Raising Bridges, Building Meander Bypasses on Buffalo Bayou Doesn’t Reduce Flooding, Study Says

New Idea is to Strip and Widen Bayou Channel in Terry Hershey Park Above Beltway 8

New Problem: Increased Flooding Downstream

 

Oct. 20. 2019

A study commissioned by the Harris County Flood Control District has found negligible flood-reduction benefits to building bypass channels through meanders or raising bridges on Buffalo Bayou.

But the District is instead contemplating stripping the trees and vegetation and digging out the engineered banks of Terry Hershey Park to widen the channel by fifty feet on both sides for some six miles below the dams in west Houston. The District is still in the process of scraping out new overflow basins on the south bank in the park.

These findings were presented at a packed public meeting Thursday, Oct. 17, in the Memorial area of west Houston. The study, the result of public pressure from property owners who flooded in neighborhoods adjacent to Terry Hershey Park, was conducted by the engineering firm Huitt-Zollars and funded with $350,000 in Harris County flood bond funds.

Buffalo Bayou originates in the prairie near Katy, Texas, and flows for some fifty-three miles through the center of Houston, emptying into the San Jacinto River and Galveston Bay. It is the main river flowing through the city and a central part of the region’s natural drainage system. Below Beltway 8 to Shepherd Drive just east of downtown, Buffalo Bayou remains a mostly winding, wooded stream, and it was these many meanders that some residents upstream of the beltway blamed for flooding their homes when the floodgates on the dams were opened during Harvey.

 

Graphic courtesy of the Biomimicry Institute

 

The Meeting and The Findings: Is Nature a Better Engineer?

Alan Black, director of operations for the Flood Control District, opened the meeting by explaining what the district does and why the region floods (reasons which did not include the fact that so much of the city is covered in impervious surface). The first priority for the district is still “deepening and widening bayous,” said Black. Unfortunately that is a futile, never-ending pursuit, like building bigger freeways. It also leads to bank collapse, lifeless streams filling with silt and polluted water, a barren landscape, and continuous costly maintenance.

Modern flood management, rather than collecting and moving as much water as fast as possible, focuses on stopping stormwater before it floods a stream and on managing flooding in place. For instance, “lag time” is the amount of time it takes for rain to fall on the ground and enter a stream. The shorter (faster) the lag time, the higher the peak flow (flooding) in the stream. Trees, deep-rooted vegetation, detention basins, rain gardens and more can help increase the lag time and reduce flooding. There are many ways that neighborhoods and individuals can take responsibility for slowing, spreading out, and soaking in stormwater. (See also here.)

The district, which has limited legal tools dating from 1937 when it was founded, does focus also on building detention basins to temporarily hold stormwater, as well as on moving people out of harm’s way through buyouts.

 

Bridges

Michael Tehrani, vice-president of Huitt-Zollars, explained the study findings, which were “not that promising,” he told the large crowd, which included politicians and representatives of the Corps of Engineers. Buffalo Bayou is relatively flat, a “lower velocity channel” with a lot of trees; the channel itself “controlling the water and determining the Water Surface Elevation, not the bridges.”

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