Floods and Floodplains

Floodplains are the low-lying areas next to creeks and rivers that are subject to flooding. Maybe most of us think about floodplains just in terms of their risk for flooding. If you’ve lived in Central Texas for more than a couple of years, you’re aware that our area is frequently subject to heavy rains which cause flash floods along our rivers and creeks. Residents near Bull Creek know to expect that seasonal downpours will force closures along the section of Spicewood Springs Road north and west of Loop 360. Of course, flash floods are more than inconvenient. They cause property destruction and loss of life, usually for motorists who drive into fast-moving flood waters.

Environmental science has a more positive perspective on floodplains. The Nature Conservancy lists several benefits of healthy floodplains. In addition to flood protection, these include:

  • Improved water quality, by acting as filters to remove sediments and nutrients.
  • Improved wildlife habitat, by providing homes for local animals and migrating birds.
  • Recharged aquifers, by allowing more area for slow-moving water to seep underground.
  • Restoration of forests, including valuable bottomland hardwood forests.

To improve and preserve floodplains, The Nature Conservancy supports strategies such as deemphasizing flood-control dams, moving levees further away from rivers and designing floodways to inundate floodplains in a prioritized way in times of severe flooding.

In Austin, management of creek floodplains is the responsibility of the City’s Watershed Protection Department. Although there are exceptions, in general, development in floodplains or modification of floodplains is not allowed in Austin. In 2018, NOAA, the National Oceanic and Atmospheric Administration, released an updated report and analysis of rainfall records for Texas. Known as Atlas-14, the study found that expected rainfall amounts have increased in many areas. As a result, new floodplain maps were created. Several areas in Austin that were considered likely to flood only once in 500 years are now considered to be in the 100-year floodplain. This has affected development projects and means that more Austin homeowners will be required to carry flood insurance.

The Atlas-14 study simply looked at rainfall records and analyzed their potential impact. It did not consider the causes of increased rainfall or make projections about rainfall amounts in the future. Projecting and predicting the impacts of climate change is the purpose of the National Climate Assessment or NCA. The NCA is produced by the U.S. Global Change Research Program, which was established by Congress in 1990. The NCA forecasts changes from 25 to 100 years in the future. Part of that work includes examining various scenarios of greenhouse gas emissions and their impacts.

The Fourth National Climate Assessment was released in 2017 and 2018. Projections for the Texas, Oklahoma, and Kansas area predict a continuation of higher temperatures and sea level rises. NCA rainfall projections forecast more frequent heavy rains combined with drier summers. In spite of an increased likelihood of flooding, the overall effect will be less soil moisture, possibly resulting in a future soil drier than anything experienced in the last thousand years.

For further reading-
Information about floodplains from The Nature Conservancy: https://www.nature.org/en-us/what-we-do/our-priorities/protect-water-and-land/land-and-water-stories/benefits-of-healthy-floodplains/

The City of Austin’s Watershed Protection Department models and manages floodplains: http://www.austintexas.gov/department/floodplain-management-and-regulations

The City’s Floodpro site has interactive floodplain maps. It also tracks road closures during severe weather.  https://www.austintexas.gov/FloodPro/

National Climate Assessment for the area including Texas: https://nca2018.globalchange.gov/chapter/23/

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