9/29/24 – When talking about using the Lake Houston Dam to help control flooding, one often hears experts say, “That’s not a flood-control dam. That’s a water-supply dam.” So, what’s the difference? And why does it make a difference?
The purpose of the dam influences its design, operation and management. An insider familiar with the effort to add more gates to the Lake Houston Dam said last week that engineers at both Houston Public Works and the Coastal Water Authority have resisted trying to modify a water-supply dam for flood control.
This is not the only reason this project has taken so long to get off the ground. But it helps explain why new, higher capacity Lake Houston gates are just now going into final design – 2588 days after the storm that made the need abundantly clear.
To put that in perspective, 2588 days is almost twice the number of days that it took to win World War II.
Conflicting Purposes, Designs
The primary purpose of a flood-control dam is to reduce flood risk by controlling the flow of water downstream during heavy rains. They accomplish this by temporarily holding back the flow of water. They then release it later in a controlled fashion to smooth out peaks and reduce flood damage.
To mitigate flooding, flood-control dams:
Often have lower water levels under normal conditions to accommodate sudden influxes of water.
Have large spillways and gates to rapidly release water when needed.
Are designed with a large storage capacity relative to the expected flood volumes.
Are sometimes kept partially empty to ensure sufficient space for incoming floodwaters.
Have more robust construction to withstand sudden large inflows and outflows.
On the other hand, the primary purpose of water-supply dams is to store water for human consumption (drinking, bathing, irrigation, industry, etc.).
To ensure consistent supply, a water-supply dam:
Prioritizes a consistent water level to ensure a reliable supply of water throughout the year, even during droughts.
Is usually kept at higher levels.
Stores water over longer periods.
Is managed to ensure sufficient supply throughout the year, with a focus on maximizing storage before dry seasons.
In summary, a flood-control dam is designed and managed to mitigate floods by managing excess water. However, a water-supply dam aims to store water for human use.
In practice, these extremes aren’t quite as mutually exclusive as the terms might imply.
Seasonal Management and Its Alternatives
Seasonal management strategies can help bridge the gap between the two. For instance, operators often manage both types of dams seasonally so they have more storage space during rainy seasons when flood risk spikes.
The SJRA adopted a seasonal lake-lowering strategy for several years after Harvey. But because of political pushback from Lake Conroe residents, the strategy was abandoned after several years.
“Stop the Drop” protesters pack an SJRA board meeting in December 2019.
SJRA now uses another hybrid strategy called “active storm management.” “Active Storm Management” seeks to manage lake levels by releasing water based on real-time weather forecasts to manage reservoir levels more effectively.
Other operators use a similar strategy known as FIRO (Forecast-Informed Reservoir Operations). Advanced forecasting models predict inflows and adjust dam releases preemptively.
Lake Houston, Lake Conroe Both Water-Supply Dams
Both Lake Conroe and Lake Houston are water-supply dams. But Lake Houston, built in the early 1950s, has a 3160-foot, fixed-height spillway with four small gates capable of releasing only 10,000 cubic feet per second (CFS) combined. Clearly, engineers prioritized consistent water level over flood mitigation when designing this dam. The small gates make it difficult and time consuming to release water before it reaches the level of the spillway.
According to the Houston Public Works Drinking Water Operations Group, Lake Houston supplies water to 2.2 million people.
Lake Conroe, built in 1973, has five large gates capable of releasing 150,000 CFS. It was designed as an alternate water supply for the City of Houston. The City financed its construction and owns two thirds of the water in the lake.
Lake Conroe has nothing comparable to the fixed-height spillway on Lake Houston.
3160-foot concrete and steel spillway on Lake Houston
Compared to spillway above, gates on Lake Houston can release only a small amount. But the spillway can release more than Lake Conroe.See below.It just can’t release that much before a storm.Lake Houston Dam during Harvey. The wall of water flowing out of the lake was 11 feet higher than the spillway.
During the peak of Harvey, an estimated 425,000 CFS went over the Lake Houston Spillway – 5 times the average flow of Niagara Falls.
In contrast, Lake Conroe released about 80,000 CFS from its gates during Harvey. So why the push to add more gates to Lake Houston?
Gates Key to Hybrid Strategy
Simple. Bigger gates are key to both water conservation and Active Storm Management. Right now, Lake Houston’s gates are so small that lowering the lake significantly can take days. During that time, storms can veer away.
That long lead time creates uncertainty that jeopardizes what Houston Public Works and the Coastal Water Authority see as their primary mission – providing water for 2.2 million people.
We just can’t create extra storage capacity in Lake Houston fast enough with the existing gates.
Why is Design Taking So Long?
But with more, larger gates, Lake Houston could release enough water in hours to create extra storage capacity. And operators would have confidence that water would not be wasted. So why are the gates taking so long?
Design of more gates for Lake Houston has just now started. Using Harvey as a starting point, we are now almost at twice the amount of time that it took to win World War II.
It’s hard to believe that if everyone agreed with the need for more flood gates, it would have taken this long to start design.
In that regard, I have heard of pushback from both Houston Public Works and Coastal Water Authority. The pushback had to do with the mission of the organizations: to supply water. They just didn’t want to risk wasting it in case we encountered drought.
But our two backup water sources (Lake Conroe and Lake Livingston) combined have 15 times the volume of Lake Houston. So the City probably won’t run short anytime soon.
Flood Mitigation Not In CWA Mission
The Coastal Water Authority, which is the City’s contract operator for Lake Houston, does not even mention “flooding” on its website. That’s right. CWA doesn’t mention the word in its mission statement, guiding principles, strategies, or tactics. They do, however, mention “pumps” 15 times on their Strategic-Plan page. That should give you some idea of their priorities: water supply.
Hopefully, Mayor John Whitmire’s recent appointment of former State Representative Dan Huberty to the Coastal Water Authority Board will help the CWA see Lake Houston from more than one perspective. Huberty has advocated for the gates since Harvey.
Posted by Bob Rehak on 9/29/24
2588 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=19681500adminadmin2024-09-29 20:13:322024-09-29 20:23:55Flood-Control, Water-Supply Dam Differences Help Explain Delay on Lake Houston Gates
9/28/24 – Forecasters predicted a very active 2024 hurricane season. After a slow start, the map is really lighting up. Currently, we have three named storms in the Atlantic Basin:
Remnants of Hurricane Helene, which is now a post-tropical depression centered over Tennessee
Hurricane Isaac, which formed in the middle of the Atlantic without much notice while Helene was barreling toward Florida earlier this week
Tropical Storm Joyce, also in the mid-Atlantic
Still Brewing
None of those named storms is a threat to Houston. However, the map shows two other areas of concern. See below.
Red Area
That elongated red area in the tropical Atlantic a couple hundred miles west of the Cabo Verde Islands continues to produce disorganized showers and thunderstorms.
According to the National Hurricane Center (NHC), environmental conditions appear conducive for gradual development of this system. A tropical depression will likely form during the early or middle part of next week. The system should move toward the west and then northwest across the eastern and central tropical Atlantic.
As of today, NHC lists formation chances for that red area as low (30%) in the next two days, but high (70%) in the next seven days.
Orange Area
Of greater concern for Texans, however, though is that orange area stretching from the northwestern Caribbean to the Gulf of Mexico. An area of low pressure should form there within a couple of days. NHC says environmental conditions are conducive for gradual development thereafter. They also say that a tropical depression could form around the middle part of next week.
This system should move northwestward into the Gulf during the latter portion of next week. NHC warns that interests in and along the Gulf Coast should monitor its progress.
As of today, formation chance through 48 hours is zero. But it’s 50% within 7 days.
Will the Gulf Go 4 for 4?
Lest anyone forget, this area has already spawned two major hurricanes and a hurricane in the last three months – Beryl, Francine and Helene.
Beryl ramped up to a Category 5 before hitting Houston in July.
Francine slammed Louisiana as a Cat 2 in September
Helene made landfall in Florida as a Cat 4 just two days ago.
Sea surface temps in that area are still 1.8 to 5.4 Fahrenheit above normal for this time of year (1-3º C).
So, don’t let your guard down.
Posted by Bob Rehak on 9/28/24
2587 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/09/two_atl_7d0-3.png?fit=900%2C665&ssl=1665900adminadmin2024-09-28 13:52:242024-09-28 14:06:39Three Named Storms in Atlantic Basin With Two More Brewing
9/27/24 – Hurricane Helene roared ashore last night and by noon today had triggered flooding in at least eight states, according to the National Weather Service.
Helene Floods Eight States
The states include: Florida, Alabama, Georgia, South Carolina, North Carolina, Tennessee, Virginia and Kentucky. See orange, red and purple areas below.
From NWS Water Prediction Center. Gage data from noon 9/26/24 to noon 9/27/24. Purple = Major Flooding, Red = Moderate, Brown = Minor. Yellow = Action.
Many of those same areas could still see additional rainfall. Through 7 AM CDT, NOAA’s Weather Prediction Center gives 15 states a chance for additional excessive rainfall. See below.
Power Outages and Deaths
Meanwhile, more than 3 million people in affected areas remain without power, according to PowerOutages.US.
The Hill reports that at least 35 people died as a result of the Category 4 storm.
At this hour, NBC puts the death toll at 42 and says more than 4 million people are without power.
USA Today reported within the hour that 4.5 million people have no electricity.
The death toll will likely increase in coming days as rescuers race to free more people trapped in flooded areas.
It could take weeks to restore all the power given the breadth of the devastation. An Associated Press report said that in Georgia, “…an electrical utility group warned of ‘catastrophic’ damage to the state’s utility infrastructure, with more than 100 high voltage transmission lines damaged.”
AP also reported that in South Carolina, “more than 40% of homes and businesses were without power.” They said crews needed to cut their way through debris just to determine what was still standing in some places.
Helene Now a Tropical Depression
At 4 PM, the National Hurricane Center has downgraded Helene to a tropical depression with sustained winds of 35 MPH and forward motion of 17 MPH.
Summary of Weather Stats
For a list of reported rainfall totals to date and peak wind gusts associated with Helene, see this list from the National Centers for Environmental Prediction as of 11 AM EDT 9/27/24. Busick, North Carolina recorded the highest rainfall total to date: 29.58 inches.
All in all, the forecasters predicted Helene’s impacts pretty accurately.
Helene is the latest reminder of why we need to continue fighting for flood mitigation. It could have happened here.
Posted by Bob Rehak on 9/27/24
2586 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/09/20240927-Helene-Flooding.jpg?fit=1100%2C614&ssl=16141100adminadmin2024-09-27 17:01:582024-09-27 17:27:06Helene Triggers Flooding in 8 States, Millions Without Power
Flood-Control, Water-Supply Dam Differences Help Explain Delay on Lake Houston Gates
9/29/24 – When talking about using the Lake Houston Dam to help control flooding, one often hears experts say, “That’s not a flood-control dam. That’s a water-supply dam.” So, what’s the difference? And why does it make a difference?
The purpose of the dam influences its design, operation and management. An insider familiar with the effort to add more gates to the Lake Houston Dam said last week that engineers at both Houston Public Works and the Coastal Water Authority have resisted trying to modify a water-supply dam for flood control.
This is not the only reason this project has taken so long to get off the ground. But it helps explain why new, higher capacity Lake Houston gates are just now going into final design – 2588 days after the storm that made the need abundantly clear.
To put that in perspective, 2588 days is almost twice the number of days that it took to win World War II.
Conflicting Purposes, Designs
The primary purpose of a flood-control dam is to reduce flood risk by controlling the flow of water downstream during heavy rains. They accomplish this by temporarily holding back the flow of water. They then release it later in a controlled fashion to smooth out peaks and reduce flood damage.
To mitigate flooding, flood-control dams:
On the other hand, the primary purpose of water-supply dams is to store water for human consumption (drinking, bathing, irrigation, industry, etc.).
To ensure consistent supply, a water-supply dam:
In summary, a flood-control dam is designed and managed to mitigate floods by managing excess water. However, a water-supply dam aims to store water for human use.
In practice, these extremes aren’t quite as mutually exclusive as the terms might imply.
Seasonal Management and Its Alternatives
Seasonal management strategies can help bridge the gap between the two. For instance, operators often manage both types of dams seasonally so they have more storage space during rainy seasons when flood risk spikes.
The SJRA adopted a seasonal lake-lowering strategy for several years after Harvey. But because of political pushback from Lake Conroe residents, the strategy was abandoned after several years.
SJRA now uses another hybrid strategy called “active storm management.” “Active Storm Management” seeks to manage lake levels by releasing water based on real-time weather forecasts to manage reservoir levels more effectively.
Other operators use a similar strategy known as FIRO (Forecast-Informed Reservoir Operations). Advanced forecasting models predict inflows and adjust dam releases preemptively.
Lake Houston, Lake Conroe Both Water-Supply Dams
Both Lake Conroe and Lake Houston are water-supply dams. But Lake Houston, built in the early 1950s, has a 3160-foot, fixed-height spillway with four small gates capable of releasing only 10,000 cubic feet per second (CFS) combined. Clearly, engineers prioritized consistent water level over flood mitigation when designing this dam. The small gates make it difficult and time consuming to release water before it reaches the level of the spillway.
According to the Houston Public Works Drinking Water Operations Group, Lake Houston supplies water to 2.2 million people.
Lake Conroe, built in 1973, has five large gates capable of releasing 150,000 CFS. It was designed as an alternate water supply for the City of Houston. The City financed its construction and owns two thirds of the water in the lake.
Lake Conroe has nothing comparable to the fixed-height spillway on Lake Houston.
3160-foot concrete and steel spillway on Lake Houston
During the peak of Harvey, an estimated 425,000 CFS went over the Lake Houston Spillway – 5 times the average flow of Niagara Falls.
In contrast, Lake Conroe released about 80,000 CFS from its gates during Harvey. So why the push to add more gates to Lake Houston?
Gates Key to Hybrid Strategy
Simple. Bigger gates are key to both water conservation and Active Storm Management. Right now, Lake Houston’s gates are so small that lowering the lake significantly can take days. During that time, storms can veer away.
That long lead time creates uncertainty that jeopardizes what Houston Public Works and the Coastal Water Authority see as their primary mission – providing water for 2.2 million people.
Why is Design Taking So Long?
But with more, larger gates, Lake Houston could release enough water in hours to create extra storage capacity. And operators would have confidence that water would not be wasted. So why are the gates taking so long?
Design of more gates for Lake Houston has just now started. Using Harvey as a starting point, we are now almost at twice the amount of time that it took to win World War II.
It’s hard to believe that if everyone agreed with the need for more flood gates, it would have taken this long to start design.
In that regard, I have heard of pushback from both Houston Public Works and Coastal Water Authority. The pushback had to do with the mission of the organizations: to supply water. They just didn’t want to risk wasting it in case we encountered drought.
But our two backup water sources (Lake Conroe and Lake Livingston) combined have 15 times the volume of Lake Houston. So the City probably won’t run short anytime soon.
Flood Mitigation Not In CWA Mission
The Coastal Water Authority, which is the City’s contract operator for Lake Houston, does not even mention “flooding” on its website. That’s right. CWA doesn’t mention the word in its mission statement, guiding principles, strategies, or tactics. They do, however, mention “pumps” 15 times on their Strategic-Plan page. That should give you some idea of their priorities: water supply.
Hopefully, Mayor John Whitmire’s recent appointment of former State Representative Dan Huberty to the Coastal Water Authority Board will help the CWA see Lake Houston from more than one perspective. Huberty has advocated for the gates since Harvey.
Posted by Bob Rehak on 9/29/24
2588 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.
Three Named Storms in Atlantic Basin With Two More Brewing
9/28/24 – Forecasters predicted a very active 2024 hurricane season. After a slow start, the map is really lighting up. Currently, we have three named storms in the Atlantic Basin:
Still Brewing
None of those named storms is a threat to Houston. However, the map shows two other areas of concern. See below.
Red Area
That elongated red area in the tropical Atlantic a couple hundred miles west of the Cabo Verde Islands continues to produce disorganized showers and thunderstorms.
According to the National Hurricane Center (NHC), environmental conditions appear conducive for gradual development of this system. A tropical depression will likely form during the early or middle part of next week. The system should move toward the west and then northwest across the eastern and central tropical Atlantic.
As of today, NHC lists formation chances for that red area as low (30%) in the next two days, but high (70%) in the next seven days.
Orange Area
Of greater concern for Texans, however, though is that orange area stretching from the northwestern Caribbean to the Gulf of Mexico. An area of low pressure should form there within a couple of days. NHC says environmental conditions are conducive for gradual development thereafter. They also say that a tropical depression could form around the middle part of next week.
This system should move northwestward into the Gulf during the latter portion of next week. NHC warns that interests in and along the Gulf Coast should monitor its progress.
As of today, formation chance through 48 hours is zero. But it’s 50% within 7 days.
Will the Gulf Go 4 for 4?
Lest anyone forget, this area has already spawned two major hurricanes and a hurricane in the last three months – Beryl, Francine and Helene.
Sea surface temps in that area are still 1.8 to 5.4 Fahrenheit above normal for this time of year (1-3º C).
So, don’t let your guard down.
Posted by Bob Rehak on 9/28/24
2587 Days since Hurricane Harvey
Helene Triggers Flooding in 8 States, Millions Without Power
9/27/24 – Hurricane Helene roared ashore last night and by noon today had triggered flooding in at least eight states, according to the National Weather Service.
Helene Floods Eight States
The states include: Florida, Alabama, Georgia, South Carolina, North Carolina, Tennessee, Virginia and Kentucky. See orange, red and purple areas below.
Many of those same areas could still see additional rainfall. Through 7 AM CDT, NOAA’s Weather Prediction Center gives 15 states a chance for additional excessive rainfall. See below.
Power Outages and Deaths
Meanwhile, more than 3 million people in affected areas remain without power, according to PowerOutages.US.
The Hill reports that at least 35 people died as a result of the Category 4 storm.
At this hour, NBC puts the death toll at 42 and says more than 4 million people are without power.
USA Today reported within the hour that 4.5 million people have no electricity.
The death toll will likely increase in coming days as rescuers race to free more people trapped in flooded areas.
It could take weeks to restore all the power given the breadth of the devastation. An Associated Press report said that in Georgia, “…an electrical utility group warned of ‘catastrophic’ damage to the state’s utility infrastructure, with more than 100 high voltage transmission lines damaged.”
AP also reported that in South Carolina, “more than 40% of homes and businesses were without power.” They said crews needed to cut their way through debris just to determine what was still standing in some places.
Helene Now a Tropical Depression
At 4 PM, the National Hurricane Center has downgraded Helene to a tropical depression with sustained winds of 35 MPH and forward motion of 17 MPH.
Summary of Weather Stats
For a list of reported rainfall totals to date and peak wind gusts associated with Helene, see this list from the National Centers for Environmental Prediction as of 11 AM EDT 9/27/24. Busick, North Carolina recorded the highest rainfall total to date: 29.58 inches.
All in all, the forecasters predicted Helene’s impacts pretty accurately.
Helene is the latest reminder of why we need to continue fighting for flood mitigation. It could have happened here.
Posted by Bob Rehak on 9/27/24
2586 Days since Hurricane Harvey