The U.S. 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.”

Citizens can check to see if their property is in a floodplain here.

Atlas 14 Rainfall

It is worthy of note that new rainfall data has been issued through publication by the National Oceanic and Atmospheric Administration (NOAA) of Volume 11 of the Precipitation-Frequency Atlas of the United States (Atlas 14).

Rainfall previously included in floodplain calculations/analyses is lower than that indicated in NOAA Atlas 14 for the Round Rock area. The City believes that if Atlas 14 rainfall data were included, the SFHA’s shown on FIRM’s would be slightly larger.

In light of the new rainfall data, the City recommends that citizens located within or near the boundaries of the 0.2% annual chance floodplain (500-year floodplain) gather as much risk information as possible to make an informed decision regarding the purchase of flood insurance if not otherwise required to make such purchase.

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 FIRM SFHA should be eligible for “preferred rates,” and the City currently understands that insurance premiums in these areas are generally quite reasonable.


Frequently Asked Questions

Why were floodplain maps updated?

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.

How often are they updated?

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.

Who initiated the update?

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.

What areas were within the updated area?

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.

What is the impact of new floodplains?

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.

Who should I talk to if I have questions?

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.