Stormwater Tunnel on Buffalo Bayou Will Not Prevent Flooding
Plans Still Evolving
Comments and Questions
Please note that the Houston Chronicle has published a highly useful explanation of the coastal protection plan for Galveston Bay known as the Ike Dike. Unfortunately the paper has not figured out how to market to nonsubscribers.
Oct. 2, 2022
Large stormwater tunnels will likely not prevent flooding on Buffalo Bayou, according to the recent report from the Harris County Flood Control District.
Tunnels draining the federal flood control dams on upper Buffalo Bayou would not even be adequate to prevent a catastrophic overtopping of the dams or flooding of properties behind the reservoirs if a Harvey-like storm parked on top of the reservoirs, according to an engineering analysis prepared for Houston Stronger, a west Houston-based group formed in the wake of Harvey in 2017.
The Harris County Flood Control District is considering a $30 billion, 133-mile system of eight large-diameter stormwater tunnels to manage flood risk in the county. The district issued its Phase 2 feasibility report at the end of March and updated it in September. The district has been holding public meetings and taking public comments in preparation for the next phase of analysis to begin in the spring.
The probability that the proposed Buffalo Bayou tunnel would not prevent flooding downstream on the bayou is based on its limited capacity. The main tunnel would connect to two short 40-foot diameter tunnels, less than two miles long, draining Addicks and Barker dams far upstream. They would have a combined capacity of 11,600 cubic feet per second (cfs). This would drain into the much longer 40-foot diameter bayou tunnel which would have a capacity of only 12,240 cubic feet per second. Inlets or intakes draining the entire bayou downstream would have to be closed to accommodate stormwater flowing into the main tunnel from the two dams. The main tunnel would traverse the city deep underground for some 22 miles all the way to the ship channel east of downtown. (p. 127) (See also p. 1130)
That means that Buffalo Bayou would still flood because the bayou floods from urban rain runoff below the dams even when the dam floodgates are closed and no stormwater is draining out of the reservoirs. (See also here.)