4/6/26 – One of the biggest “lessons learned” from Harvey is that coordinated Joint Reservoir Operations are crucial. The San Jacinto River Basin has two reservoirs controlled by dams. But coordinating their operation to reduce flooding remains elusive after 53 years.
The San Jacinto River Authority (SJRA) finished the Lake Conroe dam in 1973, but is still seeking public input on its Joint Reservoir Operations Study. They hope to have a first draft of the study by the end of 2026.
Benefits of Reservoir Coordination
Other authorities around the world have long recognized the benefits of coordinating the operations of multiple dams on their rivers. Benefits include:
Enhanced flood control and mitigation – By acting in tandem, dams can reduce flood peaks more efficiently than isolated dams.
Improved water security and drought resilience – Coordinated dam systems can manage water storage across a basin to alleviate water stress during dry seasons.
Reduced sediment transport – Tandem operation can reduce peak flows that cause heavy erosion, clogging rivers and downstream lakes.
Increased hydropower generation – Although not a factor in the San Jacinto Basin, coordinated operations allow water to be used multiple times as it passes through a series of dams, exponentially increasing total energy output from the same water resource.
Environmental sustainability – Strategic releases of water can sustain downstream ecosystems, habitats, and species, as seen in the U.S. Sustainable Rivers Program.
Improved navigation and trade – A system of coordinated locks and dams can regulate river flow consistently, facilitating the transport of goods via barges and promoting regional economic development.
Water security – Upstream dams can supplement the water supply in downstream dams that may support major metropolitan areas. Lake Conroe, for instance, provides backup to the smaller Lake Houston, which is the primary water supply for more than 2 million people.
River Authorities that Manage Multiple Dams for Flood Control
Examples of coordinated management abound. Take for instance:
In Texas, the Lower Colorado River Authority (LCRA) provides a textbook example of coordinated dam management for flood control through the Highland Lakes system. The LCRA manages a “staircase” of six dams northwest of Austin. All six assist with flood mitigation. They operate as an integrated unit to protect downstream communities.
Tennessee Valley Authority manages a network of 9 main-river dams and 22 tributary dams. The system is designed to catch heavy runoff in tributary reservoirs before it reaches the main river, significantly reducing flood risks for downstream cities like Chattanooga. The TVA operates these dams as a single unit. That way, they also ensure a consistent water depth of at least 11 feet along the entire 652-mile main channel. That lets 28,000 barges transport goods annually.
California Department of Water Resources found that “weather-informed reservoir operations” at Lake Oroville and New Bullards Bar Reservoir can further reduce flood risk for communities along the Yuba and Feather rivers during extreme atmospheric river storm events and potentially benefit water supply during drier periods.
In the Delaware River Basin, a “flexible flow management program” mitigates flooding impacts immediately downstream of reservoirs.
Two Key Houston-Area Reservoirs Have Different Missions, Management
So, why can’t the SJRA manage two dams?
For one thing, SJRA only controls Lake Conroe. The Coastal Water Authority controls Lake Houston.
For another, the two dams have slightly different goals and radically different construction.
Lake Conroe was conceived as a water supply and flood control reservoir (even though SJRA now claims Lake Conroe is strictly for water supply). Lake Conroe’s tainter gates can release 150,000 CFS.
Lake Houston, on the other hand, is primarily for water supply. It has limited flood control capability because of its fixed height spillway. Lake Houston has only four small gates with a combined release capacity of 10,000 cubic feet per second (CFS).
Engineers are currently studying ways to add more and bigger tainter gates to Lake Houston. The current plan under study would boost the release rate to 78,000 CFS, thus matching the highest release rate ever from Lake Conroe (during Harvey). That would enable better coordination between the dams.
Why It Matters
Timing of releases can materially affect downstream flooding in a densely developed floodplain. During Harvey, a wall of water 11 feet high was going over the Lake Houston spillway. 16,000 homes and 3300 businesses behind the dam flooded. It backed water up for miles. Lake Houston’s Dam had 5X more water going over it than Niagra Falls usually does – enough to fill NRG Stadium in 3.5 minutes – 425,000 CFS.
Lake Houston Dam During Harvey. Can you even see the gates at the right end of the spillway?
Twenty percent of all homes and forty percent of all businesses in the area were affected.
Lake Houston Area Flood Task Force
Getting the water out faster is crucial. But it must be done safely. In a way that doesn’t hurt downstream interests.
While Coastal Water Authority figures out how to add more gates, SJRA is building a forecasting tool for the entire watershed that has the potential to:
Improve coordination between the dams
Inform decisions about pre-releases and gate operations
See ReduceFlooding’s new Lessons page for more “lessons learned” about flooding. It’s my attempt to distill my most important findings from more than 3000 posts since Harvey.
Posted by Bob Rehak on 4/6/26
3142 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/2019/02/LakeHoustonDamDuringHarvey.jpg?fit=1500%2C968&ssl=19681500adminadmin2026-04-06 13:24:242026-04-06 18:17:53Reservoir Coordination Still Elusive After 53 Years
4/5/26 – Today’s “lesson learned” from almost nine years of research into flooding is about the counterintuitive “Limitations of Multiple Small Detention Basins at Watershed Scale.”
Research shows that hundreds of small ponds built during subdivision construction do little to reduce flooding at the watershed scale and may increase it in places. A 2009 National Academies study found (Page 422) that “In many cases the site-by-site approach has exacerbated downstream flooding and channel erosion problems as a watershed is gradually built out.”
Regional stormwater detention basins are superior to multiple small, on-site basins because they offer better flood control, higher water-quality treatment, and increased cost efficiency.
Regional basins effectively manage large-scale runoff from multiple developments by providing comprehensive peak flow reduction. Simultaneously, they reduce the maintenance burdens and land-use inefficiencies of scattered, small, and often poorly maintained small ponds.
With the exception of Lake Conroe, the 2,500 square miles upstream from the Lake Houston Area in the upper San Jacinto River Basin has no other regional detention basins/reservoirs as of this writing. And Lake Conroe controls only 13% of the watershed flowing into Lake Houston.
How Detention Basins Work
The goal of detention basins in general is to ensure post-development runoff is less than or equal to pre-development rates. That’s important because increases in impervious cover during development increase the speed of runoff. So floods peak faster and higher.
Detention basins do nothing to reduce the total amount of runoff. They just spread it out over a longer time. And that spread increases the probability that peak flow from one tributary will stack on top of another peak somewhere downstream in the river systems branching structure.
Peak Stacking
While detention basins effectively reduce peak flows at individual sites, they don’t necessarily reduce peak flows everywhere because of this stacking effect.
A flood-frequency analysis of large European river basins found that “If a flood peak in the main river is superimposed by a simultaneous peak from a tributary, the magnitude of the flood peak may be increased significantly downstream.”
This graph illustrates the concept.
What happens downstream when peaks from different tributaries arrive simultaneously instead of separately.
The simultaneousarrival of peak flows from different tributaries can increase the height of a flood even if total volume remains unchanged.
Factors that Contribute to Peak Stacking in Lake Houston Area
Several factors present in the Lake Houston Area increase the probability of this “peak stacking.” They include:
Convergence of many major tributaries and sub-tributaries
Low gradients, flat terrain
Rapid upstream growth
Largely uncontrolled sedimentation reducing conveyance and creating backwater
Detention basins usually have no way to delay or accelerate the timing of releases. Stream levels control timing; when they get low enough, water can start trickling out of the basin. But that’s precisely what maintains peaks longer. And that longer peak increases the probability of peaks merging at confluences instead of arriving at different times.
Regional Detention Prospects Look Bleak for Lake Houston Area
While regional detention may be preferable and more effective than hundreds or even thousands of small detention basins, it is difficult to find space for regional basins – at least with a Benefit Cost Ratio (BCR) that justifies the project.
A recent feasibility study on regional detention upstream on Spring Creek offered little hope after developers snapped up the land before the study was completed. The federal government also excluded social benefits from BCR calculations during the study.
The same land could have been purchased decades ago for a fraction of the cost when it was good for nothing but timber. But the BCR would have been even lower because few people lived in the “benefit” area at that time. Damage to structures would have been minimal.
Ten of 16 projects recommended by SJRA’s Master River Basin Drainage Plan involved regional detention basins.
Similarly, HCFCD’s promising Little Cypress Creek Frontier Program, which would have created regional detention, has been cancelled. Harris County Commissioners reportedly felt reluctant to spend money where few people lived.
These examples highlight a systemic problem: Most effective regional detention basin projects with available land are far upstream in their respective watersheds where few people live. That means the people who benefit from them may live across jurisdictional boundaries, such as city or county lines.
For instance, the Spring Creek detention basins were in Waller County. But most of those who benefited from them lived in Montgomery County. That makes financing and managing them more difficult.
Conclusion
Regional detention basins are more efficient and effective than small local detention basins. But until people of the river basin recognize the benefits of working together on flood mitigation, we must live with distributed detention and suffer the consequences.
Posted by Bob Rehak on 4/5/2026
3141 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/2026/04/flood_peaks_comparison.png?fit=1979%2C1177&ssl=111771979adminadmin2026-04-05 23:24:242026-04-05 23:50:27Limitations of Multiple Small Detention Basins at Watershed Scale
4/4/26 – States, counties and communities across the U.S. prioritize flood mitigation over flood prevention, despite FEMA studies that have found prevention costs up to 5-6X less than correction. What types of costs?
Examples of Mitigation Costs
Examples of mitigation costs include:
Post-flood buyouts: Government often buys and demolishes homes after repeated flooding.
Levees/dams/detention basins/channel improvements: Expensive to build and maintain — and they can fail.
Flood insurance subsidies: Taxpayers often foot the bill via programs like the U.S. National Flood Insurance Program (NFIP), which is deeply in debt.
Examples of Prevention Costs/Strategies
Examples of much more cost-effective Prevention Strategies include:
Zoning restrictions to keep development out of high-risk zones.
Green infrastructure like wetlands that absorb floodwaters.
Elevated buildings or flood-resistant designs where development is unavoidable.
Parks,buying out land, and conservation easements before development occurs.
Kingwood’s East End Park provides habitat and recreation while improving the value of neighboring homes and distancing them from flooding.
While development in floodplains may seem cheaper at first, the long-term economic, environmental, and social costs almost always outweigh the initial savings.
National Subsidies Distort Local Priorities
So, why do the inverted priorities persist? The developer reaps the profit, but taxpayers bear the costs. Economists call it an “externality problem” when the production or consumption of a good, such as housing, imposes unintended costs or benefits on third parties not involved in the transaction.
In this case, the availability of cheap, nationally subsidized flood insurance distorted the market for floodplain properties by insulating buyers and lenders from the true costs of flooding.
And when flooding did happen, FEMA and HUD were there to help bail out local communities with hundreds of billions of dollars of flood mitigation grants.
As a result…
The U.S. chronically underinvests in mitigation and over-relies on post-disaster funding.
We see this economic and policy pattern across the U.S. and locally.
Scarborough Example
For instance, in the Lake Houston Area, residents are fighting a 5,300+ acre development upstream from the I-69 bridge where the San Jacinto West Fork, Spring Creek, Cypress Creek and Turkey Creek all converge. It is one of the most flood-prone parcels in south Texas and large parts of it have just been reclassified as “floodway.”
Unbelievably, the Texas General Land Office (GLO) is helping bankroll the development. The GLO is also responsible for distributing billions of dollars of federal flood-mitigation aid in Texas. (Somebody needs to write President Trump!)
For More Information
To learn more about the cost of prevention versus correction, see:
For more on other causes of flooding, see the Lessons page of ReduceFlooding.
Posted by Bob Rehak on 4/4/26
3140 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/2018/11/SJR_704_048-e1612057029212.jpg?fit=1200%2C811&ssl=18111200adminadmin2026-04-04 17:34:192026-04-04 17:41:52How U.S. Prioritizes Flood Mitigation Over Flood Prevention
Reservoir Coordination Still Elusive After 53 Years
4/6/26 – One of the biggest “lessons learned” from Harvey is that coordinated Joint Reservoir Operations are crucial. The San Jacinto River Basin has two reservoirs controlled by dams. But coordinating their operation to reduce flooding remains elusive after 53 years.
The San Jacinto River Authority (SJRA) finished the Lake Conroe dam in 1973, but is still seeking public input on its Joint Reservoir Operations Study. They hope to have a first draft of the study by the end of 2026.
Benefits of Reservoir Coordination
Other authorities around the world have long recognized the benefits of coordinating the operations of multiple dams on their rivers. Benefits include:
River Authorities that Manage Multiple Dams for Flood Control
Examples of coordinated management abound. Take for instance:
Two Key Houston-Area Reservoirs Have Different Missions, Management
So, why can’t the SJRA manage two dams?
For one thing, SJRA only controls Lake Conroe. The Coastal Water Authority controls Lake Houston.
For another, the two dams have slightly different goals and radically different construction.
Engineers are currently studying ways to add more and bigger tainter gates to Lake Houston. The current plan under study would boost the release rate to 78,000 CFS, thus matching the highest release rate ever from Lake Conroe (during Harvey). That would enable better coordination between the dams.
Why It Matters
Timing of releases can materially affect downstream flooding in a densely developed floodplain. During Harvey, a wall of water 11 feet high was going over the Lake Houston spillway. 16,000 homes and 3300 businesses behind the dam flooded. It backed water up for miles. Lake Houston’s Dam had 5X more water going over it than Niagra Falls usually does – enough to fill NRG Stadium in 3.5 minutes – 425,000 CFS.
Getting the water out faster is crucial. But it must be done safely. In a way that doesn’t hurt downstream interests.
While Coastal Water Authority figures out how to add more gates, SJRA is building a forecasting tool for the entire watershed that has the potential to:
For More Information
See SJRA’s presentation at the Humble Civic Center on 3/5/26 for more on Joint Reservoir Operations.
See ReduceFlooding’s new Lessons page for more “lessons learned” about flooding. It’s my attempt to distill my most important findings from more than 3000 posts since Harvey.
Posted by Bob Rehak on 4/6/26
3142 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.
Limitations of Multiple Small Detention Basins at Watershed Scale
4/5/26 – Today’s “lesson learned” from almost nine years of research into flooding is about the counterintuitive “Limitations of Multiple Small Detention Basins at Watershed Scale.”
Research shows that hundreds of small ponds built during subdivision construction do little to reduce flooding at the watershed scale and may increase it in places. A 2009 National Academies study found (Page 422) that “In many cases the site-by-site approach has exacerbated downstream flooding and channel erosion problems as a watershed is gradually built out.”
Regional stormwater detention basins are superior to multiple small, on-site basins because they offer better flood control, higher water-quality treatment, and increased cost efficiency.
Regional basins effectively manage large-scale runoff from multiple developments by providing comprehensive peak flow reduction. Simultaneously, they reduce the maintenance burdens and land-use inefficiencies of scattered, small, and often poorly maintained small ponds.
With the exception of Lake Conroe, the 2,500 square miles upstream from the Lake Houston Area in the upper San Jacinto River Basin has no other regional detention basins/reservoirs as of this writing. And Lake Conroe controls only 13% of the watershed flowing into Lake Houston.
How Detention Basins Work
The goal of detention basins in general is to ensure post-development runoff is less than or equal to pre-development rates. That’s important because increases in impervious cover during development increase the speed of runoff. So floods peak faster and higher.
Detention basins do nothing to reduce the total amount of runoff. They just spread it out over a longer time. And that spread increases the probability that peak flow from one tributary will stack on top of another peak somewhere downstream in the river systems branching structure.
Peak Stacking
While detention basins effectively reduce peak flows at individual sites, they don’t necessarily reduce peak flows everywhere because of this stacking effect.
A flood-frequency analysis of large European river basins found that “If a flood peak in the main river is superimposed by a simultaneous peak from a tributary, the magnitude of the flood peak may be increased significantly downstream.”
This graph illustrates the concept.
The simultaneous arrival of peak flows from different tributaries can increase the height of a flood even if total volume remains unchanged.
Factors that Contribute to Peak Stacking in Lake Houston Area
Several factors present in the Lake Houston Area increase the probability of this “peak stacking.” They include:
Detention basins usually have no way to delay or accelerate the timing of releases. Stream levels control timing; when they get low enough, water can start trickling out of the basin. But that’s precisely what maintains peaks longer. And that longer peak increases the probability of peaks merging at confluences instead of arriving at different times.
Regional Detention Prospects Look Bleak for Lake Houston Area
While regional detention may be preferable and more effective than hundreds or even thousands of small detention basins, it is difficult to find space for regional basins – at least with a Benefit Cost Ratio (BCR) that justifies the project.
A recent feasibility study on regional detention upstream on Spring Creek offered little hope after developers snapped up the land before the study was completed. The federal government also excluded social benefits from BCR calculations during the study.
The same land could have been purchased decades ago for a fraction of the cost when it was good for nothing but timber. But the BCR would have been even lower because few people lived in the “benefit” area at that time. Damage to structures would have been minimal.
The San Jacinto River Authority Master River Basin Plan recommended ten similar detention projects in 2020. But six years later, not one is funded.
Similarly, HCFCD’s promising Little Cypress Creek Frontier Program, which would have created regional detention, has been cancelled. Harris County Commissioners reportedly felt reluctant to spend money where few people lived.
These examples highlight a systemic problem: Most effective regional detention basin projects with available land are far upstream in their respective watersheds where few people live. That means the people who benefit from them may live across jurisdictional boundaries, such as city or county lines.
For instance, the Spring Creek detention basins were in Waller County. But most of those who benefited from them lived in Montgomery County. That makes financing and managing them more difficult.
Conclusion
Regional detention basins are more efficient and effective than small local detention basins. But until people of the river basin recognize the benefits of working together on flood mitigation, we must live with distributed detention and suffer the consequences.
Posted by Bob Rehak on 4/5/2026
3141 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 U.S. Prioritizes Flood Mitigation Over Flood Prevention
4/4/26 – States, counties and communities across the U.S. prioritize flood mitigation over flood prevention, despite FEMA studies that have found prevention costs up to 5-6X less than correction. What types of costs?
Examples of Mitigation Costs
Examples of mitigation costs include:
Examples of Prevention Costs/Strategies
Examples of much more cost-effective Prevention Strategies include:
While development in floodplains may seem cheaper at first, the long-term economic, environmental, and social costs almost always outweigh the initial savings.
National Subsidies Distort Local Priorities
So, why do the inverted priorities persist? The developer reaps the profit, but taxpayers bear the costs. Economists call it an “externality problem” when the production or consumption of a good, such as housing, imposes unintended costs or benefits on third parties not involved in the transaction.
In this case, the availability of cheap, nationally subsidized flood insurance distorted the market for floodplain properties by insulating buyers and lenders from the true costs of flooding.
And when flooding did happen, FEMA and HUD were there to help bail out local communities with hundreds of billions of dollars of flood mitigation grants.
As a result…
We see this economic and policy pattern across the U.S. and locally.
Scarborough Example
For instance, in the Lake Houston Area, residents are fighting a 5,300+ acre development upstream from the I-69 bridge where the San Jacinto West Fork, Spring Creek, Cypress Creek and Turkey Creek all converge. It is one of the most flood-prone parcels in south Texas and large parts of it have just been reclassified as “floodway.”
Unbelievably, the Texas General Land Office (GLO) is helping bankroll the development. The GLO is also responsible for distributing billions of dollars of federal flood-mitigation aid in Texas. (Somebody needs to write President Trump!)
For More Information
To learn more about the cost of prevention versus correction, see:
For more on other causes of flooding, see the Lessons page of ReduceFlooding.
Posted by Bob Rehak on 4/4/26
3140 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.