SJRA to Consider Three Flood-Mitigation Studies Thursday

SJRA directors will consider accepting grant funding for three flood-mitigation studies at their board meeting on Thursday, 7/22/21. The studies include:

  • A joint reservoir operations study between Lake Conroe and Lake Houston
  • An upper San Jacinto Watershed regional sedimentation study
  • A conceptual engineering feasibility study for flood-control dams in the Spring Creek Watershed

The board will also consider executing escrow agreements related to each grant. TWDB grants work on a reimbursement basis. At the start of the project, TWDB puts the grant money into an escrow account. Then funds are drawn down as vendors submit invoices and TWDB approves them.

I posted previously about grant applications for these projects. Now that the grants have been approved, work can actually begin once the board agrees to accept the money. See details below about each project.

Joint Reservoir Operations Study

The addition of 1000-feet of crest gates to the Lake Houston Dam is a game changer for the way reservoirs on the San Jacinto work together. Right now, the gates on Lake Houston have a discharge capacity of only 10,000 cubic feet per second (CFS). The discharge capacity of the crest gates would increase that by more than 4X to 45,000 cfs. It’s still not the 150,000 CFS of Lake Conroe gates, but percentage-wise it’s much closer.

Thus, operators need to re-examine how best to synchronize their operations and plans. For instance, pre-releasing water in advance of a storm might be more viable now as a flood-mitigation strategy.

Another element of this study is a “flow forecasting tool.” It would predict rises in Lake Houston depending on the flow rates in tributaries during major storms. Matt Barrett, SJRA’s flood-mitigation director, says this tool could be useful for flood warnings and evacuations. If you knew that lake water would rise X feet in Y hours, and that your slab was a foot below X, you’d know exactly how much time you had to pack up your valuables and get out.

This study is being conducted with help from the Cities of Houston and Humble.

Upper San Jacinto Basin Sedimentation Study

The upper basin of the San Jacinto River includes everything above Lake Houston. This study has three goals:

  • Understand where the sediment is coming from
  • Learn where it ends up
  • Develop a management plan to handle it.

For the record, here is the scope of work. Note that stakeholder input and public meetings will be a big component of this project (Task 2). Tasks 3 and 6 include evaluation of sand mines. And Task 7 includes “Sand and Gravel Mining Best Management Practices.”

The San Jacinto West Fork has more than 20-square miles of sand mines in the 20-mile stretch between I-69 and I-45, exposing a swath of sediment averaging a mile wide.

The sedimentation study is being conducted with financial help from the Cities of Houston and Humble, and the Harris County Flood Control District.

A related sand-trap study is nearly complete. The SJRA should release it next month for public input.

Spring Creek Flood Control Dam Feasibility Study

About a year ago, SJRA applied for a TWDB grant to study the feasibility of building two flood control dams in the upper Spring Creek Watershed. The partners identified two preferred locations from a previous siting study that considered dozens. The two included Walnut and Birch Creek tributaries.

The objective now: to see whether the benefits justify the costs. Said another way, will the dams reduce flooding and protect enough structures to make the cost of building them worthwhile?

Together, they would have a combined capacity of 20,000 acre feet. That’s significant. But it would provide more benefit to people in the upper Spring Creek watershed than the Lake Houston Area.

The scope of work includes:

  • Environmental due diligence
  • Site investigations
  • Literature and mapping review
  • Permitting requirement investigations
  • Desktop surveys/assessments
  • Preliminary coordination with permitting agency
  • Conceptual design of dams to determine feasibility – geotechnical borings, alternative configurations development, H&H modeling analysis, etc.
  • Cost estimate development – dam construction costs, as well as costs related to land acquisition, utility conflicts and relocations, environmental mitigation, O&M, etc.
  • Update benefit/cost ratios (BCR) from SJRWMDP using data developed as part of this effort.

Partners in this effort include the SJRA, HCFCD, City of Humble, and five municipal utility districts. To learn more about these projects and others, consult pages 19 and 21 of this PDF.

To View or Participate in the Board Meeting

The SJRA board meeting starts at 8am.

If you choose to participate via webinar, register at this link and use webinar ID 950-202-179.

If you use the GoToWebinar App, you will have the opportunity to provide public comments.

To view the Agenda, visit SJRA’s website at: 07-22-21 Agenda and Coversheets.

Posted by Bob Rehak on 7/22/21

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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.