practices in the Houston area and their implications for the future.
About the Study
The comprehensive 25-page review of scientific literature is essential reading for anyone interested in understanding the history of geologic subsidence in southeast Texas. The review examines its causes, impacts, regulatory remedies, and how it’s measured.
The authors are Michael J, Turco and Ashley Greuter of the Harris-Galveston Subsidence District, and Dr. Guoquan Wang of the University of Houston’s Department of Earth and Atmospheric Sciences. They published their copyrighted article in the July/August 2025 issue of Groundwater on behalf of the National Groundwater Association.
Stunning Facts
In the study, the authors relate some fascinating facts about subsidence in the Houston region. For instance:
- Subsidence has impacted approximately 12,000 square kilometers, encompassing nearly all of Harris and Galveston Counties as well as parts of surrounding counties.
- This led to the irreversible loss of 12 cubic kilometers of groundwater storage – equivalent to 60 times the volume of Lake Houston.
- That equals 8 years worth of water usage for all of Harris and Galveston Counties (at 2023 consumption rates).
That’s significant because groundwater is our backup for surface water during droughts. And who can forget the three-year drought from 2011 to 2013 when you could virtually walk from one side of Lake Houston to the other in many places.
Due to groundwater regulations, the extent of subsidence rates has decreased significantly since 1990. By the early 2020s, the areas seeing subsidence of greater than 1 cm per year had shrunk to one twentieth of the Houston region (1500 square kilometers). And only 50 square kilometers have rates higher than 2 cm/year.
Today, most of the remaining subsidence exists in the fast growing areas to the region’s north and west, which were the last to be regulated.
History of Subsidence in Region
According to Turco et. al., the earliest documented instance of subsidence happened in Baytown’s Goose Creek Oil Field during the 1920s.
From the late 1940s to the mid-1970s, rapid subsidence, occurring at rates of up to a decimeter per year, became increasingly pronounced in the southeastern parts of Houston
Declining groundwater levels (GWLs), driven by rapid industrial expansion, resulted in over 2 meters of subsidence in the area along the Houston Ship Channel from the 1940s to the mid-1970s. By 1979, as much as 3 meters of subsidence had been documented in the Baytown area.
Since the 1990s, as Houston’s population expanded to the north and northwest groundwater pumping triggered subsidence. Areas around Katy, Jersey Village, and The Woodlands experienced subsidence rates of 1 to 3 cm per year as of the early 2020s.
Striking a balance between groundwater resource management, subsidence, urban development, and environmental sustainability is central to the Houston region’s future. The paper explores how regulatory initiatives have influenced current practices and policies as leaders seek to reduce and prevent subsidence.
Evolution of Regulatory Agencies
A large part of the paper deals with how regulatory entities have expanded their geographic scope to keep pace with population growth. The paper includes discussions of:
- The Harris-Galveston Subsidence District (HGSD) in 1975
- Updates to its groundwater regulatory plan in 1985, 1992, 1999, and 2013
- Different regulatory areas within the Houston region
- Fort Bend Subsidence District (FBSD) in 1989
- Seven additional groundwater conservation districts covering most of the counties in the region.
Evolution of Monitoring Technology
Technology aficionados will appreciate the discussion of techniques used to monitor both groundwater levels and surface subsidence.
HGSD, in cooperation with the U.S. Geological Survey, monitors water levels and pumping rates in 650 wells throughout the region. HCSD also annually monitors groundwater pumpage from all permitted wells within the District (about 7500 wells in 2024).
As more water is extracted, clay layers in the soil become compacted. A former leader of the subsidence district once described it as “squashing a brownie.” Once compacted, it will not return to its former state.
The effects of subsidence are most notable closest to sea level. We can see them in the loss of highways, subdivisions, wetlands, vulnerability to storm surge, and more.
However, even areas a 100 feet or more above sea level can feel the impacts. Differential subsidence can trigger faults, disrupt pipelines, alter the gradient of streams, and create bowls in the landscape that increase flood risk.
Prior to the 1990s, subsidence was tracked through repeated spirit-leveling surveys and extensometers. However, since then, GPS has emerged as the dominant tool for measuring subsidence. It offers greater precision and more efficiency than conventional methods.
HGSD and FBSD operate approximately 114 subsidence measuring stations that use GPS. And they continuously add new stations to areas of interest.
They also use Interferometric Synthetic Aperture Radar (InSAR) to create detailed displacement maps over time. InSAR is especially good at filling in the gaps between the GPS measuring stations to create contour maps.
The scientists also use tidal gages and borehole extensometers to cross-reference data and extend the historical record of subsidence.
Major Discoveries
According to the authors, “Before the 1960s, the connection between groundwater extraction and subsidence was not immediately evident. Other factors, such as oil and gas extraction and local fault activity, were also considered significant contributors.”
They continue, “However, as evidence from ground-water-level measurements grew, and subsidence increasingly led to infrastructure damage and altered drainage patterns, it became clear that groundwater withdrawal was the primary driver of land subsidence.”
Oil and gas extraction and fault movement were also considered serious contributors at one time. “However, as evidence from groundwater level measurements grew, and subsidence increasingly led to infrastructure damage and altered drainage patterns, it became clear that groundwater withdrawal was the primary driver of land subsidence,” say the authors.
Another major discovery was that subsidence-induced compaction of the soil has led to the loss of groundwater storage capacity.
“The volume of total land subsidence directly correlates with the loss of groundwater storage capacity,” says the paper. “Groundwater is a crucial backup supply for maintaining water security in large cities, and with decreased storage, the risk of water shortages grows, potentially impacting agricultural productivity, industrial operations, and daily life for residents.”
New Focus on Sustainability
In conclusion, the authors state, “As Houston’s population continues to grow, the increasing demand for water underscores the urgent need for sustainable water sources that extend beyond the current groundwater and surface water capacities. To address this, HGSD, FBSD, and GCDs are intensifying efforts in water conservation and exploring alternative water solutions, actively engaging local stakeholders.”
Posted by Bob Rehak on 8/17/25
2910 Days since Hurricane Harvey
