5/22/25 – The Harris-Galveston Subsidence District released its 2024 Annual Groundwater Report last week. The document represents a sort of scientifically graded report card for the District.
It shows that serious subsidence problems remain in fast growing areas where regulations have yet to be fully phased in. But it also shows that subsidence has decreased dramatically where regulations have been in place the longest.
Finally, it explains what the region’s leaders are doing to get people off groundwater in those fast-growing areas. Groundwater is the major cause of subsidence or sinking of the land and can damage infrastructure such as streets, sewers, and pipelines. It can even trigger geologic faults.
Subsidence has also been linked to flooding in several ways. The effect is obvious near the coast in areas susceptible to storm surge. But it’s less intuitive farther inland at higher elevations. It has to do with creating bowls in the landscape that alter the gradient of rivers and streams. But I’ll save that discussion for a subsequent post.
Each affects the next. Let’s look at these topics briefly, then look at what the District is doing to get fast-growing areas off groundwater.
Climate Impact Negligible Last Year
Last year, precipitation was above normal for all National Weather Service reporting stations throughout the region except for Katy. Above-normal precipitation typically reduces the demand for groundwater to irrigate lawns and crops. However, irrigation usually comprises only a small percentage of total demand.
Groundwater Use Increased in Fast Growing Areas
The District monitored groundwater use in its three different regulatory areas and then averaged all three.
Regulatory Area:
#1 is closest to the coast where the District first implemented groundwater regulations 50 years ago.
#2 is farther inland. Think of Central Harris County.
#3 is the most recently regulated and the farthest inland. Regulations won’t fully phase in until 2035 there.
Here’s what happened to groundwater demand in each:
#1 showed a small uptick compared to recent years, linked primarily to industrial use.
#2 showed a drop compared to the previous two years.
#3 also showed a drop compared to the previous two years, but an increase compared to the previous 10 years. The District attributed this to rapid population growth in Area #3.
Regulatory Area #3 accounted for a whopping 82% of all groundwater used in all three areas combined.
Looking at all three areas combined, the average declined compared to the previous two years. But growth in Area #3 water demand pulled the average up compared to the previous 10 years.
The gradual phase in of groundwater restrictions in Area #3 gives new developments time to migrate to water from alternative sources.
Groundwater Usage Decreasing as Alternative Water Usage Increases
The District defines “alternative sources” as anything other than groundwater. It usually refers to surface water from various sources such as the Trinity, San Jacinto or Brazos Rivers.
Overall, the use of alternative water is growing and reached a new high last year. Conversely, groundwater use declined despite growth in total water demand.
But growth in surface water supplies met that demand and then some.
Growth in surface water
All things considered, that’s good news.
Impact on Groundwater Levels
Restricting groundwater use reduces subsidence. To see its impact, the District measured increases and decreases in water well levels. The District can provide comparisons of hundreds of well levels today with the previous year, five years and 48 years. Predictably, the highest decreases clustered within the fastest growing areas to the north and west.
But well levels also actually rose in some areas. Where that happened, aquifers are recharging faster than they are depleting – another good sign that the regulatory regime is working.
Impact on Subsidence
The Subsidence District maintains an extensive network of GPS stations that monitor subsidence across 12 counties.
Two things stood out:
The fast-growing Area #3 subsided much faster than the other areas that already reduced their use of groundwater.
Katy showed the greatest subsidence. It received the least rain and is also among the fastest growing areas in the region.
Filling Observational Gaps Between Wells
The District also used “interferograms” to render high-resolution subsidence maps. Radio waves bounced off earth form the basis for interferograms. By measuring the timing of return signals as the satellite circles the globe endlessly, and comparing the differences, the technique can achieve an accuracy of millimeters.
Interferograms produced by the Subsidence District clearly show bands of subsidence that correspond to the length of time regulations have been in effect.
But there’s even better hope for the future.
Projects Enabling Groundwater Conversion
Area leaders have collaborated on four large projects to move people off groundwater.
Northeast Transmission Line Project, which will pipe treated surface water from Lake Houston into central and northern Harris County. (Purple line below.)
Surface Water Supply Project which will take water from the new plant to western Harris and northeastern Fort Bend Counties. (Orange Line Below)
In addition, the City and several water authorities are working on their own local distribution systems to move water to customers.
It’s comforting to see people of the region coming together to provide for the security of the next generation.
5/20/25 – Yesterday, I posted about a doom loop and virtuous cycle as they related to flooding in general. Doom Loop Part II will focus on more specific patterns that I have seen repeated in the Houston area over time.
“Doom loop” is often used in public policy debates to describe a series of events that contribute to a downward spiral, such as increased flood risk for more people.
The words and slides below are taken from a presentation delivered to the Harris County Community Resilience Flood Task Force and Infrastructure Resilience Team today. I hope they stimulate a discussion. Only through correct diagnosis of the problem can we ever hope to find a solution.
To download a copy of the presentation, click here. To review the narrative that goes with the slides, see below.
Slide One: A 75-Year Perspective
What happened in fast-growing watersheds inside Beltway 8 decades ago is now happening in fast growing watersheds outside the Beltway today. We’ve had multiple waves of expansion in the last 75 years. And we keep repeating the same mistakes.
Remember this slide. We will come back to it at the end. It shows base flood elevation – the estimated depth of a 100-year or 1% annual chance flood above ground level.
Slide 2: Doom Loop
A doom loop is the opposite of a virtuous cycle. For instance, crime increases. So people move away and tax revenue decreases. That means less money for police, crime continues to increase, etc. In flooding, in north Houston, the doom loop looks something like this.
These six things build on each other to compound risk. Let’s look at each and some real world examples inside and outside of the Beltway.
Slide 3: Inaccurate Predictions
All of our homes and infrastructure are built around estimates of future rainfall. But those estimates are a shifting target.
The estimates form the foundation of our building codes and development regulations.
Statisticians base them on a branch of mathematics called extreme value analysis (EVA). EVA tries to estimate the probability of unknown future events based on the frequency of extremely rare past events.
But because past superstorms are rare, the statisticians do not have much data to work with. So, they must revise their estimates every time we have a major new disaster such as Carla, Allison or Harvey.
Today, Houston and Harris County design infrastructure around rainfall estimates that are 50% greater than the those in place when most of Houston’s streets, homes and drainage systems were built.
Slide 4: Major Iterations of Stats
Since I moved to Houston 42 years ago, we’ve had three different standards.
Design depth listed in inches on right,
The standard developed after Carla in 1961 predicted a 1% annual chance storm would drop 12 inches of rain in 24 hours.
But since Harvey, we now think of such a storm as one that drops 18 inches in 24 hours.
That’s 50% more than the standard that shaped much of the infrastructure Houston put in place before Allison.
But adoption of these standards is not uniform. Nor is adoption fast. Some places in the region still use TP-40 estimates developed 64 years ago.
Slide 5: Infrastructure Changes with Expected Rainfall
What depends on these statistics? Lots.
Atlas 14 rainfall statistics for north Houston(right) now determine the design capacity of new infrastructure in some parts of the region.
In short, the rainfall design standards form the basis of everything that determines whether you will flood in the next superstorm.
However, they aren’t uniformly adopted throughout the region. Potential homebuyers should look upstream in surrounding jurisdictions to see whether those areas are basing their development decisions on standards that are this strict.
Slide 6: Conflicting Standards Sometimes Fight Each Other
Building codes and development regulations based on those rainfall design standards also get updated periodically. But never at the same time.
After Harvey, the county examined how all the homes built after 2008 fared during the storm. They were damaged at ONE TWENTIETH the rate of homes built before 2008.
So why didn’t all the surrounding jurisdictions immediately update their development standards and building codes?
This is where science meets politics.
Some areas use lower standards/regulations as a way to attract new development.
And some (certainly not all) developers manage to find reasons why they should be allowed to develop cheap land in floodplains.
People love living near water. They pay a premium for it.
But humans usually have a poor understanding of risk. That means low cost and high profit for developers. They can buy up cheap floodplain land and sell it for a premium.
Buyers must always look out for themselves. Governments represent many interests – sometimes conflicting. They represent developers just like they represent you.
Slide 8: The Halls Bayou Example
This slide shows Halls Bayou at what would later become Sweetwater Lane in 1953. It was all farmland.
In the 1960s, the farmer sold the land to a developer.
Slide 9: Land Built Out Before FEMA
Here’s what it looked like by 1978, a year before FEMA was formed.
Slide 10: Flood Risk Today
And here’s what the flood risk looks like today…now that we have FEMA and mapped floodplains.
That crosshatched area is floodway. The rest is floodplains.
Slide 11: Halls Bayou Mid-reach Segment
Here’s a wider shot of Halls today. The development is so dense, it’s hard to see the bayou. So I outlined it in red.
That’s 59 angling up toward the right. Talk about density!
Slide 12: Halls Flood Risk Before Latest Updates
And here are the floodways and floodplains as FEMA mapped them in 2014. FEMA has not yet updated the floodplains using Hurricane Harvey data.
Keep in mind that these could expand 50% – 100% with MAAPnext.
Slide 13: How Upstream Development Can Undermine Downstream Safety Margins
Other watersheds, such as the San Jacinto still have a lot of undeveloped area upstream. For instance, the San Jacinto watershed north of Lake Houston is 50% larger than Harris County itself and rapidly developing.
But some jurisdictions, such as Montgomery County have not seriously updated their drainage regulations since the 1980s. So much of the new development is insufficiently mitigated.
That’s why – downstream – we get 100-year floods on 10-year rains, like we did last May. There are lots of loopholes that developers can use to game the system.
I found one that mischaracterized soil surveys to exaggerate the rate of infiltration. That allowed him to get away with building 12,000 acres in wetlands with less than 10 acres of detention basins.
Another way to get away with building less detention than you should is with hydrologic timing studies. Let’s look at those.
Slide 14: Beat the Peak
The state water code stipulates that developments can have “NO ADVERSE IMPACT’ on downstream neighbors. To prove that, engineers compare pre- and post-development runoff rates. If the post-rate is no higher than the pre-, then they can claim no adverse impact.
You can see that in the two smaller curves below on the right. They illustrate a pre/post comparison where timing surveys are prohibited.
But some jurisdictions still allow timing studies, also known as beat the peak studies or flood routing studies.
The theory is that if you can get your runoff to the river fast enough, you aren’t adding to the peak of the flood. So, you shouldn’t be forced to build detention basins. But sometimes the data they use is very old, i.e., from the 1980s in the case of Montgomery County. And it ignores the cumulative effect of development since then. MoCo, by the way, is the seventh fastest growing county in America.
But there’s another problem, too. What happens when an area sends its storm water downstream from one direction as a storm like Harvey approaches from the other?
People in the middle get squeezed. Badly. That’s the runoff curve on the left above that assumed stormwater from development would be long gone by then.
If each development took care of its own runoff, we wouldn’t have this problem. We would have to worry about the uncertainty. That’s why eliminating such studies was one of Harris County’s five main recommendations to surrounding governments after Harvey.
Slide 15: Difficulty of Adapting Downstream
Downstream, it’s difficult to adapt to insufficiently mitigated upstream development.
Everything is already built out. You can’t rip up every street in the county to increase the size of storm sewers. You can’t elevate every home in the City of Houston. And you can’t always expand drainage channels because there’s often no room.
That makes change expensive, disruptive and often politically unpalatable. And it puts political leaders in a “double bind” – a “damned if you do/damned if you don’t” situation. Many families would rather live with periodic flooding if FEMA continues to insure against it – as long as they don’t have to move. Sometimes, there’s just no way to win.
Do you think if leaders had known what they were going to be up against years ago, they would have allowed building this close to the bayou?
Slide 17: An Even Closer Shave
This apartment complex, also on Brays, is so close, it looks like it could slide in.
Slide 18: Flood-Mitigation Funding
Now consider all those problems against another one: our historical unwillingness to fund flood mitigation at meaningful levels.
Before the flood bond, HCFCD had only $60 million per year for capital improvement projects. Sometimes the district had to save up for years to build one detention basin.
After Harvey, fixing flooding was the #1 priority in the region and the state. We passed the flood bond and launched a statewide flood-planning process.
But with time and distance, people lose their sense of urgency. They want to move on. So, eight years later, we have a state flood plan with $54 billion worth of projects. And $1 billion to address them. And don’t expect the feds to bail us out any time soon. FEMA and HUD are both facing unprecedented uncertainty in Washington.
Slide 19: Step and Repeat
I hope you have seen how this doom loop repeats itself as Houston expands ever outward.
Remember that house under 25 feet of water in the opening slide. It’s located at the bottom of this area outlined in red where four streams come together about a block west of 59 and Kingwood.
A foreign developer wants to build 7,000 homes in that blue area which represents floodplains.
One hydrologist told me that building that project would be like aiming a fire hose at Kingwood.
Slide 20: Other Examples
But that’s not the only example.
Remember that development that falsified the soil tests to avoid building detention. That’s Colony Ridge, upstream on the East Fork in Liberty County. They built an area 50% larger than Manhattan over wetlands which are nature’s detention basins.
The Commons of Lake Houston fought Houston Public Works for seven years all the way to the Texas Supreme Court for the right to build 500 homes in the swampy floodplain next to the East Fork. I have pictures of it under 17 feet of water.
And Romerica tried to build 50-story high-rises with underground parking in what will soon become the FLOODWAY of the San Jacinto West Fork.
And that’s why Texas has more people living in floodplains than the entire populations of 30 states. Most of them here in Harris County.
Posted by Bob Rehak on 5/20/25
2821 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.
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5/19/25 – In public-policy discussions, doom loops are self-reinforcing negative events or policies that lead to a downward spiral. Example: High crime rates force residents to move to safer neighborhoods. Then property values decline. The police get less money to patrol. And that leads to more crime. The area spirals downward.
Negative vs. Positive Cycles
A virtuous cycle is the opposite. It is a self-reinforcing, positive, upward spiral. Lower crime, for example, attracts population which provides the funding to keep the area even safer and growing.
You can see a doom loop in flooding if you look back far enough. Tomorrow, I will give a presentation to the Harris County Community Flood Resilience Task Force that looks back 75 years at how Houston’s growth has affected flooding.
How We Handle Growth Is Root Issue
Unfortunately, growth is not always positive from a flooding perspective. If not managed properly, it can create a doom loop that increases flooding. The presentation focuses on how we repeat the mistakes of the past instead of reversing that downward spiral.
The table below from ChatGPT shows a generalized Flooding Doom Loop and a Flood-Resilience Virtuous Cycle for Houston.
Flooding Doom Loop
Flood-Resilience Virtuous Cycle
Rapid, unzoned development in floodplains
Stronger land use and drainage regulations
Loss of natural absorption (wetlands, prairies)
Preservation/restoration of natural systems
Increased stormwater runoff
Reduced runoff and slower flow
Overloaded drainage systems and bayous
Improved drainage capacity
Recurring flood damage
Fewer flooded properties
Disinvestment and property value decline
Higher property values and stability
Underfunded flood mitigation projects
Increased public/political support
Continued risky development
Sustainable development patterns
Add More Layers of Complexity and Depth
Now superimpose rapid population growth in ever-expanding, outward, concentric circles. That adds a new layer of complexity that my presentation explores with specific examples. It shows how areas outside Beltway 8 are fighting the same battles that areas inside the Beltway fought decades ago.
Conflicting Development Standards Across Jurisdictions
I examine, for instance:
Conflicting development standards across jurisdictions
And our suburbs are some of the fastest growing smaller cities, too. For many years recently, Conroe was the fastest growing city in America. And new census data shows that Fulshear (near Katy) is now the second fastest growing city percentage wise.
As the metropolis sprawls, developers can exploit differences in regulations between cities and counties to increase their profit margins. My presentation shows several examples.
Check back tomorrow for Doom Loop Part II.
Posted by Bob Rehak on 5/19/25
2820 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2025/05/Flooding-Doom-Loop.jpg?fit=1100%2C561&ssl=15611100adminadmin2025-05-19 15:53:272025-05-19 16:12:26Doom Loops and Virtuous Cycles in Flooding
5/18/25 – Here’s a legislative roundup that includes bills which address dredging, mining, permitting of new developments, and funding of flood mitigation. With only two weeks left in the session, it appears that several bills important to the Lake Houston Area have died in committee including a bill to fund long-term dredging.
Money allocated to fund dredging after Harvey will soon run out leaving the future of dredging in doubt.
Left on the Table
The bills that apparently died include:
HB1532 – which would have created a Lake Houston Dredging and Maintenance District.
HB1163 – which would have required sand miners in the San Jacinto watershed to develop a reclamation plan that met certain criteria and post a bond to ensure that miners executed the plan.
HB1177 – which would have created a criminal offense for diverting or impounding water in a way that damaged the property of another.
HB2068 – which would have transformed the Harris County Flood Control District with a board appointed by the governor and by allowing surrounding counties to join the District. It would have created regional flood control. But Harris County officials testified against it and it died in committee.
To check the status of any other bills or subjects that interest you, visit the Texas Legislature Online.
Still Alive
The Senate Local Government Committee will hold another hearing on Monday May 19, 2025 to consider a small number of bills that didn’t beat Friday’s deadline.
Among them, HB23 would let developers bypass government oversight during the permitting process by hiring engineers to act as compliance inspectors on their behalf. The bills authors claim it will make housing more affordable. But it has local governments concerned that they might lose oversight.
It certainly does appear to have plenty of potential for conflict of interest. “Dad, I’ve decided to let myself borrow your car tonight.”
Senator Brandon Creighton sponsored the Senate version of the bill. In his civilian job, he works for a developer.
Flood Mitigation Funding Still Up in Air
Flood mitigation funding also took it on the chin. The legislature did not directly allocate any more money to the state’s Flood Infrastructure Fund (FIF) which has been dwindling since 2023. The fund currently has less than a billion dollars left to address $54 billion worth of projects in the State Flood Plan. Plus regional flood groups are gearing up to add more projects to the plan.
This year, the legislature did not commit any funding exclusively to the Flood Infrastructure Fund. However, two bills are still alive that could potentially result in more funding: SB7 and HJR7.
If they somehow become law:
The FIF will be moved under the umbrella of the Texas Water Fund (TWF).
The TWF will receive $2.5B in one time funding from the economic stabilization fund.
A constitutional amendment will be put to the voters in November establishing a permanent source of funding for the TWF to the tune of $1B annually.
That $1B might be required to commit 80% to “New Water Supply” if Charles Perry has his way, but others are pushing back, preferring to give the TWDB Board the discretion to distribute as they see appropriate.
Uncertainty Abounds for Future of Flood Mitigation
The uncertainty surrounding State funding for flood mitigation is especially concerning given all the uncertainty surrounding federal funding for flood mitigation.
The uncertainty extends to the local level too. Harris County Flood Control District was supposed to make a presentation to Commissioners Court on the status of Flood Bond Funding on May 22. Commissioners requested the update in late February. However, HCFCD reportedly pleaded for more time and the presentation has been delayed.
Commissioners fear that inflation could mean that a large percentage of the projects promised with the flood bond never get done. They are grappling with a $100 million drainage funding shortfall.
5/17/25 – Contractors have finally started boring under UnionPacific Railroad (UPRR) tracks to connect Northpark drainage east and west of Loop 494. That crucial connection is a key to beginning many other parts of the Northpark expansion project.
Lake Houston Redevelopment Authority first contacted UPRR about running Northpark drainage under their tracks ten years ago. And for those keeping track, it was eight years ago that the two parties signed their first contract.
Fifth Contract is the Charm
If you’re wondering why it’s taken so long, the two parties are now working on their fifth contract. But all that is in the past. So are the special UPRR training sessions that contractors and LHRA staff had to attend. So is the years-long wait for UPRR to weld single 200-foot-long sections of track into place across the ten lanes of Northpark.
All energies are positive now and the project is moving forward.
Looking W along Northpark across Loop 494 toward US59. Location of starting point for bore circled. This and all pictures below taken on Friday, May 16, 2025.
One Pole Blocking Bore Must Move
Note, however, a CenterPoint pole is still in the way. See below.
Energized electric lines must be moved to adjacent pole on right.
CenterPoint needs to transfer the energized lines from the existing wood poles on each side of Northpark to the newly installed and adjacent fiberglass poles. Those are designed to route the electricity underground at that location – out of the way of the bridge. Once electricity is rerouted, the old pole blocking progress can be removed.
Yesterday, I received word from City Councilman Fred Flickinger’s District E office that CenterPoint and UPRR are close to signing a contract that will let CenterPoint enter UPRR’s right of way to move the pole. Good news!
A steel frame and steel plates locked together by those giant timbers in the foreground will protect the operation.
Steel, Not Concrete Pipe Needed
After completing the bore pit, contractors will run six-foot steel pipes under the tracks. The tolerance is exceedingly tight. The tracks cannot move more than one-quarter inch despite the weight and vibration of mile-long trains carrying heavy loads. Hence the steel.
Pipes that will eventually bore under tracks are being stockpiled for now on S side of Northpark.
Bore Pit Built Like Underground Fortress
From the ground, construction of the bore pit looked like this.
Steel I-beams and steel frame form perimeter of pit.Then giant steel plates were slotted between the I-beams.Looking E from over Loop 494. Steel pipe will connect to a giant junction box in the dirt area (bottom center).
Junction Boxes Will Tie Drainage Together
When this operation is complete, we will have two junction boxes on either side of the tracks.
Some time ago, a third junction box was placed underground near the Shell station on the opposite side of Loop 494. Before contractors paved the new southbound lanes on Loop 494, they already connected giant 8’x8′ reinforced concrete pipe under the paving. So now, all they have to do is connect that to the center junction box west of the tracks (foreground above).
Contingent Operations
Many subsequent operations rely on the successful completion of the bore under the tracks. They include:
5/16/2025 – Harris County Flood Control District (HCFCD) made several announcements about projects recently that will affect Kingwood and areas upstream.
Two Stormwater Detention Basins Now on Bid List
The District expects two major detention basin projects to go out for bids soon. The:
East TC Jester Basin on Cypress Creek will bid in the third quarter this year.
Woodridge Village Basin on Taylor Gully will bid in the first quarter next year.
The clearcutting of the Woodridge Village flooded hundreds of homes in Elm Grove, Sherwood Trails and Mills Branch twice in 2019. HCFCD started excavating an additional detention basin in 2021 to help address the risk of downstream flooding. But they were forced to discontinue the excavation in 2023 when they applied for a HUD grant to finish the project.
HCFCD also announced 10 more maintenance projects on area channels. They expect to start eight this year.
What Will Happen Where
The map below shows the location of the projects. It’s keyed to the numbers above in the first column.
The maintenance will help ensure the continued effectiveness of the area’s flood control systems.
HCFCD will repair or replace…
Existing damaged concrete channel linings
Slope paving
Outfall pipes
…for the following channels
G103-38-02-X005 (Kingwood Diversion Ditch)
G103-80-01-X012(Green Tree Ditch)
G103-41-00-X014 (Sand Branch)
G103-33-03-X003 (Hidden Pines to Bens Branch)
G103-38-01-X015 (Chestnut Ridge Rd. to Kingwood Diversion Ditch)
G103-38-01-X016 (Chestnut Ridge Rd. to Kingwood Diversion Ditch)
HCFCD will also remove sediment from:
G103-80-01-X013 (Green Tree Ditch)
G103-33-04-X007 (Kings Crossing Ditch)
G103-41-00-X013 (Sand Branch)
They will repair erosion on:
G103-33-01-X007 (North Park Dr. to Bens Branch)
G103-80-03.1-X037 (Taylor Gully)
Finally, HCFCD will reshape side channels on:
G103-33-04-X007 (Kings Crossing Ditch)
G103-41-00-X014 (Sand Branch)
During this time, residents in work areas may notice crews with large trucks and heavy equipment such as excavators and bulldozers. Stay well clear of the equipment.
HCFCD estimates it will complete all this work by early 2026. The District and Precinct 3 Commissioner Tom Ramsey who helped arrange the work stated that each specific effort will move on its own timeline.
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.
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
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5/14/25 – This morning, I gave a presentation that compared the pace of downstream flood mitigation with the pace of upstream development. Are we gaining or losing ground in the Lake Houston Area?
Presentation Connects Many Dots
Answering that question requires connecting many dots. Here are the slides from the presentation with my narrative.
As new upstream development adds impervious cover (roads and roofs) that can increase and accelerate runoff, building flood peaks higher and faster. And that can erode the safety of downstream residents. Managing flood risk becomes a struggle between competing forces.
MoCo One of Fastest Growing Counties in Country
The Lake Houston Area lies downstream from one of the fastest growing counties in the country. Montgomery County (MoCo) grew 68% in the last 15 years and 4.8% in 12 months recently. MoCo is currently the seventh fastest growing county in the entire country.
Ryko Exemplifies Danger of Upstream Development
Let’s look at a proposed MoCo development in the headwaters of Lake Houston. A company named Ryko bought 5,500 acres about a quarter mile west of Kingwood. It’s in the southern part of a triangle formed by Spring Creek, the San Jacinto West Fork and the Grand Parkway.
US59 Bridge in foreground by the confluence of the Sand Jacinto West Fork and Spring Creek.
“Like Aiming a Firehose At Kingwood”
Ryko, which is a Syrian-owned company, is reportedly working with Wan Bridge, a Chinese company, to develop 7,000 homes on the property. One of the leading hydrologists in the area told me that developing this property would be “like aiming a firehose at Kingwood.”
Many “Guardrails” Being Removed
Government has established many guardrails over time to protect people from insufficiently mitigated upstream development. But many of the guardrails are being removed. Or people are trying to remove them.
In this case:
A change to the state property code in 2023 gave developers the right to opt out of a city’s extra territorial jurisdiction (ETJ). ETJs lay the groundwork for future annexation by ensuring new infrastructure meets the standards of areas that might annex them someday. But if developments are not in an ETJ, they could change plats without approval.
Two bills pending in the legislature, HB23 and its companion SB2354, would essentially let developers “self-permit” by hiring engineering firms that replace government oversight.
The Endangered Species Act (ESA) constrains development in areas inhabited by threatened or endangered species. But Executive Order 14192 could change that. The US Fish and Wildlife Service has proposed a change under the order that means Ryko would no longer have to work around endangered species on its property.
An ex-Senior VP of Ryko for 21 years is now chair of the Houston Planning Commission. She still reportedly represents the company as an independent consultant,
The Montgomery County Drainage Criteria Manual hasn’t had a serious update for 40 years. The County still allows controversial practices, such as hydrologic timing surveys, to “prove” that upstream developments have no adverse impact on downstream residents.
Let’s take a closer look at the Ryko property with these issues in mind.
Upstream Development Almost Entirely in Floodplains
With that as a backdrop, what’s going on with the Ryko land? The map in the background for this next slide comes from Ryko’s Drainage Impact Analysis. It shows that their property (outlined in red) lies at the confluence of four major streams. All that blue represents floodplains and floodways.
Property outline and stream names enhanced for readability.
How Bad Is Ryko’s Flood Risk?
FEMA’s base-flood-elevation viewer shows that at the southern end of Ryko’s property, any homes would be under 25 feet of water in a 500-year flood (18.7 feet in a 100-year flood). Even at the higher elevations farther north, homes would be under 7 feet of water in a major flood.
Frequent Bald Eagle Sightings
Homeowners father north report frequent sightings of bald eagles. They believe the eagles live on Ryko’s property which is currently wilderness. One resident sent me a video of two eagles that landed in a tree right outside her living room window.
The Texas Water Code contains a rule that states upstream development can have “No Adverse Impact” on downstream neighbors. To prove no adverse impact, engineers compare estimated pre- and post-development runoff.
If post-development estimates are less than or equal to pre-development, they satisfy the requirement.
Estimates Based on Hydrologic Timing Not Always Accurate
But how accurate are those estimates? Montgomery County’s antiquated drainage criteria manual still lets engineers use hydrologic timing surveys, a practice now prohibited by the City of Houston and Harris County for several reasons.
Timing studies let developers avoid building detention basins if they can show that their development’s stormwater “beats the peak” of a flood. The theory: they aren’t adding to the peak.
Not building detention basins saves developers money and adds to the number of salable lots. But “beat the peak” studies have serious limitations and can often mislead.
They assume, for instance, a uniform storm across an entire watershed. But that rarely happens. Imagine the case of a storm like Harvey, which approaches from the south as developers to the north rush to get their water to the river. God help the people caught in the middle.
Timing surveys, in the case of Montgomery County, are also based on decades old data that ignores the cumulative impacts of other developments over time.
How Avoiding Detention Can Add to Flood Peaks
What often happens in reality is that you get higher peaks than if you had built detention. This graph shows three lines. The two at the bottom show typical pre- and post-development runoff rates where/when hydrologic timing studies are prohibited.
Not building detention often leads to earlier, higher peaks.
The height difference could be the difference between flooding or not flooding.
MoCo Still Doesn’t Require More Reliable Method
In short, building stormwater detention is a sure thing. Hydrologic timing is not.
Banning hydrologic timing studies would force developers to design systems that TRULY detain and slow runoff. But Montgomery County still permits timing studies. The County’s new Drainage Criteria Manual that prohibits them has been sitting on the shelf for more than a year.
Downstream Mitigation Slowing
Now, let’s look at what downstream residents are doing to offset the impacts of upstream development.
More floodgates on Lake Houston to speed up output
Upstream detention to reduce input.
Dredging is Highlight to Date…
Dredging continues. We’ve spent approximately $200 million to date and that total is still increasing.
Images shot current West Fork dredging plan, location of dredge by FM1960, and spoils placement area by Luce Bayou.
…But More Sediment Keeps Coming
After the Army Corps finished its emergency West Fork Dredging Project, they recommended regular maintenance dredging to ensure our rivers had sufficient conveyance and our drainage ditches were not blocked. State Representative Charles Cunningham authored HB1532 to create a dredging district for the Lake Houston Area.
HB1532 passed overwhelmingly in the House and is now waiting to be heard by Senator Paul Bettencourt’s Local Government committee in the Senate.
But this legislative session ends in two weeks. Any bill not out of committee by this Friday is effectively dead. And Bettencourt has not yet scheduled Cunningham’s bill for a hearing.
Construction on More Floodgates Not Likely Before 2027
The additional floodgates on Lake Houston have been delayed repeatedly for various reasons. Simultaneously, the Coastal Water Authority (CWA) is looking at the costs of repairing the dam and replacing it altogether. The 70+ year old dam is near the end of its useful life.
CWA board member Dan Huberty stated that engineering for additional gates should be complete by 2027. At that time, the project will go out for bids.
The CWA won’t receive preliminary reports on dam repairs and replacement until at least July of this year.
No Progress on Upstream Detention, None Likely Anytime Soon
Meanwhile, virtually nothing has happened yet in terms of upstream detention. The San Jacinto River Authority identified 16 areas for upstream detention basins/lakes in its River Basin Master Drainage Study.
SJRA has no construction funds. So many of the projects were incorporated into the state flood plan. But the state’s Flood Infrastructure Fund does not have a committed revenue stream.
The Texas Water Development Board has about a billion dollars currently available to build $54 billion worth of requests in the flood plan.
So keep the pressure on elected representatives who can protect your family.
Posted by Bob Rehak on 5/14/25
2815 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2025/05/DOTS-Slide17.jpeg?fit=1100%2C619&ssl=16191100adminadmin2025-05-14 17:49:322025-05-14 17:49:33Is Downstream Flood Mitigation Keeping Pace with Upstream Development?
5/12/25 – This post contains a guide compiled with the help of ChatGPT that describes how to reduce your flood risk when buying a home.
A major flood occurs somewhere in Southeast Texas on average once every 2.5 years, according to data compiled by Harris County Flood Control District. Flooding is THE NUMBER ONE THREAT to Houston area home owners no matter whether you consider frequency, damage potential, or financial impact.
Home and heirlooms flooded during Hurricane Harvey
Why Does Houston Flood So Much?
The main factors that increase flood risk fall into four categories:
Natural and Geographic Factors
Topography: Houston has many low-lying or flat areas drain slowly and accumulate water easily.
Soil type: Our clay-heavy and compacted soils absorb less water, increasing runoff.
Proximity to water bodies: Many rivers, bayous, and streams converge near the coast, making us more vulnerable to riverine and coastal flooding.
Rainfall intensity: The area receives intense and prolonged rainfalls.
Subsidence caused by excessive groundwater withdrawals can create bowls in the landscape and alter the gradient of streams.
Land Use and Development
Urbanization: Houston has grown rapidly, replacing vegetation with impervious surfaces (e.g., pavement, roofs). That drastically increases stormwater runoff.
Building in floodplains: Encroachment into natural flood zones has reduced flood storage capacity and exposed structures to damage.
Loss of wetlands and forests: Natural systems that absorb and slow runoff have been diminished.
Compacted or altered terrain: Grading and clearing land have disrupted natural drainage patterns.
Drainage and Infrastructure Deficiencies
Undersized storm drains or culverts built in decades ago often cannot handle large storm volumes.
Aging or poorly maintained systems: Blocked drains, eroded ditches, or failing levees increase risk.
Inadequate detention/retentionupstream: If runoff is not slowed or held temporarily, downstream flooding worsens.
Lack of regional coordination: Piecemeal or inconsistent regulations across the region complicate drainage problems.
Climate and Weather Patterns
More intense rainfall events: Houston’s warm atmosphere, proximity to the Gulf, complex weather patterns cause legendary downpours.
Rising sea levels: Increases the extent and impact of storm surge in coastal areas.
Back-to-back storms: Frequent rainfalls can saturate soils and fill channels, reducing capacity to absorb new runoff.
Houston Home Buyer’s Guide to Reducing Flood Risk
So what’s a newcomer to the region supposed to do? Or even a long-time resident who is relocating within the area?
I asked ChatGPT to help me put together a home-buyer’s guide for those who wish to reduce flood risk. It compiled a comprehensive guide almost 9,000 words long, specifically geared to the Houston region. However, it contains valuable information for other areas, too.
The guide covers what to look for during a property visit, online tools to assess flood risk, reviewing a home’s flood history, understanding elevation certificates, local floodplain regulations, and flood insurance considerations.
Major sections include:
Identifying the floodplain and flood-zone designations
Locations near waterways or reservoirs
Property elevation
Drainage infrastructure and proximity to drains
Neighborhood flood history
Lot grading and slopes
Signs of water pooling and poor drainage
Nearby bayous, ditches and low areas
House elevation and foundation design
Gutters, downspouts and drainage features
Evidence of past flooding and water damage
Tools and websites for evaluating flood risk (FEMA, Harris County Flood Education Mapping Tool, First Street Foundation)
Reviewing a property’s flood history
Seller’s disclosure notices
CLUE report (Comprehensive Loss Underwriting Exchange), an insurance claims history
Elevation Certificates and Base Flood Elevations
The impact of elevation on insurance premiums
Floodplain regulations and permits
How floodplain regulations could impact improvements you might want to make to an older home
It’s filled with valuable advice and reflects many of the themes I have posted about since Harvey.
Buyers Must Exercise More Caution than Ever
One last piece of advice. With FEMA and HUD under fire from DOGE and with the future of flood-mitigation funding in doubt, buyers must exercise more caution than ever. It’s also highly recommended reading for real estate agents.
Don’t expect the government to come to your rescue after a future flood. During Harvey:
154,170 homes across the county flooded in Harvey.
That’s eight one-hundredths of one percent. You can find far better odds playing the Texas Lottery.
Posted by Bob Rehak on 5/12/25
2813 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/01/IMG-3142-scaled-e1747098548322.jpg?fit=1100%2C825&ssl=18251100adminadmin2025-05-12 20:30:192025-05-12 20:38:35How to Reduce Your Flood Risk When Buying a Home
5/11/25 – A study published in the November 2024 edition of the Journal of Applied Meteorology and Climatology by researchers from Louisiana State University and Texas A&M examined stalling and rapidly intensifying tropical cyclones.
After analyzing 1,274 storms going back to 1900, they found one of the primary areas for such storms to strike is along the central Gulf Coast. They also found that, the estimated annual frequency of stalls significantly increased from 1966 – 2020 – by 1.5% year.
Lead author of the study, called Stalling North Atlantic Tropical Cyclones, is Jill C. Trepanier of LSU. Others include: John Nielsen-Gammon of Texas A&M; and Vincent Brown, Derek Thompson and Barry Keim, all of LSU.
Stalling Storms More Damaging
The authors found that, “Storms that stall tend to have a longer average duration than those that do not stall in all categories.” By that they mean levels of intensity (Cat 1 through 5).
They say stalling storms increase rainfall rates, storm surge heights and exposure to high winds including tornado activity. “Storms that slow down or stall can increase total damage by prolonging the exposure time to intense conditions,” they say.
Stalling Storms Clustered in Central Gulf, Late in Season
They also found that stalls tend to cluster in certain places. Those include, but are not limited to the central Gulf Coast.
And they happen more often late in the season during September and October.
“Stalls tend to occur in similar places over time and happen more frequently later in the hurricane season (October) when compared to the middle (August). Emergency managers can use this information to identify the likely location and timing for stalls throughout the North Atlantic tropical cyclone season,” say the authors.
Definition of Stalling
The researchers define a stalling cyclone as one that moves less than 200 km in 72 hours. “Potentially most devastating are those stalls within 200 km of the coast, but even more so, those that stall over or partially over land.”
“This is important for emergency managers to realize,” they say, “as those stalling near the coast will have a higher potential to inflict more damage to a population.” And storms that also rapidly intensify also give:
Emergency managers less time to evacuate people.
Residents less time to prepare.
The researchers also found that Category 3+ storms such as Hurricane Harvey persist longer than weaker tropical cyclones, providing more stall opportunities. Harvey, they say, dumped more rain than any stalling storm in recorded history. They examined the historical record going back to 1899.
Harvey track in 2017. Notice how dots get closer together as storm stalled over Texas.Each dot represents 6 hours.
Rapidly Intensifying Storms Also Becoming More Frequent
These studies suggest that rapidly intensifying storms have become more frequent and are occurring closer to the coast in recent years. Rapidly intensifying storms make evacuations more difficult. More people must move in less time and with less warning.
Coastal Areas More Densely Populated
According to NOAA, coastal areas are notably more densely populated than inland regions. For instance, coastal shoreline counties have a population density more than five times greater than the U.S. average.
Approximately 39% of the U.S. population lives in coastal shoreline counties, which comprise less than 10% of the nation’s land area (excluding Alaska).
Additional Research
Before concluding, the authors called for more research on the rainfall recurrence intervals associated with stalling cyclones. They also say future analysis should include a deeper dive on rapid intensification.
Individuals Should Research Preparation
In the meantime, the best thing people living in coastal areas can do is prepare. Forecasters predict an above-average hurricane season, which starts in about two weeks. The National Hurricane Center has produced an excellent series of videos to help you protect your family and property.
