Sand trap recommendation

SJRA’s Next Steps After Public Comments on Sand Trap Study

The San Jacinto River Authority (SJRA) has completed its initial sand trap study, in partnership with Harris County Flood Control, and reviewed public comments. According to Matt Barrett PE, SJRA’s Manager of Water Resources and Flood Management, the SJRA is working toward a pilot study. But a successful pilot will require several things including funding partners and consultation with regulatory agencies, such as TCEQ and Texas Parks and Wildlife.

The goal of the project: intercept and remove sediment migrating downstream to reduce buildups elsewhere.

west fork mouth bar before dredging
West Fork mouth bar after Harvey and before dredging. A small area at the far right had been building up before Harvey. The rest appeared when Harvey’s floodwater’s receded.

The proposed pilot sand trap could not possibly remove enough sand by itself to prevent the build up of another giant sand bar like the one above. However, a network of such traps might help.

Consultation with Regulatory Agencies

In Texas, among other things, TCEQ regulates floodplains, sand mining, and water quality. Texas Parks and Wildlife regulates rivers between the vegetation on each bank.

Legislation exempts the SJRA, HCFCD and its contractors from obtaining state permits before removing sediment from the river. Regardless, the SJRA wants to work with regulatory agencies to ensure it doesn’t recommend anything that runs afoul of agency policy. Example: the newly adopted TCEQ Best Management Practices for Sand Mining. For instance, see section 2.1.1 – Vegetated Buffer Zones.

Location of proposed sediment trap.
Possible location of trap for pilot study outside Hallett Mine on West Fork. Trap would consist of a trench through the middle of the point bar in the foreground.

But a trench at this location might run afoul of new TCEQ BMPs for sand mining that specify 100-foot buffer zones adjacent to perennial streams greater than 20-feet wide.

Sand trap recommendation
Schematic diagram of proposed trap at location above from initial conceptual design study finished before TCEQ adopted new BMPs.

Finding Funding Partners

SJRA must also find funding partners as it does not have a revenue source to pay for a pilot study and full construction costs of sand traps. In that regard, Barrett mentioned Harris County Flood Control and City of Houston as potential partners.

Barrett is also exploring partnerships with APOs (Aggregate Production Operations, aka sand mines). Sand mines can help defray expenses by removing sand from the traps as it accumulates. Of course, their desire to do that will depend on the location of the traps. They would prefer something close to their mines to minimize transportation costs and logistics while maximizing salability of the sand.

Hungry-Water Concern

Barrett also mentioned the need for the preliminary engineering design to avoid a “hungry water” effect which might increase erosion downstream. Hungry water results when streams have more power to transport sediment than they have available sediment. As a result, it erodes stream beds and banks to compensate.

Would Program be Extendable if Successful?

In a wide-ranging 45-minute discussion with Barrett, I raised several other potential issues. They included:

  • Location of the test near APOs, far upstream from the heavily damaged areas near Lake Houston where sand accumulates. There are no active sand mines between Humble and Kingwood – and few on other tributaries.
  • No sediment gages upstream and downstream from the test site. Not having a way to demonstrate success could limit future expansion of the program.
  • Potential partners that could remove sand from traps NOT located near APOs. You need a way to get sand out of a trap after it fills up. If the City of Houston or HCFCD established an ongoing maintenance dredging program, that could solve this issue.
  • How long an APO will remain committed to a location near a trap. After going to the expense of building a trap, SJRA would want to make sure the APO didn’t move operations to another location in a year or two. For example, some sand miners have talked about moving to the East Fork to take advantage of expected growth associated with the new Grand Parkway extension.

The SJRA must work through such issues to protect the public’s investment in the program. It has many moving parts. And the interests of all partners must align before moving forward.

Outline of Next Steps

So the next steps are:

  • Find partners with money whose interests align.
  • Obtain commitments from them.
  • Consult with regulatory agencies to avoid potential conflicts.
  • Lock down a location near an APO.
  • Begin preliminary engineering.
  • Ensure the pilot study (based on proximity to APOs) can extend to other areas (Rehak concern)
  • Find a way to measure success to help extend the pilot program if successful

In business, there’s an old maxim: “That which can be measured will be repeated.” Doing a pilot study that can’t be measured or replicated elsewhere helps no one.

For more information, see this post about potential sites and designs for traps. It features the most likely spot for a pilot study.

The Army Corps has also published extensive research about the effectiveness of different sand-trap designs. Search for “Army Corps sand trap studies.” I originally became interested in the concept when I read a Corps study about a test of different trap geometries in the Mississippi River. There are many alternatives including some that could be located where water slows down at the entrance to Lake Houston (where the Harvey mouth bar appeared in 2017). Such a location would have the advantage of intercepting sediment from all upstream sources, not just the West Fork...if all the tumblers aligned.

Posted by Bob Rehak

1783 Days since Hurricane Harvey