Tag Archive for: Sedimentation Survey

City Applies for TWDB Grants to Turn Woodridge Village Into Detention Basin and More

Correction on 7/4/2020: The article below was based on a City of Houston District E newsletter. It inferred that the City “applied for” five grants (in bullet points below). Other entities, such as the SJRA, applied for those. Mayor Pro Tem Dave Martin personally supports them.

The City of Houston has submitted several applications to the Texas Water Development Board (TWDB) for Flood Infrastructure Fund dollars. Among the projects was one for Taylor Gully Flood Damage Reduction. It consists of evaluating flood reduction alternatives plus design, permitting, and construction of a detention basin located on a 278 acre site to the north of the Elm Grove subdivision.

Looking SW at Woodridge Village as of 6/16/2020

Woodridge Project One of Six Apps

Other applications include:

  • San Jacinto River Sand Trap Development
  • Spring Creek Watershed Flood Control Dams Conceptual Engineering
  • Upper San Jacinto River Basin Regional Sedimentation Study
  • Lake Conroe-Lake Houston Joint Reservoir Operations Study
  • Harris County MUD #153 Siltation Reduction

“All of these projects submitted for funding promote regional resiliency and future sustainability in an effort to protect life and property from future flooding,” said Mayor Pro Tem and District E City Council Member Dave Martin. “The ability to submit these projects to the TWDB for funding would not be possible without State Senator Brandon Creighton’s writing of Senate Bill 7. We continue to applaud the Senator for his forward thinking and hope to receive funding for these projects. State Representative Dan Huberty has also been a vocal proponent for resiliency within our area and just beyond the City boundary. We are thankful to have him as a local engaged leader.”

Looking NW from US59 (foreground) over San Jacinto West Fork at the confluence of Spring Creek (left) and the West Fork (right). Spring Creek splits off to left. Its watershed contains several natural areas that might make candidates for flood control dams.

Neither Martin, nor his office, provided additional details on any of the grant applications.

However, from the wording of the release, it sounds as though state leaders are fully aligned and engaged to support the projects.

Woodridge Village Project Has Long History

The grants, if approved, could help reduce flooding throughout the Lake Houston Area.

The Taylor Gully/Woodridge Village project is the most urgent. Homes around the troubled development flooded twice last year. At a Kingwood Townhall meeting in February, Martin said the County should pay for 100% of that project. But then the County demanded that the City should pay for half of the purchase price of the land. And at the next Commissioners’ Court meeting, Commissioner Ellis changed the deal again. He demanded that the City pay for half of the construction costs also.

Both the City and County have been silent on any deal since then. The County refused a Freedom of Information Act request to release the text of the motion, which was approved in a public meeting. They even protested release of the information to the State Attorney General.

Putting Application in Historical Context

The following is speculation, but speculation based on the historical context. It appears that when County Commissioners voted to demand that the City come up with half the the purchase AND construction costs, the City found it hard. The grant application, if successful, is a way for the City to help the people of Elm Grove, who flooded twice last year after Perry Homes cleared 268 acres of adjacent land.

At the time of the floods, less than 25% of the planned detention pond capacity was in place. Perry has since developed additional detention ponds that provide the other 75%.

However, even that probably won’t be enough to absorb a 100-year rain. That’s because Perry Homes rushed to have the project approved before NOAA’s new Atlas-14 precipitation frequency tables went into effect. The new Atlas-14 standard would require about 40% more detention capacity. And that’s what the purchase is all about.

Rumor has it that political forces are aligned to accelerate this particular request.

Observations on Other Grant Applications

Of the other applications, two surprise me.

A joint reservoir operations study seems necessary. Currently, FEMA is funding a preliminary engineering study to add additional gates to the Lake Houston Spillway. If FEMA also approved the money for construction of the gates, they will be a game changer.

The Spring Creek Watershed flood control dams would provide additional upstream detention. Community leaders identified that as a high priority after Harvey. They would reduce the amount of water coming downstream during a flood.

Harris County MUD #153 contains Lake Houston shoreline where silt from Rogers Gully has accumulated. Earlier this year, Harris County Flood Control cleared a large part of the Gully, but the part owned by the City remains clogged with a mouth bar.

Sand bar blocking mouth of Rogers Gully has backed up water and contributed to flooding. Photo taken 6/16/2020.

Posted by Bob Rehak on 7/3/2020

1039 Days since Hurricane Harvey

Recently Obtained Documents Raise Questions about Amount of Sediment in Mouth Bar Due to Harvey

ReduceFlooding.com has obtained a copy of the study withheld by the Army Corps that the Corps used to justify dredging only 500,000 cubic yards from the mouth bar of the San Jacinto West Fork. The Corps refused to supply it in response to my Freedom of Information Act (FOIA) request in June. However, the City of Houston did supply the Corps document in response to a similar FOIA request. Now, thanks to Council Member Dave Martin, the public has an opportunity to compare the two studies side by side for the first time.

Kings River resident near mouth bar wading in knee deep water almost to West Fork channel marker. Caution: do not let children attempt this. Pockets of deeper water may exist that could cause drowning. Picture taken eight days ago. The island being excavated in the distance has since been removed; see last image in post.

After reviewing the Corps document, I can see why the Corps refused to supply it. It has more holes in it than a West Texas stop sign.

History of Controversy

For almost a year, the City and the Army Corps have argued over how much sediment was deposited in the mouth bar of the San Jacinto river by Hurricane Harvey. That determines how much dredging FEMA will fund. Initially, the City recommended working with two Texas Water Development Board sedimentation surveys conducted in 2011 and 2018. But no measurements exist from the period immediately BEFORE Harvey – only AFTER. So the Corps rejected that idea.

Corps Demands then Rejects Stockton Protocol

To determine Harvey volume, the Corps then required the City to provide direct measurement of the sediment through something called the Stockton Protocol. (See this memo from Stephen Costello, Houston’s Chief Recovery Officer, outlining this request and the reasons for it.)

The Stockton Protocol combines ultra-high-resolution CHIRP seismic data with core sampling. The seismic identifies layer thickness and the core sampling identifies layer composition. (Note: the process is somewhat like the oil field practice of confirming seismic with core samples from exploratory wells.) The hope: that by analyzing changes in sediment composition (such as color, grain size, roundness, hardness, etc.), researchers can differentiate Harvey sediment from other floods and then measure it accurately.

Core sample from Tetra Tech Study. Different colors and consistencies indicate sediment came from different floods.

The Army Corps recommended a Texas A&M Galveston professor, Dr. Timothy Dellapenna, to do the research. However, the City of Houston and A&M could not agree on contract terms. Therefore, the City hired Tetra Tech, to perform the research that Dr. Dellapena outlined.

Corps Produces Own Analysis

Tetra Tech concluded Harvey deposited 1.4 million cubic yards in the mouth bar (although they didn’t state it that clearly). The Corps rejected Tetra Tech’s results and produced its own study. That study concluded Harvey deposited only 283,000 cubic yards in the mouth barone fifth as much. However, the Corps authorized 500,000 cubic yards to compensate for the margin of error and additional sediment they would have to dredge just to reach the mouth bar.

At the end of the day, even with 500,000 cubic yards, those two estimates still vary by almost 3X. According to Houston City Council Member Dave Martin, the Corps never explained why they rejected the Tetra Tech analysis.

The Corps simply accepted its own results and started dredging without public explanation or input. The Corps document raises many questions that may or may not have valid answers.

The USGS gauge used by the Corps for its analysis stopped working during the peak of Harvey when most sediment would have been moving. The Corps report did not acknowledge this.

Corps Analysis Requires Explanations Never Supplied

Why did the Corps:

  • Base its analysis on a gage at US59 that stopped functioning during the peak of Harvey, when most sediment was moving?
  • Assume Harvey distributed sediment in the same patterns over the same distances as lesser storms?
  • Ignore build up of sediment from Tax Day and Memorial Day storms at the mouth bar as a factor that could have increased the percentage of sediment falling out of suspension during Harvey?
  • Not consider bank erosion downstream from the gage, relying instead on standard charts for “bed-load transport” for sandy rivers?
  • Ignore approximately 20 square miles of sand mines in the West Fork floodway where loose sand and silt were inundated by 131,000 cubic feet of water per second, unlike previous storms?
  • Use a 1-D instead of a 2- or 3-D model for this complex environment?
  • Not publicly disclose model inputs/outputs and data for peer review and validation?
  • Initially reject the use of two TWDB surveys, then reverse course and base all of their findings on them – without explaining why?
  • Exclude extreme data from their study, even though Harvey was one of the most extreme rainfall events in U.S. history?
  • Mislabel all charts, graphs and photos in its report?
  • Refuse to disclose their report in response to a FOIA request, contrary to official Army policy?
  • Omit the organization’s name and the author’s name from the report?
  • Treat the volume that Tetra Tech found related to Harvey in the mouth bar area alone as if it represented the total volume deposited in the entire West Fork by Harvey?

Corps Rejects Use of TWDB Surveys, Then Bases Own Analysis On Them

To estimate Harvey-related volume, the City initially proposed analyzing two Texas Water Development Board sedimentation surveys from 2011 and 2018.

The Corps rejected that idea, suggested the Stockton Protocol, rejected those findings, then based its own analysis on the two TWDB surveys it rejected earlier. This is like following a Three-Card Monte game!

Here is the full text of the Corps’ 4-page unsigned study. We now know that…

Basically, the Corps tried to estimate the amount of sediment that Harvey’s flow could theoretically carry. That would depend on velocity and sediment size/weight. But the gage at US 59 stopped recording at the peak of Harvey. So they also had to estimate the discharge (volume of flow in cubic feet per second [cfs]). Then they used industry-standard curves to estimate sediment transport based on estimated discharge. But they discarded rates over 45,000 CFS because they produced unexpectedly high values.

They also ignored the presence of mile-wide sand mines upstream. The river ruptured the dikes of those mines and captured the pits during Harvey.

West Fork Sand Mine Complex inundated by Harvey. This reach of the river is normally about 150 feet wide. On this day, the day AFTER Harvey’s peak, the flow was more than a mile wide.

Corps Rules Out Extremes for Extreme Event

The Corps says in its report, “there are no measurements above 45,000 cubic feet per second.” Yet the combined peak flows coming from the West Fork, Spring and Cypress Creeks reached approximately 240,000 cubic feet per second during Harveyfive times more. The faster and higher the flow, the more sediment that can be transported downstream and over greater distances.

When the industry-standard sediment transport curves yielded unacceptably high results, the Corps resorted to a simple 1-D model (developed earlier for another purpose) to calculate the sediment load, because flows beyond 45,000 cubic feet per second “produced sediment loads far beyond a reasonable range.”

Corps Assumes Harvey Transported Same Percentage To Mouth Bar as Other Storms

One potentially fatal assumption: The Corps assumes that Harvey transported the same percentage of its sediment load to the mouth bar as all other storms between 2011 and 2018. Said another way, they assume that Harvey behaved LIKE all other storms. Yet not all those floods inundated sand mines.

Moreover, had the Corps measured river bank erosion at intervals between 2011 and 2018, they would have found that virtually all of it occurred during Harvey and very little occurred during Tax Day, Memorial Day and other storms.

Quantum Leap in Erosion Not Factored In

Harvey’s erosive power was NOT proportional to other storms, as the photos below show. River banks eroded more than a hundred feet during Harvey in many places. Yet the Corps report never even mentions erosion.

In 2011, the distance from the ridgeline of this home on Riverbend Drive to the West Fork was 326 feet.
On 1/23/2017, after the Tax and Memorial Day Floods, the distance had decreased only 2 feet.
This shows how much shoreline Harvey ALONE eroded. The yellow line is exactly the same length as after the 2016 floods.
After Harvey, the new distance to the river bank was 216 feet – 108 feet less.

The Tax and Memorial Day Floods combined eroded this river bank by 2 feet. Harvey alone eroded it another 108 feet – 50 times more!

Photographic analysis shows similar quantum leaps in erosion related to Harvey elsewhere along the West Fork.

  • Another home west of River Grove Park lost 27 feet between 2011 and early 2017, but 111 feet in Harvey.
  • River Grove Park lost 0 feet from 2011 to early 2017, but 74-feet in Harvey.
  • Romerica lost 62 feet between 2011 and early 2017, but 144 feet in Harvey.

Net: In four days, Harvey eroded from 2X to 75X more sediment than all other storms during the previous six years. It did NOT act proportionally.

The shearing force of 240,000 cubic feet per second coming down the West Fork literally pulled thousands of trees out by their roots and dislodged sediment disproportionately compared to previous floods (see below). The Gallery page of this web site clearly shows the extent of this devastation. It contains 450 images taken from a helicopter on 9/14/2017, two weeks after Harvey.

Hurricane Harvey ripped trees out by their roots to a degree that previous storms did not. This increased erosion exponentially compared to other storms.

Corps Assumes Mouth Bar Growth Did Not Affect Percentage Deposited by Harvey

The Army Corps also assumes that Harvey transported the same fraction of the total sediment load (20%) to the mouth bar that all storms did between 2011 and 2018. That’s a dubious assumption for several reasons:

  • Previous storms progressively built a wall across the mouth of the West Fork that grew higher and higher during the study period.
  • As it grew, that wall increasingly slowed water down and likely accelerated the rate of deposition behind it (which helps explain why the Corps had to dredge its way to the mouth bar).

Yet the Corps based its estimate on a constant 20%. Page 3 of their report spells out the assumption. Harvey, they say, deposited approximately the same fraction of sediment at the mouth bar as all other storms did during the period between surveys.

This constant 20% contradicts numerous anecdotal reports from lakeside residents and boaters claiming that Harvey carried vastly more sediment to the mouth bar (and their yards/docks) than previous storms. The wife of the resident wading across the river in the image above told me that, on a scale of 1 to 5, the Tax and Memorial Days floods deposited sediment in her yard equal to a 1. But Harvey, she said, was a 6. In other words, off the scale.

No wonder the Corps didn’t want the public looking at this!

Taxpayers Deserve Independent Scientific Review

Professionals rarely like to have their conclusions questioned. However, those who have confidence in their conclusions welcome peer and public review. They encourage second opinions and provide all of their data for review. They also welcome the opportunity to explain and defend their results. None of those things happened in this case.

Instead, the Corps concealed its results as if this involved national security, not public safety. Why? That may be the biggest question of all associated with this project.

The Corps has an excellent, hard-earned reputation. This study undermines it.

As mentioned above, the Tetra Tech study may also have flaws, but the Corps never revealed what its concerns were.

Only one thing is certain. Public safety rests on wildly differing studies. Taxpayers deserve an independent scientific review to resolve the differences between these two studies. The City concurs with the findings in this post and also calls for an independent scientific review. The Corps could not be reached for comment; their new public affairs officer does not list her phone number.

Dredging will likely end next week, with the Corps proclaiming it has restored the conveyance of the river to pre-Harvey conditions (when they have no pre-Harvey measurements).

So we need an independent scientific review to happen quickly. Email you Congressmen and Senators immediately.

Corps Plans Still Being Kept from Public

The Corps still has not released its dredging plans, despite a FOIA request made in June when mouth bar dredging started.

Visual observations of the operation suggest that they are dredging a wide area by three feet, to a total depth of about five feet, instead of trying to cut a channel through the mouth bar. That would leave something like an underwater mesa, still blocking the flow and still trapping sediment. Water coming downriver would have to climb a steep hill to get over it.

If that is an accurate assessment, the Corps would leave a sediment wall under the water approximately 30-35 feet high and 1-2 miles long in the mouth of the West Fork.

Congressman Dan Crenshaw reviews progress of dredging operation on Friday, August 16. Looking southwest towards Atascocita. Notice how the small island in the first image above has now been removed. The mouth bar itself will remain in place, most of it underwater now where it is invisible to the public.

Others Scrambling to Pick Up the Pieces

It may look like the Corps has dredged. But it also looks like the Corps will leave 80-90% of the mouth bar in place. Remember, sand bars are like ice bergs in the sense that what you see above water is small compared to the amount you can’t see below water.

At this point, City, County, State and Federal leaders are scrambling to put together a plan to address the rest of the sediment. Some of that sediment is clearly pre-Harvey. I will discuss options for removal of that portion and maintenance dredging in a future post.

Posted by Bob Rehak on 8/20/2019

721 Days after Hurricane Harvey

As in previous posts on this subject, I promise the Corps that I will print their rebuttal verbatim if they disagree with any of the points in this post.

Video Shows Highlights from U.S. Army Corps of Engineers Survey

The U.S. Army Corps of Engineers posted a video on YouTube that contains highlights of the sedimentation survey that they conducted last week between the U.S. 59 bridge and the West Lake Houston Parkway bridge on the San Jacinto River.

This short video references some trouble spots they found and gives a good description of how “shoaling” can slow down water and back it up. Check the video out. The full results of the U.S. Army Corps survey should be available sometime this week.

The Army Corps has taken over the lead role for this project. Harris County Flood Control will play a supporting role.

Posted April 16, 2018, 230 days since Hurricane Harvey

Army Corps Finishes Sedimentation Survey Field Work on First Leg of West Fork

Below is the official press release from the U.S. Army Corps of Engineers about the field work for the sedimentation survey they completed on April 9.

“HOUSTON (April 10, 2018)

“The U.S. Army Corps of Engineers, Galveston District began surveying levels of sediment deposits last weekend within the West Fork of the San Jacinto River in response to a State of Texas and FEMA request.”

“To determine the level of shoaling and silt accumulation within the West Fork of the San Jacinto River, a New Orleans District Corps survey crew and vessel began collecting GPS and sonar data near Humble and Atascocita from Apr. 6-9 along a five-mile area between Hwy 69/59 and West Lake Houston Parkway

“Corps Surveyors operated a 20 foot Xpress Boat with survey grade GPS and a sonar transducer to determine sediment deposition,” said Alicia Rea, an emergency management response official with the Galveston District.

“FEMA responded to a request from the State of Texas and under Stafford Disaster Relief and Emergency Act of 1988, FEMA directed the Corps to begin the initial assessment of the conditions. Army Corps Hydrologists will utilize the survey data and use hydrologic modeling to determine the best course of action.

“County and City officials conducted a site visit to the locations on April 10, 2018” said Rea.

“We believe this is the most prudent action to take to better define the scope of work,” said Rea. “The USACE and FEMA are working diligently to expedite the process.”   (END OF PRESS RELEASE)

Results of Survey Available Soon

Sources tell me (Bob Rehak) that the results of the Army Corps survey may be available as early as next week. This is good news with hurricane season just six weeks away.

However, there is still a lot of work to do before dredging begins. Everyone must agree on specs for the job. Bidders must be identified. A location to store or dispose of the dredged material must be found. Bidders must have time to prepare their bids. An environmental survey must be conducted. They must allow time for a comment period. The bid must be awarded. Crews must be mobilized.

Some steps can happen in parallel but others must happen sequentially. Sources, who spoke on condition of anonymity, said it could take a month or two before dredging begins – more likely two than one.

We hope that while that work is underway, preliminary work can begin on subsequent legs of the river to further expedite completion of the entire job.

At Least Four Major Blockages on West Fork

Here are four photos from the West Fork that I took shortly after Harvey. They show some of the major blockages between 59 and the lake that we hope the Army Corps addresses. The first two were taken upstream of the West Lake Houston Parkway Bridge. The second two were taken downstream. Approximately 70% of the Kingwood homes that flooded were downstream from the bridge.

The new sandbar deposited by Hurricane Harvey now forces water coming out of the drainage ditch in the background on the left to make a 90 degree left hand turn before it can reach the river. This slows the velocity of runoff and backs up water into subdivisions, like the Barrington in the background. While the sandbar looks gentle from the air it is up to 15 feet high near the ditch.

South of the Kingwood Country Club’s Island Course, Hurricane Harvey deposited several feet of sand that is filling in the back channels and expanding the islands of the West Fork of the San Jacinto River, thus reducing its carrying capacity.

Looking north toward Kingwood’s Kings Harbor subdivision, a popular entertainment district that was destroyed by Hurricane Harvey. The West Lake Houston Parkway bridge is on the left. In the foreground, sand now reaches the tree tops and is virtually as high as the bridge itself. Water used to flow under the bridge and through the area in the foreground during floods. Now it is forced north.

A giant sand dune has formed near where the east and west forks of the San Jacinto join, inhibiting the flow of the river. Engineers say that sediment is not being carried out into Lake Houston (background) as expected. Areas beyond these dunes experienced far less flood damage from Harvey than the areas behind them. That’s the FM1960 Bridge in the background.

Here is link to an Army Corps Facebook post about the project that shows 20+ additional pictures of the survey crew at work on the west fork.

By Bob Rehak

Posted April 11, 2018, 225 days since Hurricane Harvey.