HOUSTON, TX - June 21, 2022 - Large-diameter underground stormwater tunnels have the potential to significantly reduce flooding risks in Harris County and warrant deeper analysis, the Harris County Flood Control District announced today with publication of its “Feasibility Study of Stormwater Conveyance Tunnels – Phase 2” report. Preliminary information regarding a potentially “transformational” system of tunnels that could reduce persistent flooding for tens of thousands of homes were included in this update of the feasibility study, which was launched after Harris County officials challenged the Flood Control District to develop new flood risk reduction tools in the wake of Hurricane Harvey.
The second phase of the feasibility study shows that a potential tunnel system, if added to the existing bayou channels and detention basin network, could be a highly effective option for reducing flooding in densely populated areas of Harris County. The potential eight tunnel alignments (or locations) identified in the feasibility study represent the foundation of a Harris County tunnel system that could potentially reduce flooding in and around areas designated as damage centers. A damage center is a concentrated area that has and will continue to flood repeatedly, with water in homes and businesses. Damage centers were identified through a data-driven process, and then the damage centers were reviewed further to account for social vulnerability and other factors, in and around the watershed. By applying a social vulnerability screening, the feasibility study team identified the neighborhoods where people are least able to recover from a disaster. This comprehensive approach to flood damage reduction incorporates traditional engineering factors, as well as environmental and social considerations. This approach differs from one focused mainly on a cost-to-benefit ratio based on property values.
At the start of the tunnel feasibility study (Phase 1), the team confirmed that it is potentially possible to construct tunnels in many areas of the county. In the next stage (Phase 2), the team identified potential individual tunnel locations, considering various elements such as elevation, community impacts and availability of vacant land for traditional projects. As the benefits of tunnels became more evident during the feasibility study, however, the team also identified the potential benefits gained when tunnel alignments work synergistically with each other, al instead of as independent alignments. A comprehensive approach to flood risk reduction, with the use of a tunnel system in conjunction with the existing drainage system, would provide significantly more benefits by allowing the different alignments to reduce the flood risk across multiple watersheds.
So far, the Phase 2 feasibility study has found that tunnels would require the acquisition of much less property, as compared to traditional flood risk reduction projects. Also, because the majority of tunnel construction would happen deep underground, a tunnel may have a flexible alignment that is not tied as closely to a bayou or creek. For example, a tunnel could potentially provide benefits to flood damage centers in more than one watershed. Tunnels are being considered as an addition to – not a replacement for – the county’s existing stormwater management network of bayous, channels and stormwater detention basins.
The resulting tunnel system includes a potential eight tunnel concepts along the following bayous, in alphabetical order:
- Brays Bayou
- Buffalo Bayou
- Clear Creek, Berry Bayou and Vince Bayou
- Greens Bayou, Halls Bayou and Hunting Bayou
- Halls Bayou and Hunting Bayou
- Little Cypress Creek and Cypress Creek
- Sims Bayou
- and White Oak Bayou
These preliminary alignments from the Phase 2 feasibility study are conceptual and may change as more field information and modeling results are collected.These potential tunnel concepts come at a high cost, but in some situations can compare favorably against multiple smaller traditional projects totaling the same potential benefit. Preliminary construction cost estimates for a typical 10-mile tunnel segment are in the $3-$4 billion range. Funding for design and construction would require state and/or federal partnership funding, as well as a local share. If funding is secured, design and construction is estimated to take 10-15 years for a single representative 10-mile tunnel segment.
“Although the costs of a tunnel system are significant and finding partnership funding for a project of this scale is not guaranteed, we are excited about exploring tunnels as an additional tool to reduce flooding risks in Harris County,” said Flood Control District Executive Director Tina Petersen. “There is still additional analysis to be done on the economic benefits and integration into our current stormwater management network, and we are asking for public feedback as we move forward.”
Additional analysis that could occur in Phase 3 of the feasibility study would quantify countywide economic benefits of adding a tunnel system to our current stormwater management network, identify how to integrate such a system into our existing network, identify funding strategies, further investigate and refine potential tunnel alignments, and continue to gather public input. Phase 3 investigation could begin as early as Spring of 2023.
Materials from a June 16, 2022, Community Engagement Meeting, including meeting video and presentation, are available at https://www.hcfcd.org/tunnels.