An ongoing study by the Army Corps of Engineers into the Addicks and Barker reservoirs is looking into how a third reservoir on Cypress Creek could help reduce flooding. However, a new study into Cypress Creek questions how much the reservoir would help and calls for more targeted solutions to flooding downstream.

The third reservoir would mainly serve to reduce flooding in Addicks Reservoir, said Chistof Spieler, a project manager with the Greater Houston Flood Mitigation Consortium, which published the Cypress Creek study in May. For people who live in the middle and lower parts of Cypress Creek east of the Grand Parkway, the third reservoir is unlikely to provide relief, he said.

“The worst flooding in the middle of the Cypress Creek watershed is actually caused by rain that falls in the middle of the Cypress Creek watershed, not by rain that falls upstream and flows downstream,” Spieler said.

The study, which included modeling data from Hurricane Harvey and 2016’s Tax Day flood, is one of the most comprehensive studies to ever be conducted on Cypress Creek, said Phil Bedient, a study author with Rice University’s Center for Severe Storm Prediction, Education and Evacuation from Disasters—or SSPEED Center.

One of the study’s top takeaways was that much of the flooding along middle and lower Cypress Creek is amplified by Little Cypress Creek and other tributaries, Bedient said.

“If you capture all the flow upstream with the third reservoir, you’ve still got ... these big flows feeding in from Little Cypress [Creek], creating this issue that cranks all the way downstream,” he said.

The implication, Spieler said, is the fight against flooding cannot depend on one large-scale project and will have to involve many smaller projects put together. The study suggested creating smaller reservoirs in the upper creek area, and a combination of channel improvements, home buyouts and a possible underground tunnel downstream.

Underground tunnel

Flood control officials in Harris County are studying the general feasibility of building underground tunnels in the county. Brian Gettinger—a tunneling services leader with the engineering firm Freese & Nichols Inc.—said he thinks the concept could work on Cypress Creek.

Gettinger pitched the tunnel system to the Cypress Creek Flood Control Coalition in March. He said it could cost $2 billion-$3 billion and would take years to build.

“Tunnels are an option of last resort,” he said. “You do them because everything else is too expensive, too environmentally challenging to permit, or people don’t let you do it because they don’t want their [property] torn up.”

The main goal of a tunnel is to move stormwater through the system faster, Gettinger said. Where the tunnel would start and end would have to be determined as a part of a routing study, he said.

Matt Zeve, the deputy executive director with the Harris County Flood Control District, said tunnels can be a viable alternative to creek widening, a process that can entail rebuilding bridges, moving utility lines and buying property.

“What an underground tunnel does is … it allows us to avoid all those things,” Zeve said. “In fact, if we were to build a tunnel here in Harris County, you wouldn’t even know it was going on.”

The HCFCD received a $320,000 grant in February to study if a tunnel could be supported by the geology of Harris County. Another $2.5 million has been set aside for future studies that would determine the cost and possible routes for the tunnel.

Any tunnel would likely depend on federal funding sources, and Zeve said the HCFCD is working with the Federal Emergency Management Agency to find funding.

Both Bedient and Spieler pointed out what a massive undertaking it would be.

“Tunnels are always expensive ... and include real maintenance costs,” Spieler said. “You have to consider the cost of that compared to the cost of other things you can do.”