Several years ago, Harris County Flood Control District (HCFCD) made a giant leap forward with real-time inundation mapping. You could log onto the Harris County Flood Warning System, click on “inundation map,” zoom into your neighborhood, and see how close floodwater was getting in “near real time.”
It was a radical advance over earlier system. But now we need another radical advance – predictive inundation mapping.
No one, as far as I can see, offers such a service. The National Weather Service predicts how high water will get at gages, but not between them where people live.
How Close Will the Floodwater Get…At My Location?
Buyers today have much more information at their fingertips than decades ago, but no one puts it all together.
One of the most useful websites during a flood is the National Weather Service Advanced Hydrologic Prediction Service. There, you can see how fast water is rising, where it will peak, when it will fall, and a hydrologic history of the event. (See layout below.)
From June 2 at 1:41PM for West Fork San Jacinto at US59
This is a huge advance over everything before it. But unfortunately, it only predicts flood heights at gages. Most people don’t know how their distance from a gage, elevation changes, and local topography will affect the peak at their home or business. Especially if they are new to a neighborhood, like the woman below.
Kingwood resident who moved here in January from a desert, then promptly flooded in May.
The mapping feature is a great enhancement compared to the NWS site in some ways. It shows the extent of flooding between gages.
But unfortunately, the Flood Warning System won’t tell you how close water will get at its peak.
So when you realize you need to get out, you may not have enough time to make thorough preparations.
Screen capture from Harris County Flood Warning System. It shows current flooding, but not peak flooding.
Trying to Integrate the Best of Both Approaches
Those with knowledge of prior floods may be able to translate gage readings upstream to their location downstream.
But almost 10% of the American population moves every year. So, five years after a hurricane hit an area, half of the people in a neighborhood would likely have little knowledge or memory of it.
More than real-time inundation mapping, we need predictive inundation mapping.
Legal Concerns over Bad Information
One official I talked to for this article feared such a system. What if the prediction were wrong? What if it implied someone would be safe and then they died while evacuating? Imagine the legal liability!
As a result, officials often err on the side of caution. They may issue orders to evacuate in much wider areas than necessary.
We saw that during the May flood this year. The county issued evacuation maps that showed the extent of flooding during Harvey. As a result, people may be less inclined to evacuate for the next storm, even if it is warranted.
In extreme cases, such over-reaction has resulted in harm. Those who have lived in the Houston area for 20 years or more may remember the disastrous mass evacuation during Hurricane Rita in 2005.
One hundred thirteen people died from Rita in Texas, 107 of which were associated with the evacuation of the Houston metropolitan area.
Need for Better Tools
A former HCFCD employee told me that HCFCD has been working on a predictive inundation mapping system for years. But, says the source, it’s incredibly complex and requires validation.
Validation involves confirming predictions against real-world storms. However, giant, widespread floods don’t just happen every year. And every storm is unique, as we saw in yesterday’s post about the early May storm. Some areas may get feet of rain, while others get inches.
You just can’t generalize. Every storm is unique. And referring to historical analog storms may fail for several reasons:
Massive developments, such as Colony Ridge, may have changed the hydrology of the watershed. Colony Ridge has grown 50% larger than Manhattan in just ten years.
Rainfall intensity may vary in storms, even if rainfall totals don’t.
Unequal rainfall distribution means that flood peaks may combine in different ways at different times.
Potential Ways to Handle Uncertainty
To help handle those contingencies, predictive inundation maps could have buffer zones showing degrees of uncertainty. For instance, “If you’re in Zone A, there’s a 100% chance you will flood. In Zone B, 50%. In Zone C, 25%, etc.”
Plus, the legislature could craft legal protections for agencies making such predictions based on the best available information and science.
We need a public debate. Perhaps an even better approach will emerge from the dialog.
That would be far preferable, in my opinion, to causing immense anxiety among millions.
Posted by Bob Rehak on 6/2/24
2469 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/2024/05/20240510-RJR_3506.jpg?fit=1100%2C733&ssl=17331100adminadmin2024-06-02 17:49:082024-06-02 17:49:10The Next Step in Inundation Mapping
June 1, 2024 – On the first day of what experts predict will be a record-setting 2024 hurricane season, I thought it would be interesting to see how much rainfall we had in May and so far this year. How wet has 2024 been?
May 2024 rainfall caused the second highest release from Lake Conroe in the history of the San Jacinto River Authority. But whether May 2024 will go into the records books depends on where you live.
Huntsville smashed its record high precipitation total for the month and year to date (YTD).
Conroe also set a record for May, but its YTD total fell slightly behind the record set in 1935.
Bush and Galveston came close to their record high totals for May and YTD.
At all four reporting stations that I sampled, YTD rainfall was well above normal.
However, the National Weather Service showed dramatic differences between locations.
More Than 5X Difference Across Region
According to the National Weather Service, Huntsville had the rainiest May since record keeping began – 24.7 inches. That brought Huntsville’s total for the first five months to 58.97 inches – about 10 inches higher than the average rainfall for an entire year.
58.97 inches is also almost triple the normal year-to-date (YTD) total for Huntsville.
At other reporting stations during the last 25 years:
Conroe had its rainiest May – 12.58 inches
Bush Intercontinental Airport had the fifth rainiest May – 11.05 inches.
Galveston had its fourth rainiest May. But it was only 4.39 inches.
Huntsville received more than five times the rainfall in Galveston during May. That shows how high the rainfall was in the northern part of the San Jacinto River Basin.*
These statistics demonstrate three things:
May was very wet.
2024 has been very wet so far.
Rainfall across the region has varied dramatically.
Conroe, Bush Intercontinental and Galveston did not set records for May. But their monthly totals all fell into the top quintile of the last 25 years. And that helped bring YTD totals to near record highs at all sampled locations.
See graphs below arranged geographically from north to south. The boxes superimposed over the graphs show the years of the record high and low totals for YTD precipitation as well as the precipitation in a normal year.
Note: Record year at this location so green and blue lines coincide.
2024 YTD Totals Compared to Normal YTD
When comparing normal YTD totals to 2024’s, we can see that:
Huntsville is 193% ahead of normal.
Conroe is 73% ahead.
Bush Intercontinental Airport is 51% ahead.
Galveston is 58% ahead.
2X Differences in Lake Houston Area
Rainfall can vary dramatically within much smaller areas than the Houston region. Take the Lake Houston Area, for instance. According to the Harris County Flood Warning System, during May 2024, the gage at:
US59 and the West Fork received 13.76 inches of rainfall.
West Lake Houston Parkway and the West Fork received 16.56 inches.
FM1960 bridge across Lake Houston received 12.28 inches.
Slightly upstream, FM1485 and the East Fork received 22.8 inches.
That meant an almost 2X difference between the high at FM1485 and the low at FM1960. The two locations are just nine miles apart.
80% of Annual Rainfall in First 5 Months
I live just two miles from the gage at the West Lake Houston Parkway bridge and recorded an almost identical amount of rainfall in my back yard.
My gage received 16.45 inches for the month. That was just a tenth of an inch less than the Harris County Flood Control gage at WLHP.
And that brought my total rainfall for the year to 40.12 inches. Our average annual rainfall is only 50 inches. So we’re already at 80% of a normal year. I received a third of an average year in the month of May alone.
So, it was a very wet month for the Rehak household, even though we received 8 inches less than Huntsville’s mind-boggling 24 inches.
Today, another hurricane season starts. All early predictions indicate it could be a record-setting season. So keep those umbrellas handy.
Posted by Bob Rehak on June 1, 2024
2468 days since Hurricane Harvey
* Footnote: The NWS charts below all show monthly rainfall for the last 25 years. I have sorted the years in descending order based on May rainfall totals and highlighted where 2024 ranks for each reporting station.
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The San Jacinto River Basin includes 28 watersheds and all or parts of 11 counties. We’ve experienced more than $12 billion in flood damages since 1975. And yet, incredibly, no one is in charge of drainage.
Map of San Jacinto River Basin and its watersheds, courtesy of SJRA.
We also have 1092 political subdivisions with flood-related authority. Yet no one is in charge of drainage.
We Work in Silos to Solve a Common Problem
That’s right. No one person is in charge of drainage. Instead, thousands of individuals working in their own little silos are scattered across more than 5,000 square miles. Unfortunately, stormwater doesn’t respect all those jurisdictional boundaries.
The San Jacinto Regional Flood Planning Group (reporting to the Texas Water Development Board) highlighted a “critical need for interagency coordination.” But there is none.
When No One is in Charge of Drainage, We All Suffer
Ironically, Texans won independence at the battle of San Jacinto. And we’ve been fighting to maintain it ever since.
We are so fiercely independent, we deny our interdependence. Even when it means destroying our own property and lives. It’s time to take a look in the mirror, folks.
Many ways exist to rank flood-prone areas and Texas ranks high on most of them.
Most hurricanes? Out of the 300 hurricanes that made landfall in the US since 1851, Texas ranks #2 after Florida with 66 hitting the Lone Star state – 22% of the U.S. total.
Percentage of state’s total population living in floodplains? Texas ties for 10th according to a 2017 study. But a 2023 TWDB study shows that 20% of Texans now live in floodplains; that would tie us for 3rd if nothing else changed.
Most disaster declarations? Texas ranks #2 when considering all types.
Flood deaths? Texas ranks #1. Two hundred people died between 2010 and 2022. Over a longer period of time, 1959-2014, the state had over 850 flood deaths.
Flood control is one area where Texans have room for improvement. But to improve we’ll need to work together.
Posted by Bob Rehak on 5/30/2024
2466 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/05/Challenge.jpg?fit=1100%2C674&ssl=16741100adminadmin2024-05-30 22:27:392024-05-30 22:31:5228 Watersheds, 11 Counties, $12 Billion in NFIP Claims, No One in Charge
The lakefront side of restaurant row is now shut in by sand collecting trash and logs swept downstream. The restaurants there, such as Chimichurri’s, Sharky’s, Raffa’s, and Zammitti’s, serve outstanding food and even more outstanding views. But at the moment, it’s not quite the romantic place for a marriage proposal at sunset. See the pics below.
Looking south from over waterfront restaurants at sand deposited by storm. Looking SW toward West Lake Houston ParkwayReverse angle. Looking north toward restaurant row and apartments beyond.
Dredging Costs Tough on Small Associations
Perhaps dredging companies are offering “buy one, get one free” deals next month.
Seriously, mobilization costs for dredging are so high that it makes sense to spread those costs over as many jobs as possible. By working together, the Kingwood Service Association and Kings Harbor could cut their mobilization costs in half.
Origin of Sand?
During the flood, I clocked the speed of debris floating in the water near this location. It was moving at 5-6 MPH, exactly the same speed as water moving through sand mines upstream on the West Fork. That’s more than enough to transport sand as you can see below from this industry-standard Hjulström curve.
River speed shown in blue. Size range for sand shown in red.
Did all the sand come from West Fork sand mines? No. The speed was also enough to erode riverbanks as you can see above. But the sand mines between US59 and I-45 expose approximately 33 times more sand to erosion.
Yesterday, I posted about the likely source for the sand blocking the Kingwood Diversion Ditch at River Grove Park. The same arguments apply here.
We need sand, but we also need to make sand miners operate more responsibly.
Posted by Bob Rehak on May 27, 2024
2463 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.
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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.
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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
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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
May 23, 2024 – This morning, NOAA issued its highest hurricane season forecast ever. The extreme predictions are consistent with earlier forecasts by other organizations. They also exceed NOAA’s own forecasts from 2005 and 2010, two previous record-setting years.
NOAA’s forecast underscores the importance of starting your preparations early. Hurricane season begins next week.
Reasons Behind Predictions
In issuing the forecast, NOAA pointed to a combination of several factors: extremely high sea surface temperatures, the onset of La Niña, an above-normal West African monsoon and extremely high levels of Accumulated Cyclone Energy (ACE).
To sum up, more storms will come off the African coast. High sea surface temperatures will intensify them. And a reduction in shear normally associated with La Niña will let them blossom into tropical events. The high ACE levels confirm that the elements above are likely to combine in dangerous ways.
NOAA says it is currently seeing sea surface temperatures in May normally associated with August.
2024 By the Numbers
The chart below shows the number of named storms, hurricanes and major hurricanes (Cat 3, 4 or 5) that NOAA predicts.
NOAA Predictions one week before start of 2024 hurricane season.
NOAA forecasts 17 to 25 total named storms (winds of 39 mph or higher). Of those, they predict 8 to 13 will become hurricanes (winds of 74 mph or higher). And of those, they predict 4 to 7 will become major hurricanes (category 3, 4 or 5; with winds of 111 mph or higher).
The chart also shows the degree of confidence in the “above normal” prediction: 85%. The probability of an average or below normal season totals only 15%.
ACE Explained
At the press conference, a NOAA scientist explained how accumulated cyclone energy is measured. Forecasters add up the wind velocity measured at reporting stations every six hours, square the result, and divide by 10,000 to make the result more manageable.
The accumulated cyclone energy measured this year is the second highest ever.
NOAA Press Conference
New Cone Graphic Will Include Watches and Warnings
To protect lives, NOAA is enhancing communication, providing new tools for hurricane forecasting, and upgrading its systems.
For instance, the familiar “cone forecast” graphics will take on a new look this year. The maps will include watches and warnings associated with a storm. These can extend outside the cone of uncertainty
The old cones indicated only the probable centerlines of storm paths. But the width of a storm can create impacts far outside the cone. See below.
New NOAA Cone Graphic this year will feature watches and warnings
NOAA also warned this morning that threats can linger even after a storm has passed. For instance, rising water from heavy rains can create inland flooding that traps people in vehicles. It’s not only about storm surge. Remember: Turn around, don’t drown.
Ninety percent of storm-related fatalities occur from water.
NOAA
Many people are also killed during cleanup when they leave their homes too soon. Listen to local authorities.
They also reminded people to make sure they operate generators outdoors. Many die from carbon monoxide poisoning when operating generators indoors or in garages.
Seasonal Forecast Not a Landfall Prediction
NOAA’s outlook is for overall seasonal activity and is not a landfall forecast. However, other forecasters have predicted that less wind sheer associated with La Niña will let more storms enter the Gulf or form in the Gulf.
This new updated hurricane strike chart shows landfalls since 1950. Hurricanes can and have struck almost every point on the U.S. Gulf and East coasts. It only takes one storm to alter your life forever. So…
The Message: Start Preparing Now
The time to prepare for hurricane season is NOW. NOAA noted during the press conference that every Category 5 storm they have monitored was a tropical storm or less just three days earlier. That means you have only about 60 hours to prepare for and/or evacuate from the deadliest storms.
People with health or mobility issues need to take special precautions. NOAA offers extensive advice for hurricane preparation which you can find on this page in English and Spanish.
I’ve also provided a large number of links to specialized websites that focus on different aspects of preparedness. They include such things as checklists for generators, vehicles, kids, valuables, pets, etc. Look under the Preparedness heading on this Links Page.
In addition to the Atlantic seasonal outlook, NOAA also issues seasonal hurricane outlooks for the eastern Pacific, central Pacific and western north Pacific hurricane basins.
NOAA’s Climate Prediction Center will update the 2024 Atlantic seasonal outlook in early August, prior to the historical peak of the season.
Posted by Bob Rehak on 5/23/24
2459 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/05/IMAGE-Hurricane-Outlook-May-2024-ENGLISH-Pie-052324-NOAA.png?fit=3840%2C2373&ssl=123733840adminadmin2024-05-23 12:34:332024-05-23 12:46:02NOAA Issues Highest Hurricane Season Forecast Ever
5/23/24 – The past may be catching up with Montgomery County. Heavy rains earlier this month may have flooded more homes in Montgomery County than Harris.
For decades, many Montgomery County leaders refused to acknowledge that they had a flooding problem. Neither, for that matter, did they seem exceptionally concerned about the downstream impact that lax regulations and enforcement had on flooding in Harris County.
For instance, they failed to:
Establish a flood control district.
Keep drainage channels clear and well maintained.
Update floodplain data from the 1980s.
Update their subdivision and drainage criteria regulations.
Close loopholes that let developers avoid building stormwater detention basins.
Fund the inspection of new infrastructure to ensure it complied with regulations.
Adequately regulate sand mining.
In fact, they encouraged exponential growth of sand mining by giving miners ag and timber exemptions on their real estate taxes, which the Texas Comptroller says they are not entitled to.
Flooded subdivision near West Fork San Jacinto in Montgomery County. Photo 5/22/24.
Floodplains as a Shifting Target
As a result of all these issues, flooding problems got worse over time. People who had built homes and even entire developments too close to rivers and streams flooded repeatedly. Homes deteriorated and lost value.
Young first-time homebuyers and other low-income people snapped them up, hoping they wouldn’t flood. In some cases, the homeowners didn’t even think they needed flood insurance because of the out-of-date flood maps. Many lost life savings and lived in deplorable conditions until they could scrimp together enough savings to fix their homes.
Many also sought buyouts and disaster relief. But such expenses usually fall on the federal government. So Montgomery County had little incentive to change on that count.
As a result of shortsighted policies and willful blindness, some MoCo leaders presided over the decay of once-proud homes into flood-ravaged housing stock.
And now, that damaged housing stock has created festering eyesores that may tarnish the image of the county as a destination for those trying to flee Harris County’s problems.
Flooded street one mile from West Fork San Jacinto in Montgomery County. Photo 5/22/24.
Self-Destructive Policies Hit Home
The self-destructive policies listed above have become…well…self destructive.
Leaders of decades past could explain away Harvey. “A 1000 year storm!”
But what about the no-name storm of May 2024? Ten-year rains produced so-called “50-year flooding” that rose higher than floodwaters from Tropical Storm Imelda – a greater than 500-year storm. MoCo math strikes again.
I drove for six hours through Montgomery County yesterday, visiting one flooded neighborhood after another. As victims continued to drag waterlogged drywall, carpet, insulation and furniture to the curb, they did not have good things to say about some elected officials.
FEMA Disaster Recovery officials swarmed neighborhoods like this today(5/22/24).
Downriver from the scene above, the main drainage channel through a new development called Evergreen has turned into a river of mud because of rampant erosion. It appears to have no:
Silt fences.
Backslope interceptor swales.
Grass on the sides of ditches.
Evergreen in Montgomery County at SH242 and FM1314 drains into West Fork below the flooded homes above.Did the erosion here reduce the conveyance of the river, back water up and contribute to flooding?
Will Change Come Anytime Soon?
Yes, the past may be catching up with Montgomery County. But change must come from within the county. Harris County can’t dictate it.
The final figures are not yet in. But based on an unscientific “driving around” survey, it appears that Montgomery County suffered as much flooding as Harris County did this May – if not more.
This should be a wake-up call for a course correction by Montgomery County leaders before it’s too late.
Since taking office a short while ago, newly elected MoCo Precinct 4 Commissioner Matt Gray has fought hard to upgrade MoCo standards. The rest of Montgomery County drains through his precinct. Perhaps this event will open the eyes of his fellow Commissioners and County Judge.
We’re all in this together. Even the people north of Lake Conroe will live downstream from others in fast-growing, surrounding counties someday as the region expands relentlessly outward.
The sand mines will follow that growth. Get ready. They’re coming.
San Jacinto River, blocked by sand, now flows through abandoned West Fork sand mine, sending even more sediment downriver.
Dozens of Montgomery County homes flooded downstream from the fiasco in the photo above. Sedimentation may have played a role as it has in the past. It’s just too early to tell.
The time to reach out and work together is now. Not after MoCo math and stuck-in-the-past policies start to look attractive to commissioners and judges in surrounding Liberty, Waller, Grimes, Walker and San Jacinto Counties.
Posted by Bob Rehak on 5/23/24
2359 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.
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May 21, 2024 – After a second round of May floods (and the third this year), all river levels are falling today. The East Fork, West Fork and main stem of the San Jacinto River are finally falling this morning. So are the water levels in Lake Conroe and Lake Houston.
But sedimentation will likely be a problem when floodwaters totally recede.
Gage Readings For Lake Conroe
The gates at Lake Conroe are still open, but only releasing 1,599 Cubic Feet per Second (CFS). That’s about a twelfth of what the San Jacinto River Authority released at the peak of this second wave of May floods.
The graph below shows that the lake level is slowly approaching its normal conservation pool of 201 feet.
Note distances to flowage easement and top of dam. Homes around lake should be built above flowage easement.
All Gage Readings on West Fork Falling
In response, the West Fork at US59 fell below flood stage yesterday evening and continues to fall.
River Grove Park is draining, but the soccer fields are not yet playable.
River Grove Park draining on 5/20/24 at 5PM after flood peak passed
At West Lake Houston Parkway, the West Fork is well within its banks and falling.
Readings on East Fork
Upstream on the East Fork at SH105, the East Fork crest has passed and the river continues to fall.
At FM2090, the East Fork is 4 feet below flood stage and falling.
The East Fork fell below flood stage yesterday afternoon at FM1485 and continues to fall.
Lake Houston and Below
At the FM1960 bridge over Lake Houston, the level continues to fall well below flood stage, but is still about a foot above normal.
At the Lake Houston dam, water levels are also falling, but the lake is also about a foot above the spillway.
Floodwaters are still being released from the lake via both the gates and spillway.
The gates can release 10,000 CFS. That means about another 7,500 CFS are going over the spillway.
Downstream, on the main stem of the San Jacinto at Highway 90, the river is well below flood stage and continuing to fall.
West Fork Still Flowing Through Abandoned Sand Pit
That’s all great news. But the West Fork is still flowing through an abandoned sand pit near the Hallett Mine. You can see the impact at the confluence of the West Fork and Spring Creek.
Confluence of Spring Creek (left) and West Fork San Jacinto (Right) on 5/20/24 at 5 PM.
Can Water Moving at 5 MPH Transport Sand?
I measured debris coming out of the pit. It was moving at approximately 5 miles per hour (MPH).
Despite what some miners claim, 5 MPH should be more than enough to carry sand downriver.
Below is an industry-standard graph that shows the speed necessary to erode, transport and deposit sand/sediment of different particle sizes. Hydrologists and geologists call it a Hjulström curve, named after Filip Hjulström (1902–1982), the man who developed it.
After converting centimeters per second to miles per hour, I superimposed the speed of the river as a blue line over the graph.
The scientific Unified Soil Classification System defines sand as particles with a diameter of 0.074 to 4.75 millimeters. I rendered that range in red at the bottom of the chart.
Blue indicates speed of water. Red indicates range of sand sizes.
Floodwater moving at 5 MPH can transport the entire range of sand sizes according to the Hjulström curve. You can see it in the photo above.
The river will need to recede before we can see exactly how much moved down to the West Fork between Humble and Kingwood, or settled at the mouth of the river near Lake Houston.
In fairness, some of the sediment deposited downstream came from natural erosion from riverbanks. But there was also unnatural erosion from development and (I have heard) other mines. It is impossible to apportion responsibility precisely.
What we can safely say is that sand mining practices have increased sedimentation downstream and few people seem eager to fight the industry … even as we get ready to launch another round of dredging that will cost taxpayers $34 million.
Posted by Bob Rehak on 5/21/24
2457 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/2024/05/20240520-DJI_20240520175218_0749_D.jpg?fit=1100%2C619&ssl=16191100adminadmin2024-05-21 13:01:342024-05-21 13:06:00All River Levels Falling, Flood Danger Over, But…
