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1. What is Atlas 14?

The National Weather Service has completed a historical rainfall study, called Atlas 14. This study incorporated approximately 100 years of rainfall data in Texas, which shows that Fort Bend County and the City of Sugar Land are likely to experience an increase in the frequency of intense rainfall events.

2. Why is it necessary to adopt the Atlas 14 rainfall frequency values?

The existing rainfall frequency values were developed in the 1960s and 1970s. Atlas 14 incorporated an additional 4 decades of rainfall data collected by the increased number of rain gages in Texas. In addition, Atlas 14 used improved statistical methods to conduct rainfall frequency analysis. These rainfall frequency values are used for infrastructure design and planning activities under federal, state and local regulations. The values are also used to evaluate flood risks, manage development in floodplains, and delineate floodplain boundaries for FEMA’s National Flood Insurance Program.

3. Who is affected by the implementation of Atlas 14?

Areas of new development and re-development located next to Oyster Creek in the floodplain area could see an increment in the minimum required finish floor elevations. Redevelopment of properties located in levee-protected areas may need to build at a higher elevation if the original finish floor elevation did not comply with the minimum elevation requirements of the Levee District engineer.

4. What is coincidental ponding?

As per the Fort Bend Drainage Criteria Manual (7.3.1.1 –Design Criteria Assuming Coincidental Events), the maximum ponding level within the leveed area should not exceed the maximum water surface elevation associated with the 100-yr coincidental flood event computed in designing the internal drainage system of the levee area, including the required minimum freeboard of one foot and the pumping and storage capacity of the leveed system.

The coincidental ponding is determined from the coincidental probability of interior and exterior flooding and the capacity of pumps, drainage channels, and detention using the precipitation requirements of Atlas 14.

5. Are homes built to the new standards going to produce flooding in adjacent properties?

No. The Development Code and the city's design standards require that any new or existing construction collects the stormwater on the property properly and delivers it to the proper city collection point, (i.e. stormwater inlet, stormwater channel or detention pond) without affecting any neighboring properties. This is clearly specified in the flood prevention ordinances adopted by City Council.

6. What is the City doing to mitigate the impact of increased rainfall frequencies?

We are proposing to change the city code. Currently, many of our floodplain regulations are based on the 100-year flood. We are proposing an interim Atlas 14 100-year floodplain regulations until floodplain maps can be redrawn by FEMA in a few years. This interim floodplain is based on the current 500-year floodplain. This change means that property owners and businesses in the interim Atlas 14 100-year floodplain would have new restrictions if they want to develop, expand, remodel or improve their properties.

7. How do I find out what areas of town will be affected?

Sugar Land areas that will be affected by Atlas 14 implementation can be reviewed using the following maps:

• Online Interactive Map
• Printable Map [PDF, 13MB]

8. Is my flood insurance rate going to increase?

The majority of the city will not be impacted by higher insurance rates, however, homeowners that are not in the current 100-year flood zone may be remapped to the flood hazard zone when FEMA updates floodplain maps in a few years. If remapped, affected homeowners might be required to purchase flood insurance.

9. Is my home at a higher risk of flooding?

Atlas 14 shows that the frequency of major storms that can take place in our city is expected to increase. This could mean more street ponding in our area. We do not anticipate homes flooding in our area as a result of Atlas 14 estimates, however, it is recommended that all homeowners and residents purchase flood insurance.