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Will CodeNEXT help protect against the next big flood?

Tuesday, September 26, 2017 by Joseph Caterine

When Hurricane Harvey inundated Houston last month, the city’s flood mitigation deficiencies came under fire. In Austin, the Halloween Floods of 2013 and 2015 raised similar questions about Austin’s infrastructure, so commissioners at the Sept. 19 joint land use meeting grilled consultants and staff on how the second draft of CodeNEXT would improve protections before the next big storm hits.

In its analysis of the city’s housing capacity, Fregonese Associates incorporated FEMA’s 100-year flood plain map to determine what land would be able to be developed in the future. During his presentation at the meeting, John Fregonese admitted that after Harvey it would make sense to include more constraints on the land supply. Out of the FEMA claims that were made in Houston the weeks after Harvey, three out of four were for homes not in the 100-year flood plain.

CodeNEXT, in line with the Strategic Housing Blueprint adopted by City Council in April, aims to create more density in the urban core. While more housing stock may lower rent prices, it also puts more people in harm’s way from excess runoff caused by impervious cover.

One idea proposed by the city’s Watershed Protection Department to guard against this risk is to require any redevelopment projects to upgrade drainage systems for the property as if they were developing on vacant land.

Zoning and Platting Commissioner Ana Aguirre, a former member of the Flood Mitigation Task Force, asked Fregonese at the meeting if they had included information on where localized flooding occurred in these calculations. Planning and Zoning Director Greg Guernsey clarified that it hadn’t been.

Unlike the massive creek flooding that typically makes headlines, localized flooding results from impervious cover, inadequate drainage systems or other infrastructure-related problems. The city’s Watershed Protection Department has received over 6,000 complaints of this kind of flooding since it started tracking it in 1988.

Later in the meeting, Zoning and Platting Commissioner Stephanie Trinh followed up to see if the consultants knew of any best practices in mitigating localized flooding. Fregonese responded that the challenge was lack of data. Guernsey added that he would talk to Watershed Protection about sharing its information with the consultants, but that it may not be sophisticated enough to be useful.

For creek flooding, the Watershed Protection Department uses advanced computer models to plot the areas of land that could be affected by an overflow, but Guernsey said he was not sure if staff’s computer models for localized flooding were also multidimensional, or if they only charted the points where the complaints originated from.

More impervious cover does not only mean more runoff – more development could also encroach on critical water quality and environmental hazard zones. In response to a question by Zoning and Platting Commissioner Sunil Lavani, Fregonese said that those zones have been incorporated into the analysis as constraints.

The land use commissions are scheduled to make their final CodeNEXT recommendations to Council in January.

Photo courtesy of the city of Austin.

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