During Harvey, 16,000 homes and 3,300 businesses in the Lake Houston Area flooded. Local leaders identified the disparity in release capacities between the Lake Conroe and Lake Houston Dams as one of the contributing factors to the severity of flooding. The floodgates on Lake Conroe can release water 15 times faster than the gates on Lake Houston. So, adding more floodgates to Lake Houston became one of the area’s primary mitigation goals.
While the City of Houston initially obtained a $50 million grant from FEMA to add gates, two problems became apparent. The project cost more than anticipated and the benefits delivered did not justify the cost – at least the way FEMA was initially calculating them. However, a huge hurdle has been cleared.
The City of Houston has finally secured a favorable ruling from FEMA on a benefit-to-cost ratio, according to a press release from Mayor Pro Tem Dave Martin’s office on 12/7/2022. The key was the FEMA administrator’s decision to allow the inclusion of social benefits, for instance, avoidance of disruptions to business, commerce, schools and the area’s tax base. Those brought the BCR up to 2.88, according to Martin.
Martin, Mayor Sylvester Turner and Chief Recovery Officer Stephen Costello met with the Federal Emergency Management Agency (FEMA) Administrator to discuss the inequities of the Federal BCR formula associated with incorporation of social benefits.
As a result, Martin and Turner have announced that a large hurdle has been removed. The revised draft BCR for the Lake Houston Spillway Dam Improvement Project has been determined to be “federally compliant and is very favorable.”
The change affected the Lake Houston Gates and several other Houston stormwater projects including the massive, new Inwood Forest detention basin.
New BCR Based on Eleven Gates
Atkins, a City of Houston consultant, revised the BCR for an eleven-gate structure. The eleven gates will be built into the existing embankment on the east side of the Lake Houston Spillway Dam.
Building the new gate structure in the east embankment removes the high construction risk of modifying the existing gate structure. It also allows continued use of the existing gate structure during construction, and eliminates the need for a coffer dam in the lake, according to Martin.
Cost Quadruples: Additional Funding Sources Now Necessary
The new preliminary cost estimate of $200 million exceeds the City’s original FEMA grant of $48 million.
Martin, Costello, and State Representative Dan Huberty have already met with the Texas House of Representatives Speaker Dade Phelan’s Director of Finance regarding additional funding. They have positioned the project as a “life and safety initiative” that affects the survival of the community and economy of the Lake Houston Area.
Martin has bi-partisan support already lined up for financing. Key partners this legislative session include:
Congressman Dan Crenshaw
State Senator Brandon Creighton
State Senator John Whitmire (who has already announced his intention to run for Houston mayor after Turner retires)
Speaker of the Texas House Dade Phelan
State Representative & Chair of Appropriations Dr. Greg Bonnen
State Representatives Charles Cunningham and Armando Walle.
Martin plans to work with Federal and State partners to ensure the cost of the Lake Houston Spillway Dam Project is fully funded before he leaves office in December 2023.
Said Martin, “Today a significant obstacle has been surpassed as this project moves forward through the financial process.” The new BCR should let federal, state, and local partners work toward fortifying the Lake Houston Area against future storms.
It would be unfair to call this a “start over.” A huge amount of engineering and analysis has gone into the project. However, challenges turned out to be greater than anyone anticipated after Harvey.
The original timetable from 12/16/19 showed the project completed by now. The fact that it is still alive is a tribute to the persistence of Martin, Turner, Costello and others.
Let’s look forward to the benefits, not backwards to the problems. People are working in the right direction. A huge obstacle has been eliminated. We just need to keep tackling new obstacles as they occur. Next step: the House and Senate.
I will post construction plans for the 11 gates and the Atkins’ BCR analysis as soon as the City supplies them; they promised they would.
Posted by Bob Rehak on 12/7/22
1926 Days since Hurricane Harvey
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Tomorrow is the fifth anniversary of Hurricane Harvey. Many in the Lake Houston Area have asked, “Are we safer now?” The answer is yes, but we have a long way to go to achieve all our goals. Here’s a five-year flood-mitigation report card. It describes what we have and haven’t accomplished in 29 areas. So get ready for a roller coaster ride. I’ll leave the letter grades to you.
Lake Houston Area Mitigation
The most visible accomplishment in the Lake Houston Area since Harvey is dredging. The City and Army Corps removed approximately 4 million cubic yards of sediment blocking the West and East Forks. Before dredging, River Grove Park flooded six times in two months. Since dredging, it hasn’t flooded once to my knowledge.
To reduce the amount of water coming inbound during storms, the San Jacinto River Basin Master Drainage Study identified 16 potential areas for building large stormwater detention basins. Unfortunately, they had a combined cost of $3.3 billion and would only reduce damages by about a quarter of that.
So, the SJRA recommended additional study on the two with the highest Benefit/Cost Ratio. Their hope: to reduce costs further. The two are on Birch and Walnut Creeks, two tributaries of Spring Creek near Waller County. Expect a draft report in February next year.
Funding these would likely require State assistance. But the Texas Water Development Board’s San Jacinto Regional Flood Planning Group has just recently submitted its first draft report. The draft also recommended looking at detention basin projects on West Fork/Lake Creek, East Fork/Winters Bayou, and East Fork/Peach Creek.
Building them all could hold back a foot of stormwater falling across 337 square miles. But funds would still need to be approved over several years. We’re still a long way off. Results – on the ground – could take years if not decades.
The Regional Flood Planning Group also recommended something called “benching” in two places along 5 miles of the West Fork. In flood mitigation, benching entails shaving down a floodplain to create extra floodwater storage capacity. Like the detention basins, benching is still a long way off…if it happens at all.
After Harvey, many downstream residents accused SJRA of flooding downstream areas to save homes around Lake Conroe. At the time, SJRA’s board had no residents from the Humble/Kingwood Area. So Governor Abbott appointed two: Kaaren Cambio and Mark Micheletti. Cambio later resigned due to a potential conflict of interest when she took a job with Congressman Dan Crenshaw. That leaves Micheletti as the lone Humble/Kingwood Area resident on a seven-person board. However, the SJRA points out that the Board’s current president, Ronnie Anderson, represents Chambers County, which is also downstream.
State Representative Will Metcalf, who represents the Lake Conroe area, introduced a bill to limit SJRA board membership to upstream residents. Luckily for downstream residents, it failed.
7) Lake Conroe Lowering
SJRA identified temporary, seasonal lowering of Lake Conroe as a strategy to reduce downstream flood risk until completion of dredging and gates projects in the Lake Houston Area. The lowering creates extra storage in the lake during peak rainy seasons. After SJRA implemented the plan, Lake Conroe residents objected to the inconvenience. They sued SJRA and the City, but lost. After discussion with all stakeholders, the SJRA quietly modified its plan. It still lowers the lake, but not as much.
8) Lowering Lake Houston
Houston also started lowering Lake Houston, not seasonally, but in advance of major storms. The City has lowered the lake more than 20 times since beginning the program. That has helped to avoid much potential flooding to date.
9) Lake Conroe Dam Management
SJRA applied for and received several TWDB grants to enhance flood mitigation and communications in the San Jacinto River Basin. One involves developing a Lake Conroe Reservoir Forecasting Tool. SJRA has also worked with San Jacinto County to develop a Flood Early Warning System.
Finally, SJRA’s Lake Conroe/Lake Houston Joint Reservoir Operations Plan is on hold pending completion of the City’s plan to add more gates to the Lake Houston dam. Such projects may help reduce the risk of releasing unnecessarily large volumes of water in the future.
However, the location is controversial. Geologists say it wouldn’t reduce sediment in the area of greatest damage. Environmentalists worry that it could increase sedimentation through a “hungry-water” effect and open the door to river mining. And I worry that, even if successful, the pilot study would not be extendable. That’s because it relies on partnerships with sand miners. And other tributaries to Lake Houston do not have sand mines or as many sand mines.
It’s hard to get good grades on your flood mitigation report card without funding.
$1.6 million for HCFCD for Taylor Gully stormwater channel improvement.
$1.6 million for HCFCD for Kingwood Diversion Channel improvement.
$1.67 million for Harris County for the Forest Manor drainage improvement project in Huffman.
$8.2 million from FEMA the Westador Basin stormwater detention project on Cypress Creek.
$9.9 million from FEMA for the TC Jester storm water detention basin on Cypress Creek.
Crenshaw also has backed community requests for more funding in Fiscal 23. They include:
$8 million for the Lake Houston Dam Spillway (Gates).
$10 million for the Woodridge Stormwater Detention Basin (see below).
$10 million for a Cedar Bayou Stormwater Detention Basin.
Harris County Flood Control
19) Channel Maintenance and Repair
Harris County Flood Control has already completed several maintenance projects in the Lake Houston Area. In Kingwood, those projects include Taylor Gully, Ben’s Branch, parts of the Diversion Ditch and other unnamed ditches. In Atascocita, HCFCD also completed a project on Rogers Gully. Upstream, HCFCD is working on the third round of repairs to Cypress Creek. Batch 3 includes work at 12 sites on 11 channel sections. I’m sure the District has maintenance projects in other areas, too. I just can’t name them all.
In 2019, uncontrolled stormwater from the Woodridge Village development twice flooded approximately 600 homes in Elm Grove Village and North Kingwood Forest. HCFCD and the City purchased Woodridge from Perry Homes last year. HCFCD soon thereafter started removing sediment from the site to create a sixth stormwater detention basin that would more than double capacity on the site. At the end of last month, contractors had removed approximately 50,000 cubic yards out of 500,000 in the contract. This gives HCFCD a head start on excavation while engineers complete the basin’s final design.
21) Local Drainage Study Implementation
HCFCD authorized four studies of the drainage needs in the Lake Houston Area. They completed the Huffman and Kingwood studies. Atascocita and East Lake Houston/Crosby started earlier this year and are still underway.
The Kingwood study measured levels of service in all channels and outlined strategies to improve them to the 100-year level. The first two projects recommended: Taylor Gully and the Kingwood Diversion Ditch. Neither has started construction yet. But see the notes under funding above.
The Huffman Study recommended improvements to FM2100, which TxDOT will handle. It also recommended dredging in the East Fork near Luce Bayou which the City has completed. Finally, it recommended a bypass channel for Luce. However, pushback from residents forced cancellation of that project.
HCFCD completed buyouts of 80+ townhomes on Timberline and Marina Drives in Forest Cove last month. Contractors demolished the final run-down complex in August. That should improve property values in Forest Cove.
23) Regulation Harmonization
Harris County Flood Control and Engineering have been working to get municipalities and other counties throughout the region to adopt certain minimum drainage regulations. I discussed the importance of uniformly high standards in last night’s post. So far, about a third of the governments have upgraded their regs. A third are still deciding whether to act. And the remainder have taken no action. There has been little movement in the last six months.
City of Houston
As mentioned above, the City has taken a lead role in dredging, adding gates to Lake Houston, and proactive lake lowering. In addition, the City has helped with:
24) Bridge Underpass Clean-Out
The City of Houston successfully cleaned out ditches under Kingwood Drive and North Park Drive in at least six places. Bridges represent a major choke point during floods. So eliminating sediment buildups helps reduce flood risk in areas that previously flooded.
The lowest score on the flood-mitigation report card probably goes to LSGCD.
The Lone Star Groundwater Conservation District has started pumping groundwater again at an alarming rate. Projected subsidence near the Montgomery County Border equals 3.25 feet, but only 1 foot at the Lake Houston dam. That could eventually tilt the lake back toward the Humble/Kingwood/Huffman area and reduce the margin of safety in flooding. That’s bad news.
Sand Mining Regulations
Twenty square miles of West Fork sand mines immediately upstream from I-69 have exposed a swath of floodplain once covered by trees to heavy erosion during floods. Mathematically, the potential for erosion increased 33X compared to the normal width of the river. Sand mines were also frequently observed releasing sediment into the river. And the dikes around the mines often wash out.
So in 2019, the Lake Houston Area Grassroots Flood Prevention Initiative (LHAGFPI) began meeting with legislators, regulators and the Texas Aggregate and Concrete Association (TACA). The goal: to establish comprehensive Best Management Practices (BMPs) for the sand mining industry in the San Jacinto River Basin.
27) Mine Plan/Stabilization Reports Now Required
TCEQ adopted new regulations, effective January 6, 2022. They required miners to file a ‘Mine Plan’ by July 6, 2022 and also a ‘Final Stabilization Report’ when a mine is played out.
28) Vegetated Buffer Zones (Setbacks)
The new regs also stipulate undisturbed vegetative buffer zones around new mines. Buffer zones aid in sediment filtration and removal by slowing surface water. They also strengthen dikes.
The new regs require a minimum 100-foot vegetated buffer zone adjacent to perennial streams greater than 20 feet in width. However, for streams less than 20 feet wide, the buffer zone is only 50 feet for perennial streams, and 35 feet for intermittent streams.
29) Reclamation Bonds
Unfortunately, the Flood Prevention Initiative could not convince TCEQ to require ‘reclamation bonds.’ Other states use such bonds to prevent miners from abandoning mines without taking steps to reduce future erosion, such as planting vegetation.
My apologies to any projects or parties I omitted. Now it’s your turn. Give grades to those you think have done the best job on YOUR Harvey flood-mitigation report card.
Posted by Bob Rehak on 8/26/22
1823 Days since Hurricane Harvey and one day from Harvey’s Fifth Anniversary
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Initial options that the City of Houston explored for adding more flood gates to the Lake Houston Dam struggled to achieve a high enough Benefit/Cost Ratio. However, all parties involved are still hopeful that a solution can be found. They are now evaluating yet another option. It would add gates in the earthen (eastern) portion of the dam.
More Gates Would Create More Room For Floodwaters
Flooding devasted the entire Lake Houston Area during Harvey. Since then, Mayor Pro Tem Dave Martin has led an effort to find a way to lower the lake faster in advance of a storm. This would create extra room in the lake for floodwaters. And that would reduce the risk of flooding homes and businesses around it.
Currently, the dam has a fixed height spillway. That makes releasing water in advance of a storm difficult. The dam does have several small gates, but they have only 1/15th the release capacity of the gates on Lake Conroe. Adding more gates would help release water faster…to keep up with water coming downstream.
It would also let managers wait to start a release until they were certain a storm would not veer away. That would help avoid wasting water if forecasts are not accurate.
The Dual-Role Dilemma
The City built Lake Houston in 1953 to supply water. Making the dam play two roles – water supply and flood mitigation – poses a challenge.
In 2017, immediately after Hurricane Harvey, Martin began leading the effort to transform the dam to play a dual role. This would let Lake Houston provide our region with needed drinking water and reduce flood risk.
New Timeline Longer Than Hoped, But Still Shorter Than Usual
A project of this magnitude normally takes up to twelve years. However, Martin worked with federal, state, and local officials to shorten the timeline. Martin now hopes the project will take no longer than seven years. While acknowledging that he hoped completion would happen in as little as five years, Martin also cites unexpected technical and cost challenges related to the aging dam.
During that process, engineers discovered hidden challenges with some options that initially looked promising. At this point, they have determined that all six initial options cost more than the federally funded amount of $48 million.
A Complicated Path Forward
So now engineers are focusing on finding the optimal solution while Martin and others explore options to pay for it.
Martin says the City of Houston, Texas Division of Emergency Management and Federal Emergency Management Agency are working together to find the option with the highest Benefit to Cost Ratio (BCR).
Acceptable BCRs for projects like this range from .75 to 1, according to Martin. Preliminary engineering studies found that two crest-gate alternatives (already evaluated) yielded only .48 – largely due to the aging structure of the existing spillway, which drove up costs.
City Expects Answer on Latest Option Before October
Currently, the City has paused the final-design phase of the project while engineers evaluate Alternative 1A. That now consists of five new tainter-gates (not six or twelve as previously reported) on the earthen embankment east of the spillway.
While engineers work to find the best BCR, Martin is leading an effort with BOTH state and federal partners to find additional funding for the project.
For instance, Martin is working with outgoing State Representative Dan Huberty and incoming State Representative Charles Cunningham to seek funds in the upcoming Texas Legislative Session. Martin says that state dollars do not require BCRs like federal dollars do.
While all the challenges would have discouraged many, Martin says they have fortified his resolve. He vows to find a path forward. Martin promises an update in his regular fall public meeting in October and hopes to have an attractive BCR for alternative 1A.
Interim Flood-Mitigation Measures Still In Place
In the meantime, the City of Houston will continue its existing Lake Houston pre-release strategy. It calls for lowering the lake when forecasters predict three or more inches of rain in the San Jacinto Watershed. Since Hurricane Harvey, the City has lowered the lake more than twenty times and successfully avoided flooding.
Thanks to Key Contributors
Martin acknowledges the continuing contributions of Congressman Dan Crenshaw, Governor Greg Abbott, Lt. Governor Dan Patrick, Commissioner Tom Ramsey, State Representative Dan Huberty, State Representative-Elect Charles Cunningham, TDEM-Chief Nim Kidd, Mayor Sylvester Turner, Chief Recovery Officer Stephen Costello, and Harris County Flood Control District.
Martin says, “All parties are committed to constructing these additional gates to help ensure protection against future flood events.”
Posted by Bob Rehak on 8/4/2022
1801 Days since Hurricane Harvey
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Neither alternative would modify the concrete portion of the spillway, as crest gates would. Black & Veatch, the engineering firm in charge of the project, will explore adding the tainter gates in the earthen embankment to the east of the existing spillway. See below, upper right.
The eastern embankment is a solid earthen area 2800 feet long east of the spillway and existing gates (see upper right of photo above). Water cannot get over it in a storm because it is so much higher than the spillway. By adding various structures in this area, engineers could widen the current spillway capacity, allowing release of more stormwater.
Tainter gates rotate up from a central pivot point. Crest gates rotate down from a bottom hinge, like a piano lid.
Minutes from May CWA Board Meeting
Item IV(B) on Page 3 of the May 11, 2022, minutes states, “…CWA, City of Houston (COH), and Black and Veatch (B&V) met on April 14, 2022. During that meeting the COH requested that an alternate gate location to the east of the existing gate structure be further [emphasis added] evaluated.”
Following the meeting, B&V developed a scope of work to update the gate concepts and construction costs for this area. The COH provided comments and B&V modified its proposal. B&V reportedly began work on the new direction by June 1.
Additional Funding Needed
Each of the new alternatives would require additional funding; neither fit within the existing budget, according to the CWA staff. COH Public Works will pay for the new evaluation.
Wayne Klotz, P.E. and President of the CWA Board, reminded everyone present that COH owns the dam and is the FEMA grantee for this project, while CWA works for and takes direction from COH.
Minutes from the June CWA meeting have not yet been posted. The last post about gates on the COH District E website was almost a year ago on July 8, 2021.
However, City Council member and Mayor Pro Tem Dave Martin did take questions on the project at an April 2022 community meeting. At the time, Martin expected to have a final answer on gates in a “September-ish” time frame.
Currently, the release capacity of tainter gates on the Lake Conroe Dam is 15X greater than those on the Lake Houston Dam (150,000 cubic feet per second (CFS) vs. 10,000 CFS.)
Concept Studied and Rejected Once Already
Adding gates to the eastern embankment was one of the original concepts evaluated. (See Column 5, Offsite Alternative #2, Column 5, Page 4.) But engineers focused on adding crest gates instead, largely because the total estimated costs for adding tainter gates at that time exceeded $90 million for a $50 million budget. However, the Army Corps also had environmental concerns about adding gates to the eastern embankment.
FEMA initially gave the City three years to complete the project (18 months for engineering and 18 for construction). Engineering began in April 2020.
No other details about May’s change in direction have been released to my knowledge.
Posted by Bob Rehak on 7/4/2022 based on minutes from the May CWA Board meeting
1770 Days since Hurricane Harvey
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Perhaps no flood-mitigation project has generated more interest in the Lake Houston Area recently than the addition of more flood gates to the Lake Houston Dam. In recent months, as engineers worked on the project’s benefit/cost ratio, information about the project became hard to find. That fueled rumors.
But Tuesday night, at the Kingwood Community Center, Mayor Pro Tem Dave Martin put many of those rumors to rest. He denied the project was on hold, reaffirmed the City’s commitment to the project, and outlined the three main issues that engineers are currently grappling with.
Issues Still Being Evaluated
The main issues include:
Safety concerns about cutting into the concrete of a dam that’s almost 70 years old.
Getting the benefit/cost ratio up.
Finding a suitable alternative that significantly reduces flood risk within the budget.
Martin elaborated on each. Regarding:
Safety concerns – He described the risks of cutting into it to install crest gates. Among them, he said engineers worried about structural stability of the dam after construction. Accordingly, they are recommending significant reinforcement of the concrete. He also hinted that contractors might not bid on the project for fear of the potential liability.
Benefit/Cost Ratio – He said that the higher-than-expects costs on of some alternatives drove the BCR down, and that that was driving the exploration of additional alternatives. He did say, however, that FEMA allows including “social benefits” when the BCR is between .75 and 1.0. The inclusion of social benefits still must yield a BCR of 1.0 or greater. On a separate note, a federal employee told me that the Biden administration may change this policy. So significant uncertainty still exists re: calculation of the BCR.
Budget – He implied that some alternatives under consideration became non-starters because of high costs and inflation.
Alternatives Still Under Consideration
So, the search for a suitable alternative that meets all objectives continues. Among the options still in the running, Martin mentioned crest gates on the west side of the dam and adding a tainter gate to the earthen, eastern portion.
The release of 80,000 CFS from Lake Conroe contributed almost a fifth of the water going over the spillway. Lake Conroe gates can release 150,000 CFS while Lake Houston’s can release only 10,000 CFS. The disparity in release capacity caused many to ask whether more gates on Lake Houston could reduce flooding.
Martin pointed out that when water gets high enough in Lake Houston, it can escape over a 2,000-foot-wide spillway. However, more gates could play a role in a pre-release strategy.
Pre-releasing water from Lake Houston in advance of major storms, as the City does now, creates extra capacity in the lake so that it can absorb more water without flooding homes and businesses. This strategy (coupled with the seasonal lowering of Lake Conroe) has worked effectively since Harvey and prevented flooding on more than one occasion.
Time Vs. Release Capacity Vs. Water Preservation
However, right now, it takes so long to release water from Lake Houston that storms can sometimes veer away and miss us after the lowering starts. Thus, water could be wasted. But bigger gates would let dam operators release the same volume of water in less time, so operators would not have to start releasing water so far in advance. In other words they would have a higher degree of confidence that the the storm would not veer away and that release was worthwhile.
Martin reassured people that:
Smaller (i.e., less costly) floodgates can lower Lake Houston sufficiently if given enough time
The lake usually refills quickly
Even if it doesn’t, the City can always call for the release of water from Lake Conroe.
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According to minutes of the Coastal Water Authority (CWA) February 9 board meeting posted in March, work on the project to add more gates to Lake Houston was paused in January while the City of Houston updated the project’s benefit-cost ratio.
CWA Board Minutes Give High-Level Overview of Concerns, Status
Earlier, in December, the board learned that the project team was trying to get the benefit/cost ratio above 1.0, so benefits exceed costs.
At that time, the CWA hoped to receive the updated BCR later in January. But it still hadn’t happened by the February board meeting.
That leaves a lot of questions regarding this project.
History of Project
After Harvey, the Lake Houston Area Task Force identified adding additional gates to Lake Houston as one of three primary strategies to reduce flood risk in the Lake Houston Area. The idea: to equalize the discharge rates of the flood gates on Lake Houston and Lake Conroe. Conroe’s is 15X greater. That makes it difficult lower both lakes quickly in advance of approaching storms.
Back in October 2020, the engineers calculated that the upstream influence of the dam ended at approximately Lake Houston Parkway. But they never explained why. It would seem that if the influence extended upstream to US59 when the lake is at its normal level, that the influence should extend at least that far in a flood. However…
BCR Not Based on Harvey Damage
Much of the damage to the Humble/Kingwood Area during Harvey happened upstream of the West Lake Houston Parkway Bridge. It included:
$60 Million to Kingwood College
$70 million to Kingwood High School
$50 million to Kingwood County Club
283 homes in Barrington
218 homes in Kingwood Lakes
97 apartments in Kingwood Lakes
110 homes in Kings Forest
100% of businesses in Kingwood Town Center
225 homes in Kingwood Greens
30 homes in Deer Cove
3 Homes in Deer Ridge Estates
32 homes in Trailwood Village
An unknown number of homes in Forest Cove
78 townhomes in Forest Cove
All of the Big Box stores along 59
Homes and business north of Deerbrook mall
40% of all businesses in the Lake Houston Chamber
Humble ISD admin building
Destruction of US59 southbound lanes
Union Pacific Railroad Bridge
However, Black & Veatch does not base its benefit-cost ratio calculations on another Harvey. They’re basing it on 25- and 100-year storms. Almost all homes, businesses and infrastructure near the lake are already above those levels – at least based on pre-Atlas 14 standards. That may explain the difficulty and delays with benefit/cost ratio calculations and the multitude of scenarios examined.
Time, Uncertainty: More Factors to Consider in Cost and Risk Reduction
Each flood-risk reduction alternative would reduce lake levels by a different amount during a 100-year storm and therefore require its own BCR.
Other factors to consider: How much time do dam operators really need to lower Lake Houston? And how much uncertainty are they willing to live with?
Given the desire to preserve water, these are crucial considerations. If forecasters can reliably predict a need to lower the lake two days before a storm instead of one, operators may only need half the number of new gates. That could get the cost down to the point where the benefit-cost ratio needs to be.
Posted by Bob Rehak on 4/4/22 and updated on 4/5/22 with MAAPnext timetable
1679 Days since Hurricane Harvey
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May 9, 2021, was 1349 days after Hurricane Harvey ravaged Texas and the Gulf Coast. That’s the number of days it took the US and its allies to win World War II. But during that time we’ve had few victories in the fight against future flooding in the Lake Houston Area with the exception of dredging, So far, we’ve mainly completed studies. And many of those are still in the works.
For instance, the City of Houston has been studying ways to increase the release capacity of the Lake Houston Dam. Right now, the release capacity is one-fifteenth that of the gates on Lake Conroe. That makes it difficult to shed water quickly before and during floods. FEMA gave the City money to study the problem, but is still finalizing recommendations. The City hopes to make an announcement in January.
The Texas Attorney General is still suing the Triple PG Sand Mine in Porter on behalf of the TCEQ. There has been little movement on the case in the last 18 months. The mine’s owner changed legal counsel in July 2020. A TCEQ representative says the AG has not given up. The two sides are still in discovery.
Approximately 1700 homeowners in the Lake Houston Area sued sand mines for contributing to flooding during Harvey. The cases were consolidated in the 281st Harris County District Court under Judge Sylvia Matthews. She recently set deadlines in the first half of next year for motions, depositions, joinder, expert witness testimony and more. The case is known as “Harvey Sand Litigation.”
Kingwood residents reached a settlement with Perry Homes, its subsidiaries and contractors this year over two floods that damaged hundreds of homes in Elm Grove and North Kingwood Forest during 2019. The incidents had to do with development of Woodridge Village, just across the Harris/Montgomery County line.
In Kingwood, HCFCD finished excavating both Bens Branch and Taylor Gully to help restore their conveyance. Through gradual sediment built up, both had been gradually reduced to a 2-year level of service in places. That means they would come out of their banks after a 2-year rain.
Public comment periods are not only for those who object to plans. The public may also support plans. And I plan to support the plan.
The Corps’ website contains the full public notice, which features a summary of the project, the project plans, and an analysis of the alternatives. These are much more thorough and detailed than any documents published to date. For the historical record, I have copied them to Reports Page of this website under the “Lake Houston Dam Spillway Improvement Project” tab. See:
The City of Houston proposes to improve 1,000 feet of the uncontrolled Ambursen spillway with the installation of new, controlled, Obermeyer spillway gates along the western portion of the existing Lake Houston Dam structure.
To accomplish this, the existing spillway crest would be lowered approximately 3.5 ft and fitted with an Obermeyer spillway gate structure. To further stabilize the dam structure, 150,000 cubic yards of rubble backfill will be deposited within the same 1,000 ft of the existing concrete structure.
The temporary cofferdam would be installed in sections that would enable the construction of a single Obermeyer spillway gate at a time. To facilitate access from the downstream side, backfill would then be installed within the Ambursen bays and in the downstream concrete-lined channel.
The spillway crest of the existing Ambursen spillway would then be demolished and the new concrete crest with the associated Obermeyer spillway gates and hydromechanical works would be built. The timeframe to complete this project will be approximately 18 to 24 months.
Avoidance and Minimization of Negative Impacts
The City conducted a thorough and extensive planning process to design a project that avoids and minimizes impacts to wetlands, special aquatic sites, and Waters of the United States as much as possible and feasible, while also satisfying the need.
During Hurricane Harvey, rainwater entered the lake at a rate of 430,000 cubic feet per second. An estimated 20,000 homes and businesses were flooded upstream. The reservoir passed the equivalent of its own storage capacity every half hour.
Due to the large influx of water over a short amount of time, the Lake Houston Dam was not able to release water fast enough to protect area homes, businesses, and public infrastructure from floodwater. Improvements are needed to the Lake Houston Dam to enable controlled releases ahead of major storm events and to further stabilize the 70-year-old structure.
This 36-page analysis shows the alternatives considered by project engineers. It also contains a matrix comparing the pros and cons of 11 alternatives, and which among them was the Least Environmentally Damaging Practicable Alternative.
By improving the existing dam, floodwaters can be rapidly released under controlled circumstances or stored to meet drinking water needs.
Lake Houston Area leaders identified the need for a larger release capacity early on as one of three primary objectives (upstream detention to slow down inbound water, dredging to speed up throughput, and more gates to speed up outflow).
Approximately 20,000 homes and businesses flooded when water could not get out of the lake fast enough. We need this project.
Benefits of the project include:
Reduction of flood heights
Protection of property
Faster release rate reduces uncertainty associated with pre-releases when attempting to add extra capacity to the lake in advance of approaching storms.
Saves water needed for drinking
How to Submit Comments
To support this project, email comments to the Regulatory Division, U.S. Army Corps of Engineers, Galveston District by clicking this link: Public Notice Comment Email. Make sure you reference the public notice number: SWG-2020-00271, and be sure to include your name address, and phone number.
Posted by Bob Rehak on 8/21/21
1453 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2021/08/20210821-Screen-Shot-2021-08-21-at-12.28.01-PM.jpg?fit=1200%2C546&ssl=15461200adminadmin2021-08-21 13:39:392021-08-21 13:39:46Public Comment Period on Gates Closes Monday
The SJRA and its partners can now officially start three studies:
An upper San Jacinto Watershed regional sedimentation study
A conceptual engineering feasibility study for flood-control dams in the Spring Creek Watershed
A joint reservoir operations study between Lake Conroe and Lake Houston
Why Flood Mitigation Takes So Long
We are all learning together how long flood mitigation takes. It’s somewhat frustrating to see a conceptual engineering feasibility study being kicked off one month from the fourth anniversary of Hurricane Harvey.
I’m not pointing fingers at the SJRA, its partners, the TWDB, or the State. If you took the time to read all of the approximately 1500 posts on ReduceFlooding.com, you would see that:
Harvey happened right after the 2017 legislature finished its work.
Eighteen months elapsed before the legislature met again.
It took another nine months for the legislature and governor to approve flood mitigation funding.
Then, the TWDB needed to define rules for the distribution of funds, solicit public comment, refine the rules, solicit grant applications, and evaluate them in a competitive context.
Finally, add time for related preliminary studies such as the Lake Houston Spillway Improvement Project, the San Jacinto River Basin Master Drainage Study, a sand trap study, and a siting study for the flood-control dams.
And don’t forget the time to find partners and develop political consensus around solutions.
Still Years from Construction
The truly scary thing is that even when these studies are completed, we still could be years from construction and more years from completion of any of these projects.
The system seems set up to protect money more than people. We certainly don’t want people rushing off, building half-baked projects that endanger people downstream, the environment, or the safety of a dam…especially if they produce no demonstrable benefit.
But we also don’t want people to flood multiple times waiting for flood-mitigation improvements. And some have. Remember Imelda? Just a thought as we head into the heart of hurricane season.
Studies Could Take 18 Months to 4 Years
The Spring Creek Flood-control Dam study will take 18 months. The Joint Reservoir Operations Study will take 3 years. And the Sediment Study is scheduled to take 4 years, though Matt Barrett, SJRA’s flood-mitigation director, is trying to compress that to 18 months.
If you missed the original post about these three studies, you can find more details here. SJRA partners in these projects include Harris County Flood Control, City of Houston, City of Humble, Montgomery County and five utility districts.
Posted by Bob Rehak on July 23, 2021
1424 Days since Hurricane Harvey and 673 since Imelda
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2021/07/Gates-Side-by-Side.jpg?fit=1200%2C400&ssl=14001200adminadmin2021-07-23 14:37:542021-07-23 14:42:47SJRA Board Accepts Grant Funding for Three Studies
At one of the first large public meetings since Covid began, several hundred people crowded into the Kingwood Community Center last night. They came to see the City unveil floodgate and dredging plans for Lake Houston. Stephen Costello, PE, the City’s Chief Recovery Officer, addressed dredging. And Chris Mueller, PhD, PE, of engineering firm Black & Veatch discussed adding more floodgates to the Lake Houston Dam. Mayor Pro Tem Dave Martin coordinated the meeting.
Scope of Long-Range Dredging Plan Still in Development
A long-range dredging plan for Lake Houston is critical. We must understand where the sediment comes from, how fast it builds up, where it builds up, and the consequences of not removing it periodically.
Costello says the City is currently working with affected homeowner associations to discuss cost-sharing arrangements.
He also says that the City must identify a long-range site for depositing the spoils that is suitable for hydraulic dredging. He called the mechanical dredging now in progress “not sustainable.” Currently, the City is using Berry Madden’s property on the West Fork south of Kingwood’s River Grove Park to deposit the mechanical dredging spoils. That’s a long haul for barges on the East Fork.
Next Dredging Steps: Channel to East Fork and East Fork Itself
Contractors must next deepen the channel between the West and East Forks of the San Jacinto to move dredging equipment and spoils back and forth (see below).
From there, dredgers will move slightly north of where Luce Bayou (far right) enters the East Fork and begin dredging the East Fork mouth bar. See large circle above. The map shows that area grew shallower by up to nine feet between 2011 and 2018. Imelda, in September 2019, made it grow even shallower. Note the fresh deposits of sand in the photo below now poking up above the water.
Additional Floodgates for Lake Houston Dam
Chris Mueller of Black & Veatch then discussed the reasons for adding additional floodgates to Lake Houston, preliminary engineering findings, and an implementation schedule.
The primary objective: to increase the outflow capacity of the dam to reduce the risk of future flooding. However, he emphasized that reducing the risk for people upstream of the dam cannot have an adverse impact on people below it. See below.
He emphasized that Lake Houston is, first and foremost, a drinking water reservoir. He also emphasized that the dam is almost seventy years old and near the end of its useful life. Significant safety issues exist in working with such old concrete.
Calculating the Benefit/Cost Ratio of Additional Floodgates
Mueller then explained how FEMA calculates the benefit/cost ratio of additional floodgates.
On the benefit side, it considers: the reduction in water surface level; how many buildings and streets that will prevent from flooding; reduced societal impacts; and reduced impacts to business revenues. These are primarily damage costs avoided.
On the cost side of the equation, FEMA factors in construction costs and annual operation and maintenance costs.
The peak inflow to Lake Houston in a 100-year storm: 286,000 cubic feet per second (CFS), enough to fill the Astrodome in 3 minutes! However, during Harvey, SJRA estimated the peak inflow at 400,000 cfs.
Proposed Alternative Produces 11-Inch Benefit Nearest Dam
A hydrologic and hydraulic analysis conducted by Black & Veatch will help prove up the benefit/cost analysis. The San Jacinto Watershed (including Buffalo Bayou) includes flow from eight counties.
In evaluating about ten alternatives for adding floodgates, Black & Veatch considered both cost and non-cost factors listed below.
The company’s first choice was to install additional gates on the earthen portion of the dam on the east side. But environmental considerations there would have delayed the project by a decade or more.
So they decided to recommend a 1,000 feet of crest gates on the west side of the spillway instead. See example of crest gates in operation below.
Such gates would increase the discharge capacity to 45,000 cfs, more than four times the current capacity of 10,000 cfs. That’s still only about a third of the discharge capacity of the floodgates on Lake Conroe. But according to Martin, that would still be enough to lower the level of the lake 4 feet in 24 hours.
However, before floodgate construction can begin, engineers must evaluate:
Downstream impacts and how to mitigate them
Impact to the stability of the existing concrete dam
Back in the 1950s when the Lake Houston dam was built, engineers did not use rebar. So this will be a delicate operation. Contractors must cut 6 feet into the existing spillway; cap the remaining concrete with a slab; and install the crest gates on top of the slab.
Black & Veatch must also develop an operations protocol for new floodgates that maximizes upstream benefits and limits downstream impacts. Mueller shared this schedule with attendees.
Best-Case Project Timeline Shows Completion in 2024
A best-case scenario shows construction starting at the end of 2022 and finishing before the start of hurricane season in 2024. So, at least three more hurricane seasons to get through before seeing any benefit from additional gates.