Tag Archive for: mouth bar dredging

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.

Two Top Geologists Suggest Mouth Bar Dredging Strategy

Two world-class geologists, Tim Garfield and R.D. Kissling, both of whom live in the Lake Houston Area, agreed (at ReduceFlooding.com’s request) to offer their opinions on what would be the best strategy for dredging near the San Jacinto West Fork Mouth Bar. Garfield and Kissling helped bring mouth bar issues to the attention of the public after Harvey. Both have followed various dredging programs in that area closely ever since.

Looking west across the mouth bar on 9/11/2020 while hovering over Kings Point. Suspended sediment shows that main current of river is between remainder of the above-water portion of the mouth bar and Atascocita Point on the upper left. Photo taken 9/11/2020.


The Army Corps of Engineers dredged from River Grove Park to Kings Harbor in 2018 and 2019, removing approximately 1.8 million cubic yards. After a contentious battle with the City, the Corps then agreed to remove another 500,000 cubic yards south of the Mouth Bar in the Spring and Summer of 2019. This year, the City of Houston started removing the portion of the mouth bar that remained above water; they are still working on it (see above). Recently, FEMA agreed to remove another million cubic yards. And waiting in the wings is another $30 million that can be applied to additional dredging. State Representative Dan Huberty secured that money in the last legislature.

However, none of the various parties involved has volunteered to share their thinking about objectives and strategies behind mouth bar dredging alternatives. That’s why I asked Garfield and Kissling to offer their thoughts on what constituted the best strategy. Both worked for one of the world’s largest oil companies at the very highest levels.

Old Bathymetric Maps No Longer Valid

The first thing they realized was that they didn’t have enough data to make informed recommendations. The last published bathymetric maps were based on surveys taken before Imelda and before the Corps’ mouth-bar dredging.

Gathering Own Data

So Garfield and Kissling gathered their own data – with sonic depth finders, GPS, and a 14-foot pole with depth markings. They started upstream of the mouth bar, where the Army Corps finished its Emergency West Fork Dredging program near Kings Harbor. And they worked their way downstream beyond FM1960 to the railroad bridge.

Scope of Garfield/Kissling survey

Found Underwater Plateau 20′ High and 3 Miles Long

They found an underwater wall approximately 20′ high where the Corps stopped its first dredging program near Kings Harbor. It extended downstream more than 3 miles.

Cross section of river channel shows a rise of almost 20 feet wall on the upstream side of the mouth bar near Kings Harbor and an even greater drop near FM1960. The result: a 3-mile long underwater plateau.

That wall, they say, “…constitutes a significant and abrupt hydraulic barrier that will likely exacerbate flooding and sedimentation.”

That wall is the leading edge of a 3-mile-long underwater plateau.

Note abrupt drop north of FM1960 Causeway.

Recommend Following Original Channel

The cross-section graph of the river bed above represents the deepest part of the river. On either side of that centerline, the riverbed rises to two or three feet below the surface of the water. The centerline closely follows the paleo (original) channel of the river before the Lake Houston dam was built.

Garfield and Kissling recommend dredging along the deepest path (see below). They reason that would save money.

Recommended and alternate routes identified by Garfield and Kissling that take advantage of deeper water.

“This might not only be the most beneficial dredging plan, but could also be the most cost effective as it leverages the paleo-channel as much as possible,” they say. “It harnesses nature, rather than fighting it.”

The geologists also identified a second possible route farther to the east but still south of the above-water portion of the stream mouth bar (labeled SMB in diagram above).

They caution that hydraulic modeling should be used to decide the best dredging plan. Political considerations drove initial mouth bar dredging rather than data. The Corps was authorized only to dredge an amount that it believed Harvey deposited. “We should be past the politics at this point and looking to get the most bang for our bucks,” say the geologists.

Whichever strategy the City settles on, Garfield and Kissling recommend excavating a channel, not a broad area, to get the best results for the dollars invested.

Objective: Re-establish Full Channel From Kings Harbor to Lake Houston

“This new channel should be no shallower, nor narrower than the upstream dredged channel at its end dredge location (450’ wide x 26’ deep),” say the geologists.

As a minimum, the future dredging plan should re-establish a continuous and down-stream deepening channel volume from where the Corps channel dredging ended to the 1960 bridge.

Tim Garfield and RD Kissling

This will help reduce sediment build up upstream from the plateau. By accelerating water through the blockage, it will let the river carry sediment farther out into the deeper portion of the lake. It will also reduce water backup that contributes to flooding.

Read Garfield and Kissling’s full study, Evaluating West Lake Houston Bathymetry, Dredging Status and Recommendations.

Recommendations Consistent With City’s Preliminary Findings

The City has been methodically surveying Lake Houston and is in the process of developing its own maps, objectives and strategies. Stephen Costello, the City’s flood czar said they are not finished with that effort yet. However, he also said that the preliminary information they obtained suggested that a route south of the mouth bar might be the most effective.

Posted by Bob Rehak on 9/25/2020 with thanks to Tim Garfield and RD Kissling

1123 Days after Hurricane Harvey

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

How Much Will Dredging Another Million Cubic Yards Reduce the West Fork Mouth Bar Area?

Earlier this month, the City of Houston announced that FEMA would pay to dredge another million cubic yards of sediment from the West Fork Mouth Bar. What does that mean in practical terms? What are the objectives of the program? How wide and deep will they go? Neither the objectives, nor a dredging plan, have yet been released.

The official plan will hopefully rely on new survey work and hydraulic modeling. A survey boat has been seen on the lake for several weeks now.

Since January of this year, the City of Houston has been trying to reduce the above water portion of the mouth bar with mechanical dredging, a much slower process than hydraulic dredging. Note how shallow the water is in the foreground.

How to Play Armchair Engineer

In the meantime, since fall football is in doubt due to COVID, here’s a simple way to keep your armchair quarterbacking skills finely honed. What would you do if you were the project engineer or manager? Play what if and experiment with different scenarios.

  • Download and open Google Earth Pro. It’s free.
  • Zoom in on the West Fork Mouth Bar.
  • Select the measuring tool.
  • Click on the polygon tab.
  • Select square yards for the unit measurement for the areas you will define.
  • Now start second guessing the project engineers. Play “what if” by defining an area that you would like to see dredged.
  • Readjust the points that define the area by dragging them in, out, up or down.
  • Watch the total square yards recalculate as you move the points.

Examples of Different Scenarios

Here are some examples to show you what I’m talking about.

4.3 Million Square Yard Area, Roughly 8 inches Deep
Largest area. This scenario takes in everything between where the Corps stopped dredging in its Emergency West Fork Program and the FM1960 Bridge.

The scenario above takes in the mouth of Ben’s Branch, plus all the other drainage ditches that empty Fosters Mill, Kings Point, and Atascocita north of the FM1960 Bridge.

The scenario above covers 4.3 million square yards. But with a budget to dredge only 1 million cubic yards, you would divide 1/4.3 = 0.23 yards of depth. That’s less than a third of a yard. It works out to about 8 inches.

3 Million Square Yard Area, 1 Foot Deep
In the next scenario, I pulled the boundaries in so that the area equaled 3 million square yards.

This scenario is a little more intuitive. You’re dredging 1 million cubic yards across an area of 3 million square yards. Within this bounding box, you could reduce the level of sediment roughly a foot.

2 Million Square Yard Area, 18 inches Deep
If you reduced the area to be dredged to 2 million square yards, you could reduce the level of sediment by half a yard or 18 inches.
1 Million Square Yards, 3 Feet Deep
Path followed by the relict channel before Lake Houston was built.

If you reduced the area further, to 1 million square yards, you could dredge to 3 feet. With the five feet of depth already there, you could have an eight foot channel connecting the river and the lake. Make it narrower and you could even go deeper. And perhaps, just perhaps, keep sediment from accumulating so rapidly upstream of the FM1960 bridge.

Difficult Choices Ahead

As you can see, engineers have some difficult choices ahead. They must chose between unblocking channels and streams, or dredging a channel roughly the size of the upstream west fork all the way to the 1960 bridge.

Last year, the Corps reduced the 600-acre area between the mouth bar and Atascocita Point to an average depth of 5.5 feet. So we have a good head start. But there are other considerations:

The West Fork was roughly 22 feet deep where the Corps stopped dredging just west of the mouth bar. Because of scouring, it’s at least that deep where the west fork passes under FM1960.

As a result, water coming down the west fork hits an underwater mesa that still blocks off three quarters of the conveyance.

Prominent area geologists, such as Tim Garfield and RD Kissling, theorize that that wall traps sediment and is rapidly diminishing the value of previous dredging programs. They believe that the most important objective for this phase of dredging should be to “reconnect the West Fork with the Lake.”

But Advancing Delta Now Blocks Major Streams, Channels

Meanwhile, consider this, too. In 2014, Bens Branch and the drainage ditch that empties large parts of Fosters Mill and Kings Point had a clear path to the river. Today, both are blocked by the mouth bar and an advancing delta within the lake. Compare the two images below.

Google Earth view from 2014 shows steams could still easily connect with relict channel.
Today, however, an advancing delta within the lake blocks them.

These are some of the real world trade offs that engineers and project managers must deal with every day.

So to return to the football analogy, do you send your receivers wide or deep? Do you have them hug the sidelines or cut for the goal post?

Understand that this isn’t a game, however. It’s a struggle to return a community to prosperity.

What would you do? And why?

Posted by Bob Rehak on 8/31/2020

1098 Days since Hurricane Harvey

Buzzing The Mouth Bar: Low Altitude Flyover at 30 MPH Takes 1 Minute 9 Seconds

It’s hard to get a feeling for the enormity of the West Fork mouth bar in a still photo. Something more than half a mile long is reduced to 1200 pixels. That fundamentally alters the scale between nature and humans. Instead of being a thousand times bigger, it’s a hundred times smaller. That does not produce the same emotional impact. It’s like looking at a picture of a mountain instead of standing at the base of one and feeling dwarfed as you look up.

Video Comes Closer to Capturing Imensity

However, tonight, at sunset, I flew a drone over mouth bar and captured the entire flight on video. At 30 miles per hour, it took 1 minute and 9 seconds to get from one end to the other.

The rapidly vanishing San Jacinto West Fork mouth bar. Mechanical dredging reduces the size a little more every day.
Looking south from Scenic Shores in King’s Point across mouth bar toward FM1960 Causeway downriver.
Looking west toward West Lake Houston Parkway.
Excavators working western tip of mouth bar. They shaver one row after another off, as if they are nibbling an ear of corn.
From the upstream to downstream tip measures more than half a mile.
At the eastern end, it almost look as if a bored dredging is carving his initials in the bar so that they can be seen from outer space.
Looking south across the eastern edge toward the FM1960 bridge again.

Tonight, as we watch Tropical Storm Cristobal dump torrential rains on Mexico, it’s hard to escape thinking of Hurricane Harvey. It dumped torrential rains on Houston and formed this monster mouth bar almost overnight. Remember, like an ice berg, the part you see above water is only a tiny percentage of what you can’t see below water.

Thinking of Cristobal, Remembering Harvey

As I look at the cloudless skies and soft sunset, I can’t help but wonder. Will Cristobal miss us. Or is this just the calm before the storm?

Cristobal has produced life-threatening flash flooding in Mexico and Central America. The National Hurricane Center forecasts it to move northward across the Gulf of Mexico on Friday. Risks include storm surge, rainfall and wind impacts this coming weekend across the US Gulf Coast from Texas to Florida. NHC reiterates that it’s too soon predict the exact location, timing and magnitude of these impacts.

Posted by Bob Rehak on 6/3/2020

1009 Days since Hurricane Harvey

Mouth Bar Dredging: First Pictures of Next Phase

Earlier this month, the State, Harris County and City of Houston announced the next phase of West Fork mouth bar dredging. Late last week, it got underway in earnest.

West Fork mouth bar on Monday 1.20.2020 before mechanical dredging started.

How Mechanical Dredging Works

Rachel Taylor took the ground-level pictures below earlier today from her back yard in Atascocita Point. They show mechanical excavators eating away at the mouth bar and loading the spoils on barges.

Sunday afternoon, 1.26.2020, two mechanical excavators worked the western end of the mouth bar. They loaded the spoils on waiting barges (right). Photo courtesy of Rachel Lavin Taylor.
Service boats then pushed the barges upriver. Photo courtesy of Rachel Lavin Taylor.
Barge loaded with spoils passes the Deerwood Country Club. Photo courtesy of Rachel Lavin Taylor.
Barges then anchor at Berry Madden’s property on the south side of the West Fork opposite River Grove Park. That black object jutting into the photo from the lower left is the skid of the helicopter. Photo taken 1.20.2020.
From there, other trucks move the spoils inland. For orientation, that water tower in the upper left is south of Kings Lake Estates. Photo taken 1.20.2020.

Mechanical dredging is slower and more labor intensive than hydraulic dredging, but can mobilize faster. In hydraulic dredging, dredgers pump the spoils to a placement area via pipelines. That is faster, but has higher overhead. It also creates more noise.

Hydraulic Dredging Options

The hydraulic pipelines can stretch miles. In the case of the first phase of West Fork mouth bar dredging, they stretched 10 miles upstream. It took five booster pumps to get the material all that way to a sand mine on Sorters just south of Kingwood Drive.

Luckily for us, the pipe from the first phase of mouth bar dredging is still at the Army Corps dock opposite Forest Cove.

Pipe from the first phase of mouth bar dredging still sits at the former Army Corps command post and could be rewelded into longer sections if needed.
The Great Lakes Dredge also remains at the dock. Here you see the pieces below and behind the crane.

At some point in this project, dredging may switch from mechanical to hydraulic. The fact that the Great Lakes dredge remained here bodes well. It chewed through 500,000 cubic yards of debris at the West Fork mouth bar in less than three months. Officials expect mechanical dredging of 400,000 cubic yards to take 8 -12 months.

Additional Dredging Targets and Financing

Other targets reportedly include the East Fork Mouth Bar and several mouth bars that have formed at the mouths of ditches or streams leading into the lake.

State Representative Dan Huberty helped bring $30 million to this phase of dredging via an amendment to SB500 in the last legislature. That money will funnel through Harris County via the Texas Water Development Board. The County also included $10 million in the 2018 flood bond. And the City is applying $6 million left over from a FEMA/TDEM grant for debris removal from Harvey.

For more details on this next phase of dredging, see the previous post on this project.

Two Phase Project Outlined In Grant

Harris County’s proposal for the grant from the Texas Water Development Board (TWDB) calls for splitting the project into two phases. 

  • Phase One will focus on the West Fork Mouth Bar using the City’s $6 million and $10 million from the TWDB grant.
  • Phase Two will focus on the East Fork Mouth Bar using the remaining $20 million from the grant.
  • The $10 million from the County flood bond will fund surveys, formulation of specs, bidding, project management and more.

Progress Result of Pulling Together

All this is great news for the Lake Houston Area. The entire community worked since Harvey to make this happen through all levels of government.

As we look at other flooding problems in the area, it’s important not to get discouraged and to remember that we can make progress if we all pull together.

Posted by Bob Rehak on 1/26/2020 with photos from Rachel Lavin Taylor

880 Days since Hurricane Harvey