5/26/24 – Now that the flood has completely receded, aerial photos show that the Kingwood Diversion Ditch at River Grove Park has become completely blocked by sand again … for the third time in six years.
Without serious sand-mine reform (which is an unrealistic dream), dredging will become more frequent and costlier. We’re on an unsustainable path. Let’s look at the problem and a possible solution.
Already Dredged Twice Since Harvey
The mouth of the ditch has already been dredged twice since Harvey: once by the Army Corps and once by the Kingwood Service Association (KSA). But earlier this year, two floods redeposited sand that now blocks the channel mouth again.
Boaters report that river access has become increasingly difficult. Now it’s virtually impossible.
KSA owns the park and the boat launch, but not the Diversion Ditch which cuts through the park. The City and County have responsibility for that.
Regardless, KSA has obtained dredging bids north of $800,000 to keep the boat docks open. To put that in perspective, it’s one third of the organization’s cash reserves. And that will force KSA to decide whether it wants to continue funding a boat launch.
But a bigger, more important question remains. If the sediment continues to accumulate, how many people will flood? Hundreds flooded behind a Diversion-Ditch blockage during Harvey.
As sand builds higher, the problem will become more dangerous. So, where is all the sand coming from?
For this story, I started at River Grove and worked my way upriver toward a hellish, out-of-control sandscape on the West Fork just above Kingwood. It typifies 20 square miles of sand mines in a 20-mile reach of the West Fork between US59 and I-45. But let’s talk about River Grove first.
River Grove Boat Launch Blocked
Today, on a hot Memorial Day Weekend, every boat owner in Kingwood would normally flock to River Grove. But the parking lot was virtually empty this morning. Here’s why.
An emerging sand bar has totally blocked the boat launch.
While I took pictures at this location, one man with a small, flat-bottomed johnboat came in. He had to get out of his boat and drag it on foot across the sand bar. The sand bar totally blocks larger boats. To that point, note the virtually empty parking lot in the picture above.
Following the Sand Upstream
So, I took a short drive upstream to see where the sand came from. The next stop: the confluence of Spring Creek and the West Fork, a few hundred yards upstream from the US59 Bridge. The confluence has looked like this for the last month.
Slightly upstream from the US59 bridge. Spring Creek (left), West Fork San Jacinto (right).5/26/24.
That water on the right looked very dirty. So I followed the sediment trail upstream. It led to the hellish sandscape mentioned above. See below.
Full Scope of Damage Near Hallett Mine Now Apparent
As floods have receded, the damage to mines in the river’s floodway and floodplains has become apparent. So has damage to the river system itself.
During the storms, the river cut through the dike of an abandoned sand pit owned by Hallett until January 2024. That’s when Hallett sold it to a real estate developer, according to the Montgomery County Appraisal District records.
Within days of the sale, the year’s first flood breached the dike at the downstream, southern end of the pit. Later, in May, a second flood breached a dike on the upstream, northern end.
Then the river started flowing through the mile-long, half-mile-wide pit and abandoned its normal channel. It churned up massive amounts of exposed sand and carried it downriver. The river’s velocity was more than sufficient to transport sand.
As more and more stormwater went through the sand pit, less and less went down the normal river channel. Water velocity slowed in the channel and sand dropped out of suspension. That created an enormous blockage that now appears to have cut off the river channel.
No one has yet taken steps to rebuild the broken sand mine dikes. Nor has anyone cleared the river channel. Meanwhile, the West Fork is running through an abandoned sand mine and carrying sediment downstream. See pictures below.
Looking upstream over West Fork San Jacinto. Channel has filled in with sand and river has rerouted itself through an abandoned pit(upper left).
In the picture above, it’s hard to tell where the river even was. It formed an S starting at the lower left.
Where river exits southern end of pit and continues down river.
Between the entrance and the exit, the river looked like this.
Former West Fork Channel. The channel is totally cut off by sand. Nearby residents estimate the depth of the sand to be 5-6 feet high near the northern breach.
This one-minute video shows where the river now enters the sand pit and the blockage in the former river channel.
Video shot on 5/26/24
Rain, River-Depth Impacts on Photographs
Environmental factors often influence photography. So, I recorded the following.
Harris County’s Flood Warning System shows that it hasn’t rained at all in the last week. That has reduced rates of flow in the West Fork.
I took all pictures above on 5/26/24. At the time, Lake Conroe was finally approaching its normal level of 201 feet above mean sea level. But the San Jacinto River Authority (SJRA) was still releasing water at a modest 350 cubic feet per second (CFS).
Screen capture from SJRA dashboard, 12:07PM, 5/26/24.
The SJRA release from Lake Conroe increased flow in the river past the sand mines.
Downstream, the Coastal Water Authority was discharging almost 4,000 CFS from Lake Houston at the same time in preparation for some repairs on the dam beginning later this week.
Screen capture from Coastal Water Authority website at 12:18 PM, 5/26/24.
The CWA release would lower the water level slightly in Lake Houston and near River Grove Park. But it would not affect areas as far upstream as the sand mines.
The Lake Houston water level was several inches to a foot below normal when I took these pictures. The CWA lists the normal pool at 42.4 feet. However, the Texas Water Development Board says that the spillway on the lake has a crest elevation of 41.73 feet.
So, What’s Next?
Note that the Kingwood Diversion Ditch affects drainage of the entire western half of Kingwood. The Harris County Flood Control District listed it as one of the top two priorities among flood-mitigation projects in the Kingwood Area.
Leaving this ditch silted in is not an option. Take boating out of the discussion. Hundreds of homes flooded during Harvey near this ditch when it previously became silted in and backed up.
KSA, a small, volunteer organization, cannot continue to fund the dredging of City and County property as dredging intervals become more frequent. Especially since no one is attempting to reign in irresponsible mining practices upstream.
Kingwood needs help. As a result of the disaster declaration that came after recent flooding, the Harris County Flood Control District should explore using FEMA debris removal funds to remove this dangerous blockage immediately.
The Diversion Ditch project would be an excellent candidate for those funds. We need to make our elected representatives aware of the issue and a possible funding solution.
Hurry. We only have 30 days from the disaster declaration.
Posted by Bob Rehak on 5/26/24
2462 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/2024/05/20240526-DJI_20240526093138_0792_D.jpg?fit=1100%2C619&ssl=16191100adminadmin2024-05-26 19:07:482024-05-26 20:20:00Kingwood Diversion Ditch Completely Blocked At River Grove
5/25/24 – Houston City Council Members Fred Flickinger and Twila Carter met at the Lake Houston gates yesterday with members of the Coastal Water Authority (CWA), Black & Veatch engineering, and Houston Public Works. They reviewed the status of repairs to a broken gate and a program to add 11 new gates to the dam.
Meeting at Lake Houston gates on 5/24/24 to discuss broken gate and 11 new gates.
Broken Gate Stuck in Down, Not Up Position
During the early May floods of 2024, news of a broken gate on the Lake Houston Dam spread rapidly on social media. Flooding concerns fueled rumors. Some folks heard the gate was stuck in the closed position. Others heard it was open. A visit to the gates yesterday confirmed that it was stuck in the down position.
A CWA employee said that one of two chains used to raise and lower the gate broke. That raised the possibility of the gate becoming jammed sideways in its frame if they tried to raise it with the remaining chain attached only to one side. If the gate did jam, CWA would have no ability to re-lower it.
That, in turn, meant the lake would continue losing water after the flood subsided. So they opted to leave it closed during the flood.
Gate stuck in down positionhas only one chain.I could not safely get a camera angle that showed the area of missing chain.Winch used to raise/lower tainter gates.Tainter gates (left) rotate via radial arms. Two gates on right raise/lower from bottom hinge.(Picture taken last year. Only one tainter gate was releasing yesterday.)
As of yesterday afternoon, waterwas no longer going over the spillway, but Lake Houston was filled to max. However, operatorswere still releasing water through working tainter gateto reduce the lake levelfor repairs.The chain on one side of this gate was pulling it up unevenly.
Repairs to Begin Next Week
The Coastal Water Authority (CWA) plans to fix the broken tainter-gate chain next week when the water level in the lake is lower. CWA manages Lake Houston for the City.
The repair team will include divers who will re-attach the broken chain to the upstream side of the gate underwater.
The operation was too dangerous to attempt during the flood because other gates were open. And at the peak of the flood, water going over the 3160-foot-wide spillway was SIX feet high.
Divers could have easily been swept away by the strong currents. One cubic foot of fresh water weighs about 62 pounds. And at the height of the flood, more than 100,000 cubic feet per second were flowing over the spillway and through the dam’s gates. That’s a lot of force!
Current Lake Houston Gates Have Limited Capacity
The current Lake Houston gates have a combined release capacity of only 10,000 cubic feet per second (CFS) – about 2,500 CFS each.
They are useful in pre-release scenarios, i.e., releasing water before a storm to create extra storage capacity in the lake for stormwater. That can reduce flood peaks both up- and downstream from the dam.
However, the current Lake Houston gates are so small, that it can take days to lower the lake significantly. And during that time, storms can veer away. Meteorologists just cannot offer precise estimates about where a storm will hit that far in advance.
Status of New, Bigger Gates
Adding more and bigger gates to the dam could reduce the lead time necessary to lower the lake. And that would give dam operators more certainty that they aren’t wasting the water.
To release water faster, before and during a storm, the City of Houston plans to add 11 more Lake Houston gates to the earthen portion of the dam just east of the old gates.
The new gates could release a total of 80,000 CFS, bringing the total pre-release capacity up to 90,000 CFS – 9X higher than the current rate.
New gates would be installed to right of existing gates in sunny area.
When complete, the CWA will be able to pre-release as much water in 2-3 hours as it currently does in a day.
The extra storage capacity for stormwater in the lake could then help reduce flood peaks both up- and downstream.
Extra Lake Houston gates could also release water faster during a storm.
According to the CWA, studies show that the extra gates would not worsen downstream flooding. Homes have already been bought out in downstream areas that would be affected.
The City is currently in the design phase for the new gate structure. Construction should start sometime in 2025 according to Council Member Flickinger.
However, the new gates would have to be custom manufactured. No one offers gates that size as off-the-shelf items. So, supply-chain staffing shortages could delay delivery of the gates. Reportedly, the companies that manufacture gates are still being affected by staffing shortages that started during the Covid pandemic.
Multiple Benefits of More Lake Houston Gates
When complete, the 90,000 CFS release capacity of the 15 Lake Houston gates (4 old, 11 new) would exceed the largest release ever made by the SJRA from Lake Conroe – 79,000 CFS during Hurricane Harvey.
That would help improve joint operations of the two lakes during flood events.
But engineers at yesterday’s meeting cautioned that the new gates are not a silver bullet.
They say pre-release won’t be needed during small floods. And pre-release will have minimal impact during giant floods, such as Harvey.
That’s because large events like Harvey can replace the entire volume of the lake dozens of times during the event. In such floods, lowering the lake a foot or two beforehand will provide negligible benefits. Another monster flood could replace that volume in minutes.
However, the gates will provide significant improvements during 25-, 50- and 75-year flood events. That will provide greater safety margins for many people who previously flooded or were on the verge of flooding during such events.
Posted by Bob Rehak on 5/25/24
2461 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/05/20191104-RJR_3873.jpg?fit=1100%2C733&ssl=17331100adminadmin2024-05-25 14:16:352024-05-25 20:10:34Update on Lake Houston Gates
5/24/24 – The SJRA board reviewed a presentation yesterday about Lake Conroe release rates during the early May storm this year. Sadly, while some people flooded, far fewer flooded than in Harvey, despite the fact that the peak inflow to Lake Conroe was higher during this storm than it was in Harvey.
Better management of the temporary floodwater storage space between Lake Conroe’s normal lake level and flowage easement may have made the difference. But there may be opportunities to make an even bigger difference.
Dissecting a Disaster
In early May this year, the headwaters of Lake Conroe received half a year’s rainfall in a few days. It was extreme to say the least. At the peak of the inflow, dam operators were releasing almost 72,000 cubic feet per second, yet the lake level still rose.
That was the second highest release rate in the history of the San Jacinto River Authority (SJRA). Only during Hurricane Harvey did the SJRA release more – 79,000 CFS at the peak.
The peak inflow was greater during this event than during Hurricane Harvey, according to Bret Raley, the San Jacinto River Authority’s Lake Conroe Division Manager.
This time, hundreds of homes flooded downstream. Thousands more were threatened. But it wasn’t nearly the disaster that Harvey was.
Regardless people who flooded or nearly flooded want to know why the release rate was so high and whether it could have been lower. Raley’s after-action report to the SJRA board meeting yesterday provides some answers.
Or you can review the slides below and my summary.
Note: some slides in this presentation use slightly different time periods.
Temporary Storage Provides Partial Buffer Against Flooding
Raley began with a recitation of SJRA’s top priorities re: operation of the Lake Conroe Dam.
He stated that “Our number one priority is … to preserve and protect the structural integrity of the dam. If we did not, the ramifications would be unimaginable.”
“I contend we are protecting public safety. How? Through a vigorous inspection and maintenance program; post-event assessments; and safe spillway operations.”
The dam, he says, provides a buffer against the full brunt of floodwaters. You’ll see later in the presentation, that at times, the inflow exceeded the outflow. Even though the Lake Conroe dam wasn’t designed for flood control, it still provides a modest buffer of temporary storage that helped reduce downstream impacts.
Only 15% of Upper Basin Protected by Dam
The Lake Conroe dam controls only about 15% of the square mileage in the upper San Jacinto River Basin.
The upper San Jacinto River basin includes nine different watersheds that all drain to Lake Houston. Said Raley, “Ours is at the very, very top of what I sometimes refer to as a funnel. Tthe bottom of the funnel is Lake Houston, the Lake Conroe watershed is at the top.”
Raley continued, “The Lake Conroe watershed is only 450 square miles. But it’s also the only watershed in the entire 3000 square miles controlled by a gated structure. The other nine watersheds flow through seven different counties.”
When rain makes its way to Lake Houston depends on when and where the rain fell. In this event, the heaviest rain fell in the West Fork (Lake Conroe) and East Fork watersheds. It could have been much worse if heavy rains had also fallen in Lake, Spring, and Cypress Creek watersheds.
Permit Limits Storage Higher Than 201 Feet Above Sea Level
The Lake Conroe Dam’s operating permit imposes several limitations that operators must contend with.
Said Raley. “The dam was constructed pursuant to a permit from the State of Texas. It authorizes us to store up to an elevation of 201 feet above mean sea level permanently. We also have the authorization to store above 201 temporarily during storm flows.”
“The permit also requires us to pass the inflows once the lake level gets above 201. But any water released below 201 must be used against permitted water rights. So there must be a permittee with available water, and then that permittee can ask to use the water.”
“The City of Houston may have, from time to time, water that’s available, and if so, they can call on it.”
Storage, Mitigation and Pre-Release
Raley then discussed the three main things he wanted people to remember from his presentation. He summarizes them in this slide.
Raley says that water which rises above 201 feet above mean sea level (MSL) cannot be held back; the lake’s operation procedures mitigate peak downstream flows; and that if the City of Houston wants to lower Lake Conroe, the City must ask for the water out of the two thirds of the lake that it owns.
Raley never addressed why the SJRA discontinued its seasonal lowering program that was in effect for several years after Harvey. The existence of that program contradicted some of the points he made in his presentation. That leads one to wonder how firm the rules he describes really are in emergencies.
Water Must Be Released as it Starts to Rise
After introducing his key points, Raley goes into more detail on each.
Raley discussed the differences between water-supply and flood-control reservoirs. “Lake Conroe is a water supply reservoir,” he said. “The intent is to keep the reservoir as full as possible to maintain your supply. In a flood control reservoir, you want to maintain capacity. You want to maintain space that can accept inflows so that you can absorb that water before having to pass it.”
Normally, Only 18″ Between Top of Water and Top of Gates
The design of the tainter gaits on Lake Conroe is another constraint. They do not allow much room for water to rise.
The photo on the left shows a gate in the normal resting position with the lake at the normal level. Water can rise only 18 inches before overtopping the gate.
If that happens, operators lose control. So, as the water rises, they must elevate the gate to stay ahead of rising levels. Remember, storms often pack high winds that create waves. Water can be choppy, not placid as shown here.
“Our gates are not designed to be overtopped” said Raley. “So, we must raise them incrementally to maintain safe freeboard.” Freeboard is an engineering term that, in this context, means “safety margin.”
The second photo shows the downstream side of a gate. Sheet flow coming over the top could destroy this support structure says Raley. “They’re just not designed to withstand that kind of force.”
Six Feet of Buffer Space
A flowage easement lets the SJRA flood properties surrounding Lake Conroe during extreme events. “We’ve got six feet of buffer that we can use,” said Raley. “Our operating protocol helps balance lake-level rise upstream and outflows downstream.”
As the water in the lake rises, SJRA must raise the gates. Still, rising water indicates that more water is coming in than going out…at least temporarily.
In extreme events, SJRA could certainly use even more stormwater storage. (But that would require pre-releasing water. Raley describes the constraints on pre-release several slides further down.)
Areas north and east of Lake Conroe received about half a year’s rain in a few days, testing the limits of the system that Raley described. It wasn’t just the amount of rain. It was also the intensity.
The basin wide average for May 2nd, for instance, approached 7 inches.
The lake at at FM1375 received more than an inch (or close to) it in several 15-minute periods. At that same location, they also received three inches in one hour.
It’s also important to realize that SJRA came into this event coming off another heavy rain. Note how the solid black line below (at the left) was just starting to return to normal when it suddenly peaked.
Note also the steepness of the rise when the black line turns up. “In a ten hour period, we went from 8,000 to 72,000 cfs,” said Raley. “That is fast. Very fast.”
The backline represents the inflow and the blue line represents the outflow. The rapid rise caused operators to open the gates wide at first. However, they also reduced the outflow when the inflow dropped. The two curves follow each other.
Inflow Higher than Harvey
The peak inflow during that rapid rise exceeded the peak inflow rate during Harvey.
The map and tables on the right indicate the peak flows coming from each tributary into Lake Houston.
Note how peak inflows from Lake, Spring and Cypress Creeks on the west were fractions of the volume coming from Lake Conroe.
Pre-Release Capabilities Constrained
Raley finished his presentation with a discussion of pre-release as a possible mitigation measure. The headline below says it all. Gone are the days of seasonal lowering.
At 700 cfs, the permit limit, Raley says it would take weeks to lower the lake. But weather predictions are not accurate that far in advance.
And if the storm misses Lake Conroe, a big release from the lake could make flooding in Lake Houston worse – especially if the storm misses Lake Conroe to the south.
So the SJRA tosses the responsibility back to the City of Houston, They make the City call for the water (out of its share of the lake) if the City wants Conroe lowered
Conclusion and Insight
Raley’s presentation won’t make flood victims feel better. But it may help them understand how difficult managing floods can be.
The important thing to take away from this is that there’s room in Lake Conroe for temporary storage of stormwater. And releasing that water so that it reaches populated areas downstream before or after the peaks coming from other tributaries will be the key to minimizing flood damage.
For instance, releasing a smaller amount after a larger peak has already passed won’t flood any more homes.
Remember, flood peaks are not necessarily additive. You can’t automatically assume that all peaks will hit at the same time and pile on top of each other.
I’m sure more knowledge can be acquired from close examination of this event. For instance, one of the big differences between this storm and Harvey was the downstream representation on the SJRA board by Mark Micheletti.
But Micheletti is the only downstream representative on a seven-person board. lf that continues, you can bet no substantial changes will be made in the long-term operation and policies of Lake Conroe.
Another thing to look at is whether keeping Lake Conroe at slightly lower levels during wet seasons would give dam operators more temporary storage, and thus protect more homes and businesses both upstream and down.
Posted by Bob Rehak on 5/24/24
2460 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/05/4f_LC-Division-Update_FINAL-Rev_Page_02.jpg?fit=2000%2C1125&ssl=111252000adminadmin2024-05-24 21:39:442024-05-25 09:34:43How SJRA Set Lake Conroe Release Rates During May Storm
Kingwood Diversion Ditch Completely Blocked At River Grove
5/26/24 – Now that the flood has completely receded, aerial photos show that the Kingwood Diversion Ditch at River Grove Park has become completely blocked by sand again … for the third time in six years.
Without serious sand-mine reform (which is an unrealistic dream), dredging will become more frequent and costlier. We’re on an unsustainable path. Let’s look at the problem and a possible solution.
Already Dredged Twice Since Harvey
The mouth of the ditch has already been dredged twice since Harvey: once by the Army Corps and once by the Kingwood Service Association (KSA). But earlier this year, two floods redeposited sand that now blocks the channel mouth again.
Boaters report that river access has become increasingly difficult. Now it’s virtually impossible.
KSA owns the park and the boat launch, but not the Diversion Ditch which cuts through the park. The City and County have responsibility for that.
Regardless, KSA has obtained dredging bids north of $800,000 to keep the boat docks open. To put that in perspective, it’s one third of the organization’s cash reserves. And that will force KSA to decide whether it wants to continue funding a boat launch.
But a bigger, more important question remains. If the sediment continues to accumulate, how many people will flood? Hundreds flooded behind a Diversion-Ditch blockage during Harvey.
As sand builds higher, the problem will become more dangerous. So, where is all the sand coming from?
For this story, I started at River Grove and worked my way upriver toward a hellish, out-of-control sandscape on the West Fork just above Kingwood. It typifies 20 square miles of sand mines in a 20-mile reach of the West Fork between US59 and I-45. But let’s talk about River Grove first.
River Grove Boat Launch Blocked
Today, on a hot Memorial Day Weekend, every boat owner in Kingwood would normally flock to River Grove. But the parking lot was virtually empty this morning. Here’s why.
While I took pictures at this location, one man with a small, flat-bottomed johnboat came in. He had to get out of his boat and drag it on foot across the sand bar. The sand bar totally blocks larger boats. To that point, note the virtually empty parking lot in the picture above.
Following the Sand Upstream
So, I took a short drive upstream to see where the sand came from. The next stop: the confluence of Spring Creek and the West Fork, a few hundred yards upstream from the US59 Bridge. The confluence has looked like this for the last month.
That water on the right looked very dirty. So I followed the sediment trail upstream. It led to the hellish sandscape mentioned above. See below.
Full Scope of Damage Near Hallett Mine Now Apparent
As floods have receded, the damage to mines in the river’s floodway and floodplains has become apparent. So has damage to the river system itself.
During the storms, the river cut through the dike of an abandoned sand pit owned by Hallett until January 2024. That’s when Hallett sold it to a real estate developer, according to the Montgomery County Appraisal District records.
Within days of the sale, the year’s first flood breached the dike at the downstream, southern end of the pit. Later, in May, a second flood breached a dike on the upstream, northern end.
Then the river started flowing through the mile-long, half-mile-wide pit and abandoned its normal channel. It churned up massive amounts of exposed sand and carried it downriver. The river’s velocity was more than sufficient to transport sand.
As more and more stormwater went through the sand pit, less and less went down the normal river channel. Water velocity slowed in the channel and sand dropped out of suspension. That created an enormous blockage that now appears to have cut off the river channel.
No one has yet taken steps to rebuild the broken sand mine dikes. Nor has anyone cleared the river channel. Meanwhile, the West Fork is running through an abandoned sand mine and carrying sediment downstream. See pictures below.
In the picture above, it’s hard to tell where the river even was. It formed an S starting at the lower left.
Between the entrance and the exit, the river looked like this.
This one-minute video shows where the river now enters the sand pit and the blockage in the former river channel.
Rain, River-Depth Impacts on Photographs
Environmental factors often influence photography. So, I recorded the following.
Harris County’s Flood Warning System shows that it hasn’t rained at all in the last week. That has reduced rates of flow in the West Fork.
I took all pictures above on 5/26/24. At the time, Lake Conroe was finally approaching its normal level of 201 feet above mean sea level. But the San Jacinto River Authority (SJRA) was still releasing water at a modest 350 cubic feet per second (CFS).
The SJRA release from Lake Conroe increased flow in the river past the sand mines.
Downstream, the Coastal Water Authority was discharging almost 4,000 CFS from Lake Houston at the same time in preparation for some repairs on the dam beginning later this week.
The CWA release would lower the water level slightly in Lake Houston and near River Grove Park. But it would not affect areas as far upstream as the sand mines.
The Lake Houston water level was several inches to a foot below normal when I took these pictures. The CWA lists the normal pool at 42.4 feet. However, the Texas Water Development Board says that the spillway on the lake has a crest elevation of 41.73 feet.
So, What’s Next?
Note that the Kingwood Diversion Ditch affects drainage of the entire western half of Kingwood. The Harris County Flood Control District listed it as one of the top two priorities among flood-mitigation projects in the Kingwood Area.
Leaving this ditch silted in is not an option. Take boating out of the discussion. Hundreds of homes flooded during Harvey near this ditch when it previously became silted in and backed up.
KSA, a small, volunteer organization, cannot continue to fund the dredging of City and County property as dredging intervals become more frequent. Especially since no one is attempting to reign in irresponsible mining practices upstream.
Kingwood needs help. As a result of the disaster declaration that came after recent flooding, the Harris County Flood Control District should explore using FEMA debris removal funds to remove this dangerous blockage immediately.
The Diversion Ditch project would be an excellent candidate for those funds. We need to make our elected representatives aware of the issue and a possible funding solution.
This FEMA Fact Sheet outlines eligibility for the funds.
Hurry. We only have 30 days from the disaster declaration.
Posted by Bob Rehak on 5/26/24
2462 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.
Update on Lake Houston Gates
5/25/24 – Houston City Council Members Fred Flickinger and Twila Carter met at the Lake Houston gates yesterday with members of the Coastal Water Authority (CWA), Black & Veatch engineering, and Houston Public Works. They reviewed the status of repairs to a broken gate and a program to add 11 new gates to the dam.
Broken Gate Stuck in Down, Not Up Position
During the early May floods of 2024, news of a broken gate on the Lake Houston Dam spread rapidly on social media. Flooding concerns fueled rumors. Some folks heard the gate was stuck in the closed position. Others heard it was open. A visit to the gates yesterday confirmed that it was stuck in the down position.
A CWA employee said that one of two chains used to raise and lower the gate broke. That raised the possibility of the gate becoming jammed sideways in its frame if they tried to raise it with the remaining chain attached only to one side. If the gate did jam, CWA would have no ability to re-lower it.
That, in turn, meant the lake would continue losing water after the flood subsided. So they opted to leave it closed during the flood.
The Lake Houston Dam also has a 3160 foot wide spillway in addition to the four gates.
Repairs to Begin Next Week
The Coastal Water Authority (CWA) plans to fix the broken tainter-gate chain next week when the water level in the lake is lower. CWA manages Lake Houston for the City.
The repair team will include divers who will re-attach the broken chain to the upstream side of the gate underwater.
The operation was too dangerous to attempt during the flood because other gates were open. And at the peak of the flood, water going over the 3160-foot-wide spillway was SIX feet high.
Divers could have easily been swept away by the strong currents. One cubic foot of fresh water weighs about 62 pounds. And at the height of the flood, more than 100,000 cubic feet per second were flowing over the spillway and through the dam’s gates. That’s a lot of force!
Current Lake Houston Gates Have Limited Capacity
The current Lake Houston gates have a combined release capacity of only 10,000 cubic feet per second (CFS) – about 2,500 CFS each.
They are useful in pre-release scenarios, i.e., releasing water before a storm to create extra storage capacity in the lake for stormwater. That can reduce flood peaks both up- and downstream from the dam.
However, the current Lake Houston gates are so small, that it can take days to lower the lake significantly. And during that time, storms can veer away. Meteorologists just cannot offer precise estimates about where a storm will hit that far in advance.
Status of New, Bigger Gates
Adding more and bigger gates to the dam could reduce the lead time necessary to lower the lake. And that would give dam operators more certainty that they aren’t wasting the water.
To release water faster, before and during a storm, the City of Houston plans to add 11 more Lake Houston gates to the earthen portion of the dam just east of the old gates.
The new gates could release a total of 80,000 CFS, bringing the total pre-release capacity up to 90,000 CFS – 9X higher than the current rate.
The extra storage capacity for stormwater in the lake could then help reduce flood peaks both up- and downstream.
Extra Lake Houston gates could also release water faster during a storm.
According to the CWA, studies show that the extra gates would not worsen downstream flooding. Homes have already been bought out in downstream areas that would be affected.
The City is currently in the design phase for the new gate structure. Construction should start sometime in 2025 according to Council Member Flickinger.
However, the new gates would have to be custom manufactured. No one offers gates that size as off-the-shelf items. So, supply-chain staffing shortages could delay delivery of the gates. Reportedly, the companies that manufacture gates are still being affected by staffing shortages that started during the Covid pandemic.
Multiple Benefits of More Lake Houston Gates
When complete, the 90,000 CFS release capacity of the 15 Lake Houston gates (4 old, 11 new) would exceed the largest release ever made by the SJRA from Lake Conroe – 79,000 CFS during Hurricane Harvey.
That would help improve joint operations of the two lakes during flood events.
But engineers at yesterday’s meeting cautioned that the new gates are not a silver bullet.
They say pre-release won’t be needed during small floods. And pre-release will have minimal impact during giant floods, such as Harvey.
That’s because large events like Harvey can replace the entire volume of the lake dozens of times during the event. In such floods, lowering the lake a foot or two beforehand will provide negligible benefits. Another monster flood could replace that volume in minutes.
However, the gates will provide significant improvements during 25-, 50- and 75-year flood events. That will provide greater safety margins for many people who previously flooded or were on the verge of flooding during such events.
Posted by Bob Rehak on 5/25/24
2461 Days since Hurricane Harvey
How SJRA Set Lake Conroe Release Rates During May Storm
5/24/24 – The SJRA board reviewed a presentation yesterday about Lake Conroe release rates during the early May storm this year. Sadly, while some people flooded, far fewer flooded than in Harvey, despite the fact that the peak inflow to Lake Conroe was higher during this storm than it was in Harvey.
Better management of the temporary floodwater storage space between Lake Conroe’s normal lake level and flowage easement may have made the difference. But there may be opportunities to make an even bigger difference.
Dissecting a Disaster
In early May this year, the headwaters of Lake Conroe received half a year’s rainfall in a few days. It was extreme to say the least. At the peak of the inflow, dam operators were releasing almost 72,000 cubic feet per second, yet the lake level still rose.
That was the second highest release rate in the history of the San Jacinto River Authority (SJRA). Only during Hurricane Harvey did the SJRA release more – 79,000 CFS at the peak.
The peak inflow was greater during this event than during Hurricane Harvey, according to Bret Raley, the San Jacinto River Authority’s Lake Conroe Division Manager.
This time, hundreds of homes flooded downstream. Thousands more were threatened. But it wasn’t nearly the disaster that Harvey was.
Regardless people who flooded or nearly flooded want to know why the release rate was so high and whether it could have been lower. Raley’s after-action report to the SJRA board meeting yesterday provides some answers.
Presentation to SJRA Board on May 23, 2024
Here’s a link to Raley’s entire presentation to the SJRA Board.
You can watch it starting at 37 minutes and 40 seconds into this video. It lasts 15 minutes.
Or you can review the slides below and my summary.
Temporary Storage Provides Partial Buffer Against Flooding
Raley began with a recitation of SJRA’s top priorities re: operation of the Lake Conroe Dam.
He stated that “Our number one priority is … to preserve and protect the structural integrity of the dam. If we did not, the ramifications would be unimaginable.”
“I contend we are protecting public safety. How? Through a vigorous inspection and maintenance program; post-event assessments; and safe spillway operations.”
The dam, he says, provides a buffer against the full brunt of floodwaters. You’ll see later in the presentation, that at times, the inflow exceeded the outflow. Even though the Lake Conroe dam wasn’t designed for flood control, it still provides a modest buffer of temporary storage that helped reduce downstream impacts.
Only 15% of Upper Basin Protected by Dam
The upper San Jacinto River basin includes nine different watersheds that all drain to Lake Houston. Said Raley, “Ours is at the very, very top of what I sometimes refer to as a funnel. Tthe bottom of the funnel is Lake Houston, the Lake Conroe watershed is at the top.”
Raley continued, “The Lake Conroe watershed is only 450 square miles. But it’s also the only watershed in the entire 3000 square miles controlled by a gated structure. The other nine watersheds flow through seven different counties.”
When rain makes its way to Lake Houston depends on when and where the rain fell. In this event, the heaviest rain fell in the West Fork (Lake Conroe) and East Fork watersheds. It could have been much worse if heavy rains had also fallen in Lake, Spring, and Cypress Creek watersheds.
Permit Limits Storage Higher Than 201 Feet Above Sea Level
The Lake Conroe Dam’s operating permit imposes several limitations that operators must contend with.
Said Raley. “The dam was constructed pursuant to a permit from the State of Texas. It authorizes us to store up to an elevation of 201 feet above mean sea level permanently. We also have the authorization to store above 201 temporarily during storm flows.”
“The permit also requires us to pass the inflows once the lake level gets above 201. But any water released below 201 must be used against permitted water rights. So there must be a permittee with available water, and then that permittee can ask to use the water.”
“The City of Houston may have, from time to time, water that’s available, and if so, they can call on it.”
Storage, Mitigation and Pre-Release
Raley then discussed the three main things he wanted people to remember from his presentation. He summarizes them in this slide.
Raley says that water which rises above 201 feet above mean sea level (MSL) cannot be held back; the lake’s operation procedures mitigate peak downstream flows; and that if the City of Houston wants to lower Lake Conroe, the City must ask for the water out of the two thirds of the lake that it owns.
Raley never addressed why the SJRA discontinued its seasonal lowering program that was in effect for several years after Harvey. The existence of that program contradicted some of the points he made in his presentation. That leads one to wonder how firm the rules he describes really are in emergencies.
Water Must Be Released as it Starts to Rise
After introducing his key points, Raley goes into more detail on each.
Raley discussed the differences between water-supply and flood-control reservoirs. “Lake Conroe is a water supply reservoir,” he said. “The intent is to keep the reservoir as full as possible to maintain your supply. In a flood control reservoir, you want to maintain capacity. You want to maintain space that can accept inflows so that you can absorb that water before having to pass it.”
Normally, Only 18″ Between Top of Water and Top of Gates
The design of the tainter gaits on Lake Conroe is another constraint. They do not allow much room for water to rise.
The photo on the left shows a gate in the normal resting position with the lake at the normal level. Water can rise only 18 inches before overtopping the gate.
If that happens, operators lose control. So, as the water rises, they must elevate the gate to stay ahead of rising levels. Remember, storms often pack high winds that create waves. Water can be choppy, not placid as shown here.
“Our gates are not designed to be overtopped” said Raley. “So, we must raise them incrementally to maintain safe freeboard.” Freeboard is an engineering term that, in this context, means “safety margin.”
The second photo shows the downstream side of a gate. Sheet flow coming over the top could destroy this support structure says Raley. “They’re just not designed to withstand that kind of force.”
Six Feet of Buffer Space
A flowage easement lets the SJRA flood properties surrounding Lake Conroe during extreme events. “We’ve got six feet of buffer that we can use,” said Raley. “Our operating protocol helps balance lake-level rise upstream and outflows downstream.”
As the water in the lake rises, SJRA must raise the gates. Still, rising water indicates that more water is coming in than going out…at least temporarily.
In extreme events, SJRA could certainly use even more stormwater storage. (But that would require pre-releasing water. Raley describes the constraints on pre-release several slides further down.)
Areas north and east of Lake Conroe received about half a year’s rain in a few days, testing the limits of the system that Raley described. It wasn’t just the amount of rain. It was also the intensity.
The basin wide average for May 2nd, for instance, approached 7 inches.
The lake at at FM1375 received more than an inch (or close to) it in several 15-minute periods. At that same location, they also received three inches in one hour.
It’s also important to realize that SJRA came into this event coming off another heavy rain. Note how the solid black line below (at the left) was just starting to return to normal when it suddenly peaked.
Note also the steepness of the rise when the black line turns up. “In a ten hour period, we went from 8,000 to 72,000 cfs,” said Raley. “That is fast. Very fast.”
The backline represents the inflow and the blue line represents the outflow. The rapid rise caused operators to open the gates wide at first. However, they also reduced the outflow when the inflow dropped. The two curves follow each other.
Inflow Higher than Harvey
The peak inflow during that rapid rise exceeded the peak inflow rate during Harvey.
Note how peak inflows from Lake, Spring and Cypress Creeks on the west were fractions of the volume coming from Lake Conroe.
Pre-Release Capabilities Constrained
Raley finished his presentation with a discussion of pre-release as a possible mitigation measure. The headline below says it all. Gone are the days of seasonal lowering.
At 700 cfs, the permit limit, Raley says it would take weeks to lower the lake. But weather predictions are not accurate that far in advance.
And if the storm misses Lake Conroe, a big release from the lake could make flooding in Lake Houston worse – especially if the storm misses Lake Conroe to the south.
So the SJRA tosses the responsibility back to the City of Houston, They make the City call for the water (out of its share of the lake) if the City wants Conroe lowered
Conclusion and Insight
Raley’s presentation won’t make flood victims feel better. But it may help them understand how difficult managing floods can be.
The important thing to take away from this is that there’s room in Lake Conroe for temporary storage of stormwater. And releasing that water so that it reaches populated areas downstream before or after the peaks coming from other tributaries will be the key to minimizing flood damage.
For instance, releasing a smaller amount after a larger peak has already passed won’t flood any more homes.
Remember, flood peaks are not necessarily additive. You can’t automatically assume that all peaks will hit at the same time and pile on top of each other.
I’m sure more knowledge can be acquired from close examination of this event. For instance, one of the big differences between this storm and Harvey was the downstream representation on the SJRA board by Mark Micheletti.
But Micheletti is the only downstream representative on a seven-person board. lf that continues, you can bet no substantial changes will be made in the long-term operation and policies of Lake Conroe.
Another thing to look at is whether keeping Lake Conroe at slightly lower levels during wet seasons would give dam operators more temporary storage, and thus protect more homes and businesses both upstream and down.
Posted by Bob Rehak on 5/24/24
2460 Days since Hurricane Harvey