Houston officials consider $30 billion tunnel project to curb impact of future floods

(UC) — The Harris County Flood Control District (HCFCD) is considering a massive underground tunnel project to alleviate the region's centuries-long flooding, according to the Stormwater Report.

HCFCD manages stormwater on approximately 4,700 sq. km (1,800 sq. miles) of land in the greater Houston area. The project's planning efforts, which would cost around $30 billion, began shortly after Hurricane Harvey flooded more than 100,000 properties in the HCFCD service area in 2017.

Given the region's low elevation and soft, clay-rich soils, the agency recently completed the second phase of a long-term investigation into whether a series of eight large-diameter stormwater tunnels located as deep as 30 m (100 ft) underground would be a feasible and cost-effective option.

During a virtual meeting on June 16, HCFCD Assistant Director of Operations Scott Elmer explained that while building the proposed tunnels would be both costly and complex in comparison to aboveground flood-control measures, the project's benefits would benefit the entire HCFCD service area.

Furthermore, as available space for aboveground infrastructure shrinks, exploring underground options could provide new flexibility for stormwater management in the region's most developed and flood-prone areas. The current proposal calls for 210 km (130 miles) of underground tunnels with diameters of up to 14 m (45 ft). These tunnels have the capacity to collect and transport up to 24.6 billion L (6.5 billion gal) of water at a time.

The feasibility study, which was funded by a grant from the US Department of Housing and Urban Development, identified 11 watersheds out of the 23 that encompass HCFCD's service area where underground tunnels would likely be more cost-effective than aboveground alternatives.

Aboveground alternatives include expanding existing stormwater conveyance channels and constructing new detention and retention basins. They could theoretically handle the same amount of stormwater as the proposed tunnel system, but would have a much larger physical footprint and would cause significant community disruption, according to Elmer.

Because there is little available space in the target watersheds, conventional options would necessitate the city purchasing and demolishing dozens of privately owned properties, a costly and disruptive process that could take decades to complete before construction could begin.

The district's next phase of investigation, set to begin in early 2023, will pinpoint specific points where a tunnel system could connect with existing aboveground flood-control structures, including intakes and outfalls. HCFCD staff will also conduct public outreach to learn more about the project's potential impacts on the communities it will serve. It will also improve the tunnel system's design and better quantify its benefits.

HCFCD will also investigate funding and financing options for the project. Elmer emphasized that the tunnel system proposal must receive substantial financial support from state and federal sources in order to reduce burdens on local taxpayers.

Elmer estimates that if HCFCD decides to pursue the tunnel project, construction will take at least 10 to 15 years. According to its current design specifications, the system could prevent up to 120,000 instances of flooding in the HCFCD service area over the next 100 years.

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