Black & Veatch Archives - Reduce Flooding

Harvey’s Seventh Anniversary Update on Lake Houston Floodgates Project

8/28/24 – In its July 10 board meeting, the Coastal Water Authority (CWA) unanimously approved a motion to move forward with final design for 11 new Lake Houston floodgates. Houston will now consider the same motion at its September 11th City Council Meeting. If approved, final engineering design of the gates will commence.

Separately, Houston Mayor John Whitmire appointed former State Representative Dan Huberty to the CWA board. Huberty, an early proponent of the gates project, may be able to help accelerate it moving forward.

The Most Talked About Flood-Mitigation Project

Since Hurricane Harvey seven years ago, I’ve authored 278 posts discussing additional Lake Houston floodgates. From the public’s standpoint, beyond a doubt, the gates are the most eagerly anticipated flood-mitigation measure considered after Harvey.

The most recent post appeared on 5/25 of this year after meeting with members of the Coastal Water Authority, Houston City Council and Houston Public Works at the dam. Not much has changed since then with the exception of some legal formalities.

The Coastal Water Authority Board met on July 10 to vote on an amendment to an Interlocal Agreement (ILA). FEMA and the Texas Division of Emergency Management previously approved the ILA amendment in April. It covers additional engineering services, the cost of final design, and changes from the initial scope of work.

The CWA board approved the ILA amendment unanimously. Final engineering of the new Lake Houston floodgates can now move forward with Black & Veatch as soon as the City approves it.

Minutes of the CWA meeting indicate that, before voting, members discussed potential downstream impacts. The minutes also noted that no significant impacts were found after extensive hydraulic modeling.

Next Up: City Council Vote on 9/11

The amended interlocal agreement will now go before Houston City Council on September 11th for consideration. If approved, final design of the gates could begin soon thereafter.

Need for Lake Houston Floodgates

The Lake Houston Floodgates Project will add 11 new gates to the dam in the earthen embankment to the east of the concrete spillway.

Proposed location for new tainter gates — *Approximate location for 11 new Lake Houston floodgates.*

The new floodgates will increase the current discharge capacity by an additional 80,000 cubic feet per second (CFS). That roughly equals the discharge rate from Lake Conroe during Hurricane Havey – 79,000 CFS.

Currently, Lake Houston floodgates can only release 10,000 CFS. Increasing the discharge rate would enable the City and CWA to:

Coordinate pre-releases between Lakes Conroe and Houston before major storms without swamping the Lake Houston Area.
Discharge as much water from Lake Houston in 2-3 hours as they now do in a day.
Release water when approaching storms are much closer, reducing the risk of wasting water if storms veer away.
Create extra storage capacity in both lakes, reducing flood risk for residents around them.
Reduce flood peaks, helping protect residents between the lakes and downstream from the Lake Houston Dam.

Key to Active Storm Management

All these benefits are especially important because the San Jacinto River Authority (SJRA) has abandoned its seasonal lake-lowering strategy for Lake Conroe. The SJRA has gone to an as-needed lake-lowering strategy called “Active Storm Management” instead. Active storm management requires much more speed and agility than simply having extra storage capacity in the lakes ready and waiting when storm seasons begin.

Lake Houston Area residents got a taste of “Active Storm Management” without the extra gates in May this year. SJRA got surprised by a spring storm and started releasing water at 70,000 CFS. Hundreds of homes flooded downstream in Harris and Montgomery Counties. Thousands more nearly flooded.

The May floods highlighted the risks involved with ad hoc lowering of Lake Conroe. They also underscored the need for more Lake Houston floodgates to handle the extra water that SJRA may send downstream.

2556 days have now elapsed since the storm that motivated the Lake Houston floodgates project – without moving one shovel of dirt. That’s almost twice the time that it took to fight and win World War II – 1349 days.

I’m going to go way out on a limb here and say that there may be some room for improvement in the business processes surrounding flood mitigation.

Whitmire Appoints Huberty to CWA Board

On the good-news front, Mayor John Whitmire has appointed former State Representative Dan Huberty, a Lake Houston Area resident, to the CWA board. Huberty fought years for this project and helped land much of the early funding. He knows the people and already knows the project. He should be able to step in and start making an immediate impact.

Huberty has already had meetings with the CWA staff. He told me, “This will be my highest priority moving forward to meet the needs of Lake Houston Area constituents.”

Posted by Bob Rehak on 8/28/2024

2556 Days since Hurricane Harvey

Recommended Floodgates Could Release at Rate of Lake Conroe During Harvey

City of Houston Mayor Pro Tem Dave Martin’s office has supplied ReduceFlooding.com with the Black & Veatch Engineering report on the recommended alternative for adding floodgates to Lake Houston. One key finding immediately jumped out at me that wasn’t in Martin’s press release last week. The recommended gates would have a release capacity that virtually equals the highest release rate of Lake Conroe during Hurricane Harvey.

The Lake Conroe release rate during Harvey maxed out at 79,000 cubic feet per second (CFS).

The eleven tainter gates recommended by Black & Veatch would have a release rate of 78,700 CFS.

New Possibilities, More Certainty

That opens up a world of possibilities. For instance, the City could wait to start releasing water until it knew water was coming downstream from Harvey.

Said Martin, “Once constructed, we can release with a moments notice which gives us great opportunities to coordinate release protocols with the SJRA!!”

Previously, Public Works has been reluctant to release water in advance of a storm because the release rate of the existing gates is so small. They have to start lowering the lake so far in advance of storms that a storm can veer away before it gets here. If it does, that means water has been wasted.

The recommended floodgates should provide much more certainty for operators and avoid waste.

Key Elements of Recommendation

site of proposed gates for Lake Houston on east side of dam — *Gates would be placed at the original channel for the San Jacinto River seen in foreground.*

Other key elements of the recommendation include:

Locating the floodgates in the earthen eastern portion of the dam near the old channel of the San Jacinto River.
Creating baffles and a dissipation basin downstream from the new gates to break up the flow and reduce water velocity
“Outdenting” the gates (i.e., building them in front of the current dam)
A bridge between the two parts of the earthen dam
Using tainter gates, the same type used at Lake Conroe.
A 3.5 year construction schedule.

The last point means that if construction started in January, the earliest completion date would be mid-2026.

However, given the need to line up additional funding in the state legislature, 2027 is a more realistic date.

For a complete discussion of the project history, constraints, alternatives, recommended options, construction drawings, rationales, and costs, see the entire 28-page Black and Veatch Report by Chris Mueller, PhD, P.E.

Posted by Bob Rehak on 12/14/22 based on the Black & Veatch Report

1933 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

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

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

May 2021 Gate Project Update for Lake Houston Dam

In its March 10th board meeting, the Coastal Water Authority (CWA) accepted the recommendation of a preliminary engineering report to add one thousand feet of crest gates to the uncontrolled spillway portion the Lake Houston Dam. The additional release capacity would let operators shed water faster before, during or after major storms to reduce the risk of flooding.

At the March meeting, directors also approved $4.4 million to begin Phase II of the project. Phase II calls for Black & Veatch to proceed to final engineering of the gates and a coffer dam to protect the work area during construction.

Read the minutes of the March board meeting here. The discussion of the gates starts on page 4 under Item B.

This morning, at its May board meeting, directors received an update on the progress of Phase II work to date and plans for the remainder of the project.

Start of Phase II Engineering Approved in March

In the March meeting, CWA approved funds to begin Phase 2 of the engineering which includes the final design of the selected alternative by Black & Veatch. The selected alternative was “crest gates” constructed on the uncontrolled spillway portion of the dam on its west side. (See below.)

Looking NE at the Spillway of the Lake Houston Dam is in foreground. One thousand feet (about a third) of this spillway will be replaced with crest gates. Gates will be placed at the end closest to the camera position in the image above.

Dam operators can raise or lower crest gates from a bottom hinge, much like the lid on a piano. When in the up position, gates hold water back. When lowered, they release water.

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.

Scope of Phase II Design Work

Also in March, CWA and Black & Veatch completed negotiation of the scope and fee for the final design. The key deliverables during Phase II will include:

Plans to modify the spillway to support the 1,000 linear feet of crest gates (in five 200-foot long sections)
Design of the cofferdam system to protect the work areas during construction
Preparation of a new gate operations plan for CWA Lake Houston Dam operators.

Director Douglas Walker moved to authorize the Executive Director to issue a contract amendment with Black & Veatch Inc. in the amount of $4,465,727.00 for “Phase 2 – Final Design of the Lake Houston Dam Spillway Improvement Project.” Director Giti Zarinkelk seconded the motion. The Motion carried unanimously.

May Update

In the May board meeting this morning, directors received an update on Phase II work to date and plans.

In April, the design team held a number of workshops and coordination meetings.

Black & Veatch also completed three weeks of field surveying of the existing spillway; that’s why CWA temporarily lowered Lake Houston during that period.

In other news, for next steps CWA will:

Submit the permit application to the US Army Corps of Engineers by the end of May.
Support City of Houston in a public outreach meeting scheduled for June 17. The public outreach meeting will coincide with the public comment period for the permit application. CWA expects permitting to take nine months, i.e., through March of 2022.
Complete final design by the end of September 2022.

*Screen capture from portion of CWA Board meeting today shows status of Phase II Design work on the dam.*

Next Steps

Does all this mean construction is assured? No. The Army Corps could reject the permit or FEMA could find some fault with the plans. But at least it shows progress. If all plans and permits are approved, construction dollars have already been committed by FEMA. Originally, construction was supposed to have been completed within three years from April 8, 2020. That now looks unlikely unless the City can obtain a deadline extension from FEMA..

Posted by Bob Rehak on 5/12/2021

1352 Days after Hurricane Harvey

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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