The Harris County Flood Control District has released the results of a study showing that it’s both economically feasible and physically possible to build a massive tunnel system under Harris County to more efficiently ferry stormwater into the Houston Ship Channel.

The tunnels could handle much larger water volumes than existing bayous and creeks – closer to the rates of the Addicks and Barker reservoirs than above-ground channels and bayous.

Preliminary estimates show that a 10-mile-long, 25- and 40-foot diameter tunnel would cost approximately $1 billion and $1.5 billion, respectively, to build.

The deep tunnel concept is similar to a 1996 Flood Control District feasibility study that considered a trenched box culvert system along Interstate 10. Unlike those tunnels, the large-diameter tunnels can transport much larger water volumes into the Houston Ship Channel. The benefits include avoiding flooding that endangers lives and property.

The tunnels were modeled after similar tunnels in Washington, D.C., the first of which was finished in October 2016. At 23 feet in diameter, the D.C. tunnel is smaller than those proposed for Harris County. DC Water, the area’s flood control authority, estimates that the tunnel has reduced the area’s annual flooding probability to 15%, down from 50%.

The Harris County Flood Control District paid for the phase-one study through a $320,000 grant from the U.S. Economic Development Administration and an $80,000 cost-share from the Flood Control District’s 2018 Bond Program. Considerations for the next phase of the study are in development.

To learn more about the project, click here.