As Flood Risk Increases, Austin Will Revisit Its Floodplain Building Rules

Oct 15, 2018

After a new study showed thousands of additional homes were at risk of flooding in Austin, the city is preparing to revamp rules on building within a floodplain.

The study, known as Atlas 14, revised the city's understanding of historical rainfall data, adding 3,000 properties to the city's 100-year floodplain – which impacts everything from what people pay for insurance to how they can build homes.

Now, the Watershed Protection Department is proposing changes to construction rules within the floodplain.

One of the proposals would increase the minimum elevation for new construction in the floodplain from 1 foot above flood level to 2 feet, which would, ideally, better protect properties against severe flooding.

Another proposal would expedite some construction projects in the floodplain by allowing city staff to approve redevelopment through an administrative process. Right now, builders must go before the Austin City Council to get approval for projects in the floodplain.

The city's floodplain administrator, Kevin Shunk, says speeding up the process should help replace existing flood-prone properties with structures that are more flood-resistant.

A third proposal would allow for more construction within the 100-year floodplain along the Colorado River. Currently, it’s allowed below the Longhorn Dam and on Lady Bird Lake, but the rule change would also permit it along Lake Austin and parts of Lake Travis.

Shunk said that that rule would serve to create regulatory uniformity along the river as it flows through Austin.

Before the update, about 4,000 properties in Austin were thought to sit in the 100-year floodplain, meaning there's a 1 percent chance of major flooding in any given year. Now, around 7,000 properties sit in that floodplain.

One-in-a-hundred may seem like a relatively low chance of flooding, but it's not, Shunk says.

"If you own a home in the 100-year floodplain, there’s a 26 percent chance that you’ll have a flood during your 30-year mortgage,” he says.

That’s why properties in the 100-year floodplain face special regulations. People who own those properties are often required to carry flood insurance as part of their mortgage and often have to elevate any new construction above possible flood levels.

The proposed changes would need approval from the Austin City Council.