Tag Archive for: Stephen Costello

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.


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

Above-Water Portion of Mouth Bar Could Be Gone by Christmas

At the current rate that crews are removing sand from the West Fork San Jacinto Mouth Bar, the remainder of the above-water portion of this once-behemoth sand bar could be gone by Christmas. See the two pictures below. The first taken after Harvey and the second taken today.

These two shots show the West Fork mouth bar two weeks after Harvey and todaymore than three years later.

Much Yet to Dredge

Of course, even when the above water portion of the Mouth Bar is removed, that will still leave a huge portion below the surface. However, all progress is welcome.

Like an iceberg, most of a sand bar exists below the waterline. Photo taken 10/26/2020. I can’t say with certainty that this is submerged sand, or water stirred up by dredging. It seems too uniform to be the latter. Compare the picture below looking toward the WLHP bridge from a slightly different position and note how irregular the stirred-up sediment looks. Also note that the picture above was taken upstream from the current dredging.

At the start of October, the above-water (sub-aerial) extent of the mouth bar was down to the width of one excavator. Two excavators are now working toward the middle from each end. See below.

Looking WNW toward the West Lake Houston Parkway Bridge and Kings Harbor. Taken 10/26/2020.
From the wet mark on this excavator’s arm, it looks as though they are excavating up to 10 feet below the waterline. The 10-foot estimate closely agrees with the profile chart below. Taken 10/26/2020.

Like an Iceberg, Most of a Sand Bar Exists Below Water

That’s significant progress given what we started with. But much sand remains below the surface.

Tim Garfield and RD Kissling, two leading geologists now retired from one of the world’s largest oil companies, mapped the depth of the river using sonar and depth poles. They found an underwater plateau exists in this region of the river. See chart below.

The blue line represents the water surface. The gold line indicates the deepest part of the channel as you move downstream from the WLHP bridge to the FM1960 bridge. Numbers on the left scale indicate water depth. Numbers on the bottom scale indicate distance in feet downstream from the WLHP bridge.

Plans for Next Phase Still Not Revealed

FEMA has approved dredging another million cubic yards. And Dan Huberty’s amendment to SB500 in the last legislature dedicated $30 million for dredging the West Fork Mouth Bar. The City is drawing up plans, but they have not been announced yet. The last time I talked to Stephen Costello about this, he said the City was leaning toward dredging a channel somewhere south of the mouth bar. But many details remained to be worked out, such as:

  • Method of dredging (hydraulic vs. mechanical)
  • Exact location
  • Channel width
  • Finding qualified contractors
  • Bidding
  • Determining a suitable placement area, etc.

More news when its available.

Posted by Bob Rehak on 10/26/2020

1154 Days after Hurricane Harvey

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.

Tetra Tech Study Provides Clues To Possible Mouth Bar Dredging Strategies

FEMA has agreed to dredge another million cubic yards from the the area near the San Jacinto West Fork Mouth Bar. A report produced for the City of Houston by Tetra Tech helped convince FEMA. The report relied on sonar, LIDAR, and core sample data to estimate the total volume of sand deposited by Hurricane Harvey in that area: approximately 1.4 million cubic yards.

Need for Ruthless Efficiency

While another million cubic yards may sound like a lot, the area is huge. Dredging the whole 4.3 million square yard area would add only about 8 inches of water depth and leave an underwater mesa between the West Fork and the Lake. According to local geologists Tim Garfield and RD Kissling, who have studied the problem extensively, that would create a sediment trap that accelerates accumulation of sand from future storms.

So, what to do?

Three Strategies Discussed to Date

Those close to the project have discussed several strategies to date.

  • The Corps’ initial strategy: Dredge upstream from the mouth bar. They said 1D modeling showed that would accelerate water flowing into mouth bar and give it the velocity needed to push sand from the mouth bar farther out into the lake.
  • Another strategy: dredge downstream from the mouth bar and let the river push the mouth bar into the dredged area.
  • A third strategy: reconnect the river and the lake with a narrow channel that accelerated the flow of water and carried suspended sediment out into the broader lake south of the 1960 bridge.

2019 Tetra Tech Report

Stephen Costello, the City’s flood czar, says that new survey and modeling work has yet to be completed. That will ultimately determine where new dredging happens. However, he also added that consulting Tetra Tech’s exhibits would help provide clues as to where dredging might be most effective, based on knowledge accumulated to date.

The first chart in Appendix A showed the coring locations and transects (survey lines) of the lake’s bottom profile.
The second chart shows what they found in various coring locations. The feet indicate the thickness of the top layer.

Composition of the core samples provides clues as to what was laid down when. Sand (the yellow dots) is generally laid down during floods which have the energy to transport the heavy particles. However, clay and silt (the green and blue dots) are smaller. So they tend to drop out of suspension when water is calmer.

Finding sand above silt in a core sample indicates that a storm like Harvey likely laid down the sand.

The third chart is the most crucial. It’s a difference map that shows areas of deposition and scour pre- and post-Harvey. This shows two things: where most sediment fell out of suspension and where the main flow of the river tried to churn a path through the mounting muck.

From the difference map above, you can see that the river tried to scour its way through the sediment along a path from LH-16 to LH-21 to LH-23. You can see another area of scour to the far right from LH-15 to LH-25 to LH-26.

Where River Flowed Before Lake Was Impounded

Interestingly, the area of scour to the left follows the river’s relic channel.

San Jacinto River map before Lake Houston was impounded

Note how the West Fork hugged what is now Atascocita Point – the thumb of high land that sticks up in the Tetra Tech illustrations.

Harnessing Natural Energy of the River

From the third and fourth illustrations above, one might conclude that excavating a channel near Atascocita Point represents the best way to harness the natural energy of the river. That’s the shortest channel where scour is deepest.

Given the million cubic yard limit, that path also represents a chance to dig the deepest, widest channel possible within the budget. When technicians compiled the difference map above, most of that path was already at or below its 2011 level.

500,000 square-yard path outlined in yellow would let dredgers excavate six feet. Average bottom depth is already 5.5 feet in that area.

Following that path also lets you funnel future sediment through the FM1960 causeway and disperse it out into the wider, deeper lake.

Next Steps and Timing

At this point, we don’t know what Imelda did to this area. Imelda struck shortly after the Army Corps completed its post-dredging survey in this area last year.

Before the additional dredging can begin, several things must happen.

  • Completion of a new survey
  • Model different scenarios
  • Identify best strategy
  • Locate suitable placement area
  • Compile scope of work
  • Bid job
  • Mobilize

Based on past experience, that could take months to a year or more. It took 13 months after Harvey for the Corps to put equipment in the water for its Emergency West Fork Dredging Project. However, we don’t have as many unknowns this time.

Posted by Bob Rehak on 9/5/2020

1103 Days since Hurricane Harvey

Town Hall Meeting Thursday at 6:30 Will Cover Wide Variety of Topics

Houston City Council Member Dave Martin will host a town hall meeting tomorrow, Thursday, October 17 at 6:30 p.m. It will be at the Kingwood Community Center, 4102 Rustic Woods, Kingwood, TX 77345. Hear from city and community representatives about news related to the Kingwood and Lake Houston areas of District E. 

Houston Mayor Sylvester Turner at Kingwood town hall meeting in October of 2018. Flooding was a hot topic then and even hotter now.

List of Speakers and Topics

  • Texas State Senator Brandon Creighton will kick off the town hall meeting, providing an update on Proposition 8 and sand-mining legislation. 
  • Mayor Sylvester Turner will attend.
  • Stephen Costello, City of Houston Chief Recovery Officer, will update residents on the progress of projects such as additional Lake Houston Spillway Dam Improvement Project (Flood Gates) and dredging. 
  • Houston Public Works and the Coastal Water Authority will address the Lake Houston Dam Maintenance Project. It’s why the lake will be one foot below normal through next November.
  • Stan Sarman, TIRZ 10 board chair, will discuss the Northpark Drive Mobility Improvement Project. 
  • Chuck Gilman, San Jacinto River Authority Director of Flood Management, will address the regional watershed study.
  • Chip Place from the Houston Parks Board will update residents on the Bayou Greenways 2020 project along the San Jacinto River. 
  • Texas Department of Transportation will update residents on the Loop 494 expansion project. 

Information About Kingwood Docks and More

Those who arrive early can browse information stations starting at 6:00 p.m. hosted by:

  • Lovett Commercial (Kingwood Docks)
  • Houston Public Works
  • Houston Police Department Kingwood Division
  • Houston Permitting Center to assist residents with questions related to storm damage repairs and rebuilding. 

Tables will remain open after the town hall meeting for those who arrive late.

For more information, please contact Council Member Martin’s office at (832) 393-3008 or via email at districte@houstontx.gov.

Posted by Bob Rehak on October 16, 2019

778 Days since Hurricane Harvey and 27 since Imelda