Lafayette’s flood risk is worse than it seems, and we’ve built right into it

For decades, the Lafayette community has grown into flood prone areas, taking advantage of cheap and easily developable farmland, much of it in the parish’s low-lying south.

Nearly half of these newly sprouted developments in Lafayette Parish between 2001 and 2021 occurred in areas within the 500-year floodplain, according to The Current’s analysis of national land cover data and modeling by UL Lafayette’s Watershed Flood Center. 

That’s about 5,600 acres that have, for the most part, been converted into residential neighborhoods and other new developments in the span of just two decades. And it adds to more than 21,000 acres of developed land already in the parish’s 500-year floodplain, that is, development at some risk for flooding in a major storm. 

For many, this is a hidden risk. Federal maps haven’t kept up with newer models or accounted for some of the principal causes of flooding — namely, intense rain events — leaving local policies virtually outdated. In other words, Lafayette developed largely unaware of the risk, not necessarily in spite of it. As local government spends tens of millions on stormwater management and insurance rates rise, the costs of that pattern are becoming more obvious.

Where Lafayette has grown is one of the biggest factors influencing its flood risk. Determinations about which parts of the parish can be developed and which parts can’t have essentially been made by FEMA’s official flood maps, which delineate areas vulnerable to flooding. 

But there’s a major flaw in letting those maps dictate development patterns: FEMA doesn’t account for flooding from localized rainfall, a major source of risk for Lafayette. That obscures Lafayette’s true flood risk from policymakers and the public alike. 

“FEMA does not do what’s called pluvial flooding, local rain flooding. It’s only riverine flooding,” says Emad Habib, director of UL’s Watershed Flood Center. “Pluvial is from the rain, and fluvial is from the rivers and channels flooding. FEMA is primarily fluvial, and they are working on updating that, but they are not there yet.”

The difference is stark. UL’s modeling puts almost 50% more new development in the parish’s 500-year flood zone than FEMA’s official flood maps, which cover about 3,700 acres developed between 2001 and 2021.

FEMA’s flood maps also put just 20% of the parish development inside the 100-year flood zone, according to Lafayette Consolidated Government. Meanwhile, the nonprofit First Street Foundation’s Flood Factor model, which accounts for surface water flooding and which projects a major increase in rainfall intensity caused by climate change, says that number is closer to 40%. 

That statistic isn’t surprising, says Habib, whose own modeling, which doesn’t account for increases rainfall amounts, finds about 30% of buildings parishwide are within the 500-year flood zone, though only about 8% total would be expected to take on water because of their first floor elevations. 

The parish’s flood risk is also growing because of increased rainfall caused by climate change, according to data from the First Street Foundation, which published estimates this summer that dramatically increased the amount of rain expected to fall once every 100 years in Lafayette. 

The National Oceanic and Atmospheric Administration estimates that a 100-year storm in Lafayette would drop around 4.5 inches of rain in one hour, but FSF raises that estimate to 6.3 inches, above what would be considered a 1,000-year storm by NOAA. 

“American communities continue to be surprised by these heavy rainfall events that are resulting in flooding,” First Street’s Chief Data Officer Ed Kearns said in a virtual press conference on the foundation’s updated model in August. “We’re trying to call out and quantify exactly what that risk is so people can be prepared and communities can be prepared for this current and growing risk.”

That’s at least part of the difference between FSF’s data and UL’s model, which was based on NOAA’s rainfall estimates. Habib says that while he does expect NOAA to update its estimates to show increased rainfall in Lafayette in the next few years, it’s not likely that they will be as high as First Street’s because they were last updated in 2013. First Street also relied on a much shorter time period of data for its calculations, which increases the uncertainty around those findings, he says. 

But the prevailing result remains that storms are becoming more intense in Lafayette, adding to the parish’s risk of flooding, particularly as more of its open land continues to be developed.

In fact, FEMA’s Community Rating System, which gauges local efforts to reduce flooding, gives Lafayette a particularly lacking grade for its efforts to preserve open, undeveloped land. Preserving open spaces can help lower flood risk by reducing investments in areas that could be damaged by flooding and by giving stormwater areas to collect that don’t result in property damage. 

The average community scores 25% of the CRS’s possible points for open space preservation policies, which include efforts to keep flood-prone land vacant and to restore it to its natural state. But the city of Lafayette gets just 6% for its efforts, and the parish doesn’t even break 1%. 

In 2001, just over 31% of the parish — about 53,600 acres — had been developed. But by 2021, that figure jumped to 38%, putting another 12,600 acres of undeveloped land into uses that exacerbate flood risk. 

The sprawling nature of growth in Lafayette is a factor that contributes to increased runoff and potential flooding, says Gary Kinsland, professor emeritus of geosciences at UL, who authored a 1998 study on the correlation between increased development in Lafayette and rising water levels in the Vermilion River. 

Just the shift from raised houses on piers to homes built on concrete slabs has made the parish more vulnerable to flooding, says Kinsland. 

“Once you build on a slab, you’ve got to raise that slab and grade your whole yard because, if you don’t, just a normal, healthy rain will flood over your 3-inch slab,” says Kinsland. 

“When it rains, there ain’t no water standing in that yard,” he adds. “But where’d it go? We’re not just draining the roofs that we have, or in fact, the parking lots that we have. We’re draining everything.”