Fort Bend Subsidence and Faults: What They Mean for a Slab

Subsidence is the land surface slowly sinking. Around Houston, the Fort Bend Subsidence District says it comes from pumping groundwater out of the aquifer. As water levels drop, fine-grained layers of silt and clay deep underground compact. The USGS says that's where most of the region's sinking happens.

The Houston area knows this problem well. The USGS has written that the region, "possibly more than any other metropolitan area in the United States," has been hurt by subsidence. Most of the early sinking was near the coast. More recently it has shifted north and west, to places still relying on groundwater.

That's why Texas has two subsidence districts, and only two. The Harris-Galveston Subsidence District dates from 1975. The Legislature created the Fort Bend Subsidence District in 1989 to regulate groundwater pumping in Fort Bend County. Neither inspects houses; they regulate wells. The Harris-Galveston district adds a hard truth: "once this subsidence occurs, it is irreversible."

The Fort Bend district tracks sinking with GPS stations and satellite radar. Its 2025 report, marked provisional, found:

• Fastest: more than 2 centimeters (0.8 inch) a year in the northern part of the county, around Katy, Fulshear and Cinco Ranch.
• Slowest: under half a centimeter a year near Richmond and Rosenberg, and across the county's western part, which the district calls little to no subsidence.

Three stations carry a town's name in the district's own exhibits:

• P004, located in Sugar Land: about 33.1 centimeters (about 13 inches) since 1994; 0.86 centimeters a year from 2021 to 2025, about a third of an inch.
• P010, located in Rosenberg: about 9.9 centimeters since 1999; 0.23 centimeters a year, under a tenth of an inch.
• P111, near Fulshear: about 15.3 centimeters (6 inches) since monitoring began in 2021; 3.32 centimeters a year, about 1.3 inches.

On the Harris County side, the Harris-Galveston district reports that station P029, located in Katy within Fort Bend County, has dropped about 35 centimeters since 2007. Its 2021 to 2025 rate was 2.64 centimeters a year. Satellite radar also picked up isolated spots of faster sinking in northwestern Brazoria County, near Iowa Colony and Manvel.

Two cautions. These totals start in different years, so compare the yearly rates, not the totals. And each number describes the land around a survey station, not your house or your street.

Fort Bend's only borehole extensometer sits near Cinco Ranch. It measures how much the ground compacts between the surface and a point 2,000 feet down. By the end of 2023, the USGS reports, it had measured 0.038 feet since 2017. That's a different measurement from GPS sinking, so the two can't be compared.

Where towns have moved off groundwater, the water underground is coming back. The district's 2025 report says levels from 1990 to 2026 rose almost 80 feet in Missouri City and almost 40 feet in parts of Sugar Land, as those areas began using other water supplies. Where pumping continued, they fell: over 200 feet near Cinco Ranch, almost 160 feet in Fulshear, and close to 120 feet in parts of Richmond.

The district's plan, adopted in December 2025 and amended in February 2026, sets a goal: groundwater at no more than 40% of total water demand. In the regulatory area that includes Sugar Land, Katy, Missouri City, Rosenberg and Richmond, large users must already limit their groundwater share. Groups under a groundwater reduction plan may use up to 70% for now, dropping to 40% for permits from 2030. In 2025, the district says, other water supplies passed groundwater as the county's main source for the first time.

There's hopeful history here, too. A 1983 USGS bulletin found that Houston-area faults stopped or slowed where water levels recovered.

None of this is new. In 1974, the Bureau of Economic Geology told a Texas House committee that the Katy area had already sunk about a foot. It added that faults most often became active where the ground had dropped more than 1.5 feet.

The USGS later measured more than 2.5 feet of sinking near Addicks, just north of the Fort Bend line, between 1973 and 1996. Its 1999 report says the sinking pushed inland as fast-growing areas north and west of Houston kept pumping. That is part of why the Fort Bend district was created in 1989.

The lesson the agencies draw is simple. Where towns switched to surface water, both sinking and fault movement slowed. Where pumping grew, they picked up. That pattern still shows in the 2025 numbers above.

The agencies are consistent about the main effects:

• Flooding and drainage. The USGS says subsidence raised flood frequency around Houston and changes how ditches and pipes drain. The Fort Bend district says the land around Houston is "very flat and, therefore, prone to flooding."
• Infrastructure. The district's plan says compaction damages wells and pipelines.
• Fault movement. The district's plan and the USGS both link subsidence to faults moving.

The Harris-Galveston district goes a step further. It lists "problems with foundations" and damage to "homes" among the region's subsidence effects. It doesn't explain how, or say where. The USGS describes Houston-area sinking as having "generally occurred on a broad scale."

What we couldn't find is any agency statement that slow, even sinking across a whole area cracks a single slab. So if your slab has a new crack, the usual suspects around Sugar Land remain the swelling clay under the house and the water around it. Where subsidence matters most for a homeowner is flood risk, which can change over the years as the land drops. Re-check your flood zone from time to time, and see our flood zones guide.

Faults are a different matter. The USGS counts more than 150 historically active faults in the Houston area. Many move 0.2 to 0.8 inch a year. They grow slowly, without earthquakes, and the USGS ties their movement to falling water levels and subsidence.

When a fault runs under a building, the damage can be real. A USGS study of the Clodine fault, on Houston's western edge, lists foundation failure, tilted floors, distorted window and door frames, leaking roofs, and damage to walls. But it also says the damage is narrow:

• Most damage happens in a zone typically 2 to 3 meters wide, about 7 to 10 feet, along the fault.
• Tilt is minor for most faults beyond 20 to 30 meters, about 65 to 100 feet.
• "Any given fault will directly affect only those relatively few structures built on or close to the fault scarp."

The same study adds that houses on the lower side of a fault lose a little elevation each time it moves, which can raise flood risk.

Which towns the fault maps cover

The USGS's 2005 map of principal faults in the Houston area reaches the eastern half of our study area: Sugar Land, Stafford, Meadows Place, Missouri City, Mission Bend, Four Corners, Pecan Grove, Fresno, Arcola, Pearland and Manvel. Richmond, Rosenberg, Katy, Cinco Ranch, Fulshear, Needville, Sienna and Iowa Colony fall outside it.

Being on the map isn't the same as being well mapped. The fault positions were refined using elevation data for Harris County. The USGS warns that areas with no faults shown "are considered insufficiently mapped rather than unfaulted." So a blank spot on the map doesn't prove there's no fault.

The Clodine fault is the named fault nearest our area. The USGS traced it for at least 12.5 kilometers, about 7.8 miles, from Figure Four Lake toward Alief-Clodine Road. Its 1979 authors called the evidence that it was still moving "at best only a weak indication." The USGS's own advice for any site near a fault holds: "Site-specific problems require site-specific studies."

If a fault map shows a line near your lot, an engineer's site-specific study is the way to find out what it means.