4/8/26 – Water extraction from aquifers, driven by population growth, causes subsidence. It is a well-recognized phenomenon across the U.S. and in southeast Texas. Here in the Lake Houston Area, differential subsidence is creating a bowl in the landscape that amplifies flood risk for people in southern Montgomery and northern Harris Counties.

Let’s look first at how, why and where subsidence happens. That understanding will help explain how it amplifies flood risk in the Lake Houston Area.

How Subsidence Happens

Extraction of groundwater – faster than nature recharges it – can cause silt and clay layers underground to compact. That compaction is permanent. Think of smashing a brownie; it will never regain its original shape. Innumerable tiny voids in the soil (or brownie) disappear, causing the surface above to sink.

For a more scientific explanation see the Harris Galveston Subsidence District FAQ on “What is Subsidence?”

Why Subsidence Happens

Population growth creates demand for the water in those aquifers, often at the fringes of major metropolitan areas. Developers build new subdivisions faster than water authorities can build pipelines to them from local surface water supplies, such as lakes.

Drilling wells is a much faster, more cost-effective solution at that stage of development – for both the water authorities and developers.

Plus, it’s not just the cost of the pipeline. You need to consider the cost of the water treatment plant. Both together can cost billions of dollars – far more than even a large subdivision could support.

Where Subsidence Happens

As a result, subsidence afflicts fast-growing regions across the U.S. Several examples include:

• Atlantic Coast
  • NASA reports that that more than half of infrastructure in major cities such as New York, Baltimore, and Norfolk is built on land that sank, or subsided, by 1 to 2 millimeters per year between 2007 and 2020. Land in several counties in Delaware, Maryland, South Carolina, and Georgia sank at double or triple that rate. 
• Chicago
  • 98% of the city reportedly sinks at 2 to 3 millimeters per year.
• San Joaquin Valley
  • To feed the hungry growing population of the U.S., agricultural interests in the California’s San Joaquin Valley began over-pumping groundwater in the 1920s. According to the U.S. Geological Survey, the land surface there had subsided 30 feet by 1980.
• Las Vegas
  • The city subsided 5 feet by 1980. But fast-growing Las Vegas extracts three times more groundwater than the natural recharge rate to this day. Subsidence in northern parts of the city forced residents to relocate.
• Houston
  • During the last 100 years, Houston has consistently ranked among the fastest-growing major U.S. cities according the Census Bureau, frequently placing in the top five and even top two. Its subsidence problems are legendary. Parts of Baytown subsided more than 10 feet before the formation of the Harris-Galveston Subsidence District, causing the Brownwood subdivision to sink beneath Galveston Bay.

Differential Subsidence in the Lake Houston Area

But subsidence is not just a coastal issue. It also can threaten areas far inland. According to Mike Turco, general manager of the Harris-Galveston Subsidence District, areas in Spring has subsided by almost 4 feet and the area around spring has subsided by about 4 feet. Recent subsidence rates in Spring have generally been between 0.5 and 1.0 foot per decade. That’s much faster than at the Lake Houston Dam. So, in effect, we’re creating a bowl in the landscape.

And that bowl amplifies flood risk.

Even though homes may be 75-100 feet above sea level, they may only be one foot above the floodplain.

As water, from say Spring Creek or the San Jacinto West Fork, goes into that bowl, it increases erosion on the upstream side and deposition on the downstream side. That deposition contributes to pooling within the bowl. A double whammy.

So, when a major storm comes along homes may have had their “freeboard factor” wiped out. In engineering and insurance, “freeboard” means your “safety margin above the floodplain.” Live in a place long enough and you may find water creeping closer and closer to your home in successive storms.

Of course, subsidence is only one of many factors that could cause that. But it amplifies those other factors and increases your flood risk.

To complicate matters for the poor homeowners shown in the picture above, Dallas-based Scarborough recently purchased 5,300 acres nearby between Spring Creek and the West Fork. Any new subdivisions built on that property would use well-water and further contribute to subsidence.

For More Information

Your safety ultimately depends on maintaining a healthy safety margin – much like the distance between you and the car in front of you on the freeway. We’ve all seen what can happen without enough distance.

For a discussion of other factors that contribute to flood risk, see the Lessons page of this website.

For more on subsidence and flooding, see:

• Houston-Region Groundwater, Subsidence Studies Reveal Stunning Facts
• New Subsidence District Report Shows Improvements, Challenges
• Building 7,000 Homes Here Would Accelerate Subsidence
• Subsidence District to Study Alternative Water Supply for NE Harris County
• Harris-Galveston Subsidence District

Posted by Bob Rehak on 4/8/26

3144 Days since Hurricane Harvey

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.