Tag Archive for: gates

City Gets Favorable Ruling on BCR for Lake Houston Gates Project

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.

New gates would let the City rapidly lower the water level of Lake Houston in advance of a storm to prevent or reduce upstream flooding.

gates for Lake Houston and Conroe
Lake Houston (l) and Lake Conroe gates (r). Conroe release capacity is 15X greater.

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.

Hurdle Removed: Project Now Federally Compliant

Earlier this summer, Martin announced challenges related to the Lake Houston Spillway Dam Improvement Project. The City needed to secure a benefit to cost ratio (BCR) between .75 and 1 and had examined multiple alternatives to find a favorable balance between costs and benefits.

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.

New gates would be added to the earthen portion of dam in foreground, not spillway at far end as originally planned.

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.

The new gates would likely align with the original course of the San Jacinto River, the channel on the left.

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

Harvey: A 5-Year Flood-Mitigation Report Card

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

1) Dredging

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.

west fork mouth bar before dredging
West Fork mouth bar after Harvey and before dredging. Now gone, but not forgotten.

State Representative Dan Huberty secured additional funding during the last legislature to continue maintenance dredging. That includes clearing drainage canal outfalls into the lake, such as the entrance to Rogers Gully. The dredging operation is now moving around the lake, according to the City’s District E office.

2) Adding Floodgates

Engineers keep looking for a cost-effective alternative. They first identified 11 options in a preliminary review. They then studied the most promising – spillway crest gates – in more detail. Now they’re looking at tainter gates in the earthen portion of the dam. In case the Benefit/Cost Ratio still doesn’t meet FEMA requirements for moving forward with construction, Houston Mayor Pro Tem Dave Martin is also exploring additional funding sources. But so far, no construction has started on additional gates. Martin hopes to reveal a recommendation in September.

Lake Houston Dam, area for new gates
Potential location for new tainter gates east of the spillway portion of the dam (out of frame to the right.
3) Upstream Detention

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.

4) “Benching”

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.

5) West Fork Channel Widening

Finally, the Regional Flood Planning Group recommended widening 5.7 miles of the West Fork to create more conveyance. But again, at this point it’s just a recommendation in a draft plan.

San Jacinto River Authority

6) SJRA Board Composition

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.

Coordination between Lake Conroe and Lake Houston has already improved. You can see it in the SJRA’s new dashboard. It shows releases requested by the City of Houston to lower Lake Conroe.

10) Sediment Reduction

Huge sediment buildups in the West and East Forks of the San Jacinto clearly contributed to flooding. The Army Corps stated that the West Fork was 90% blocked near River Grove Park. To reduce future dredging costs, SJRA also studied the use of sediment traps. SJRA may implement a pilot study soon on the West Fork near the Hallett mine.

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.

Sand bar blocking West Fork after Harvey. The Corps has since removed it.

Federal Funding

It’s hard to get good grades on your flood mitigation report card without funding.

11-18) Appropriations

In March this year, Congressman Dan Crenshaw secured appropriations that should help advance projects in the San Jacinto Basin. They included:

  • $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.

Bens Branch
Bens Branch near Kingwood High School after sediment removal.
20) Woodridge Stormwater Detention Basin Expansion

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.

22) Buyouts

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.

forest cove townhome demolition
Completion of demolition of one of the last Forest Cove Townhome Complexes in July 2022.
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.

City excavation crews working to remove sediment on Bens Branch under Kingwood Drive
Excavation of Bens Branch under Kingwood Drive by City crews.
25) Storm Sewer Inspections, Clean-Out, Repairs

The City has inspected storm sewers throughout Kingwood and cleaned those that had become clogged. It also repaired sinkholes and outfalls that had become damaged.

Lone Star Groundwater Conservation District

The lowest score on the flood-mitigation report card probably goes to LSGCD.

26) Subsidence

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

All Parties Still Focused on Finding Solution for Adding Flood Gates to Lake Houston Dam

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.

Looking south over eastern portion of Lake Houston Dam at area under consideration for five new tainter gates. The spillway is out of frame to the right. Picture taken on 7/22/22.

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.

Difficulty of Finding Best Alternative

The age of the Lake Houston Spillway, built in 1953, has proven to be a bigger obstacle than expected. Engineers initially proposed six different alternatives for adding different types of gates in different locations, with variations on several.

As engineers started precisely calculating costs and benefits of preferred approaches, they weighed those against environmental impacts, construction challenges, safety risks, and available budget.

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. 

The comprehensive, final BCR analysis for the embankment alternative should be completed by the end of September 2022. The preliminary engineering report suggested the 1A alternative could reduce flood heights by half a foot for a cost of $47.3 million with a BCR of .89. So initially, on the surface, this appears feasible.

Martin Widens Search for Funding

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

CWA Exploring Alternate Plan for Adding Lake Houston Dam Gates

Coastal Water Authority (CWA) recently posted minutes from its May 11th board meeting that reveal a possible new direction for adding more flood gates to the Lake Houston Dam. After months of discussing various crest gate alternatives to increase the release capacity of the dam, engineers will now focus on examining two tainter gate alternatives. One would add six tainter gates, the other twelve.

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.

Looking ENE at Lake Houston Dam. Black and Veatch is now exploring adding tainter gates to the earthen portion of the dam in the 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.

7/4/22 Screen Capture from District E Website.

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.

Based on costs of the Addicks and Barker dam modifications by the Army Corps, some remain skeptical of any alternative for adding gates to the dam. The reason: budget and the Benefit/Cost Ratio.

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

Martin Updates Community on Additional Gates for Lake Houston

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.

Martin shared a timetable that shows construction beginning in November. However, FEMA must approve the benefit/cost ratio before they release construction funds.

Schedule for adding gates to Lake Houston, first shown in July 2021. Also shown on 4/19/2022. Martin emphasized the schedule has not changed, but could.

Background of Project

At the peak of Harvey, 425,000 cubic feet per second (CFS) went over the dam’s spillway. That’s five times the average flow of Niagra Falls. Floodwater backed up so far that it flooded thousands of homes and businesses. It also killed 13 people in the Lake Houston Area, 12 of them in one retirement center.

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.

We should know within a few months whether Black & Veatch, the engineering company leading the project, has succeeded in designing additional gates within the budget that meet all other objectives.

Staying on the schedule above will be ambitious. FEMA must approve the BCR before releasing money for construction.

Posted by Bob Rehak on April 21, 2022

1696 Days since Hurricane Harvey

City of Houston Re-evaluating Benefit-Cost Ratio on Lake Houston Gates Project Alternatives

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.

gates for Lake Houston and Conroe
Lake Houston and Lake Conroe gates side by side. Lake Conroe’s gates (right) can release water 15 times faster.

CWA Board Minutes Give High-Level Overview of Concerns, Status

Screen capture from CWA Feb. 9, 2022, minutes approved and posted in March.

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.

Screen capture from CWA January 12, 2022, board minutes.

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.

Martin Says “September-ish” for BCR Report

City of Houston Mayor Pro Tem Dave Martin said he hopes to have the BRC report in a “September-ish” time frame. I asked him whether the Community Impact report was accurate when it said the project had been scaled back to 500 feet of crest gates as opposed to the original 1500 feet. He said “no,” and that the engineers were looking at multiple options. He also said “1.0 is incorrect as well,” but did not elaborate.

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.

As a temporary strategy, the City and SJRA agreed on a temporary, seasonal lake lowering strategy to create more capacity in Lake Conroe until more gates could be added to Lake Houston. But the strategy met with significant pushback from Lake Conroe residents and lawmakers. The Lake Conroe Association even took the SJRA to court to stop it.

At various times, City representatives have discussed 10 and 6 additional tainter gates, plus 1500-, 1200-, and 1000-feet of crest gates. Engineers and City officials have repeatedly emphasized the need to balance costs, downstream impacts, and flood risk reduction.

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.

But don’t forget another element of uncertainty: Atlas 14. FEMA has not yet approved the new flood maps based on the higher rainfall totals. Those could put more people in or closer to the floodplains. Below is the timetable for flood map updates currently posted on the MAAPnext website.

Timetable for flood map updates from MAAPnext.

Posted by Bob Rehak on 4/4/22 and updated on 4/5/22 with MAAPnext timetable

1679 Days since Hurricane Harvey

Top Stories of 2021 in Review

Below are my personal picks for the top flood-mitigation stories of 2021.

The Fight for Funding

In 2019, Commissioners Court established “equity” guidelines that prioritized projects in Low-to-Moderate Income watersheds. Then this year:

Still no word from HUD on a possible direct allocation of $750 million. We may hear in January.

To help you follow this story, I make quarterly FOIA requests for Harris County Flood Control District spending and post the analyses on a dedicated funding page.

Sand-Mining Best Management Practices

Activists led by the Lake Houston Area Flood Prevention Initiative and the Bayou Land Conservancy petitioned the Texas Commission on Environmental Quality (TCEQ) to establish best management practices for sand mines in the San Jacinto watershed. We didn’t get everything we wanted, but we got a vast improvement over what we had. And the new BMPs may help reduce erosion that contributes to future floods in this area.

West Fork Sand Mine illustrates need for vegetative controls to reduce erosion.

Relentless Development

Fueled by low interest rates and flight from city crowds during Covid, suburban and rural development surged in 2021. Flood-mitigation felt like an afterthought in many developments. We saw that with Colony Ridge in Liberty County. Colony Ridge clearcut wetlands, paved over floodplains and ignored county regs designed to reduce erosion.

In the Kingwood Area, the Laurel Springs RV resort took advantage of a grandfathering clause in permitting to build a detention pond one-half the size of current requirements. These represent just two examples of many.

The Laurel Springs RV Resort got its detention pond approved one day before stiffer regs went into effect.

After Harvey, we saw how such practices made flooding worse. How soon we forget!

Houston Housing and Community Development Meltdown

Houston’s Housing and Community Development Department, which was responsible for distributing more than a billion dollars in Harvey disaster relief funds, came unglued again this year. Last year, it sued the Texas General Land Office to keep money it couldn’t give away. This year, the Department’s Director publicly denounced the Mayor of Houston for trying to steer multi-family housing subsidies to the Mayor’s former law partner. The Mayor claimed ignorance of the partner’s involvement and announced a City Attorney investigation which never materialized.

Meanwhile, flood victims were victimized a second time. Bureaucratic bungling denied aid to people who deserved it.

World War II And Lake Houston Gates

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.

Lawsuits

The Lake Conroe Association had its lawsuit against the SJRA thrown out of court…with prejudice. The LCA hoped to prohibit the SJRA’s policy of seasonal lake lowering, which was designed to help protect the Lake Houston Area until other flood mitigation efforts could be put in place.

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.”

Various lawsuits against the SJRA for flooding during Harvey are still working their way through the legal system.

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.

Woodridge Village

Harris County Flood Control District purchased Woodridge Village from Perry Homes in February this year and hired a contractor to begin doubling the current floodwater-detention capacity on the site. When complete, the additional capacity will help protect homes in Elm Grove, North Kingwood Forest and downstream along Taylor Gully.

Expansion of Dredging

After three and a half years of dredging in the San Jacinto West Fork, dredging has now moved to the East Fork. State Representative Dan Huberty secured $50 million earlier this year to extend the dredging program to other inlets around Lake Houston in the future.

East Fork Dredging. Photographed in early December between Huffman and Royal Shores in Kingwood. Looking south toward Lake Houston.

Bens Branch and Taylor Gully Cleanouts

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.

Final phase of Bens Branch maintenance between Kingwood Drive and Rocky Woods. Note Kingwood High School in upper right.

Subsidence

Years of fighting over subsidence between the Lone Star Groundwater Conservation District and Groundwater Management Area 14 came to a head earlier this year. LSGCD fought any mention of subsidence in Desired Future Conditions (DFCs) for Montgomery County. GMA-14 wanted to include it, but finally recommended allowing each groundwater conservation district to make a subsidence measure optional. Unlimited groundwater pumping in southern Montgomery County could tilt Lake Houston toward homes at the northern end of the lake. That’s because subsidence would be greater there than at the Lake Houston Dam by TWO FEET.

GMA-14 will take a final vote on January 5 on the final DFCs. You still have time to protest.

Posted by Bob Rehak on 12/31/2021

1585 Days since Hurricane Harvey

Public Comment Period on Gates Closes Monday

The Army Corps’ public comment period for adding additional gates to Lake Houston will close on Monday, 8/23/2021. The Army Corps first posted the public notice on 7/22/21.

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.

Cross section of proposed improvements to dam.

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:

Project Description

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.

Please Support

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

 

SJRA Board Accepts Grant Funding for Three Studies

Yesterday, the San Jacinto River Authority (SJRA) Board accepted three grants from the Texas Water Development Board (TWDB) to conduct studies for various projects. This was expected. The SJRA had applied for each of the grants about a year ago. The vote, however, now obligates the SJRA. It’s somewhat like applying for a loan and then signing the contract after it is approved.

Three Studies Now Teed Up

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
Lake Houston Gates can discharge only 10,000 CFS (left), while Lake Conroe’s can discharge 150,000 CFS. To help provide better watershed management, the Coastal Water Authority is studying the addition of 1000 crest gates to Lake Houston, necessitating the joint reservoir operations study.

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.

For instance, we just started final engineering on the Lake Houston Spillway Improvement Project. Best-case projections show completion of the project in mid 2024 – 7 years after Harvey.

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

Floodgate, Dredging Plans Unveiled

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.

To see both presentations, click here. Or see the summaries below.

Dredging: About Half Done

In late 2019, the Army Corps finished hydraulic dredging in the area south of the West Fork mouth bar. Then in early 2020, the City of Houston began mechanical dredging to extend the effort. In terms of the estimated dollars designated for dredging, the effort is about halfway done.

The first four rows on this chart are done or almost done. They total $114 million out of a projected total of $222 million.

The last two rows on the chart above are estimates because they depend on bids currently in progress and a long-range plan not yet complete. The need for a long-term plan and maintenance dredging were identified early on by the Army Corps so that any benefits of dredging were not immediately wiped out by future sedimentation.

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.

The numbered dots in the photo above show channels south of the East and West Forks draining into Lake Houston where sediment can also build up.

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).

Current location of dredging is near yellow dot.

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.

Growth of East Fork Mouth Bar after Imelda in September 2019. Photo taken in November 2019.

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.

To win project approval, the City must show that the benefits of additional floodgates exceed the costs in a 100-year storm, similar to Imelda. Such a storm elevates the lake 10 feet.

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.

An air bladder near a bottom hinge raises or lowers the floodgates to let water in/out

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

Schedule as of 7/8/2021. Detailed engineering could take another year.

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.

Posted by Bob Rehak on 7/9/2021

1410 Days since Hurricane Harvey