Harris County Commissioners Vote Tuesday on Feasibility Study of 2 Dams on Spring Creek Tributaries

Harris County Commissioners will vote tomorrow, 6/8/2021, on whether to enter into an interlocal agreement (ILA) for a feasibility study of two dams on Spring Creek tributaries. The ILA is with the San Jacinto River Authority (SJRA), the City of Humble, five Utilities Districts and the Texas Water Development Board.

The conceptual feasibility study includes the design of two dams with three alternatives for each. One potential site will be along Birch Creek and another along Walnut Creek.

Spring Creek forms the Harris/Montgomery County Line for most of its length. It also bridges precincts 3 and 4 in Harris County.

Dry Dams with Fixed Height Spillways and Low-Flow Culverts

The San Jacinto River Basin Master Drainage Plan originally identified both sites. And both would feature “dry dams.” That means, they would contain no permanent water. Specs call for building the dams high enough to hold back a hundred year flood.

Each would contain a permanent fixed-height spillway. Water would flow over the spillway when it reaches 100-year level as defined in Atlas 14. The dams would also contain low-flow culverts allowing water lower than the spillway to drain slowly after a flood, as it would from a detention pond. None of the potential designs will consider gated structures.

Initial estimates in the SJR Master Drainage Plan released last year suggest that:

  • A 41-foot-high, 0.7 mile long dam on Birch Creek could contain 7,731 acre-feet of water in a hundred-year storm. That’s a foot of rain falling over a 12-square-mile area.
  • Likewise, a 46-foot-high, 1.2 mile long dam on Walnut Creek could contain 12,159 acre-feet. That’s a foot of rain falling over a 19-square-mile area.

Components of Study

The feasibility study will include:

  • Wetland, endangered species, hazardous-waste assessments
  • Documentation of conditions at each proposed site
  • Estimating the extent of potential inundation
  • Identifying ways to minimize or avoid environmental impacts
  • Soil surveys with borings up to 75 feet deep
  • Spillway design
  • Conceptual recommendations for dam design at each site
  • Estimating probable construction costs
  • Estimating land needs and costs
  • Identification of potential utility issues, such as pipeline crossings
  • Plans for raising or relocating roads, cemeteries and utilities outside the Atlas-14, 100-year floodplain
  • Estimating total project costs, financing costs, annual operations and maintenance costs
  • Developing a benefit/cost ratio based on reductions in flood damages over a 50-year period.

SJRA would lead the Spring Creek feasibility study. The local partners are seeking up to $1 million in matching funds from the Texas Water Development Board’s Flood Infrastructure Fund.

One Part of an Upstream Detention Solution

The big question is: How much benefit would people downstream in the Lake Houston Area get from Spring Creek dams? The answer is “some, but not as much as you might think.” That’s because, as you move farther downstream, the dam blocks a smaller percentage of the watershed. Think about it. Right below the dam, everything less than a 100-year storm would be intercepted. But by the time you get down to US59, you’re also getting water from Cypress Creek, Lake Creek, the West Fork and dozens of smaller streams and ditches.

So while the Spring Creek Dams could be part of a solution to offset future releases from the Lake Conroe Dam, it’s not the total solution for the Lake Houston Area. Regardless, it still would help many homes and businesses upstream along Spring Creek. Exactly how many? We’ll have to wait to see until we get the study results.

For more information about the Walnut and Birch Creek locations, see pages 39-61 in the San Jacinto River Basin Master Drainage Plan, Appendix G.

For the full text of the proposed interlocal agreement that Commissioners will vote on Tuesday, click here.

Cost of the study to local partners will depend on the match supplied by TWDB, which has not yet been finalized.

Posted by Bob Rehak on 6/7/2021 based on draft of a proposed Interlocal Agreement and the SJR Master Drainage Plan

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