Tag Archive for: subsidence

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.

Page 13 of presentation

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.

Page 17

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

3166 Days since Hurricane Harvey

How Subsidence Amplifies Flood Risk in Lake Houston Area

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.

Northeast Water Treatment Plant
Houston’s new Northeast Water Treatment Plant under construction in 2020. Projected cost was $1.7 billion.

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.

Past catching up with Montgomery County
Woodloch Subdivision damage near San Jacinto West Fork in Southern Montgomery County from May 2024 flood.

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:

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.

Easy Way to Make Your Community More Resilient to Flooding

2/9/2026 – The Harris County Infrastructure Resilience Team wants public input on ideas to make the area more resilient to flooding. As someone who believes that all of us are smarter than one of us, I’m passing the request on to ReduceFlooding.com readers.

  • Do you see a situation that could lead to flooding? On your street? In your neighborhood? In your city or county?
  • What would reduce the potential for flooding in your opinion?
  • What would help us recover from flooding faster?

Please email your thoughts to the contact page on this website and I will forward them to the people who can do something about them.

As thought starters, here are several ideas I see that could make living here safer.

Create a River-Basin-Wide Flood Control District

Much flooding originates in cities and counties that let development happen in floodplains. Sometimes they let development happen with insufficient mitigation. This problem is exacerbated by the dozens of municipalities, counties, MUDs, PUDs, and drainage districts each of which have their own regulations and few of which of effective enforcement.

Entire San Jacinto River Basin by SJRA. Note: the area draining past Kingwood is larger than all of Harris County.

A flood control district that covers the entire river basin could solve flooding due to this fragmentation and a patchwork quilt of regulations across the region. There is no central coordinating body.

In the last legislation, Rep. Dennis Paul introduced HB204. It would have let other counties join Harris County to create an expanded flood control district. However, the bill never made it out of committee.

Senator Bettancourt and Representative Paul introduced similar bills in the previous legislative session. Perhaps next year, they will succeed with your support.

Control Erosion Better

Erosion can reduce the carrying capacity of our rivers and streams. It displaces water that may end up in your living room during a flood event because the stream can no longer hold it. Fighting erosion is two-front war. We need to reduce it at its source. And we need to remove sediment that makes its way downstream, blocking our rivers and channels.

Colony Ridge ditch erosion
Uncontrolled erosion in Colony Ridge, Liberty County, in East Fork Watershed.

This means addressing the main sources of sediment, such as sand mining and insufficiently mitigated upstream development. It also means removing any sediment that makes its way downstream by scrupulous adherence to maintenance intervals.

We’ve seen numerous examples of blocked drainage ditches and even rivers such as the mouth bars on the East and West Forks, the Kingwood Diversion Ditch, Rogers Gully.

Reduce Subsidence Across a Wider Area

Subsidence, caused by excessive groundwater withdrawals, can alter the gradient of rivers and create bowls in the landscape. The Harris Galveston Subsidence District has put regulations in place to reduce it. And they’ve worked where they have been in effect the longest.

But newly regulated areas are still subsiding at alarming rates. And that subsidence can erase the safety margin of your home above the floodplain (usually one or two feet above the 100-year floodplain, depending on the age of your home and where you live).

Houston area subsidence map from satellite data.
From Subsidence District 2024 Annual Report

The way to solve this problem is to get rapidly subsiding areas on surface water. But that’s more expensive. So, we also need educational campaigns that explain the benefits of surface water. People may not argue about paying a few dollars more each month if they know it could save them hundreds of thousands in a high water event.

Locate Assisted-Living Centers Outside of Floodplains

Twelve people, aged 75-95, died at Kingwood Village Estates as a result of Harvey. That’s one third of all the people who died in Harris County. Evacuating them by life boats put their lives and the lives of first responders at risk. They weren’t warned in time to make a safe, orderly evacuation by cars or buses.

Residents trying to escape as Harvey's floodwaters rose
Residents trying to escape Kingwood Village Estates as Harvey’s floodwaters rose

Warning Sirens

Install warning sirens in areas that flood frequently to give people time to evacuate. Floods frequently knock out communications or happen in the middle of the night. The chain of communication can be disrupted. But wailing sirens can wake up even the soundest sleepers in the middle of the night.

With sirens, many lives could have been saved in Kingwood and along the Guadalupe last July.

Flood Education in High Schools

We have drivers’ ed. Why not flood ed? Greater awareness of the causes and dangers of flooding could eventually shift housing demand to safer locations.

Perhaps the State Board of Education could create course materials that they distribute to school districts. They might educate young people how to research flood risk before buying a home. Or where to find information about projected flood crests in an emergency.

Better to learn before you buy a home than after!

Create County/City Parks in Flood-Prone Areas

It’s hard to tell people that they can’t build on their land. So why not buy dangerous flood-prone land and convert it into parks or recreational space?

The Houston Parks Board has been doing this for decades. Texas Parks and Wildlife did it with Lake Houston Wilderness Park (which they gave to the City.)

If people don’t live where it floods, they can’t flood. No buyouts. And no demand for expensive flood-mitigation projects. Prevention is always much cheaper than correction in the long run.

What Are Your Ideas?

Please send me your thoughts on how to make your community more resilient to flooding. Just write a paragraph or two. It doesn’t have to be elaborate. Then email your thoughts through the contact page of this website.

I’ll make sure the Harris County Infrastructure Resilience Team sees them.

The deadline for submissions is February 12, 2026. Thanks in advance for your help!

Posted by Bob Rehak on 2/9/26

3086 Days since Hurricane Harvey

Why Harris County Had 31 100-Year Floods in 100 Years

2/7/26 – According to Harris County Meteorologist Jeff Lindner, the county has had at least 31 100-year floods in the previous 100 years. That’s between 1925 and 2025. “How can that be?” you ask. “Doesn’t a 100-year flood only happen once in a 100-years?”

Short answer, NO. To increase your safety and protect your home, read on.

Main Reasons for Apparent Contradiction

Numerous reasons exist for the apparent contradiction in the headline. They fall into three broad categories.

  • Widespread misunderstanding of the definition of a “100-year flood”: the term means different things to hydrologists and to the public.
  • Physical changes to floodplains and channels since the last flood-map update: Upstream development, sedimentation, lack of maintenance, etc. can all increase your flood risk.
  • Evolving statistical estimates of floodplains: Reliable weather records only go back about 130 years in this region. Predicting future risk using such a small statistical base has inherent risks of its own.

Widespread Misunderstanding of Definition

Let’s address misunderstanding of the definition first. The term “100-year flood” emerged in the early part of the 1900s to describe a flood that has a 1% chance of happening each year at any given geographic point.

So, technically, 100-year floods could occur in back-to-back-to-back years. And they have. See Lindner’s list of Harris County’s 31 “100-year floods” below.

  1. 5/31/29: Buffalo Bayou
  2. 12/9/35: Buffalo Bayou
  3. 10/9/49: Cypress Creek
  4. 9/11/61: Sims Bayou
  5. 6/20/73: Sims Bayou
  6. 6/11/75: Sims Bayou
  7. 7/25/79: Clear Creek, Armand Bayou, Sims Bayou, Vince Bayou
  8. 9/20/79: Clear Creek, Sims Bayou
  9. 5/3/81: Vince Bayou
  10. 8/18/83: Sims Bayou, Vince Bayou, Halls Bayou
  11. 9/19/83: Sims Bayou
  12. 6/26/89: Greens Bayou
  13. 8/1/89: Sims Bayou
  14. 10/18/94: Clear Creek, Sims Bayou,  San Jacinto River, Spring Creek, Little Cypress Creek, Cedar Bayou
  15. 10/18/98: South Mayde Creek, Bear Creek, Spring Creek, Little Cypress Creek
  16. 11/14/98: Little Cypress Creek, Spring Creek
  17. 6/5/01: Clear Creek, Vince Bayou
  18. 6/9/01: Clear Creek, Armand Bayou, Brays Bayou, White Oak Bayou, Hunting Bayou, Vince Bayou, Little Cypress Creek, Willow Creek, Carpenters Bayou, Greens Bayou, Halls Bayou, Buffalo Bayou
  19. 10/29/02: White Oak Bayou
  20. 8/16/07: Vince Bayou
  21. 9/13/08: Vince Bayou, Bear Creek, South Mayde Creek
  22. 4/28/09: Bear Creek, South Mayde Creek, Buffalo Bayou
  23. 7/12/12: Little Cypress Creek
  24. 5/13/15: Armand Bayou
  25. 5/26/15: Keegans Bayou, White Oak Bayou, Buffalo Bayou
  26. 10/31/15: Cedar Bayou
  27. 4/18/16: Keegans Bayou, Spring Creek, Little Cypress Creek, South Mayde Creek, Bear Creek, Horsepen Creek
  28. 5/27/16: Spring Creek, Little Cypress Creek
  29. 8/27/17: Nearly every watershed
  30. 9/19/19: San Jacinto River, Cedar Bayou
  31. 5/2/24: San Jacinto River

Many of these watersheds have seen 5 to 10 extreme floods in the last 100-years.

“100-Year Flood” is an estimate of probability and not a guarantee of frequency.

Keep that in mind if you’re shopping for a new home or considering cancelling your flood insurance.

Physical Changes to Floodplains/Channels

The other thing to keep in mind is that floodplains constantly change. You could be high above them one year and far below the next because of changes to the terrain upstream.

I once owned a home in Dallas that went from 2 feet above a 100-year floodplain to 10 feet below it in less than three years. How? One insufficiently mitigated, new development upstream. Think it can’t happen here? Look at Colony Ridge in the East Fork Watershed. It didn’t exist 15 years ago and is now 50% larger than Manhattan.

When buying a home, consider such factors as:

  • Subsidence from excessive groundwater withdrawals in Montgomery County (MoCo) could reduce a home’s elevation relative to the Lake Houston Dam. That would reduce the safety margin between your slab and floodwaters.
  • Sedimentation could reduce the conveyance of a channel or massively block it. During Harvey, sand washing downstream reduced conveyance of the West Fork by 90%, according to the Army Corps.
  • Much of that sand came from sand mines in MoCo. Mines have deforested 20 square miles in a 20-mile length of the river between I-45 and I-69. That exposes a swath of sediment averaging a mile wide to floodwaters.
  • MoCo actually gives tax breaks to those mines that encourage deforestation, rapid sedimentation and downstream flooding.
  • Until recently, the state didn’t require minimum setbacks from the river for mines. Because of erosion, the river now runs through mines in at least six places on the West Fork.
  • MoCo is one of the ten fastest growing counties in America. Roads, driveways and rooftops increase the volume and speed of runoff, causing floodwater to peak higher and faster downstream.
  • Complicating that, MoCo has not enforced its own floodplain regulations. I have published dozens of stories about that, including the blatant transgressions that flooded 600 homes in 2019 along Taylor Gully across the county line from Perry Homes’ Woodridge Village development.
  • When most of the region adopted new drainage and floodplain regulations shortly after Harvey in 2017, MoCo took until late 2025. And their new regs didn’t meet the minimum standards adopted elsewhere.
  • One MoCo legislator fought for the right to develop new subdivisions in floodplains, even as another voted against establishing a Dredging and Maintenance District for the Lake Houston Area.

Evolving Statistical Estimates/Building Codes

Climate change aside, such factors as those above make estimating flood risk a shifting target. Worse, the small statistical base for those estimates gives them a large margin of error.

Complete rainfall records for Harris and Montgomery Counties only go back to the early 1890s. So, we’re trying to estimate 100-year rainfalls by looking at one complete 100-year cycle out of 4.56 billion years. That’s as difficult as predicting a statewide election outcome by interviewing one person!

As a result, scientists update rainfall estimates after most major storms such as Harvey and Allison. But that can take years. FEMA is just now releasing new flood maps based on high-water marks and elevation data acquired after Harvey. And MoCo’s population has grown by about a third since then – enough to skew results significantly.

As upstream counties pursue growth, downstream counties must require higher elevations in building codes. But that won’t help already-built homes in older neighborhoods. To help those residents, we must pursue expensive flood mitigation to offset the increased flood peaks resulting from upstream growth.

There’s just no option; it will never end. We can never give up trying to offset competing interests. Or we’re sunk.

Posted by Bob Rehak on 2/7/2026

3084 Days since 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.

SJRA, Conroe Settle Lawsuit after Nine Years

8/15/25 – The San Jacinto River Authority and City of Conroe issued a joint press release about the settlement this morning of their nine-year legal battle over water rates. This press release just came in. I’ve added subheads to help highlight key points. Otherwise, the text between the lines is verbatim:

SJRA Directors Unanimously Approve

Conroe, Texas—Today the San Jacinto River Authority (SJRA) Board of Directors unanimously approved the execution of a Mutual Release and Settlement Agreement with the City of Conroe to end current litigation related to the SJRA Groundwater Reduction Plan (GRP). The City of Conroe considered and approved the Mutual Release and Settlement Agreement at a City Council meeting on Thursday.

End to Legal Squabbles is Mutually Beneficial

SJRA General Manager, Aubrey Spear, said “We appreciate the City of Conroe’s efforts in working with SJRA in reaching this settlement agreement. Putting this litigation behind us is best for all GRP participants and their rate payers. With Conroe’s payment and savings on legal fees, the wholesale water rates will go down. Ending the litigation also strengthens our partnership with Conroe to continue supplying water to its growing population.” 

Conroe City Administrator, Gary Scott, said “After months of negotiations, I am pleased with an outcome that is truly beneficial to both parties. Securing additional water is critical to Conroe’s economic growth and long-term vitality. We recognize and appreciate the efforts of the San Jacinto River Authority in working with us. This agreement represents a shared commitment to the betterment of us all. This is a historic decision that sets Conroe on the path to the future.”  

The agreement settles legal disputes between the parties dating back to 2016 when the City of Conroe disputed increases in wholesale water rates related to SJRA’s 2010 Groundwater Reduction Plan contract. 

Conroe Agrees to Pay Full Amount

In the settlement, the City of Conroe agrees to pay the full amount that it has short-paid SJRA since 2017 to the present that it has been holding in escrow. Conroe also agrees to begin paying the current rate for treated surface water from Lake Conroe and the groundwater pumpage fee going forward. 

SJRA Agrees to Provide More Surface Water and More

On the other hand, SJRA agrees to provide Conroe with additional surface water, reduce the term of Conroe’s GRP contract from 80 years to 40 years, forgive penalties and fees on past due amounts, and clarify in the contract that there is no obligation by the City of Conroe to participate in future GRP phases or expansion of the GRP water treatment plant.

Documents Not Yet Available 

Agreement documents are in the process of being fully executed.

 Reliance on Groundwater Has Contributed to Subsidence

This is good news for both parties. It will reduce the amount they spend on legal fees that rate- and taxpayers have funded.

However, the press release did not address how it will affect the amount of groundwater that Conroe pumps aside from saying that SJRA will provide Conroe with “additional surface water.”

Subsidence in southern Montgomery County including Conroe and the Woodlands is among the most severe in the region. SJRA’s Water Treatment Plant and the Groundwater Reduction Plan were at the heart of the lawsuit. Both were intended to reduce subsidence. And they did briefly when the plant first came online in 2015. Then the Lone Star Groundwater Conservation District (LSGCD) started pumping huge amounts of groundwater, claiming there was no connection between the loss of groundwater and subsidence.

LSGCD says on their Resources Page under the subsidence tab that, “…the rate at which [their] compaction occurs is 10 times (10x) slower than the rate at which compaction occurs in Harris County.”

Regardless, a huge area is still sinking 8 to 12 millimeters per year. And most of Montgomery County is sinking at least 6 according to this subsidence map recently published by the Harris-Galveston Subsidence District.

Subsidence Has Triggered Faults

The subsidence has triggered faults in the area. That in turn has damaged homes, streets and drainage infrastructure. I spent a whole day last week taking a fault tour of the Woodlands with area residents. Below are three of dozens of pictures I took at day.

Fault line under the foundation cracked this Woodland’s home’s slab and walls.
Front steps are now twice their original height because the front yard sank relative to the front door.
Faulting damage in parking lot of Woodland’s High School.

Millimeters may not sound like much. But 12 millimeters per year is half an inch per year. During the life of a 30-year mortgage, that’s 15 inches…plus a lot of home and street repairs, and a lot of foundation leveling.

Inland subsidence has also been linked to flooding. It can change the gradient of streams and rivers, so water moves more slowly and builds higher during floods.

And differential subsidence (between two areas) can reduce the height of structures above floodplains. For instance, the subsidence rate in Conroe is far higher than subsidence at the Lake Houston Dam. That means homes north of the dam have less freeboard (height above expected floods). Said another way, it’s like tilting Lake Houston toward the homes north of the dam.

SJRA has not yet responded to questions about how the settlement will affect Conroe’s groundwater pumping.

Posted by Bob Rehak on 8/15/25

2908 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.

New Study Finds Houston Is Fastest Subsiding City in Country

5/15/25 – According to a new study by researchers at Columbia University, on average, Houston is subsiding faster than any major city in America. The study looked at the 28 most populous cities in America. Satellite measurements collected between 2015 and 2021 showed all are sinking to some degree. However, the sinking is not uniform.

Parts of Area Sinking at Different Rates

More than 40% of Houston’s area is subsiding more than 5 millimeters (about 1/5 inch) per year. 12% is sinking at twice that rate, according to the study.

“Subsidence-induced infrastructure damage can occur even with minor changes in land motion,” the study’s authors wrote in the journal Nature Cities on May 8, 2025. “One of the most harmful yet less visible effects of urban land subsidence is the potential damage to buildings, foundations and infrastructure, primarily caused by differential land motion,” they say.

Damage Caused by Subsidence

Imagine underground pipes, for instance, that reach the limit of the flexibility and then get pushed beyond it.

Other subsidence studies have shown that subsidence can trigger geologic faults and exacerbate flooding.

The Columbia study also showed high levels of subsidence elsewhere in Texas, including Dallas, Austin, San Antonio and Fort Worth.

Subsidence Linked to Groundwater Extraction Due to Growth

The primary cause: ground water extraction related to rapid growth. The study found that about 80% of all subsidence relates to groundwater extraction.

As if on cue, the Census Bureau released today updated population statistics. They showed that from 2023 to 2024, Houston gained more people than any other major city in America with the exception of New York.

The new census data also shows that Fulshear on Houston’s west side had the second highest percentage gain in population of any city in America in 2023. Fulshear, on Houston’s west side, grew an astonishing 26.9% from 2023 to 2024.

Subsidence Hotspots in Houston Area

Coincidentally, the Harris-Galveston Subsidence District released its 2024 Annual Groundwater Report today and an updated interactive subsidence map. They showed that the highest rate of subsidence in the Houston region was near Fulshear. That area is subsiding at a rate of 1.3 inches/year – more than a foot per decade!

One of the most visible signs of subsidence is cracks in pavement and parking lots.

The Subsidence District’s latest groundwater report shows that their efforts have almost halted subsidence where they have succeeded in shifting areas from ground to surface water. Those are the areas where the Subsidence District first started regulating groundwater 50 years ago.

However, the relentless growth of Houston, especially on the north and west sides, has created a belt of subsidence where new areas have largely not yet converted to surface water. See below.

Average annual subsidence from 2020 to 2024. Green = <.5 cm/yr. Dark red = > 2 cm/yr.

More on that in coming days. I’ll also discuss how differential subsidence can create bowls in the landscape that exacerbate flooding. And I’ll cover the largest water infrastructure project in the country. It will bring more surface water to those fast subsiding areas above.

Being the fastest subsiding city in America is one claim that I am sure Houston would be happy to relinquish.

Posted by Bob Rehak on 5/15/25

2816 Days since Hurricane Harvey

Building 7,000 Homes Here Would Accelerate Subsidence

4/19/25 – Ryko, a development company, has announced plans to build 7,000 new homes in an environmentally sensitive, flood-prone area immediately west of Kingwood. Moreover, the area already experiences the highest subsidence in the north Houston region.

Residents in the area currently use groundwater. Assuming an average household size of 2.5 people, Ryko would add 17,500 new residents to the area. That could accelerate declines in groundwater levels and increase subsidence.

Base map from Harris-Galveston Subsidence District. 1.83 centimeters = 0.72 inches per year.

Reviewing the Subsidence District’s latest annual report revealed that the issue at this one reporting station is part of a larger problem. And the problem is very bad in southern Montgomery County.

Impacts of Subsidence

I have been posting about the issue for five-plus years. Subsidence happens too slowly to notice in most cases. But over time, it can be very disruptive:

  • Excessive groundwater withdrawals can create bowls in the landscape that alter the gradient of rivers and streams. That can increase local flooding. For instance, when land at the county line sinks faster than land at the Lake Houston Dam, it tilts the lake toward the county line.
  • Projected subsidence rates upstream could erase your freeboard factor (the height at which your home was built above the 100-year floodplain). That would increase your flood risk.
  • Subsidence can also crack pipelines, storm sewers, and pavement.
  • Uneven settling can cause your doors and windows to stick; crack foundations; split wallboard; and break tile.
  • Near Galveston Bay, a whole subdivision even sank beneath the waves.
  • Subsidence can also trigger long-dormant geologic faults.
Front steps of Woodland’s homeowner Dr. Mark Meinrath in 1992 and 2014. Part of Meinrath’s home straddles a fault which subsidence triggered. Relative to the rest of his house, these front steps dropped 9.9 inches in 22 years.

For more examples of the impacts of subsidence in the north Houston area, visit StopOurSinking.com, a site developed by a Woodlands resident. There, subsidence has triggered faults and flooded multi-million-dollar homes through the “bowl effect.”

High Cost of a Little Flooding

Getting even an inch of water in your home can be very costly. According to FEMA, just 1 inch of floodwater in an average 2,000 square foot home can cost $10,000 to $20,000 to repair.

Higher-end finishes, such as wood floors, built-in cabinetry, granite, etc., can push those estimates past $25,000.

Why is one inch so expensive?

  • Flooring usually needs to be completely replaced (carpet, wood, sometimes even tile if the water gets underneath).
  • Baseboards and lower drywall (often up to 2 feet) usually must be cut out and replaced.
  • Insulation in walls may need replacing if water wicks up.
  • Cabinet bases and interior doors are often ruined.
  • Appliances like washers, dryers, and even low-mounted electrical outlets might be affected.
  • Mold prevention requires fast and sometimes professional drying and remediation.

In homes larger than 2,000 square feet, the cost would go up proportionately. For instance, FEMA estimates repair costs for a 3,000 square foot home to be 50% greater – in the $15,000 – $30,000+ range.

Disasters/accidents are rarely caused by one thing. They usually result from a combination of factors eroding margins of safety.

For instance, the risk of a driving accident increases when you’re tired, it’s dark and the pavement is wet. That’s why it’s important to pay attention to little things that can degrade your margin of safety. They may not be so little in the next big storm.

Posted by Bob Rehak on 4/19/2025

2790 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.

Ramsey, Flickinger Discuss Status of Flood Projects

1/16/2025 – Harris County Precinct 3 Commissioner Tom Ramsey, PE, and Distict E Houston City Council Member Fred Flickinger discussed the status of numerous flood projects at a meeting of the Kingwood Area Republican Women today at the Oakhurst Golf Club.

Ramsey addressing Kingwood Area Republican Women’s Club today.

Among the projects they covered were:

  • Taylor Gully Improvements/Woodridge Village Detention
  • Kingwood Diversion Ditch Improvements/Upstream Detention
  • Additional Floodgates for Lake Houston
  • Legal Changes Governing Pre-Release of Water from Lakes
  • Edgewater Park
  • Dredging
  • Medians
  • Flood Tunnels
  • Subsidence

Below are the highlights. They also discussed other issues such as median maintenance, vine control, crime, taxes, government waste, elections and more. But I will focus primarily on infrastructure issues related to flooding – especially Taylor Gully and Woodridge Village, because of pending approvals this month.

Taylor Gully/Woodridge Village

After Perry Homes clearcut approximately 270 acres in Montgomery County, hundreds of Kingwood homes flooded twice in 2019 along Taylor Gully. Taylor Gully runs through the northern part of Kingwood from Kingwood Park High School to White Oak Creek.

Taylor Gully/Woodridge Village

Harris County Flood Control District (HCDFC) began working on mitigation plans in 2021 and presented preliminary recommendations to the community in December, 2022.

The county had high hopes for funding from the Texas General Land Office (GLO) and U.S. Department of Housing and Urban Development (HUD), but those ran into a potential snag. Taylor Gully improvements fit within available HUD funding, but Woodridge Village (the former Perry Homes Property) did not. HCFCD hoped to build more stormwater detention basin capacity on Woodridge to help control Taylor Gully expenses downstream.

Regardless HCFCD pressed forward. They combined the two projects. And according to HCFCD, both now fit with available funding capacity (see “above the line” list on page 2) of the list being presented to Commissioners Court next week on 1/23/25.

The county purchased Woodridge Village in February 2021. Shortly thereafter, HCFCD began an excavation and removal (E&R) contract to get a “head start” on the basins. Indeed, the head start brought the total stormwater detention on the site almost to Atlas-14 standards.

However, HCFCD was forced to terminate the E&R contract before the basins could be completed. That was to comply with HUD requirements while HUD considered the grant application.

This is potentially great news for the people who live in Sherwood Trails, Elm Grove, Mills Branch and Woodstream.

Watch commissioner’s court closely next Thursday. The Kingwood area drainage study named this project as one of the two most important in Kingwood.

Kingwood Diversion Ditch and Upstream Detention

The Kingwood Diversion Ditch was the other of the two most important projects. The Diversion Ditch takes floodwaters out of Bens Branch, which runs diagonally through the center of Kingwood from St. Martha Catholic Church to River Grove Park.

Improving the Diversion Ditch would reduce flood risk for hundreds of homes and apartments, Kingwood High School, Town Center, and Kings Harbor. Both Bens Branch and the Diversion Ditch currently have a two-year level of service. That means they have a 50% chance of coming out of their banks in any given year.

The District started preliminary engineering in mid-2021. HCFCD will finally present that report to Commissioners Court on February 6, 2025.

Ramsey estimated today that the project could cost $60 million. However, he also indicated that U.S. Congressman Dan Crenshaw “got us enough money so we can do the final engineering.”

Eric Heppen, Precinct 3 engineer, later stated that once Commissioners Court approves the preliminary report, it will be made public.

Flickinger emphasized that he is talking with Montgomery County, trying to get them to retain more of their floodwaters. He raised concerns about a new 200,000 sq. ft. convention center planned for US59 at Valley Ranch. “That will generate a lot of runoff that could come down to us, unless we work together to find a way to hold that water up there.”

Houston City Council Member Fred Flickinger at same meeting.

Additional Floodgates for Lake Houston

Shortly after Harvey, many people pinned their flood-mitigation hopes on additional floodgates for the Lake Houston dam. The idea: to lower the lake faster when it becomes certain that a storm will flood the area. The existing gates have 1/15th the capacity of Lake Conroe’s. So Lake Houston must start releasing far earlier in advance of storms than Lake Conroe. And by the time Lake Houston is lowered, storms can veer away, wasting valuable water.

So Conroe tends to hold its water back until it is absolutely certain. At that point, it has no other choice than to release water at high rates that flood people downstream.

Being able to lower Lake Houston faster would let Lake Conroe release earlier and slower, smoothing out flood peaks downstream.

Ramsey estimated the cost of 11 new floodgates that could release 80,000 cubic feet per second at $150 million. He said the final engineering should be completed this year. He also said that bidding and construction could start in 2026.

Legal Changes Governing Pre-Release of Water

Flickinger addressed a related legal issue. State law limits the release of water from lakes; it must be only for defined beneficial uses and flood control is not one of them.

So, Flickinger is working with State Rep. Charles Cunningham to change that and increase the limit. “Bottom line,” he said, “is that we need to release more water sooner rather than holding it back until we’re adding to the crest of the flood.”

Flickinger is also working with the San Jacinto River Authority on these changes.

Edgewater Park

After Harvey, the County acquired land on the northeast corner of the West Fork and US59, which will turn into Edgewater Park. It will also connect the Houston Parks Board’s West Fork Greenway with the Spring Creek Nature Trail. Ramsey said the plans will be made public very soon. After the meeting, Precinct 3 engineer Eric Heppen confirmed the plans were 99% complete.

Ramsey said, “Soon, you’ll be able to go from Kingwood to Tomball and not cross a road.” That should be a tremendous draw for hikers and bikers and the entire area.

Dredging

Flickinger discussed two aspects of dredging not covered in last night’s post. First, he is seeking additional funding to continue the current program while the dredge is on the lake. Second, he feels opportunities exist to increase efficiency.

I asked what he meant by that. FEMA restrictions on the funds currently being used limit the dredging to “pre-Harvey” conditions. That means, Callan Marine, the contractor, must dredge to different depths to match the exact bottom profile that existed before Harvey. And that requires repositioning the dredge more than if you were just dredging to a uniform depth across wide areas.

The search for additional funding has led Flickinger to the City, the Coastal Water Authority (CWA) and former State Representative Dan Huberty. Huberty was appointed to the board of CWA last last year by Houston Mayor John Whitmire.

Medians

Several people from the audience questioned Flickinger about the medians along Kingwood Drive. He touted the success of his first Median Madness event in November 2024 and announced another on February 22, 2025. Mark your calendar now.

More than 50 volunteers participated in the last vine-cutting extravaganza. He hopes for many more volunteers this time.

Flood Tunnels

The county is getting ready to launch the next phase of its flood tunnel study. Ramsey emphasized that there isn’t enough room in Harris County to poke enough holes in the ground to solve all of our flooding problems. He sees tunnels that carry floodwater from strategic locations as essential parts of the solution.

Eric Heppen, Ramsey’s engineer said that by burying the 40 foot tunnels 80 feet underground, you can double the conveyance in some watersheds, sidestep environmental issues, and avoid having to condemn property.

But many issues have yet to be worked out. For instance, will tunnels be constructed to relieve 2-year, 5-year, 10-year, 25-year or 50-year flooding? More to follow when details become available.

Subsidence

Harris County estimates the area east of Lake Houston will grow by 18,000 homes in the next 10 years. But there currently are no plans to provide them with surface water. So, they will pump groundwater. That means subsidence. And subsidence means flooding, according to Ramsey. He pointed to Conroe as an example. The City’s groundwater pumping has caused subsidence as far south as Harris County.

Posted by Bob Rehak on 1/16/25

2697 Days since Hurricane Harvey

Subsidence District to Study Alternative Water Supply for NE Harris County

11/21/24 – Last week, the Harris-Galveston Subsidence District published a request for qualifications (RFQ) for consultants interested in conducting an alternative water supply feasibility study for Northeast Harris County.

Mike Turco, the District’s general manager, said he is specifically focused on the area east of Lake Houston, which is experiencing tremendous growth. The completion of the Grand Parkway has triggered much of that growth. And with it will come increased water demand, which has the potential to trigger subsidence.

“Alternative Water” Reduces Effects of Subsidence

The District defines “an alternative water supply” as a source that does not trigger subsidence. That most often means a source other than groundwater. Subsidence frequently results from excessive groundwater extraction. That can cause compaction of the earth and a whole range of consequences.

Such compaction caused an entire Baytown subdivision to sink into Galveston Bay.

Subsidence can also cause bowls in the landscape that trap water and increase flood risk Subsidence can even change the gradient of streams, slowing water down and backing it up.

An SMU study found that subsidence can cause faulting and damage structures such as homes, roads, pipelines, storm sewers, sanitary sewers and more.

Differential subsidence can create another set of problems altogether. For instance, the rate of subsidence at the Harris/Montgomery county line is much greater than the rate at the Lake Houston Dam.

That has the potential to tilt the lake toward its headwaters. And that could reduce the freeboard factor (feet above flood level) for homes in northern Harris County.

But alternative water sources can reduce all those impacts.

Examples of Alternative Water

In this region, surface water, i.e., from Lake Houston, is the most common “alternative water source,” according to the District’s definition. Lake Houston provides water for more than 2 million people without causing any subsidence.

alternative water source
One example of an alternative water source. Lake Houston from Kingwood’s East End Park. By Dr. Charles Campbell.

So if we already have the major source of water in the area, why look at other alternatives? The planning horizon for water projects is typically 50 years. The RFQ specifically mentions recommendations to meet demand through 2070.

Given expected population growth during that period, the region may need more than Lake Houston. So it behooves us to look at all available alternatives.

According to Turco, right now, the City is already aggressively expanding water distribution from Lake Houston to areas like Spring, which has experienced some of the worst subsidence in the region – 30.5 centimeters, slightly more than a foot since 2007. See below.

The City is also expanding the Northeast Waster Purification Plant and bringing in water from Lake Livingston via the Luce Bayou Inter-basin Transfer Project. But will it be enough to meet demand 50 years from now?

Other alternative sources could conceivably reduce demands on Lake Houston. They include but are not limited to:

  • Building a new reservoir
  • Constructing pipelines from existing reservoirs
  • Using reclaimed water for specific needs, such as irrigation or agriculture
  • Desalination of Bay water

For More Information

A District spokesperson said they want to look at all options, costs and timing. To review the RFQ, click here.

For the District’s latest annual report on subsidence, see this six-page executive summary, this 47-page presentation, or the 307-page full report with appendices.

Subsidence is widely considered to be irreversible. It’s comforting to know that people are already planning for the welfare of our grandchildren.

Posted by Bob Rehak on 11/21/24

2641 Days since Hurricane Harvey

Easy Way to Reduce Water Usage, Costs, Subsidence and Flood Risk

The Texas A&M Agrilife Extension Service, working with local government organizations, has developed a free, customized program that might help you reduce water usage, costs, subsidence and flood risk. It’s called the WaterMyYard program.

A large percentage of the water used in urban areas goes to watering lawns. On average, the EPA estimates 30-60% of residential water irrigates lawns. Your percentage may vary depending on your location, distance inland, average temperature, rainfall, size of yard, etc. But in general, 50% is a good average estimate.

Grass is the most watered crop in America. And many of us overwater our lawns, running up water bills needlessly.

How WaterMyYard Program Works

WaterMyYard uses local weather data in participating areas to provide free, weekly watering advice.

The system collects data from an extensive network of weather stations and rain gauges. It then correlates that data with evapotranspiration rates for major grass types; air and soil temperatures; rainfall; wind; and dew points so you can put the precise amount of water on your lawn that it needs to stay healthy.

Example: data for North Houston in the last 7 Days used as basis for calculations.

When you sign up for the service, you answer a few questions about the type of sprinklers you have and the inches per hour they spread on your lawn. Based on measured weather data, the system then sends you customized weekly water advice for your specific lawn and irrigation system.

The system takes the guess work out of knowing when and how much to water.

Texas A&M Agrilife Extension

For instance, it could tell you how much to cut back after a major rain or how much to increase watering during a dry spell.

If you don’t know how much water your system puts out per hour, don’t worry, you can change the amount after you sign up. You can use typical rates for different types of sprinkler systems. Or you can actually measure it by placing cans around your yard during watering cycles.

You can also add sprinkler systems, for instance, if you have one type for your lawn and another for flower beds and shrubs.

Testimonial: Water Usage Cut in Half

One user I know said he was able to cut his water usage by 50%. “I dropped home consumption in half and my lawn is still green and everything’s still fine,” he said. “Most of us just don’t have enough information. When we go into new homes, we just leave the sprinkler settings the way the last guy had them.”

“I really didn’t pay much attention to them,” he continued. “As long as my grass was green, I was good. But a lot of research out there says that we can be more efficient with that. And that’s what the WaterMyYard program does.”

With water rates constantly going up, it’s easy to see how eliminating wasted water, can save you money. But how does lawn watering affect subsidence and how does that affect flood risk?

Connection to Subsidence, Flooding

Large parts of the region still aren’t on surface water; they use groundwater. And if we use groundwater faster than it’s being replaced, we experience subsidence. Places in northwest Harris County sank 50 centimeters (almost 20 inches) between 2000 and 2022.

From presentation to Harris-Galveston Board of Directors on 12/8/2023.

In a flat area like Houston, an inch per year can be significant. One subsidence expert said it can be enough to reduce the gradient of whole watersheds over a decade or two. That means stormwater doesn’t move away as quickly as it once did. So, in large rainfalls, flood peaks build higher faster.

Now consider this. If lawn irrigation accounts for half of residential water use, and if half of lawn irrigation is unnecessary, up to 25% of water we use could have stayed in the ground. And that could significantly reduce subsidence and flood risk while reducing your monthly water bill.

The sooner you act, the more you save. So sign up for WaterMyLawn weekly watering advisories today.

Posted by Bob Rehak on 3/23/2024

2398 Days since Hurricane Harvey