ENVIRONMENT New report provides more data in ongoing subsidence debate
BY VANESSA HOLT & EMILY LINCKE
damage to property, pipes and roads, Khan said. It also makes an area more susceptible to ooding. Although the conditions that cause subsidence can be lessened by cities using alternative sources, such as surface and potable water, the e ects of subsidence are permanent, said Robert Mace, water policy director at Texas State University. “If you reduce your pumping, you can then decrease the maximum sub- sidence that would have occurred,” he said. “But for the most part, land subsidence is a one-way trip. Once it’s compressed, it’s not coming back up.” Local entities weigh in The UH report found the biggest contributor to subsidence was the use of groundwater. Wells can be drilled into an aquifer, which consists of layers of under- ground, water-bearing rock, and water can be pumped out for use by residents. Since property owners own the rights to water produced from wells on their properties, pumping groundwater is also a property-rights issue, which o cials with the Lone Star Groundwater Conservation Dis- trict have said they want to defend. However, o cials with local entities that govern water in the Conroe area said in February they are still analyzing what the Jan. 12 report means for their understanding of how subsidence is a ecting the area. Jim Spigener, president of the LSGCD board of directors, said at a Feb. 14 board meeting the agency would try to provide comments within the public comment period before the April 17 deadline. “The [ground] compaction data incorporated into the GULF-2023 model is not from Montgomery County or the Jasper Aquifer,” Spigener said in an email, citing the district’s technical consultants. “This ... further supports the need to perform Phase 3 of the [LSGCD] subsidence study.” O cials with the LSGCD previously told Community Impact they do not believe that subsidence can be attributed entirely to groundwater withdrawal based on current studies, and they questioned methodologies used. O cials said the district launched a study in 2019 to better WA
LOSING GROUND Subsidence contours in the GULF-2023 report released Jan. 12 outline the areas in the Greater Houston region that have been sinking at approximately the same rate since measurements were rst taken in 1906.
A Jan. 12 report from the Oklahoma-Texas Water Science Center outlines land sinking that has occurred in the Greater Houston area, according to information released by the Texas Water Development Board. As of 2021, The Woodlands saw an average of 2.5 feet of sinking over the past century, and Conroe saw an average of 1.5 feet, according to the Jan. 12 report, with most of the land movement occurring since 1987. This gradual, vertical decline is known as subsidence, or the sinking of the land due to movement beneath the Earth’s surface. John Ellis—who authored the Jan. 12 study also known as the GULF-2023 report and who serves as the center’s Gulf Coast studies chief— said this subsidence worsens ooding in watersheds by “altering the base ood elevations.” “[Subsidence] is an important phenomenon to document and study. ... It can result in permanent loss of land, increased risk of ooding and the damage to the infrastructure,” Ellis said. The Jan. 12 report comes on the heels of an August report from the University of Houston on land subsidence, tracking land deformation in Houston’s suburbs from 2016-21. Subsidence is chie y caused by pumping water from underground reserves, which compacts sublayers of clay and silt in aquifers beneath the Earth’s surface, according to the UH report. The resulting sinking is a problem experienced all over the Greater Houston area. Shuhab Khan, a UH geology pro- fessor and one of the August report’s authors, said he believes there is a bal- ance to using groundwater sustainably. “Groundwater is the cleanest water all over the world,” Khan said. “It is a means for drinking, for agri- culture, for industry, and when we start pumping more water than the amount of water that is replenishing [aquifers], that balance is gone.” The UH study states its ndings also imply subsidence may be responsible for fault movement in the Greater Houston area based on analysis of land displacement. Over time, subsidence can cause
Cumulative subsidence contours, 1906-2021
Key:
1-2 feet
2-3 feet 3+ feet
MONTGOMERY COUNTY
1
105
45
249
2
69
99
290
Montgomery
Liberty
Harris
Waller
Average sinkage 1906-2021
Chambers
2 The Woodlands: 2.5 feet 1 Conroe: 1.5 feet
Fort Bend
Galveston
Brazoria
N
SOURCE: OKLAHOMA TEXAS WATER SCIENCE CENTER COMMUNITY IMPACT
“ SUBSIDENCE IS AN IMPORTANT PHENOMENON TO DOCUMENT AND STUDY. … IT CAN RESULT IN PERMANENT LOSS OF LAND, INCREASED RISK OF FLOODING AND DAMAGE TO INFRASTRUCTURE.”
John Ellis, chief of Gulf Coast studies for the Oklahoma-Texas Water Science Center
determine the underlying causes, but that is on pause while it comments on the GULF-2023 study. O cials with the San Jacinto River Authority, which manages and provides surface water for the region, said the new study provides more accurate information on subsidence, which they believe is the result of
groundwater withdrawal. SJRA General Manager Jace Hous- ton said the new model uses informa- tion from a broad range of sources. “This latest version will increase the accuracy even more, especially around the edges of the model where data is more recent,” Houston said. Asia Armour contributed to this report.
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CONROE MONTGOMERY EDITION • MARCH 2023
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