flood tunnel butterhead being lowered into launch shaft

Virtual Meeting on Flood Tunnels Thursday Night

The Harris County Flood Control District (HCFCD) will hold a community engagement meeting to share Phase 2 results for the Feasibility Study of Stormwater Conveyance Tunnels. The meeting’s purpose: to inform residents about the status of the Tunnels study and share study information.

At the highest level, the study looks at the potential to reduce flooding risks in Harris County via large-diameter, deep underground tunnels that convey stormwater.

The study includes three phases:

  • Phase 1 examined the feasibility of tunnels in this area.
  • Phase 2 looked at potential routes and alignment concepts for areas with unmet needs.
  • Phase 3, if needed, will include a preliminary design to validate assumptions.
Stock photo from Phase 1 report shows tunneling machinery (cutterhead and shield) being lowered into a launch shaft.

Tunnel Tradeoffs

The primary benefit of tunnels: they add stormwater conveyance without disturbing development on the surface. In highly developed or environmentally sensitive areas, this is important. But tunnels also come with technical and financial challenges. For instance, you must route them around oil wells, water wells, and geologic faults. And the cost can be considerable: up to $150 million per mile for a 40-foot-wide tunnel.

More about Phase 2

In Spring 2022, HCFCD completed Phase 2 of its feasibility investigation. The purpose of Phase 2 was to identify unmet flood mitigation needs in Harris County’s watersheds. Phase 2 also developed distinct tunnel concepts to meet those needs. 

This phase of the study focused on identifying:

  • Watersheds that met the criteria for a tunnel 
  • Flood damage centers that presented the highest risk and determining whether the tunnels would be more cost-effective over traditional flood control measures (e.g. stormwater detention, channelization, or buyouts)
  • Potential strategic locations for intakes and outfalls
  • Opportunities to integrate tunnels with existing and proposed flood damage reduction systems
  • Geologic and man-made hazards.

Phase 2 found that a tunnel SYSTEM, rather than one or more individual tunnel alignments, should be the focus of further study. Thus, we would need additional study before a final decision on whether to move forward with tunnels. 

Phase 2 received funding from the U.S. Department of Housing and Urban Development’s Community Development Block Grant Disaster Recovery program.

Meeting Details: How to Register

Community engagement is an important component of this study. So, HCFCD invites your participation.

The Virtual Community Engagement Meeting will be held on: 
Thursday, June 16, 2022
6:30 p.m. – 7:30 p.m.
Join online at: PublicInput.com/Tunnels
Or by phone* at 855-925-2801 with Meeting Code: 9622

*If you attend by phone only, maps and other exhibits will not be visible. However, information will be available after the meeting on the project webpage at hcfcd.org/tunnels.

The meeting will begin with a brief presentation to share project updates. A moderated Q&A session will follow. You can submit questions, comments and input before, during and after the meeting. Any comments not addressed during the Q&A session will receive a response after the conclusion of the public comment period.  

Even if you can’t attend the live meeting, still register to receive project updates. Video of the meeting will be available on the Flood Control District’s website and YouTube channel after the event.

Accommodations can be made for those with disabilities. If needed, please contact 346-286-4040 at least three business days prior to the meeting. For questions, please contact the Flood Control District at 346-286-4000, or fill out the comment form online at hcfcd.org/tunnels.

Overview of Other Phases

For a brief history of the tunnel investigation, visit this page on the HCFCD website.

Phase 1 took a high-level look into the feasibility of constructing large-diameter deep tunnels to help move stormwater out of Harris County. It considered soil types, geotechnical challenges, hydraulic capacity, impacts, scheduling, and cost projections. Phase 1 was not watershed specific. Nor did it focus on any particular alignment/location.

Phase 1 findings include:

  • Geotechnical conditions do not appear to present any remarkable, nor non-negotiable concerns.
  • Geologic faults may require special design and construction considerations if crossed by the tunnel; not considered fatal flaws.
  • Tunnels can move a significant rate of stormwater operating by gravity as an inverted siphon.
  • Tunnel cost, including a 50 percent contingency, for a representative 10-mile long, 25- and 40-foot diameter tunnel is approximately $1 billion and $1.5 billion respectively.

For the complete 1700-page, 300-megabyte final report, click here.

Phase 3 will include preliminary design. The purpose:

  • Prove project benefits and costs
  • Select locations
  • Investigate geologic faults
  • Validate assumptions made during Phase 1 and 2
  • Identify internal and external sources of funding.

This post will give you more background about flood tunnels.

Posted by Bob Rehak on 6/12/2022

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