ADUs and Flood Mitigation

[Michael Gaudini]

Council Member Pool wished to share the following thoughts ahead of the ADU discussion at tomorrow’s (November 19) meeting:

--

Neighborhoods across our city have experienced increased flooding and drainage problems, including in large parts of District 7.

According to the Watershed Protection Department (WPD), Austin currently has over $2 billion in infrastructure needs to improve our storm drain system and our creeks and man-made channels. However, the department is only able to address about 1 percent of this need annually (with roughly $25 million in annual funding).

At this rate, it will take decades to address these needs through the city’s investments alone. We may need to adopt a multi-pronged approach, including encouraging developers to help improve this situation, if we truly want to address flooding issues in Austin.

With these problems in mind, I asked WPD at the October 15 Council meeting to analyze how expanding construction of accessory dwelling units (ADUs) would impact flooding risks and aging drainage infrastructure, especially in our city’s older neighborhoods. Staff has provided this information in the back-up to Item 80 for tomorrow’s meeting (November 19).

You can read the full two-page analysis by clicking on the following link: http://assets.austintexas.gov/austincou ... 174624.pdf.

However, I wanted to highlight my main takeaways from this analysis:

• WPD staff is concerned about “continued, incremental increases in impervious cover in areas with flooding concerns.”
• While the ADU proposal Council is considering does not technically increase the allowable base zoning impervious cover, it does provide an avenue for redevelopment that could effectively increase the amount of impervious cover in our neighborhoods.
• The changes in impervious cover that would accompany expanding ADUs in our neighborhoods, if not done carefully and accompanied by mitigation efforts, can “cause localized drainage problems.”

Expanding ADUs are only one part of our flooding issues in the city, but they are still a part. If we are serious about addressing flooding in Austin, we must consider how the policy changes we make will affect our storm drainage system.