Tag Archive for: sand trap

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

Lake Houston Area Flood Prevention Initiative Takes Position on SJRA Sand Trap Proposal

Bill McCabe of the Lake Houston Area Flood Prevention Initiative submitted this letter in response to the SJRA’s Request for Public Input on its Sediment Removal and Sand Trap Pilot Study proposal. He raises a concern that no one else has so far: The proposal may run afoul of the recently adopted Best Management Practices for Sand Mining in the San Jacinto River Watershed. The essence of the study’s recommendation: allow sand miners to remove sediment from the point bars outside mines. However, the BMPs stipulate undisturbed buffer zones between mines and the river.

Page 8 of the Freese & Nichols Sediment Removal and Sand Trap Study for the SJRA shows this schematic of the recommended solution.

McCabe has given ReduceFlooding.com permission to reproduce his letter. See below.

To the SJRA:

Thank you very much for the opportunity to respond to the Sand Trap Study you have formulated. I think your initial work is excellent and commend you on your data gathering.  However, there are a few points I would like you to consider before proceeding.

As you know, my group worked very hard with TCEQ to establish Best Management Practices (BMPs) for Sand Miners in the San Jacinto watershed.  This Rulemaking was approved in early 2022 and incorporated into 30 TAC Chapter 311, Subchapter J.  Also approved was corresponding Regulatory Guidance document RG 555, implementing the BMP Rules.

Key Provision: Undisturbed Buffer Zones

A key provision of the Regulatory Guidance is:

2.1.1 Vegetative Buffer Zones Vegetative buffer zones are continuous undisturbed or planted vegetated areas that surround a development, or land disturbance activity, or that border an intermittent stream or permanent water body. Buffer zones aid in sediment filtration and removal by slowing surface water flow through these areas. Disperse construction site runoff over the entire buffer zone if possible. A minimum 100-foot buffer zone is required adjacent to perennial streams greater than 20 feet wide, 50 feet for perennial streams less than 20 feet wide, and 35 feet for intermittent streams. Measure buffer zones from the stream bank to the nearest area of disturbance at the site.”

Study Recommendation is “Counterintuitive”

We had fought very hard to establish these buffer zones (at one time we had proposed buffer zones of 1,500 feet).  The very essence of this provision was to KEEP the miners out of the San Jacinto riverbed.  Now to go back and allow in-stream mining seems counter-intuitive to me.

Legal Complications of Waiving Buffer Zone

Additionally, I am not certain how you would get this buffer zone condition waived.  HB 1824 issues a waiver per the Parks and Wildlife Code, Sec. 86.017.  However, it does not address TCEQ regulation at 30 TAC Chapter 311(J), which was implemented AFTER HB 1824 was passed.  You need to have your staff look at the interaction between the two conflicting provisions.

More Holistic Approach Needed

Before proceeding, I would suggest looking closely at Bob Rehak’s Holistic approach to reducing sedimentation, as outlined in one of his recent articles:

  • Revegetating riverbanks
  • Dredging more often where the sand builds up near the mouth of the West Fork
  • Dredging a channel through the mouth bar area
  • Reinforcing sand-mine dikes to withstand floods
  • 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
  • Decreasing the slope of sand mine dikes

Yours truly,

William McCabe, Lake Houston Area Grassroots Flood Prevention Initiative 

If you have questions or comments on the SJRA’s Sediment Trap Proposal, please submit them via email to: floodmanagementdivision@sjra.net

Deadline: No later than April 29, 2022

Posted by Bob Rehak on 4/15/22 based on a letter by Bill McCabe, Chairman of the Lake Houston Area Flood Prevention Initiative

1690 Days since Hurricane Harvey