In a back room of the Johnston Library on Tuesday evening, James Nichols peered at a computer screen, checking to see if a property he owns is located within the floodplain on the San Antonio River Authority’s proposed new maps.

Other residents did the same, sitting at tables with river authority staff who walked them through the new maps, which is overlaid with different blues and striped areas representing various levels of flood risk. Some picked through a throng of pamphlets labeled with information regarding floods and flood insurance.

They were all there at the invitation of the river authority, which will host 12 more open houses across Bexar County through the end of March so that residents and businesses can view the new maps to see if their property is affected — and learn what they should do about it.

The maps were last updated in 2010 using land use data from 2004 and rainfall estimates data based on 1960s data. With new rainfall, land use and topography data for Bexar County, the river authority, acting in cooperation with the Federal Emergency Management Agency, is officially launching the lengthy process of updating the maps.

Nichols, who owns an investment property on the northwest side of the city and who works as a real estate developer and construction manager, told the San Antonio Report he had seen social media ads for the meetings, and had marked the first one on his calendar to see how his property might be affected.

According to the maps, Nichols’ property, which is undeveloped, is in the floodplain. He seemed unbothered by that fact, but appreciative of the information. “The new maps seem to be more accurate,” he said, “so I was glad to see that.”

While FEMA is required to review its flood insurance rate maps every five years, “there’s no set schedule for how often we update the maps,” said Erin Cavazos, a senior engineer with the river authority. “In this case, the biggest driver was that the National Weather Service and [the National Oceanic and Atmospheric Administration] released updated rainfall estimates.”

As a “cooperating technical partner” of FEMA, the river authority is the official maintainer of Bexar County’s floodplain maps. To begin the process of updating it for the whole county (as opposed to the small day-to-day changes it makes regularly), the river authority first draws up a draft for FEMA, which it recently submitted.

“Then they go through a very formal process of creating the flood insurance rate maps based on our data,” Cavazos said.

After it has created those, FEMA then launches its own process, issuing preliminary maps that go before the public, which then has 90 days to comment or appeal before the publication of finalized maps.

From start to finish, the whole process can take 18 to 24 months, Cavazos said. Meanwhile, the river authority does its own outreach, which it’s beginning now to give the community plenty of time to review the maps.

Flooding can happen anywhere

San Antonio lies in the middle of what’s known as “Flash Flood Alley,” a ribbon of the state from Dallas to Uvalde that consists of shallow soil, steep terrain and a lot of rainfall — when it’s not in drought (which paradoxically, can exacerbate flood conditions). Flash Flood Alley is one of the most flood-prone regions in North America.

Anyone who has lived in San Antonio for any length of time knows flash flooding is as common to the area as drought. The city’s rich history has been shaped by past floods — from the tragic flood of 1921 that destroyed the city’s West Side and killed 51 people, to the 100-year flood in 1998, during which much of downtown was spared severe damage thanks to a $10 million river tunnel completed just 10 months earlier.

San Antonio lies in the middle of what's known as Texas' "Flash Flood Alley," which is a flood-prone area that stretches from Dallas to Uvalde.
San Antonio lies near the tail end of what’s known “Flash Flood Alley,” which stretches from the top of the state to Medina County. Credit: Courtesy / San Antonio River Authority

“Our floods tends to be faster moving than places we see in the news a lot,” Cavazos said. “Where that really comes into play is at low water crossings; people can get caught by surprise, especially if it’s dark, by how fast that water moves. Those need to be taken very seriously.”

In the 1960s, to help communities understand their risk of flooding, the federal government instituted a national flood insurance program and began creating flood maps. FEMA defines a floodplain as “any land area susceptible to being inundated by floodwaters from any source.”

But officials from FEMA on down emphasize that flooding can happen anywhere; the maps simply show where a community is most at risk of flooding. Insurance companies and lenders then use flood maps to determine flood insurance requirements and policy costs.

The river authority’s draft maps outline areas that would be inundated during a 100-year flood — a flooding event that statistically has a 1% chance of occurring in any given year. The maps, which can be difficult for the layperson to decipher — hence the open houses — shows risk levels through different color blues and various hash marks.

What do the new maps mean for my property?

Because the new boundaries take into account recent data, residential property and businesses that have not been located in the floodplain in the past may now be in it, and vice versa, said Brian Mast, the river authority’s government affairs manager.

Capital improvement projects have shrunk the floodplain in some areas, he said, while new rainfall data, updated topography and new development have expanded other boundaries.

Properties with federally backed mortgages located within a floodplain are required to have flood insurance. Most property owners will be contacted by their mortgage provider after FEMA’s new flood insurance rate maps go into effect, Mast said, but they don’t have to wait.

“Floods don’t wait for new maps,” he said.

To help mitigate risk to citizens and property, Bexar County and all the cities within it have additional regulations for building in or around the floodplain, the river authority notes in one of its informational pamphlets. For example, residents and business owners in Bexar County are generally required to obtain a permit for construction in or near the floodplain.

Mast and Cavazos both stressed that just because someone’s home isn’t in the floodplain doesn’t mean it’s not at risk, just that it’s in a lower-risk zone.

“Everyone should consider flood insurance,” she said.

Or as Bexar County puts it on its flood information page, “Everyone is in a floodplain. What you really want to know is if you are in a high-risk zone.”

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Lindsey Carnett

Lindsey Carnett covers the environment, science and utilities for the San Antonio Report.