Lake Houston Spillway Improvement Project Archives

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 1/15^th 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

Reminder: Floodgate Meeting at Kingwood Community Center on Thursday, July 8

On Thursday, July 8, Mayor Pro Tem Dave Martin will host a pubic meeting to discuss the status of adding more floodgates to the Lake Houston Dam. Preliminary engineering finished earlier this year. In March, the Coastal Water Authority board approved Black & Veatch to begin final engineering.

Need for More Gates

The Lake Houston Area Task Force identified more and higher capacity floodgates as a key element in the area’s flood-mitigation strategy. The current gates have one-fifteenth the capacity of those at the Lake Conroe Dam. That makes it difficult to shed water from Lake Houston before people flood if Lake Conroe opens its gates as it did during Harvey.

During Harvey, Conroe released 79,000 cubic feet per second. That was one third of all the water coming down the West Fork between Humble and Kingwood. All by itself, that 79,000 CFS would have been the ninth largest flood in West Fork history. And that made the difference between flooding and not flooding for thousands of homes and businesses near the lake.

During Harvey, the peak flow over the spillway was five times the average flow over Niagra Falls. A wall of water 11 feet tall cascaded over the spillway above. Enough to fill NRG stadium in 3.5 minutes.

*Lake Houston Dam During Harvey*. *The proposed crest gates would go in the far upper left of the spillway.*

Floodgate Meeting Details

See the meeting details below.

Thursday, July 8, 2021
At the Kingwood Community Center (4102 Rustic Woods)
Doors Open 5:30 PM
Dredging Update Starts 5:45 PM
Gate Update Starts at 6 PM

Chief Recovery Officer, Stephen Costello, will provide a very brief update on Lake Houston Dredging operations at 5:45 p.m. before the Spillway Improvement Project program begins.

The program to discuss the Lake Houston Dam Spillway Improvement Project will start at 6:00 p.m. and conclude at 7:45 p.m. But don’t worry about sitting through a 2 hour meeting.

The main presentation by Black & Veatch, the project engineers, will be followed by a short Q&A session. The meeting will then transition into breakout sessions. Breakout tables will let residents engage with project management staff and engineers in small groups to ask more detailed questions.

Project Benefits

The Lake Houston Dam Spillway project will increase the outflow capacity of the Lake Houston Dam. The project proposes installing new crest gates in the existing uncontrolled spillway. This will allow for a rapid decrease of water levels in Lake Houston in advance of storm events to prevent or reduce upstream flooding. Engineers estimate the recommended alternative could help about 35,000 residents and 5,000 structures. It’s important for people to understand that if they flooded from streams or channels far from the lake during Harvey, this may not help them.

Funding

A Federal Emergency Management Agency (FEMA) Hazard Mitigation Grant Program provides $4.3 million for engineering and positions the city to receive another $42.7 million for construction.

Posted by Bob Rehak on 7/6/2021 based on info provided by Dave Martin’s Office

1407 Days since Hurricane Harvey

October 2020 Gate Update

On Friday, October 16, 2020, stakeholders in the Lake Houston Spillway Improvement Project met at the dam to review gate alternatives and progress on the project. The main item of interest: a review of options still under consideration to increase the outflow during major storms, such as Harvey.

History of Project

Shortly after Harvey, representatives from the Lake Houston Area identified “increasing outflow” as one of the main strategies to reduce flooding. Harris County Flood Control District even conducted a pilot study. Flood Control included $20 million for the project in the 2018 bond fund (CI-028). With matching funds identified, grants were then written.

FEMA approved the project. And in April of this year, the clock started ticking on the first of two phases.

Phase One Includes…

Phase One includes preliminary engineering and environmental permitting. It should take 18 months and is on schedule at this point. A key deliverable for phase one is verification of the benefit/cost ratio. But, of course, to determine that, you need to know the cost.

Alternatives Still Under Consideration

FEMA allotted 18 months for Phase 1. We’re six months into that. Work to date has focused on determining the optimal alternative. Five remain:

Expanding the existing spillway by adding new tainter gates
Adding a new gated spillway within the east embankment
Creating a new uncontrolled spillway within the east embankment
Building crest gates within the east embankment
Developing crest gates within the existing spillway

Tainter gates lift up from a radial arm. The tainter gates on Lake Conroe have 15X more release capacity than the lift gates on Lake Houston.

Crest gates flop down from a bottom hinge.

*Above: the current conditions at the Lake Houston Dam.* *Looking slightly upstream. East is on the right.*

The east embankment is a solid earthen area 2800 feet long east of the spillway and existing gates. Water cannot get over it in a storm. By adding various structures in this area, engineers could widen the current spillway capacity, allowing release of more stormwater.

One main benefit: additional gates would reduce uncertainty associated with pre-releases. Operators could wait longer until they were certain an approaching storm would not veer away at the last minute. That would avoid wasting water.

*Reverse angle.* *Note the difference in height between the east embankment (left) and the spillway (right).* *Looking downstream toward Galveston Bay.*

*Looking west toward Beltway 8. This shows the major segments of the dam.*

Benefit/Cost Ratio Must Be > 1.0

The lake-level reduction benefits of these gate alternatives during major floods range up to roughly 8x. The costs also vary by roughly 4x. Those are order-of-magnitude, back-of-the-envelope estimates and far from final. Much hard work remains to develop tighter costs and tighter estimates of flood-level reductions. The latter will determine flood-prevention savings in a storm. And the benefits divided by the costs will determine the benefit/cost ratio.

In FEMA’s eyes, the benefit/cost ratio must exceed 1.0 to justify the project. Said another way, it must produce more benefits than it costs.

FEMA allotted 18 months for phase 1. We’re six months into that phase with a year left. Project partners expect results of the alternatives analysis before the end of the year.

Benefit/Cost Calculation

Given the ballpark costs of some of these gate alternatives, we will need very tight estimates of the benefits.

Potential Benefits include:

Upstream flood risk reduction
Reduced maintenance (debris management) for CWA
Improved Water Quality (post storm)

Potential Impacts include:

Increased scour and erosion potential to wetlands downstream
Increased water surface elevations to structures downstream

Calculating Benefits

Benefit Cost Ratio = (Net Present Value of Benefits)/(Project Costs)

Project Costs = (Capital costs) + (Net Present Value of Operations and Maintenance Costs)

Major Tasks Remaining in Phase 1

Barring surprises, the preliminary engineering report is due in February 2021 and environmental permitting should be complete by the Fall of 2021. Other tasks that must be completed by then include:

Hydrologic modeling of flows into and out of Lake Houston using the latest Atlas 14 data
Hydraulic modeling of Lake Houston, its Dam, and the San Jacinto River downstream of the dam to Galveston Bay
Calibration of models to historic storms
Examination of upstream benefits to residents/businesses removed from flood impacts
Examination of downstream impacts associated with additional flow release scenarios

It’s important to understand that not everyone who flooded in the Lake Houston Area did so because of the lake level. Some on the periphery of the flood flooded because water backed up in streams leading to the lake. If you got two feet of water in your living room, it doesn’t automatically mean a lake level reduction of two feet would eliminate your flooding by itself.

*Congressman Dan Crenshaw (left) reviews the project with team members at the Lake Houston Dam and listens to their needs.*

Phase 2 Still Not Certain

Assuming all goes well in the planning, accounting, and conceptual validation, FEMA will make a go/no go decision on construction at the end of next year or the beginning of the following year. Construction should take another 18 months.

Credits

Funding for this project comes from FEMA, Texas Division of Emergency Management, City of Houston and Harris County Flood Control. Other stakeholders include the Coastal Water Authority, Harris County, Fort Bend County, Baytown, Deer Park, and other communities adjacent to Lake Houston.

Posted by Bob Rehak on 10/17/2020

1145 Days since Hurricane Harvey and 394 since Imelda

Preliminary Engineering Starts for Adding More Gates to Lake Houston Dam

In early April, the Coastal Water Authority (CWA) quietly finalized the scope of work for engineers working on adding more gates to the Lake Houston Dam. Engineering firm Black & Veatch’s contract was approved. And their work has now begun. Here’s what it involves.

*Looking upstream at the Lake Houston Dam. Photo taken 11/4/2019.*

Background: Why More Gates?

After Hurricane Harvey, a pilot study by HCFCD and Freese & Nichols showed additional gates could have helped lower floodwaters.

The current gates on Lake Houston’s dam have one fifteenth the discharge capacity of Lake Conroe’s – 10,000 cfs vs. 150,000 cfs.

Additional gates could help synchronize the release rates of the two dams and thus reduce flood risk. More/bigger gates could lower the Lake Houston faster in advance of a storm and add width to the spillway during a storm. Both help reduce flooding.

Avoiding Unnecessary Releases

Currently, it takes several days to lower Lake Houston enough to significantly reduce flood risk. During that time, approaching storms can veer away or dissipate. So a conservation angle exists here, too. More gates release water faster. That lets CWA wait until weather-forecast certainty is higher before lowering the lake. And that, in turn, helps avoid unnecessary discharges and conserve water.

18-Month Project Starting from April 8th

The addition of gates is a three-year project broken into two 18-month phases.

Phase 1 involves preliminary design of conceptual alternatives, selecting the “best” based on criteria described below, and permitting.

The clock for Phase 1 started ticking on April 8, 2020, the day Black and Veatch’s contract was approved. Phase 1 should conclude in September 2021.

Phase 2 involves final design and construction. Assuming all goes well, we could have more discharge capacity at the Lake Houston dam by March 2023 at the earliest. However, there will be an evaluation period between the two phases that could push the completion date out further. Also…

Phase 2 Depends on Outcome of Phase 1

One objective of Phase 1 is to prove up the concept, the budget, and the benefit/cost ratio.

Proceeding to construction in Phase 2 will depend on the outcome of Phase 1. In Phase 1, engineers will examine several possible designs to determine the most effective alternative. They will consider flood reduction benefits, downstream impacts, cost, environmental impact, constructibility and more.

Then FEMA will evaluate the benefit/cost ratio of the winning design to ensure it meets or beats initial projections in the grant request.

If it does, FEMA will release money for Phase 2, the final design and construction.
If it doesn’t, the whole project could die.

FEMA does not guarantee Phase 2 funding at this time.

What Happens Now?

The scope of work document reveals who will do what in the next 18 months on the Lake Houston Spillway Improvement Project (LHSIP).

Objective: To relieve upstream flooding by increased discharge capacity that supports pre-releases.

Modifications could include (but are not limited to):

Additional crest gates on or adjacent to the existing dam or…
New, as-yet-unspecified hydraulic structures that provide for releases elsewhere on the embankment

Unlike tainter gates which swing up from a radial arm, crest gates swing down from a bottom hinge.

The project will consider both upstream benefits and downstream impacts.

*Looking downstream over the Lake Houston Dam in foreground gives you some idea of the courage that it requires to live or work below a dam.*

After defining alternatives and constraints, the contractor, Black & Veatch, will analyze the alternatives to quantify and compare costs and benefits of each configuration.

Five Major Tasks in Phase 1

Preliminary engineering involves five major tasks:

Management plans
Hydrology and Hydraulic Modelling
Permitting
Field Investigation
Development of alternative concepts

Let’s look at each.

Management Plans

Black & Veatch will begin Phase 1 by developing project-, quality-, and risk-management plans.

H&H Studies

Hydrology and hydraulics (H&H) studies will evaluate the ability of the various concepts to reduce upstream flooding and downstream impacts. Black & Veatch will develop H&H models that combine both the San Jacinto River and Buffalo Bayou basins to evaluate downstream impacts of any dam.

The combined model will extend all the way to Galveston Bay and evaluate design alternatives for up to nine events:

2-, 10-, 50-, 100-, and 500-year storms
Extreme historic events (e.g. Harvey, Ike or Memorial Day), including at least one with storm-surge effects
A hypothetical Probable Maximum Precipitation event.

The process includes collecting, reviewing, adjusting and validating existing models before performing simulations.

Permitting Gauntlet

To save time, permitting will begin concurrently with design. The permitting schedule is aggressive and may spill over into Phase 2 as details are refined. Permitting includes (but is not limited to) coordination with federal, state and local agencies for:

Environmental Assessment
Environmental Impact Statement
Wetland delineations
Threatened and endangered (T&E) habitat assessment
T&E species-specific surveys
Migratory Bird Treaty Act (MBTA) surveys
Freshwater Mussel survey
Stormwater pollution prevention
Clean Water Act
Flood Plain Construction

The environmental team will also consider:

Topography and Soils Construction Impacts
Land Use
Indirect and Cumulative Impacts
Geology, Hydrology and Drainage
Sediment Quality
Vegetation
Air Quality
Invasive Species
Coastal Zone Management Wildlife and Endangered Species
Essential Fish Habitat
Existing Facilities and Utilities
Noise Quality
Socioeconomics
Traffic and Circulation
Waters of the U.S., including Wetlands
Environmental Justice
Cultural Resources (historical and archaeological)
Recreation
Floodplains
Visual/ Aesthetic Appeal
Water Quality
Hazardous Materials

Field Investigations

Black & Veatch will also conduct site surveys and a geotechnical investigation, complete with borings, to evaluate soil conditions, depth-to-water, permeability, and seepage control.

A bathymetry team will measure water depth and develop contour maps for an area that extends 500 feet upstream from the dam.

Preliminary Engineering/Conceptual Design

Finally, preliminary engineering will develop conceptual layouts and site plans for several alternatives.

This exercise will also evaluate areas of impact, site access and utilities, staging and borrow areas, dewatering extents, existing structure tie-in, general facilities layout, and downstream channel alignment.

These site plans will be used for costing and evaluating the feasibility for each alternative.

Criteria for Choosing Best Alternatives

The engineers will also develop an evaluation matrix that includes, but is not limited to:

Ability to meet project goals
Environmental clearance
Construction costs, including any environmental mitigation
Long-term operation and maintenance costs
Benefit/cost analysis
Risks in design, construction, and operation.

From all the feasible options, engineers will then chose the three best based on:

Cost
Upstream impact
Downstream impact
Environmental impact
Permitting requirements
Constructibility

Timing on Phase 2

Assuming we get to Phase 2, the second 18 months may not start immediately. FEMA will need time to evaluate Phase 1 results. And the CWA will need to develop bid specs, bid the job, select a winner, and develop a contract with a scope of work, just as they did for Phase 1. That could talk several months and push completion well into 2023.

For More Information

All that, just to figure out what to do! To read the full 27-page Scope of Work, click here. I will also post this document for future reference in the Reports page of this web site under a new tab titled Lake Houston Dam Spillway Improvement Project.

Posted by Bob Rehak on 5/1/2020

976 Days after Hurricane Harvey

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