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 firstname.lastname@example.org.
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.
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.
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.
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).
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.
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.
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.
My Biggest Fears
My biggest fears with the proposed pilot study are that it:
- Asks people to chose from a limited menu.
- Could divert attention from better solutions that would reduce flood risk faster in the headwaters of Lake Houston.
- Might make the public think the problem is solved.
- Could open the door to river mining and further destabilize the riverine environment.
- 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
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:
- Revegetating riverbanks
- Decreasing the slope of sand mine dikes.
- Reinforcing sand-mine dikes to withstand floods (like HCFCD does with detention ponds)
- Leaving more natural green space between mines and the river
- Moving sand mine stockpiles out of floodway/floodplain areas
- Only clearing areas actively being mined
- Dredging more often where the sand builds up near Lake Houston
- Dredging a channel through the West Fork mouth bar area
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.