New City of Houston Floodplain Regulations Post-Harvey
The City of Houston recently updated floodplain regulations after massive flooding and damages occurred throughout Harris County and surrounding areas in recent years. The flood damages have resulted from major rainfall events; Hurricane Harvey (2017), the 2016 Tax Day Flood, and the 2015 Memorial Day Flood. The regulations were updated to better ensure the welfare and safety of the public and to increase the resiliency of communities as they recover and prepare for future rainfall events.
On April 4, the Houston City Council voted to modify regulations within Chapter 19 of the City Code of Ordinances to require new and substantial improvements (expanding an existing building footprint by 33 percent or more) to buildings within the 500-year floodplain be built two feet above the adjacent FEMA 500-year floodplain elevation. The FEMA 500-year floodplain refers to the limits of flooding from a rainfall event with a 0.2 percent chance of being equaled or exceeded in a given year. Other notable changes include requiring new and substantial improvements to critical facilities built in the 500-year floodplain to be built or floodproofed to 3-feet above the 500-year floodplain elevation and expanding the City’s Zero Net Fill requirement to the 500-year floodplain for all new development and substantial improvements. The more expansive regulated area, referred to as the “Houston Special Flood Hazard” area, includes FEMA flood zones A1-30, AE, AH, A, A99, X (shaded), and AO.
The new regulations will take effect Sept. 1. In developing these new regulations, the City has also considered the NOAA Atlas 14 rainfall values that have been released in draft form for the State of Texas and are currently in technical peer review. These rainfall values have become the standard precipitation dataset used for FEMA studies in other states and are typically used to develop rainfall data used in local drainage studies. It is anticipated that the new rainfall totals will be finalized in late 2018 or early 2019 and will result in greater base rainfall intensity values for the area. Upon the adoption of effective floodplain maps that reflect NOAA Atlas 14 rainfall totals, the Director of Houston Public Works will have 60 days to make recommendations to the Mayor regarding any changes to regulated areas.
Similar code that requires new buildings in the 100-year floodplain within Harris County be built two feet above the 500-year floodplain elevation was approved by Harris County commissioners Dec. 5 and made effective Jan. 1. Fill is no longer accepted as a means to elevate structures within the 100-year floodplain. Instead, open foundations, such as piers, or continuous foundation walls with properly sized and located openings may be utilized. The Harris County code does not affect lands that lie within municipalities such as the City of Houston.
More information on the Houston City Council meeting and other code modifications can be found at the following links: