Tunnels could be a viable solution to flooding in Houston

Downtown Houston is shown with Buffalo Bayou rising with floodwaters from Tropical Storm Harvey on Monday, Aug. 28, 2017, in Houston. ( Brett Coomer / Houston Chronicle ) Downtown Houston is shown with Buffalo Bayou rising with floodwaters from Tropical Storm Harvey on Monday, Aug. 28, 2017, in Houston. ( Brett Coomer / Houston Chronicle ) Photo: Brett Coomer, Staff / Houston Chronicle Photo: Brett Coomer, Staff / Houston Chronicle Image 1 of / 12 Caption Close Tunnels could be a viable solution to flooding in Houston 1 / 12 Back to Gallery

For Harris County Flood Control District and other entities around the city working to mitigate flooding, especially since Hurricane Harvey, the solution may be 150 feet underground.

Brian Gettinger, engineer and tunneling services lead with engineering consulting firm Freese and Nichols, gave a presentation on the viability of tunnels as a solution for the flooding issues plaguing Houston. The event was held at the Northgate Country Club as part of the Houston Northwest Chamber of Commerce Community Luncheon on Aug. 15.

Gettinger stressed that the projects are currently being studied and no plans for tunnel design or construction have been finalized. However, he said that tunnels could reduce the impact of major rain events on communities and land by directing water underground and pushing it to the Houston Ship Channel.

Freese and Nichols has partnered with HCFCD to research viable flood mitigation options including the tunnels.

RELATED: Harris County Flood Control District proposes tunnel idea to drain stormwaters

Gettinger pointed to Austin and San Antonio as cities currently using underground tunnels for flood mitigation. Dallas is currently in the middle of constructing tunnels.

Tunnels could be constructed with earth pressure balance tunnel boring machines, which are built to match the diameter of the tunnel needed.

During his presentation, Gettinger said tunnels would use an inverted siphon system to move water during flooding events from a point of higher elevation to a point of lower elevation underground. The water would be caught by inlets in the path, built near larger bodies of water such as Cypress Creek.

Tunnels could be anywhere from 20 ft. in diameter to 57 ft. in diameter, although 30 ft. to 40 ft. would be ideal for the Houston area, Gettinger said. Although no location for a tunnel has been determined, Gettinger said possible locations would be near Cypress Creek and Buffalo Bayou.

“(How fast the water moves) depends how big a diameter tunnel you build, and that’s simply a scalable technology,” he said. “It’ll push out to the other side, no pump station required. The rate that water is moved is a pretty simple equation: how big is your tunnel? How long is your tunnel? How rough is the tunnel lining? How much difference in elevation do you have?”

Gettinger explained that development has impacted flooding in Houston, although it is not the sole cause.

RELATED: Harris County poised to receive grant to study flood tunnel idea

“I grew up in Kansas City,” he said. “Everyone makes fun of Kansas for being flat. Coastal Texas is flatter than Kansas. Much flatter. We also have soils that are not conducive to absorbing very much water. They can absorb water, but they can’t absorb 30 inches of water.”

As for the viability of putting tunnels underground in Houston, Gettinger said he viewed tunnels working in an area with similar geology, Washington, DC.

Gettinger said the tunnels would not completely fix flooding, but could significantly reduce it along with other flood mitigation concepts and plans. He said Houston needs more water conveyance along larger bodies of water, such as Buffalo Bayou and Cypress Creek, to solve a large part of the flooding problem without tunnels.

Gettinger said the additional conveyance needed, up to 400 ft. in some areas, is not viable due to buyouts needed and the lack of land. He also said the tunnels being underground would reduce deforestation and impacts on natural environments.

“We don’t want all of the trees cut down on Cypress Creek and we don’t want the channel to be 700 feet wide,” he said. “Texas is a private property state. Nobody wants to take property from people and put a piece of flood control. But, we don’t want to flood so we’re kind stuck and we have nowhere to build conditional detention.”

According to Gettinger, the tunnels would cost approximately $100 million a mile. As an example, Gettinger said 15- to 20-mile-long tunnels 30 to 40 feet in diameter would cost $3 billion each. Comparatively, buying land to build conveyance around Buffalo Bayou or Cypress Creek could easily cost $4 billion each, he said.

“That’s a non-starter discussion,” he said. “To buy the property on Buffalo Bayou from the reservoirs to the ship channels to provide that conveyance would cost $4 billion just to buy property without turning any dirt yet. That’s assuming we even buy it. I think there’s some people that live along Buffalo Bayou that have pretty well-paid lawyers that are probably not going to let that happen.”

As of now, the tunnels are only being studied for potential use and have not been approved for construction. For more information, or to give feedback, visit www.hcfcd.org.

chevall.pryce@chron.com