Subsidence Update: HGSD 2025 Groundwater Report

4/30/26 – The Harris-Galveston Subsidence District (HGSD) has published a presentation that summarizes the major findings of its 2025 Annual Groundwater Report. HGSD also heard public comments on the report this morning, which the HGSD Board will review on May 13 before the report becomes final.

The major finding: serious subsidence continues in a band that stretches across southern Montgomery County into northwest Harris County out to Katy. See red area below.

*Page 40 from HGSD 2025 Groundwater presentation.*

A monitoring station in Katy measured a total of 35 cm of subsidence since 2007 with an average rate between 2021-2025 of 2.64 cm/yr. Thirty-five centimeters is 13.77 inches. 2.64 centimeters equals 1.03 inches.

What Causes Subsidence and What it Affects

Groundwater withdrawals lead to compaction of soils which, in turn, leads to subsidence or a sinking of the land surface.

Subsidence is critical near the coast. A whole subdivision in Baytown sank below the waves. But even in inland areas, differential subsidence can create bowls in the landscape that make structures more susceptible to flooding.

In places the cumulative rate of subsidence has been enough to erase the safety margins between foundations and floodplains.

Subsidence also causes cracks in pipelines, storm drains, roads, driveways, and foundations that can lead to expensive repairs. Problems are especially severe near fault lines because subsidence can activate fault movement.

History of HGSD and Subsidence in Houston Region

The Texas Legislature created HGSD 50 years ago to regulate groundwater withdrawals and slow subsidence. HGSD divided the region up into three regulatory areas, based on need at the time. The area with the lowest need then has the highest need now, because it took longer for regulations to kick in.

The regulations create incentives for people to reduce usage of groundwater.

Since 1988, groundwater-level altitudes in wells are down 200 to 300+ feet in portions of southern Montgomery County and west-central Harris County.

This year’s annual report covers four main areas. Discussions of a) climate, b) water use and c) groundwater levels. Those three factors result in d) subsidence. Next, let’s briefly look at the three contributing factors.

Climate

Drought spread throughout the region last year and accelerated in the second half. The tan areas in the graph below show the rainfall deficit versus the average from 1991 to 2020. Each monitoring station showed significant deficits.

*Page 7 of 2025 Annual Report Presentation*

Less rain means more irrigation of lawns and crops. And much of that supplementary water comes from the ground.

Groundwater Use

The discussion of groundwater withdrawals starts with the three different regulatory areas.

*Page 12 of presentation*. *Note the different requirements for Area 3.*

The next two pages show dramatic declines of groundwater usage in Areas 1 and 2. However, it’s a different story in Area 3 which also has the greatest subsidence. Groundwater usage is down slightly in the last 25 years, but still hovering near the 50-year average.

When you add up groundwater usage from all three areas, you can clearly see two things:

Overall decline in usage
Region 3 represents 83% of the total

*Page 14. Note how Region 3 comprised roughly a third of groundwater usage in 1976.*

As we reduce groundwater consumption, we’re relying more on alternative water sources, such as surface water from the three major rivers that feed our region. Increasingly, we rely on water from the Trinity River and Lake Livingston.

So how does all that actually translate into water-level declines? HGSD has observed declines in wells throughout the region. Those wells are drilled into three aquifers that supply us: the Jasper, Chicot and Evangeline. The last two are undifferentiated and effectively form one unit for research purposes.

In the next two charts, note how areas with the greatest water-level declines have experienced the most subsidence.

*Page 27 focuses on declines in the Chicot/Evangeline aquifers.*

*Page 28 focuses on declines in the Jasper aquifer.*

The full 40-page presentation contains much more detail. For instance, it describes water level declines at individual wells. The presentation also reviews data from multiple sources/technologies as a cross-check for consistency and reliability.

Next Steps

HGSD has not yet published its full 2025 Annual Groundwater report. This presentation was intended to give the public a chance to comment on a preview this morning. HGSD’s board will consider a resolution to approve the report at its regularly scheduled meeting on the third Wednesday in May.

Upon approval, HGSD will publish the report, all supporting documents and an updated interactive subsidence map on its website.

Posted by Bob Rehak on 4/30/26

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