4/9/2026 – Another “lesson learned” about flooding since Hurricane Harvey has been role of sedimentation from industrial-scale sand mining upstream from Lake Houston. It can only be appreciated from the air.
May 2024 flood at Hallett Mine on San Jacinto West Forknear Northpark Drive in Kingwood.Note the difference in water quality in the ditch.
Few, if any, urban watersheds have such dense clusters of sand mines directly upstream from their water reservoirs in major river channels. This is one of the most distinctive features of flooding in the San Jacinto Watershed.
The mines not only contribute to flooding in an outsized way, they impair water quality, damage the environment and harm wildlife.
Chronic Sediment Mobilization During Floods
Most erosion happens during floods. And most sediment moves during floods.
More than 20 square miles of sand mines in the floodway and floodplains of the San Jacinto immediately upstream from Lake Houston provide a ready source of exposed sediment, ripe for mobilization.
I have photographed:
Sand mines pumping sediment over and through dikes
Dike failures.
Rivers capturing sand pits during floods
Mines dumping sediment directly into rivers
See a small sampling of photos below.
LMI sand mine on West ForkBreach of sand-mine dike into San Jacinto West ForkBreach of Triple PG mine dike into Caney Creek in East Fork Watershed. Mine dumping sediment in West ForkSame mine overflowing onto neighboring properties and then West ForkPit capture at Hallett Mine. River now flows through mine instead of around it.FM2090 is now threatened by the East Fork which has rerouted itself through an abandoned sand mine.Pipelines carrying highly volatile liquids undercut by erosion from sand mine on West Fork.East Fork Sand Mine undercutting more pipelines and leaking into Caney Creek Abandoned sand mine equipment leaking oil into West ForkRusting dredge in abandoned sand mine in Humble on North Houston AvenueConfluence of Spring Creek and West Fork in August 2019. TCEQ cited Liberty Mines for discharging 56 million gallons of white sludge into the West Fork.Sand freshly deposited during Harvey blocked West Fork 90%, according to Army Corps. Farther downriver, a mouth bar blocked the West Fork backing water up into thousands of homes and businesses. Army Corps has since dredged this.
The Houston area certainly isn’t the only place in the U.S. with alluvial floodplain mining. But rarely, if ever, do such practices take place with such impunity so close to the water supply for two million people.
For More Information
See the sand-mining page of this website for Best Practices in the U.S. and abroad; academic studies on sand mining; Texas sand mining laws/regulations; observations; and tax appraisal practices. An investigation found that virtually all of the sand mines shown above are in Montgomery County which taxed them as ag- and timberland rather than depleting assets.
Also search on the tag “sand mining” to find more than 300 posts containing thousands of pictures of mining practices in the San Jacinto River Basin.
Posted by Bob Rehak on 4/9/26
3145 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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/11/RJR_4154-e1775771233982.jpg?fit=1100%2C733&ssl=17331100adminadmin2026-04-09 16:19:172026-04-09 16:47:27Role of Industrial-Scale Sand Mining in Lake Houston Area Flooding
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.
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.
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:
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.
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.
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.
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.
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.
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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/05/20240522-RJR_3549.jpg?fit=1100%2C733&ssl=17331100adminadmin2026-04-08 13:04:282026-04-09 14:11:04How Subsidence Amplifies Flood Risk in Lake Houston Area
Flat terrain is one of the most under-appreciated aspects of flood risk. It complicates virtually every aspect of flood control.
Flat terrain increases flood risk primarily by reducing the speed of runoff. It causes water to pool rather than drain away. Also, lack of gradient lets floodwaters spread wider, increases sedimentation, backs water up into storm sewers, and creates unpredictable backwater effects.
Spreading Wider
In steep, mountainous areas, a one-foot rise in a river can be relatively contained; it won’t spread out much. But in flat areas, water spreads out easily. Even a slight rise in water level can submerge numerous properties. And that water may not drain away quickly. As water fills channels, it backs up water into storm sewers and may cause street flooding.
Increases in rainfall can also shift floodplain boundaries significantly, as we saw recently with the introduction of new draft flood maps based on Atlas 14. Homes once considered outside of floodplains are now within them.
Increasing Sedimentation
Flat terrain also makes rivers move slowly. This enables suspended sediment to settle and reduces a river’s capacity to convey stormwater, leading to more frequent flooding.
It can also lead to the creation of sand bars, especially where rivers meet standing bodies of water, such as Lake Houston. During Harvey, we saw “mouth bars” grow thousands of feet on the East and West Forks above Lake Houston.
San Jacinto West Fork Mouth Bar after Hurricane Harvey
Mouth bars are sand bars found at the mouths of rivers. Such blockages create partial sediment dams that back water up and promote even more deposition upstream. For instance, see below.
Farther upstream from the West Fork mouth bar, additional freshly deposited sand during Harvey reduced West Fork conveyance by 90% at this location, according to the Army Corps.
The Army Corps has since dredged the West Fork. However, while dredging can temporarily deepen a channel, it does nothing to increase the slope (gradient). Without a steeper slope, the river remains slow, and new sediment quickly refills the dredged areas.
In steep river systems, flood waves pass quickly. But in Southeast Texas, flood waves move slowly down rivers. Peaks linger and lengthen. This increases the probability that the peaks will synchronize, i.e., stack on top of each other.
That’s especially true in large storms, such as hurricanes, that may stall over an area for days and dump rain uniformly across the region. Stormwater peaks from different tributaries then stack on top of each other as they moves downstream.
The highest flooding in Harris County during Harvey occurred at the confluence of Spring Creek (L) and West Fork (R). Looking NW from over I-69 Bridge.
Other Backwater Effects
The low gradient of streams in southeast Texas makes them extremely sensitive to a variety of backwater effects.
In flat river basins like the San Jacinto, Trinity and Brazos, mild slopes amplify “backwater effects.” Examples include
Bridges, culverts, sand bars, levees, dikes, and new developments
Can constrict conveyance and back water up
Same confluence as shown above but from a different angle shows how floodplain fill is constricting floodplain storage and the floodway near a critical choke point, the I-69 Bridge
Implications for Policy Making
In low gradient systems, many streams become hydraulically coupled during floods. So, basin-wide coordination is essential.
West Fork sand mine frequently inundated by floods illustrates need for vegetative controls to reduce erosion.
Summary
To summarize, in flat coastal plains with low-gradients:
Low slope = low velocity = poor drainage
Water spreads laterally instead of moving quickly downstream, flooding many structures
Stormwater from different tributaries has a higher chance of stacking up
Sediment accumulates faster
Infrastructure bottlenecks can have large spatial impacts.
Posted by Bob Rehak on 4/7/26
3143 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.
Role of Industrial-Scale Sand Mining in Lake Houston Area Flooding
4/9/2026 – Another “lesson learned” about flooding since Hurricane Harvey has been role of sedimentation from industrial-scale sand mining upstream from Lake Houston. It can only be appreciated from the air.
Few, if any, urban watersheds have such dense clusters of sand mines directly upstream from their water reservoirs in major river channels. This is one of the most distinctive features of flooding in the San Jacinto Watershed.
The mines not only contribute to flooding in an outsized way, they impair water quality, damage the environment and harm wildlife.
Chronic Sediment Mobilization During Floods
Most erosion happens during floods. And most sediment moves during floods.
I have photographed:
See a small sampling of photos below.
The Houston area certainly isn’t the only place in the U.S. with alluvial floodplain mining. But rarely, if ever, do such practices take place with such impunity so close to the water supply for two million people.
For More Information
See the sand-mining page of this website for Best Practices in the U.S. and abroad; academic studies on sand mining; Texas sand mining laws/regulations; observations; and tax appraisal practices. An investigation found that virtually all of the sand mines shown above are in Montgomery County which taxed them as ag- and timberland rather than depleting assets.
Also search on the tag “sand mining” to find more than 300 posts containing thousands of pictures of mining practices in the San Jacinto River Basin.
Posted by Bob Rehak on 4/9/26
3145 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.
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.
Where Subsidence Happens
As a result, subsidence afflicts fast-growing regions across the U.S. Several examples include:
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.
As water, from say Spring Creek or the San Jacinto West Fork, goes into that bowl, it increases erosion on the upstream side and deposition on the downstream side. That deposition contributes to pooling within the bowl. A double whammy.
So, when a major storm comes along homes may have had their “freeboard factor” wiped out. In engineering and insurance, “freeboard” means your “safety margin above the floodplain.” Live in a place long enough and you may find water creeping closer and closer to your home in successive storms.
Of course, subsidence is only one of many factors that could cause that. But it amplifies those other factors and increases your flood risk.
To complicate matters for the poor homeowners shown in the picture above, Dallas-based Scarborough recently purchased 5,300 acres nearby between Spring Creek and the West Fork. Any new subdivisions built on that property would use well-water and further contribute to subsidence.
For More Information
Your safety ultimately depends on maintaining a healthy safety margin – much like the distance between you and the car in front of you on the freeway. We’ve all seen what can happen without enough distance.
For a discussion of other factors that contribute to flood risk, see the Lessons page of this website.
For more on subsidence and flooding, see:
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.
How Flat Terrain In Southeast Texas Increases Flood Risk
Flat terrain is one of the most under-appreciated aspects of flood risk. It complicates virtually every aspect of flood control.
Flat terrain increases flood risk primarily by reducing the speed of runoff. It causes water to pool rather than drain away. Also, lack of gradient lets floodwaters spread wider, increases sedimentation, backs water up into storm sewers, and creates unpredictable backwater effects.
Spreading Wider
In steep, mountainous areas, a one-foot rise in a river can be relatively contained; it won’t spread out much. But in flat areas, water spreads out easily. Even a slight rise in water level can submerge numerous properties. And that water may not drain away quickly. As water fills channels, it backs up water into storm sewers and may cause street flooding.
Increases in rainfall can also shift floodplain boundaries significantly, as we saw recently with the introduction of new draft flood maps based on Atlas 14. Homes once considered outside of floodplains are now within them.
Increasing Sedimentation
Flat terrain also makes rivers move slowly. This enables suspended sediment to settle and reduces a river’s capacity to convey stormwater, leading to more frequent flooding.
It can also lead to the creation of sand bars, especially where rivers meet standing bodies of water, such as Lake Houston. During Harvey, we saw “mouth bars” grow thousands of feet on the East and West Forks above Lake Houston.
Mouth bars are sand bars found at the mouths of rivers. Such blockages create partial sediment dams that back water up and promote even more deposition upstream. For instance, see below.
The Army Corps has since dredged the West Fork. However, while dredging can temporarily deepen a channel, it does nothing to increase the slope (gradient). Without a steeper slope, the river remains slow, and new sediment quickly refills the dredged areas.
That is why the Army Corps recommended a maintenance dredging program and why State Rep. Charles Cunningham’s Lake Houston Dredging District is so important.
Unpredictable “Stacking” Effects
In steep river systems, flood waves pass quickly. But in Southeast Texas, flood waves move slowly down rivers. Peaks linger and lengthen. This increases the probability that the peaks will synchronize, i.e., stack on top of each other.
That’s especially true in large storms, such as hurricanes, that may stall over an area for days and dump rain uniformly across the region. Stormwater peaks from different tributaries then stack on top of each other as they moves downstream.
Other Backwater Effects
The low gradient of streams in southeast Texas makes them extremely sensitive to a variety of backwater effects.
In flat river basins like the San Jacinto, Trinity and Brazos, mild slopes amplify “backwater effects.” Examples include
Implications for Policy Making
In low gradient systems, many streams become hydraulically coupled during floods. So, basin-wide coordination is essential.
That’s why the SJRA’s Joint Reservoir Operations Study is so crucial and why fragmented governance increases flood risk. We need river-basin-wide flood control.
We must also be more sensitive to:
Summary
To summarize, in flat coastal plains with low-gradients:
Posted by Bob Rehak on 4/7/26
3143 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.