Feds Fund Houston-Area Stormwater Tunnel Feasibility Study

The Harris County Flood Control District, whose systems were overwhelmed by Hurricane Harvey in 2017, is set to begin a $400,000 study into the feasibility of constructing large-diameter, deep underground stormwater conveyance tunnels.

Soldiers arrive in Houston in August 2017 to aid residents affected by Hurricane Harvey. (photo: Texas Army National Guard)

The study will be funded by a $320,000 grant from the U.S. Economic Development Administration (EDA), to be matched by $80,000 in local funds provided through a $2.5 billion bond program approved by voters in 2018.  That program includes a total of $20 million for preliminary engineering in connection with the tunnel concept.

The four-month study, slated to begin this year, will include a review of soil and groundwater conditions, as well as other geotechnical, geological and environmental assessments. The study also will aim to develop better cost information for tunnel construction in the area.

“We will be looking at our soil and water table conditions and compare those to the technology that exists in the tunnel construction industry to ensure there is a fit,” the flood control district said in an announcement of the grant. “If the use of tunnels is found to be feasible, future efforts could examine potential tunnel routes, complete hydraulic analyses to determine the required tunnel diameters, and determine proposed inlet and outlet shaft locations.”

If proven feasible and ultimately funded through the bond program, tunnels would collect stormwater at upstream locations along the bayous, convey the stormwater downstream via gravity in deep underground tunnels measuring 20 feet or more in diameter, and discharge the stormwater into the Houston Ship Channel at a safe location. The goal would be to significantly reduce flood risks in Harris County watersheds where tunnels could be constructed.

The initial study will examine whether this technology is even possible in our area, which is characterized by soft soils and a high groundwater table.

While costly, tunnels have been employed to carry stormwater in other locations in Texas and nationwide as an alternative to traditional stormwater conveyance improvement projects. Tunnels can utilize existing public rights-of-way – such as roadway corridors – and with relatively little disruption to developed urban areas, which helps to reduce cost. Cost per mile may vary widely – between roughly $40 million and $163 million per mile for projects in San Antonio, Dallas and Austin – depending on soil conditions and other factors. Tunnels typically are constructed using tunnel boring machines, at a depth of from 100 to 150 feet.

The grant comes via an EDA grant program in connection with the 2017 Hurricane Harvey presidential Disaster Declaration. The grant could be submitted to Commissioners Court for authorization to accept as early as the Feb. 26 meeting, an action that would trigger the matching bond funds.

UC Staff Report

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