Data from GPS monitoring sites shows instances of ongoing subsidence and falling elevation in Montgomery County, including Conroe and Montgomery.
A CLOSER LOOK
Since supplementing groundwater use in Montgomery County with surface water in 2015 and implementing restrictions in 2016, the subsidence rate at this gauge near FM 1488 and FM 3083 in Conroe has slowed. The data below shows the average elevations of dozens of measurements made each year.
SUBSIDENCE RATES PER YEAR
16.09 cm subsidence from 2005-20
Subsidence is more heavily concentrated in southern Montgomery County, however northern areas are also seeing elevation changes.
1.9-1.5 cm 1.4-1 cm 0.9-0.5 cm Less than 0.5 cm
Subsidence rate from 2005 to 2015: 1.14 cm per year 1
Subsidence rate from 2016 to 2020, after restrictions are in place: 0.47 cm per year 2
4.66 cm subsidence from 2012-20
SOURCE: HARRIS-GALVESTON SUBSIDENCE DISTRICT/ COMMUNITY IMPACT NEWSPAPER
MAP NOT TO SCALE N
-16.09 cm | Total subsidence as of Jan. 21, 2020
deregulation, … [efforts to slow sub- sidence have] been undone,” said Mike Turco, the general manager of the HGSD. Slow sinking Subsidence is more heavily con- centrated in southern Montgomery County, according to data from the HGSD. However, areas of Conroe and Montgomery have recorded over half a centimeter per year on average, with one gauge near Lake Conroe recording nearly 1 centimeter per year. To reduce the county’s reliance on groundwater, certain large-volume groundwater users in Montgomery County entered into an agreement with the SJRA in 2010 for the latter to provide surface water to certain entities beginning in 2015 using a $497 million surface water treatment plant on Lake Conroe and water pipe transmission system paid for by the entities. In 2016, large-volume groundwater users in Montgomery County were required to cut back their groundwater usage by 30% of their 2009 usage. Consequently, the subsidence rate has since decreased, Turco said. For example, the sub- sidence rate in one area of Conroe decreased from 1.14 centimeters per year from 2005-15 to 0.47 centime- ters per year from 2016-20, according to HGSD. “In those areas where we’ve done some reasonable regulations to diver- sify [water sources], subsidence rates
CONTINUED FROM 1
2016 : Certain entities are required to restrict groundwater pumpage.
2020 : Restrictions are removed in September. 2020 values only extend through Jan. 21, 2020.
2015 : Surface water from Lake Conroe is introduced.
falling and in five years we’re going to have abandoned neighborhoods here, but … you can’t undo subsidence,” Houston said. “Once the ground sinks an inch, you can’t make it come back.” Hydrologists widely agree excessive groundwater use from aquifers—or water-bearing underground rock lay- ers—can lead to subsidence, which can cause flooding and infrastructure dam- age as well as exacerbate the activity of fault lines, or cracks in the earth. Several entities are closely watching subsidence in Montgomery County, including the SJRA, the HGSD and the Lone Star Groundwater Conservation District, the entity tasked with regu- lating groundwater in Montgomery County. However, officials disagree on how much groundwater the county should be allowed to pump and how much subsidence is acceptable. Newly implemented groundwa- ter rules and upcoming decisions pertaining to groundwater usage are highlighting this difference. In May, groundwater conservation dis- tricts within the region will consider new goals for the aquifers. And the LSGCD’s new groundwater usage reg- ulations, which went into effect in September, abolish prior restrictions on groundwater pumpage—a move district officials said puts them in line with the law but some fear could deplete aquifers faster. “The concern is now with the
SOURCE: HARRIS-GALVESTON SUBSIDENCE DISTRICT/COMMUNITY IMPACT NEWSPAPER
have been reduced or been elimi- nated,” Turco said. Subsidence can exacerbate flooding conditions and increase the activity of fault lines, which can lead to infra- structure damage, according to a 2019 study by Southern Methodist Univer- sity. Wade Oliver, senior hydrologist at Intera Geoscience and Engineering Solutions, discussed evidence of this correlation in the Greater Houston area at a Jan. 20 meeting of Groundwater Management Area 14. GMA 14 includes five groundwater conservation dis- tricts—including LSGCD—that manage the Gulf Coast Aquifer System. “Even if the faults are naturally occurring, the movement of those faults canbeaccelerateddue toground- water production, drops inwater levels and subsidence,” Oliver said. Fault lines crisscross Montgomery County, including Big Barn, which runs through The Woodlands, and the Conroe Fault Line. The latter caused about $100,000 in damages to the Conroe Aquatic Center from about 2010-18, Conroe Recreation Manager Rob Hamilton said. Several years after he was hired in 2004, Hamilton began to notice
reoccurring cracks in the pool. “The repairs were becoming an annual occurrence,” he said. A new solution was needed. Last summer, the city opened a newaquatic center away from the fault line. At odds How groundwater should be regu- lated in Montgomery County is a topic of debate. Some are looking to the LSGCD to enact stricter groundwater regulations and prevent subsidence. Meanwhile, LSGCD officials said they are tasked with a balancing act: pro- tecting groundwater while upholding private property rights—and these two are not mutually exclusive. “The district’s job is to have clear, fair and impartial rules that strike the appropriate balance to groundwater management under the law so permit holders can conduct their own water planning in the manner they deem best to meet their needs,” LSGCD Gen- eral Manager Samantha Reiter said. In 2018, a judge declared the groundwater reduction rules for large volume users void and unenforce- able. To comply with the judge’s rul- ing, LSGCDwas required to adopt new
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