Tag Archive for: Freese & Nichols

SJRA Seeks Public Input on Sediment Trap Proposal

The San Jacinto River Authority (SJRA) recently completed a 246-page conceptual design study, in partnership with the Harris County Flood Control District, that explored the feasibility of implementing sediment trapping facilities (“sand traps”). The purpose: to remove sediment from the West or East Fork of the San Jacinto River. The results and findings of this study have been documented in an engineering report entitled “San Jacinto River and Tributaries Sediment Removal and Sand Trap Development.” 

Prior to proceeding to preliminary engineering design and any subsequent project phases, SJRA is seeking public input on the proposed project alternatives detailed in the report. The full report, as well as a brief summary document, are located on SJRA’s Flood Management Division website. 

How to Provide Input or Ask Questions

Please submit input and questions via email to floodmanagementdivision@sjra.net

Deadline: No later than April 29, 2022

Caution: The full study is dated 1/7/22. But the “brief summary” is dated 3/9/22. Make sure you at least read the executive study of the full report as well as the brief summary. There are important differences.

Overview/Purpose

SJRA says the purpose of the sediment trap study was to assess the feasibility of implementing a pilot project to trap and remove sediment from the West OR East Fork of the San Jacinto. The study only assessed locations where one or more Aggregate Production Operations (APOs) could partner with the the SJRA. They restricted the study this way to reduce costs; the SJRA does not have a source of funding to clean out sand traps and would rely on sand miners.

Initial Concerns

The decisions to:

  • Define the study objective as sediment reduction, not damage reduction and…
  • Only consider locations near sand mines…

…give me mixed emotions about this project.

Pros

On one hand, I look at this and say, “It’s a pilot project. Try it and see if there’s a benefit.” Sediment IS a problem and they believe they can remove up to 100% of the annual sediment load (from the West Fork).

Cons

On the other hand, the study authors, Freese & Nichols (F&N) claimed (in the San Jacinto River Basin Master Drainage Study) that of all the sediment coming into Lake Houston, two thirds comes from Spring and Cypress Creeks while only 13% comes from the West Fork upstream of US59.

Perhaps that’s because they’re using model inputs from a sediment gage at I-45 located 8.5 miles upstream from most of the large West Fork sand mines (page 34, paragraph 3 of full study).

Also, in their discussion of downstream sedimentation mitigation (page 51, paragraph 3 of full study), F&N says that their evaluation was confined to areas where natural processes rather than breeches of sand mine ponds likely contributed to sediment deposition. To see how limiting that is, see the photos of sand mine breeches and their results in this post.

West Fork Mouth Bar
The “Mouth Bar,” a giant sand bar that blocked the West Fork of the San Jacinto, backing the river up into Kingwood and Humble. Thousands of homes and businesses flooded behind this blockage. The above-water portion has since been removed, but most of the underwater portion remains.

In the entire 246-page F&N study and the three-page summary, the word “damage” occurs only once…in relation to erosion damage, NOT flood damage.

It appears that F&N did not even look at creating sand traps where they were most needed, in the headwaters of Lake Houston, because of cost and logistical considerations. Yet the Army Corps, City of Houston, and State of Texas are spending $200 million to dredge that area. One wonders whether SJRA should have looked harder for partners to clean out the traps.

Finally, if sediment traps only work financially near sand mines, the “solution” will not work on other tributaries that F&N alleges contribute 5X more sediment than the West Fork. They just don’t have the sand mines that the West Fork has.

Nature of Proposed Solution

Five years after Harvey, we have a conceptual design and a recommended location: rock-lined channels cut through one or two point bars at the West Fork Hallett mine.

Page 8 of the F&N study shows this schematic of the recommended solution.

The shot below shows the same area in real life. To put the magnitude of the proposed solution into perspective, the solution would cover a little more than an acre. But sand mines like Hallett cover 20 square miles on the banks of the West Fork between US59 and I-45.

2021 photo of sand bar outsde Hallett mine that would have a narrow channel cut through it to trap sand.

My Biggest Fears

My biggest fears with the proposed pilot study are that it:

  1. Asks people to chose from a limited menu.
  2. Could divert attention from better solutions that would reduce flood risk faster in the headwaters of Lake Houston.
  3. Might make the public think the problem is solved.
  4. Could open the door to river mining and further destabilize the riverine environment.
  5. Is not a transferrable solution.

For a pilot study, that last point is troubling.

Also, F&N worries that removing too much sediment from the West Fork could create a “hungry-water” effect that increases erosion downstream. But they have no way of directly measuring how much sediment the West Fork transports. Or what percentage they would remove. That’s because they’re relying on a sediment gage upstream from the sand mines. This introduces an element of risk in the pilot study.

Recommendations Should Be Based on a Holistic Examination of Alternatives

Note lack of vegetation on this steep-sided, eroding bank of Hallett mine on West Fork in foreground.

Before moving forward with the pilot study, I suggest a more holistic examination of additional alternatives that might have a greater impact on reducing flood damage, not just sedimentation. Examples include, but are not limited to:

More on the sand trap proposal in coming days. In the meantime, please review the SJRA’s sediment trap proposal and forward your comments to the SJRA. I will also print thoughtful letters, both pro and con, from responsible parties. Send them to: https://reduceflooding.com/contact-us/.

Posted by Bob Rehak on March 27, 2022

1671 Days since 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.

Details of SJRA Application to TWDB for Grant to Develop Sand Traps

In March, the San Jacinto River Authority (SJRA) awarded engineering firm Freese & Nichols a $250,000 work order for “Conceptual Design” of sand traps. Then in June, SJRA applied for a $200,000 grant from the Texas Water Development Board (TWDB) for “Preliminary Design” of sand traps on the West Fork. What’s this all about? How do the projects relate? Are they worthwhile?

West Fork 90% Blocked After Harvey

After Harvey, the Army Corps documented that the West Fork had become 90% blocked by sediment in places. That contributed to the flooding of thousands of homes and businesses. It also triggered a massive dredging program that is still ongoing. Finally, it launched a search for solutions that stretched all the way to Austin (plus, interestingly, Kerrville and San Antonio). See more below.

SB1824 Opens Door for Sand Traps

House Bill 1824 was introduced by State Rep. Murr from Kerrville and sponsored by Senator Flores from San Antonio. Approved last year, it allows SJRA and Harris County Flood Control District (HCFCD) to remove material from the San Jacinto River and its tributaries to restore, maintain, or expand storm flow capacity without the need for “state permitting” or royalty payments to the state.

SJRA and HCFCD hope to mitigate flooding by constructing one or more “sand traps.” Their plan calls for partnering with Aggregate Production Operations (APOs) in the vicinity of the sand trap(s) to clean them out periodically. It’s not yet clear whether APO’s would do this for a fee, or do it for the sand. One thing is clear, at this point, however. APO’s don’t want to go far. All the locations under consideration are next to sand mines.

Freese & Nichols Already Underway with Phase 1

The first phase of the project, Freese & Nichols’ conceptual design, is currently underway. It includes:

  • Evaluating potential sand trap locations and trapping effectiveness
  • Developing conceptual sand trap designs
  • Determining downstream benefits of potential sand trap solutions
  • Recommending which site(s) to carry forward into preliminary engineering.

Phase 2 of Pilot Goes Further

The goal: to move forward with preliminary engineering on two sites, with the likely construction of at least one. This small scale effort, involving only one or two sand traps, is intended to act as a “pilot” before a more costly, full-scale program.

Preliminary results in the first phase indicate that the sand traps will likely be located along the West Fork.

However, to move beyond conceptual design, even on the pilot, SJRA needs more money to supplement local match resources.

If successful, the TWDB grant application for preliminary design will cover:

  • Environmental permitting investigation
  • Preliminary land acquisition efforts
  • Survey
  • Geotechnical investigation
  • 30% design efforts.

Need for Sediment Control of Some Sort

To date, more than 2.3 million cubic yards of material have been removed from the West Fork, at a cost of more than $90 million. An additional $30 million has been dedicated to continue these efforts. SJRA hopes sand traps will help protect that investment.

It seems, though, that reducing sediment coming out of sand mines might be a simpler, less-risky, more cost-effective solution.

Benefits

Long-term benefits beyond the initial sand trap development “pilot” project are anticipated to potentially extend beyond the immediate benefit area.

Benefits include potential reduction of sediment load entering Lake Houston.

Primary benefit area is in purple along West Fork. Secondary benefit area is in green (Lake Houston).

SJRA can not yet quantify the level of flood mitigation provided by the sand trap(s). However, restoring or expanding storm flow capacity could potentially remove structures from the floodplain, they say. The conceptual design phase currently underway will attempt to evaluate downstream hydraulic benefits.

Timing

If this abridged application succeeds, SJRA will need to submit a more detailed application. TWDB won’t report results on that until late this year.

Freese & Nichols should report the results of their conceptual study this September.

SJRA anticipates it can complete the preliminary engineering study in 18 months. However, construction will take longer – up to 36 months.

Next Steps

If results of this pilot project indicate that sand traps are a feasible and effective solution, a larger program in various locations throughout the basin could be implemented.

Preliminary cost estimates will be developed as part of the conceptual design phase currently underway. So SJRA has not yet determined a benefit/cost ratio.

However, the cost of dredging has proved substantial. And the cost of flooding during Harvey proved astronomical. Reducing those costs just 1% could easily justify the cost of this project.

We have too many unknowns at this point to pass judgment.

  • How much will the project cost?
  • Will sand traps be effective?
  • Who will maintain a trap when a sand mine goes out of business?
  • What will the environmental impact be?
  • Will the traps accelerate erosion and jeopardize infrastructure such as pipelines and bridges?
  • Is this the opening volley in an effort to begin large-scale river mining?

Scientific literature and news reports on sand traps generally indicate mixed results.

I will withhold judgement until I learn more.

To review the abridged application, click here.

Posted by Bob Rehak on 7/9/2020

1045 Days after Hurricane Harvey

HCFCD Partners with SJRA on Sediment Trap Project

The SJRA announced earlier this week that the Harris County Flood Control District will partner with the River Authority on a “sediment trap” pilot study for the East and West Forks of the San Jacinto. The two have hired engineering firm Freese & Nichols to conceptually design the traps and identify the optimal locations for them.

Finding the Right Combination of Factors

Most sediment traps are big holes dug in a river or channel though some are off to the side. As water passes them, velocity decreases. Suspended sediment and sand being pushed along the river bed fall into them.

Source: EPA. The hole reduces water speed which accelerates deposition in a fixed location that’s easy to clean out.

Sediment traps vary by depth, width, length, shape (wide, long, triangular, etc.), and placement relative to the channel. And as this Army Corps study shows, modifying any one of those factors can greatly affect their efficiency. The challenge: to find the optimal shape, size and location.

The optimal length, for instance, depends on the speed of floodwaters and the settling rate of sediment particles. The trap needs to be long enough to give suspended sand time to fall out of suspension. Otherwise, sand just passes over the trap and continues downriver.

The hope: that the right type of traps placed in the right locations could help reduce flooding by reducing the amount of sediment migrating downriver and then blocking the mouths of each river branch.

Coming Out of HB1824 and River Basin Study

House Bill 1824, passed just last year, helps make sediment traps financially feasible. It allows the partners to remove material from the San Jacinto River and its tributaries to restore, maintain, or expand storm flow capacity without the need for state permitting or a royalty payment to the state.

Also note that the project will use data developed for the San Jacinto River Basin Master Drainage Study. It started in April of 2019 and is now about two-thirds complete.

Scope of Work Outlined

The scope of work outlined for Freese & Nichols includes, but is not limited to:

  • Reviewing and comparing: current and historical LiDAR surveys and aerial photos to gauge sediment erosion, deposition and location
  • Evaluating digital elevation maps to identify constrictions
  • Identifying the ten areas with the largest volumes of sediment deposition, including the two largest at a sand mine.
  • Reviewing FEMA floodplain, National Wetland Inventory, Texas Historical Commission and Texas Parks and Wildlife information for any problems related to each potential site.
  • Core sampling of sand bars to determine silt content
  • Ranking preliminary locations using the following: sediment deposition volume, potential sediment storage volume, proximity to existing roads, proximity to existing APO facilities.
  • Selecting the four locations with the highest potential based on drainage area, sediment load, geology, road access, etc.
  • Narrowing that to three locations in conjunction with SJRA and HCFCD
  • Developing sediment trap conceptual solutions specific to each of the final three selected sites
  • Estimating rate of sediment accumulation and clean-out intervals
  • Estimating reduction of sediment accumulation due to trapping
  • Submitting a final report.

The project does NOT extend into Lake Houston. Freese & Nichols will examine both the East and West Forks plus three miles upstream from the East and West Forks along certain tributaries. Tributaries would include, for instance, Lake Creek and Caney Creek. The idea is to intercept sediment before it can make its way into the lake.

Project Timing

The project timetable indicates completion in early fall of 2020, about the same time as the entire San Jacinto River Basin Study. Thus, any recommendations coming out of this project would not be constructed for this hurricane season. SJRA currently hopes to have the trap(s) installed by the end of 2022.

Pros and Cons of Sediment Traps

Proponents say sediment traps can reduce expensive dredging, restore fish habitat, reduce flood risk and more. However…

The scientific literature on sediment traps reveals mixed reviews. Many efforts fail, primarily because of lack of maintenance budgets and regular clean-outs. The SJRA and HCFCD plan to address that issue upfront by involving the sand mining industry. Notice that of the four location-ranking criteria bolded above, three favor proximity to sand mines:

  • Sand mines have pits to store sediment.
  • They have roads that lead to the river that can carry heavy equipment.
  • Mines have cleaning, sorting and transportation facilities onsite to reduce transportation costs, and thus make material more attractive for resale.

Compensation for Sand Miners

A compensation agreement for sand miners who remove sediment from traps has not yet been worked out. However, Matt Barrett, SJRA’s project engineer, says, “The intended benefit to the APOs of participating in the public-private partnership would be that they could utilize or sell the material they remove from the trap(s). ” 

Concerns of Environmental Groups

One of the concerns environmental groups have had about HB1824 (which began life as SB2126) is that it could potentially open the door to river mining and all of its risks.

River mining is outlawed in Europe, many other first-world nations, and even in some third world countries.

It tends to alter the gradient of rivers; cause upstream and downstream erosion; destroy private property along river banks; and undermine infrastructure such as bridges and pipelines.

Thus, the sediment traps raise a question of potential liability. If a pipeline or bridge is undermined or if property is eroded by the traps, who is responsible?

“Stability of the river is key to the long term safety and well-being of our community. We know that our public agencies have an important task. Before spending additional taxpayer dollars, don’t we want to make sure that projects won’t make problems worse AND won’t raise taxpayer costs?” said Jill Boullion, Executive Director of the Bayou Land Conservancy.

SJRA Response to Concerns

The SJRA has consistently denied that it would permit wholesale river mining. Most recently, Matt Barrett, the River Authority’s engineer for the sediment trap project said, “SJRA has no intention of engaging in or facilitating river mining in the San Jacinto River or any of its tributaries. The legislative language in HB1824 allows for the removal of material for the purpose of restoring, maintaining, or expanding the capacity to convey storm flows. Any projects undertaken by SJRA to remove or facilitate the removal of material from the San Jacinto River or its tributaries would be for this purpose.”

“River mining is not part of what we are doing. Only sediment in the trap will be removed,” he said.

Barrett is aware of potential hazards. “SJRA and its consultant are aware of the potential negative impacts that can be caused by trapping and removing sediment from a river or stream – changing the sediment balance – and prior to constructing any sediment trap or implementing removal of any material will perform analysis to ensure that any potential negative effects do not offset the positive.”

He sees the current design project as part of a pilot study that can scale up later. “One of the goals of this relatively small scale project is to serve as a “pilot” that gives us data on the real-world effectiveness of sand traps.  If data indicates this is a viable flood risk mitigation solution, then additional funding and partnerships could be sought to expand the concept.  We are excited to start this project and seek solutions to reduce flood risk.

For More Information

For more on how on sediment traps work, see this presentation found on the EPA site about a project in Michigan. It’s not directly analogous to south Texas because rainfall rates, soil types and gradients differ. But helps explain the theory of traps.

Click here to see Freese & Nichols’ full scope of work on the sediment trap project on the San Jacinto.

Posted by Bob Rehak on 4/3/2020

948 Days after Hurricane Harvey and 197 since Imelda