Floodplain

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Check if your property is in a floodplain

The Federal Emergency Management Agency (FEMA) has updated the Williamson County Flood Insurance Rate Maps (FIRMs), effective 12/20/19 that encompass a great deal of the City of Round Rock. FEMA identifies floodplains to calculate flood risks for insurance purposes, particularly within Special Flood Hazard Areas (SFHA). These are defined as “the area that will be inundated by the flood event having a 1 percent chance of being equaled or exceeded in any given year.” The 1 percent annual chance flood is also referred to as the base flood or 100-year flood.”

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New Data Shows Increased Flood Risk

The National Oceanic and Atmospheric Administration (NOAA) recently completed the rainfall intensities study of Texas, called Atlas 14. The study shows that Central Texas is experiencing heavier rainfall during flash flood events than previously thought.

NOAA Atlas 14 is the most current and accurate rainfall data. The current regulatory FEMA floodplain maps do not yet reflect this new data as it was published after FEMA’s Flood Insurance Study (FIS). When Atlas 14 is considered, a more accurate estimate of the 100-year floodplain (1% annual chance floodplain) in the vicinity of Round Rock is the current FEMA 500-year floodplain (0.2% annual chance floodplain). The City of Round Rock and other local communities are incorporating Atlas 14 to better assess flood risk, properly plan and design future infrastructure, and update portions of city floodplain standards.

The City recommends that all owners and renters determine if their property is within the current FEMA 500-year floodplain, FEMA 100-year floodplain, or is otherwise threatened by flooding, and if so, seriously consider purchasing flood insurance. A map showing the FEMA floodplains can be found here: View map.

The City of Round Rock participates in the National Flood Insurance Program (NFIP); therefore, flood insurance may be purchased for structures and contents by any owner or resident within the City. Properties/structures outside the current FEMA 100-year floodplain should be eligible for “preferred rates,” and the City currently understands that insurance premiums for these areas are generally quite reasonable.

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Glossary

  • ACF:  Annual Chance Floodplain
  • Atlas 14: NOAA publication intended as the U.S. Government source of precipitation frequency estimates and associated information for the United States and U.S. affiliated territories. | NOAA Atlas 14, Volume 11: Texas
  • 100-year floodplain or 1% ACF: The area that has a 1% or greater chance of being flooded in any given year.
  • 500-year floodplain or 0.2% ACF: The area that has a 0.2% or greater chance of being flooded in any given year. 
  • FEMA: Federal Emergency Management Agency within the U.S. Department of Homeland Security | FEMA Website
  • FIS: Flood Insurance Study is an engineering study performed by FEMA to determine a community’s risk to flood hazards. | FEMA Flood Insurance Study
  • Floodplain:  Any land area susceptible to being inundated by floodwaters from any source.
  • NOAA:  National Oceanic and Atmospheric Administration within the U.S. Department of Commerce | NOAA Website

Frequently Asked Questions

The previous maps were based on analyses performed over 30 years ago. Watershed conditions such as topography have changed, and there has been significant added development. Furthermore, analysis tools and historical data collection have improved over time, which provides increased accuracy.

Flood hazard mapping is the basis of the NFIP regulations and flood insurance requirements. FEMA maintains and updates data through FIRMs and risk assessments.

There is no set timeline. Flood zone designations may be revised when new and more accurate information becomes available because of a FEMA-funded restudy or because the community makes the information available to FEMA. Several factors influence the frequency with which flood maps may be updated, such as the extent of new development and the completion of flood-control projects.

There are no comprehensive updates foreseen in the next 10 years.

FEMA initiated a partial update in 2010. In 2012, the Upper Brushy Creek Water Control and Improvement District (WCID) initiated a flood protection plan that included watershed modeling. Communities within the watershed desired to use the modeling as the basis for a comprehensive mapping update. The WCID then partnered with FEMA and the Texas Water Development Board to complete the process.

The updated maps encompass the Upper Brushy Creek WCID boundary, which includes much of southwest Williamson County. Changes in the San Gabriel Basin, north of Round Rock, were also included.

When new maps are issued, your risk may have changed along with your flood insurance requirements. Property owners are encouraged to review the updated maps and discuss implications with their insurance agent.

If your property is mapped into a high-risk area, you will be required to purchase flood insurance if your mortgage is through a federally regulated or insured lender. It is possible to save money through a process known as grandfathering provided by the NFIP.

If your property is mapped out of a high-risk area, your flood insurance costs will likely decrease.

If your property is mapped out of a high-risk area, your flood insurance costs will likely decrease.

Property owners or other persons with floodplain questions or concerns should consult their community’s Floodplain Administrator. This is the local official who keeps the community’s flood hazard maps and Flood Insurance Study report.

In the City of Round Rock, City Engineer Danny Halden is the Floodplain Administrator. For inquiries, please email floodplain@roundrocktexas.gov or call 512-218-6610.

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City of Round Rock Stormwater Division

Phone: 512-218-7046 | Email: floodplain@roundrocktexas.gov

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