We are in the process of changing our floodplain regulations in light of a National Weather Service study of historical rainfall.
Austin regulates new development, redevelopment and remodeling in the floodplain. These regulations are meant to protect Austinites from flooding and reduce public expense in the aftermath of a flood. We have started the process to change these regulations.
Austin also requires developers to include drainage pipes, detention ponds and/or other drainage infrastructure in their projects. The drainage criteria tell developers what options they have and how big their drainage infrastructure needs to be. We plan to change the drainage criteria in a separate process once the National Weather Service study is complete.
Currently many of our floodplain regulations and drainage criteria are based on the 100-year flood, which has a 1% chance of occurring in any given year. It is currently defined as 10.2 inches of rain in 24 hours. The National Weather Service study indicates that this definition is too small. The current 500-year rainfall, which is 13.5 inches of rain in 24 hours, more closely represents the rainfall that has a 1% chance of occurring every year.
For this reason, we are proposing to use the current 500-year flood for our regulations until floodplain maps can be redrawn. This change means that the current floodplain regulations will apply to more properties.
Property owners and businesses in the interim 100-year floodplain would have new restrictions if they want to develop, expand, remodel or improve their properties. We estimate that there are approximately 3,600 buildings and 4,400 acres in the interim 100-year floodplain that would be affected.
These changes are being proposed in light of a National Weather Service study of historical rainfall. This study is called Atlas 14. It shows that large storms are more likely than previously realized. In the next few years, we plan to submit revised floodplain maps to FEMA based on this study. The future 100-year floodplain should be similar to the current 500-year floodplain. The proposed changes discussed on this page will update our regulations and criteria faster than the floodplains can be revised.
We held stakeholder meetings on July 17 and August 2.
There will be public meetings in September and October.
There will be public hearings about the proposed regulations at the Environmental and Planning Commission meetings in the fall.
The Austin City Council will hold a public hearing and consider adopting the proposed regulations in the fall.