On the Eve of the First Hurricane Season Since Harvey, Is Houston Ready?
The 2018 hurricane season officially starts in a month. Houston residents, municipalities, and politicians don’t seem to have noticed. Eight months post-Hurricane Harvey and little, if any, progress has been achieved regarding long-term plans (or short-term plans) for the way Houston development should occur to avoid flooding of homes and businesses. The terms 100-year flood and 500-year flood have become part of our lexicon and yet many struggle to understand what those terms mean.
According to the U.S. Department of the Interior, the term “100-year flood” is used to simplify the definition of a flood that statistically has a 1-percent chance of occurring in any given year. Likewise, the term “100-year storm” is used to define a rainfall event that statistically has this same 1% chance of occurring.
A “500-year flood” is an event that has a 1 in 500 chance of occurring in any given year. “For a 500-year flood, there is a 0.2% chance of having a flood of that magnitude occurring” in any year, according to the National Weather Service.
The problem, of course, is that we don’t know precisely what has occurred in the last 100 or 500 years regarding flooding. When the government decided to map flood-prone areas to improve the National Flood Insurance Program in the early 1970s, the maps couldn’t just use the worst flood ever from historical records in an area to judge what a “bad flood” might look like. The standard set for mapping flood-prone areas was apparently a compromise between existing Army Corps of Engineers standards for dams and levees, and the (more modest) standards that most communities set for flood prevention.
The 100-year flood level is statistically computed using existing historical data, as more data comes in, the level of the 100-year flood will change, especially if a huge flood event occurs. As data is collected or if the ground changes and affects the flow of water, scientists re-evaluate the frequency of flooding. Dams and urban development are examples of some man-made changes in a basin that affect floods.
Additionally, the amount of rain that defines a “100-year storm” has risen by 3 to 5 inches in Harris County since the last estimates were put in place in 2002, according to the National Oceanic and Atmospheric Administration.
Prior to Hurricane Harvey, very little flood mitigation occurred according to the Storm Surge Prediction, Education, and Evacuation from Disasters Center at Rice University. It is said we have had three 500-year floods in the past three years.
So, has anything happened since Hurricane Harvey?
- In March 2018, the Subcommittee on the U.S. Interior, Energy, and Environment held a hearing to highlight ways for improved communication between the U.S. Army Corp of Engineers and the local governments and public where it has projects.
- In April 2018, Houston City Council passed an ordinance, effective September 1, 2018, requiring homes to have flood insurance if built in a 100-year floodplain on the map. It also requires new homes must be built 1 foot above the floodplain. For homes in the 500-year floodplain, that increases to 2 feet. This affects new construction and any existing home that’s expanded by 33 percent or more — existing homes are grandfathered, and don’t have to be elevated.
- This week, Houston City Council approved a plan for the creation of a Municipal Utility District to serve about new 900 homes to be built in a floodplain, despite concerns about developing in flood-prone areas after Hurricane Harvey.
Has any progress been made? Do we have a plan? Are we prepared? We have a month to figure it out.
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