Travis County Commissioners voted to evaluate possible new floodplain and development regulations and associated costs ahead of the official publication of Atlas 14--a historic rainfall frequency analysis drafted by the National Oceanic and Atmospheric Administration.

Atlas 14, a draft of which was released in November 2017 and has since been peer-reviewed, will redefine rainfall intensities for a 100-year storm. The final study is expected to be published in October.

“Clearly from the flooding we’ve seen in Central Texas and in Houston with [Hurricane] Harvey, it’s obvious that we’re having more severe flooding on a more regular basis,” Commissioner Brigid Shea said. “Knowing what we know now, [re-evaluating regulations] seems really prudent to me.”

The current 100-year storm for Travis County is based on a data set that extended through 1994. Atlas 14 is based on data through 2017. The new data defines a 100-year event as 13 inches in a 24-hour period, which is approximately the current 500-year rate. Atlas 14 has the current 100-year rate at about a 25-year flood.

“I can’t stress enough how much cost this is going to add to both private and public development,” said Travis County floodplain administrator Stacey Scheffel.

Rainfall intensity data is used by FEMA to produce flood insurance rate maps and by engineers to design detention ponds, storm sewers and road side drainage systems. It will take years for flood modeling to reflect the new understanding of rain fall intensities. However, Travis County–alongside the city of Austin–is taking steps to be proactive in amending development and floodplain regulations in all areas of the county except Lake Travis and the Colorado River floodplains, as the data do not suggest changes will be necessary in those areas.

County staff said they anticipate the cost of all drainage structures located within the current 500-year floodplain to increase by 30 to 60 percent and design periods will likely be extended by six to nine months. Additional right-of-way acquisitions will add cost to new and existing development as well, according to the presentation.

“There will be costs associated with this either way," County Judge Sarah Eckhardt said. "I would prefer the costs be financial rather than in lives.”