The entrance to Olmos Basin Park at East Basse Road is flooded following heavy rainfall throughout South Texas.
The entrance to Olmos Basin Park at East Basse Road is flooded last summer following heavy rainfall throughout South Texas. Credit: Bonnie Arbittier / San Antonio Report

The San Antonio City Council voted Thursday to adapt to increasingly heavy rainstorms by incorporating the most recent data on flooding into the city’s development code.

Council members approved the code update 9-0, with Councilman Rey Saldaña (D4) and Councilwoman Rebecca Viagran (D3) absent for the vote. The approval means engineers designing channels, retention ponds, and other drainage features must incorporate the latest data from the National Oceanic and Atmospheric Administration (NOAA).

NOAA’s analysis, published as Atlas 14, Volume 11, shows that heavy rainstorms have become more frequent across Texas than originally thought. It relies on rainfall data from thousands of weather stations across Texas.

“This is one of those examples of the climate changing, the best data showing us what’s happening to rainfall, and us adapting to that to ensure that our population and our development is safe going forward,” Councilwoman Ana Sandoval (D7) said before the vote.

Atlas 14 is mentioned in the City-led Climate Action and Adaptation Plan, which has drawn flurries of controversy over some of its proposals to cut greenhouse gas emissions. City Council’s vote on the plan has been postponed until fall.

The proposal to incorporate the new rainfall data into the building codes drew far less heat. Nefi Garza, assistant director of the City’s Transportation and Capital Improvements department, and his staff were able to gain the support of private-sector groups like Professional Engineers in Private Practice (PEPP) and the Real Estate Council of San Antonio (RECSA).

“We believe the proposed rollout plan for Atlas 14 is fair and reasonable and does not create undue financial burden on developers or unreasonable design for engineers,” wrote RECSA President Cara Tackett, a senior vice president of Pape-Dawson Engineers. “We understand the Atlas 14 data is a function of NOAA, and not the City of San Antonio, and therefore your actions should … be applauded.”

The City’s current design manual considers a 100-year storm to be 10 inches of rain over 24 hours. According to the NOAA study, a 100-year storm is now considered to range from 11.14 inches in southern Bexar County to 12.88 inches in northern Bexar County.

Even before NOAA’s recent data-crunching, San Antonio has long been considered part of Central Texas’ Flash Flood Alley. Bexar County leads the state in the number of flash flood deaths, with 68 people dying in floodwaters between 1959 and 2008, according to University of Texas at San Antonio research.

The change in the building codes likely will increase the costs of drainage projects, not only for local governments, but also private developers. Garza said local officials began meeting with the private sector in May 2018 to talk through the changes.

In letters to City staff, PEPP and RECSA leaders expressed support for how the City handled the new rainfall totals.

“The multiple meetings your staff held with the engineering and stakeholder groups in the City should help make the transition to the new criteria as smooth as can be expected,” wrote PEPP Chairman Eric Neuner, a manager at Raba-Kistner Consultants.

Garza told council members that he and his staff “made the decision to stick to our code,” which requires drainage structures to be more than capable of handling a 100-year storm.

“Our 100-year storm is changing, but we’re not going beyond [the code],” Garza said.

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Brendan Gibbons

Brendan Gibbons is a former senior reporter at the San Antonio Report. He is an environmental journalist for Oil & Gas Watch.