Houston City Council voted last Wednesday and approved revisions to the Chapter 19 Floodplain Ordinance. There are several key aspects to this revision that will affect future development within incorporated areas of the City of Houston.
Previously, Houston’s code applied to property in the 100-year floodplain. The new revisions include property in the 500-year floodplain as well. Land in the 100-year floodplain has a 1% chance of flooding in a single year while the 500-year floodplain has a 0.2% chance of flooding.
The existing Chapter 19 regulations required a finished floor elevation at the 100-year floodplain elevation plus one foot. The updated regulations require a minimum elevation at the 500-year floodplain level plus two feet.
Zero Net Fill
Zero net fill restrictions had previously applied to property in the 100-year flood zone. The new regulations, will extend the zero net fill criteria to the 500-year flood zone.
Only incorporated areas of the City of Houston are affected by these revisions; although, it is possible that other small cities and floodplain administrators in the area will adopt these same standards. Location will have a large impact on the effect that these new regulations have. The area north of Lake Houston will likely have one of the largest differentials between the previous 100-year elevation requirements and the new 500-year requirements at an estimated six to eight-foot difference.
Implications could be different for commercial development such as large warehouses. FEMA has varying levels of stringency for commercial developments versus residential developments, so there may be some options to work around these new requirements.
Regardless of the development type, this revision adds an additional 51,200 acres of land (13% of the overall city limits) to the Special Flood Hazard Area. Therefore requiring all development within the 500-year floodplain be submitted for City review to ensure adherence to the floodplain regulations.
FEMA Floodplain Considerations
Prior to Hurricane Harvey, The Hydrometeorological Design Studies Center (HDSC) within the Office of Water Prediction (OWP) of National Oceanic and Atmospheric Administration’s (NOAA) National Weather Service (NWS) was updating precipitation frequency estimates for various parts of the United States and affiliated territories, which are published as Volumes of NOAA Atlas 14 (NA14). HDSC is currently updating estimates for the state of Texas that will be published in 2018 as NOAA Atlas 14 Volume 11 Version 2 the National Oceanic and Atmospheric Administration (NOAA). This update to precipitation estimates would most likely lead to revisions of the current floodplain maps by FEMA. Along with the Chapter 19 regulation revisions, an addendum was passed stating that if the FEMA floodplain maps within Harris County are updated, the City of Houston City Council will vote within 60 days on whether to amend the floodplain regulations again.
If the FEMA maps are updated, the 100-year water surface elevation would likely rise and may be as high as the existing 500-year water surface elevation in certain areas. In the past, the process of updating the FEMA maps has proven to be lengthy. Future updates to maps would take likely take several years and be adopted on a watershed by watershed basis.
It is likely that additional amendments to Chapter 19 will continue to be made, and we will follow along with the updates and their associated impacts.
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