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.
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.
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.
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)
Finding qualified contractors
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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/10/BeforeNow.jpg?fit=1200%2C1200&ssl=112001200adminadmin2020-10-26 17:09:182020-10-26 17:09:22Above-Water Portion of Mouth Bar Could Be Gone by Christmas
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.
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.
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.
That wall, they say, “…constitutes a significant and abrupt hydraulic barrier that will likely exacerbate flooding and sedimentation.”
Garfield and Kissling recommend dredging along the deepest path (see below). They reason that would save money.
“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.
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
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/09/Slide6-1.jpeg?fit=1200%2C900&ssl=19001200adminadmin2020-09-25 12:33:102020-09-25 23:08:43Two Top Geologists Suggest Mouth Bar Dredging Strategy
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.
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.
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.
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.
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.
Following that path also lets you funnel future sediment through the FM1960 causeway and disperse it out into the wider, deeper lake.
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
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
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/09/Tetra-Tech-Study_Page_26.jpg?fit=2550%2C1650&ssl=116502550adminadmin2020-09-05 15:39:592020-09-05 15:53:16Tetra Tech Study Provides Clues To Possible Mouth Bar Dredging Strategies
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.
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
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
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
1 Million Square Yards, 3 Feet Deep
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:
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.
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
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/08/20200831-DJI_0613.jpg?fit=1200%2C900&ssl=19001200adminadmin2020-08-31 20:38:392020-08-31 20:52:02How Much Will Dredging Another Million Cubic Yards Reduce the West Fork Mouth Bar Area?
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.
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
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/06/20200602-DJI_0005.jpg?fit=1200%2C900&ssl=19001200adminadmin2020-06-02 22:27:092020-06-02 22:52:41Buzzing The Mouth Bar: Low Altitude Flyover at 30 MPH Takes 1 Minute 9 Seconds
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.
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.
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.
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.
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
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