6/11/26 – Those seeking to understand flooding in the Lake Houston Area need to understand the placement and construction of the dam within the larger San Jacinto River Basin. Lake Houston is what hydrologists call a “terminal reservoir.”
Flood risk in the Lake Houston area is governed less by any single upstream factor and more by how all upstream factors converge at one critical place. And that critical place (the Lake Houston Dam) has extremely limited flood-gate capacity to lower the lake in advance of approaching storms.
Lake Houston gates (l) can release 10,000 cubic feet per second (CFS). Lake Conroe gates (r) can release 150,000 CFS.
How All Risk Factors Converge in Terminal Reservoirs
As a terminal reservoir, Lake Houston backstops everything that happens anywhere upstream. A terminal reservoir is a reservoir located at (or very near) the downstream end of a watershed, such as the San Jacinto River Basin. It receives the cumulative inflows from all upstream tributaries before water exits to a larger receiving body, like a bay or Gulf of Mexico.
Lake Houston is the tip of a funnel draining more than 2,500 square miles from seven counties. That’s an area 50% larger than all of Harris County itself. See below.
Percentages represent sub-watershed’s portion of acreage within Lake Houston’s drainage area which includes parts of seven counties. Lake Conroe controls only 13% of the drainage area.
Because of Lake Houston’s location, peak flows from multiple tributaries (East Fork, West Fork, Caney Creek, Peach Creek, Luce Bayou, Spring Creek, Cypress Creek, Lake Creek, etc.) can stack on top of each other.
During a storm, if peak flows from those tributaries arrive at different times, they may be manageable.
But if peaks arrive simultaneously, as they likely would in a large storm like Harvey, they create an exponential spike in water levels. And that can create catastrophic flooding in a terminal reservoir with limited gate capacity.
Terminal reservoirs catch more than water. They also trap sediment from all uncontrolled upstream tributaries. Those include the mining corridors along the West Fork, East Fork and Caney Creek.
This leads to the progressive loss of storage volume behind the Lake Houston dam. That reduces flood-buffering capacity over time. It also increases reliance on dredging.
This is a much bigger issue in the Lake Houston Area than in Lake Conroe. Lake Houston traps sediment from an area seven times larger than Lake Conroe does.
Sediment from 87% of the river basin ultimately ends up in Lake Houston.
Plus, the largest sources of sediment are between the two lakes. Virtually all sand mines in the river basin are downstream from Lake Conroe and upstream from Lake Houston.
Low Gradient and Urbanization Increase Flood Risk
The low gradient in our flat coastal plain, also means that this terminal reservoir can back water up into tributaries, such as Bens Branch, where 12 people died at an assisted living facility for seniors during Harvey.
Urbanization compounds all these risks. Incremental upstream development in Montgomery, Waller and Liberty counties creates a cumulative increase in runoff volume and speed which amplifies peaks at the terminal location.
In other posts, I showed how even if each upstream development project meets the “no-net-runoff-increase” mandate locally, a system-level effect still concentrates peak flows at the terminal reservoir.
Peak flows in Lake Houston watershed during Hurricane Harvey.400,000 CFS went over Lake Houston Dam.
The 400,000 CFS going over the Lake Houston Dam during Harvey created a wall of water 11 feet high. The volume was five times more than the volume of water going over Niagra Falls on an average day.
Implications
In summary, Lake Houston is the control point for a 2,500 square mile watershed. Lake Conroe controls only 13% of upstream drainage. Lake Houston controls 100%. The entire drainage area flows through this one control point with little help.
This heightens sensitivity to timing (when flood peaks arrive) and coordination (with Lake Conroe). Other than Lake Conroe, there is NO redundancy built into the system.
Sediment accumulation is not only inevitable, it is accelerated – by sand mining and rapid upstream development. This limits the buffering capacity of the lake for flood-control purposes. Sediment management is not optional. Safety requires it. Luckily, State Representative Charles Cunningham was able to start a Lake Houston Area Dredging and Maintenance District in the 2025 legislature.
The design of the Lake Houston dam also limits flexibility for flood management. Lake Houston has a 3,100-foot wide spillway but extremely limited gate capacity – 1/15th the capacity of Lake Conroe’s gates.
That limits pre-release capacity. It takes days in advance of a storm to lower Lake Houston enough to absorb anticipated incoming stormwater. But storms can veer away during that time. Yet millions of people depend on water from Lake Houston.
So dam managers must be extremely cautious about pre-releasing water. Before they open the gates, they must be sure the storm will replenish any water discharged.
Conclusion
Thus, gate capacity has outsized importance for flood safety. That’s why Houston Public Works and the Coastal Water Authority have studied the best way to add more gates to the dam ever since Harvey. But they haven’t yet finalized a design.
Meanwhile, people live with the flood risk of a terminal reservoir with limited gate capacity and little upstream help from other reservoirs.
For information about other factors that create flood risk, see the Lessons Page of this website.
Posted by Bob Rehak on 4/11/26
3147 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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2021/07/Gates-Side-by-Side.jpg?fit=1200%2C400&ssl=14001200adminadmin2026-04-11 12:15:012026-04-11 12:23:21How A Terminal Reservoir with Limited Gate Capacity Increases Flood Risk
The design of the Lake Houston Spillway doesn’t facilitate sediment discharge.
Lake Houston provides water for millions of people and loss of storage capacity is critical
Consequences of Sedimentation
This combination of factors is not unique, but it is unusual in its magnitude and consequences. Here’s why.
Lake Houston has a 3,160 foot long fixed height spillway for its primary discharge feature.While common in older water supply reservoirs, it provides few flood-control benefits.Studies to add tainter gates are not yet complete.
There is no way to remove sediment from Lake Houston except by dredging. Texas Water Development Board studies show that the lake has lost about 20% of its original storage capacity.
But the total storage loss is not the only issue; also consider where the loss is. Most sediment concentrates in the headwaters of the lake upstream from the FM1960 causeway where the river slows down as it meets a standing body of water.
Deceleration causes sediment to drop out of suspension. A delta has formed at this location, creating a hydraulic chokepoint that backs water up.
The Army Corps dredged approximately 2.1 million cubic yards from the area above FM1960.
Looking S over West Fork mouth bar after Harvey and before dredging.
East Fork Mouth Bar after Imelda, but before dredging
We have seen what happens when we ignore sediment buildups. Thousands of people can lose homes and businesses in a major flood.
Need for Ongoing Sediment Removal and Preservation
The SJRA has studied sedimentation and sand traps for years to help control such buildups. But they have yet to implement any solutions.
Thankfully, a bill by State Representative Charles Cunningham created a Lake Houston Dredging and Maintenance District during the 2025 legislature. That should help manage sediment buildups in the future before they become critical.
5,300 flood-prone acres between the confluence of Spring Creek (l) and the San Jacinto West Fork (r) are slated for development by Scarborough, a Dallas-based developer and the Texas General Land Office. Note first of many upstream sand mines in upper right.
The area above borders 20-square miles of West Fork sand mines.
The loss of forests due to mining exposes more sediment to erosion during floods.
The loss of forests and riparian buffers leads to a triple whammy in terms of sedimentation. It increases the natural rate of erosion. It costs taxpayers hundreds of millions of dollars to remove it. And until they do, it increases flood risk.
As sand production on the West Fork winds down, now is the perfect time to discuss creating a Montgomery County Lake District or a new state park in this area. It could turn into a win/win for upstream and downstream interests.
For More Information
For more about the causes of flooding and how they can compound each other in the Lake Houston Area, see the Lessons Page.
Posted by Bob Rehak on 4/10/26
3146 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/2026/04/DJI_0724.jpg?fit=1200%2C900&ssl=19001200adminadmin2026-04-10 12:19:232026-04-10 17:22:12How Sediment-Induced Loss of River Conveyance Increases Flood Risk
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
How A Terminal Reservoir with Limited Gate Capacity Increases Flood Risk
6/11/26 – Those seeking to understand flooding in the Lake Houston Area need to understand the placement and construction of the dam within the larger San Jacinto River Basin. Lake Houston is what hydrologists call a “terminal reservoir.”
Flood risk in the Lake Houston area is governed less by any single upstream factor and more by how all upstream factors converge at one critical place. And that critical place (the Lake Houston Dam) has extremely limited flood-gate capacity to lower the lake in advance of approaching storms.
How All Risk Factors Converge in Terminal Reservoirs
As a terminal reservoir, Lake Houston backstops everything that happens anywhere upstream. A terminal reservoir is a reservoir located at (or very near) the downstream end of a watershed, such as the San Jacinto River Basin. It receives the cumulative inflows from all upstream tributaries before water exits to a larger receiving body, like a bay or Gulf of Mexico.
Lake Houston is the tip of a funnel draining more than 2,500 square miles from seven counties. That’s an area 50% larger than all of Harris County itself. See below.
Because of Lake Houston’s location, peak flows from multiple tributaries (East Fork, West Fork, Caney Creek, Peach Creek, Luce Bayou, Spring Creek, Cypress Creek, Lake Creek, etc.) can stack on top of each other.
During a storm, if peak flows from those tributaries arrive at different times, they may be manageable.
But if peaks arrive simultaneously, as they likely would in a large storm like Harvey, they create an exponential spike in water levels. And that can create catastrophic flooding in a terminal reservoir with limited gate capacity.
Six years ago, the SJRA’s River Basin Master Drainage Plan recommended 10 areas for additional upstream regional detention. But not one has even been bid.
Sediment Trap for the River Basin
Terminal reservoirs catch more than water. They also trap sediment from all uncontrolled upstream tributaries. Those include the mining corridors along the West Fork, East Fork and Caney Creek.
This leads to the progressive loss of storage volume behind the Lake Houston dam. That reduces flood-buffering capacity over time. It also increases reliance on dredging.
This is a much bigger issue in the Lake Houston Area than in Lake Conroe. Lake Houston traps sediment from an area seven times larger than Lake Conroe does.
Plus, the largest sources of sediment are between the two lakes. Virtually all sand mines in the river basin are downstream from Lake Conroe and upstream from Lake Houston.
Low Gradient and Urbanization Increase Flood Risk
The low gradient in our flat coastal plain, also means that this terminal reservoir can back water up into tributaries, such as Bens Branch, where 12 people died at an assisted living facility for seniors during Harvey.
Urbanization compounds all these risks. Incremental upstream development in Montgomery, Waller and Liberty counties creates a cumulative increase in runoff volume and speed which amplifies peaks at the terminal location.
In other posts, I showed how even if each upstream development project meets the “no-net-runoff-increase” mandate locally, a system-level effect still concentrates peak flows at the terminal reservoir.
The 400,000 CFS going over the Lake Houston Dam during Harvey created a wall of water 11 feet high. The volume was five times more than the volume of water going over Niagra Falls on an average day.
Implications
In summary, Lake Houston is the control point for a 2,500 square mile watershed. Lake Conroe controls only 13% of upstream drainage. Lake Houston controls 100%. The entire drainage area flows through this one control point with little help.
This heightens sensitivity to timing (when flood peaks arrive) and coordination (with Lake Conroe). Other than Lake Conroe, there is NO redundancy built into the system.
Sediment accumulation is not only inevitable, it is accelerated – by sand mining and rapid upstream development. This limits the buffering capacity of the lake for flood-control purposes. Sediment management is not optional. Safety requires it. Luckily, State Representative Charles Cunningham was able to start a Lake Houston Area Dredging and Maintenance District in the 2025 legislature.
The design of the Lake Houston dam also limits flexibility for flood management. Lake Houston has a 3,100-foot wide spillway but extremely limited gate capacity – 1/15th the capacity of Lake Conroe’s gates.
That limits pre-release capacity. It takes days in advance of a storm to lower Lake Houston enough to absorb anticipated incoming stormwater. But storms can veer away during that time. Yet millions of people depend on water from Lake Houston.
So dam managers must be extremely cautious about pre-releasing water. Before they open the gates, they must be sure the storm will replenish any water discharged.
Conclusion
Thus, gate capacity has outsized importance for flood safety. That’s why Houston Public Works and the Coastal Water Authority have studied the best way to add more gates to the dam ever since Harvey. But they haven’t yet finalized a design.
Meanwhile, people live with the flood risk of a terminal reservoir with limited gate capacity and little upstream help from other reservoirs.
For information about other factors that create flood risk, see the Lessons Page of this website.
Posted by Bob Rehak on 4/11/26
3147 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 Sediment-Induced Loss of River Conveyance Increases Flood Risk
4/10/26 – Sediment buildups reduce river conveyance everywhere. But sedimentation is especially threatening in the Lake Houston Area because:
Consequences of Sedimentation
This combination of factors is not unique, but it is unusual in its magnitude and consequences. Here’s why.
There is no way to remove sediment from Lake Houston except by dredging. Texas Water Development Board studies show that the lake has lost about 20% of its original storage capacity.
But the total storage loss is not the only issue; also consider where the loss is. Most sediment concentrates in the headwaters of the lake upstream from the FM1960 causeway where the river slows down as it meets a standing body of water.
Deceleration causes sediment to drop out of suspension. A delta has formed at this location, creating a hydraulic chokepoint that backs water up.
The Army Corps dredged approximately 2.1 million cubic yards from the area above FM1960.
Subsequently, the City of Houston commissioned Callan Marine for a separate dredging effort to address additional buildups in Lake Houston’s headwaters.
We have seen what happens when we ignore sediment buildups. Thousands of people can lose homes and businesses in a major flood.
Need for Ongoing Sediment Removal and Preservation
The SJRA has studied sedimentation and sand traps for years to help control such buildups. But they have yet to implement any solutions.
Thankfully, a bill by State Representative Charles Cunningham created a Lake Houston Dredging and Maintenance District during the 2025 legislature. That should help manage sediment buildups in the future before they become critical.
But it’s no excuse to ignore things that contribute to excessive sedimentation. Those include failure to observe best management practices in mining and construction. They also include loss of riparian buffers and forests.
The loss of forests and riparian buffers leads to a triple whammy in terms of sedimentation. It increases the natural rate of erosion. It costs taxpayers hundreds of millions of dollars to remove it. And until they do, it increases flood risk.
As sand production on the West Fork winds down, now is the perfect time to discuss creating a Montgomery County Lake District or a new state park in this area. It could turn into a win/win for upstream and downstream interests.
For More Information
For more about the causes of flooding and how they can compound each other in the Lake Houston Area, see the Lessons Page.
Posted by Bob Rehak on 4/10/26
3146 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.