In this entry, we’re going to explore how the new code is working to help meet Imagine Austin’s goal to sustainably manage our water resources by conserving our water supply and improving watershed health. Imagine Austin calls on the City to plan for and adapt to increased droughts, severe weather, and other potential impacts of climate change on the water supply. In addition, Imagine Austin sets a goal of reducing the threats flooding poses to public safety and private property.
For more than 30 years, Austin has protected its natural resources through a number of regulatory measures, including stream setbacks, floodplain protection, sensitive feature protection, tree protection, stormwater controls, and impervious cover limits. CodeNEXT will carry forward Austin’s historic watershed regulations, like the Save Our Springs Ordinance, as well as the improvements of the 2013 Watershed Protection Ordinance. The new code will build upon this solid foundation with measures to enhance the environmental function and resiliency of sites.
Historically, the code has regarded stormwater as a nuisance to be dealt with, instead of a valuable resource to be utilized. Current code provisions do a good job of cleaning up polluted runoff, but they do not significantly address other important goals, like enhancing creek baseflow, supporting onsite vegetation, and reducing potable water consumption. The new code will require sites to beneficially use their stormwater on-site for smaller storms, which is a big opportunity to do more with rainfall, create more sustainable developments, and take pressure off our water supply lakes.
In addition, older sites built before modern watershed regulations lack detention facilities of any kind, and the runoff from these sites can contribute to downstream flooding and erosion. Current code requires development projects to demonstrate they will not result in additional flooding on other properties. However, redevelopment projects that are not increasing impervious cover or changing drainage patterns generally are not required to provide flood mitigation — even if significant downstream flooding exists. The new code will ask development projects to contribute their fair share to solutions that address threats to public safety and property.
Along with revisions to the land development code, the CodeNEXT initiative also will be rezoning the entire city. The Watershed Protection Department is conducting an analysis to determine how the new proposed zoning will affect the amount of allowed impervious cover, which can directly impact the extent of the floodplain and the capacity of existing stormwater infrastructure. When rainwater falls on impervious surfaces, the increased volume and velocity of runoff from these surfaces can contribute to erosion and flooding and impair water quality by carrying contaminants — sediment, bacteria, and nutrients — into Austin's aquifer and creeks. Impervious cover also displaces soils, trees, and other plants, increasing ambient temperatures and reducing stream base flows and natural habitat.
Initial results of the Watershed Protection Department's analysis found CodeNEXT would reduce the maximum amount of impervious cover by 0.4% in our urban watersheds — the watersheds located in the core of our city, where we face the most severe challenges to flooding, erosion, and water quality. The analysis found CodeNEXT would lead to a slight increase (0.3%) to that maximum for the rest of the city. However, that increase is almost entirely due to rezoning large parcels to be more in line with the current land use (e.g., Onion Creek Metro Park would be rezoned from rural residential to public).
The Watershed Protection Department is working on additional modeling efforts related to the new code, including quantifying the potential downstream benefits of flood mitigation for redevelopment; the potential flood-related impacts associated with residential infill; and an updated impervious cover analysis using revised mapping information. This additional modeling is expected to be completed in October.
Projected changes in Austin’s climate include a shift in rainfall patterns toward cycles of heavy rainfall, followed by more frequent extreme temperatures and drought conditions. Given this challenging trend, CodeNEXT provides a significant opportunity to enhance the resiliency of our natural and built environment while also advancing the planning needs of our growing city.