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Tropical Storm Elsa is headed for NC: Here’s how to learn if you live in a flood zone, near environmental hazards

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Elsa’s projected path (Map: NOAA.gov)

Have a tip about environmental hazards in flood waters? Text me at 919-536-2341; for privacy I also use the Signal app [2] at the same number. Other ways to reach me: via Twitter @lisasorg , Facebook, and by office phone, 919-861-1463. 

The first tropical system of the summer, named Elsa, is expected to cause localized flooding [3] in North Carolina tomorrow, as it crosses into Scotland and Richmond counties in the morning and then travels through the central part of the state. Here is a brief tutorial for learning whether you’re in a flood zone and what other environmental hazards could lurk below the water.

Do I live in a flood zone? And what does a “100-year flood plain” mean? Am I good until the year 2121?

The state’s Flood Risk Information System [4] allows you to search by address or county to view the flood zones. It will also show you what buildings are at risk, whether flood insurance is mandatory and other information. There is a key next to the maps that explains what the various symbols mean.

Since Elsa is supposed to hit Richmond and Scotland counties first, below is a flood map showing areas in Hamlet, in Richmond County. I picked a random spot on the map that is prone to flooding. The blue striped zone (AE) is an actual floodway. The solid blue zone represents areas that have a 1% or greater chance of flooding each year. [5] You might have heard this described as the 100-year flood plain. That does not mean — I repeat, does not mean — that these areas will flood only once in 100 years. With climate change, 100-year flood plains can be under water multiple times a year. So no, you’re not good until 2121.

Yellow areas represent 500-year flood plains, areas where there is a 0.2% or greater chance of flooding each year. Don’t be lulled into complacency by these odds either. Hurricanes Florence and Matthew blew those statistics out of the water, so to speak.

You can also click on individual buildings to see their flood risk.

And the numbers with the straight lines through them “287.1” and “285.3” signify elevation above sea level. (Some coastal areas are at or even below sea level.) The important aspect of this Hamlet map is that the water will flow from the highest point, 287, downhill. So folks living at lower elevations are more likely to bear the brunt of flooding as gravity exerts its magical powers.

 

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Source: Flood Risk Information System

Yeah, but it’s never flooded in my neighborhood before.

Lucky you! But be aware flood zones can shift over time. Heavier rain and stronger storms associated with climate change can inundate areas that otherwise seemed immune to high water. If a lot of development has occurred in your neighborhood — new shopping centers, subdivisions, construction zones — that involve enormous swaths of pavement or disturbed earth, that can change the flow of stormwater. This occurs because asphalt and concrete are impervious surfaces that don’t absorb the rain like grass, soil and gravel do. Construction zones disturb the ground cover and create new paths for water to flow.

I live near a river. How can I learn when it will crest?

River flooding is not forecast for this storm, but conditions can change quickly. The NC Flood Inundation Mapping and Alert Network [7] shows real-time and forecast river conditions. The US Geological Survey has installed several river cams in the Southeast [8], including areas of North Carolina. Here’s one for the French Broad [9] in the western part of the state.

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Water is not supposed to be this color: Stormwater runoff entered a stream in Raleigh after recent rains. The source is dirt that has been dislodged from nearby construction. The State Fair/Department of Agriculture have clear-cut 19 acres of forest for a parking lot. It’s a violation of state law to allow stormwater to pollute streams, creeks and rivers. (Photo: Lisa Sorg)

What is stormwater? The same as rainwater?

Stormwater can contain rainwater, but it’s not as benign. I think of stormwater as rain’s evil twin. Stormwater is essentially runoff from land surfaces. It can be polluted with antifreeze, fertilizers, gasoline, oils, sewer and septic system overflows, feces (this is why you must pick up after your dog), dirt, and other contaminants. These hazards are why the state regulates stormwater. When you see a rainbow sheen on a puddle, that puddle is not your friend. This is why it’s important to avoid wading or walking in flood waters unless it’s an emergency. Also: snakes.

What if I’m on a private drinking water well or septic system?

More than 2.1 million people in North Carolina rely on private septic systems, and roughly a third of the population is on a private well.

Flooding can contaminate drinking water wells and overwhelm septic systems. Last week, the NC Environmental Justice Network held an online meeting about how folks on these private systems can prepare for hurricanes and flooding, and what to do afterward. I pulled some slides from the presentation with important tips. The state and local health departments [11] regulate and inspect private wells, not DEQ.

 

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What other environmental hazards could be released by flood waters?

The NC Department of Environmental Quality has a community mapping system [14] in which you can plug in an address and discover what potential pollution sources are nearby. This isn’t a comprehensive list because the data are limited to what sites the state has either permitted or knows about. Nonetheless, it’s breathtaking to see all of the sources laid out on a map.

On a local level, let’s look at a map that shows potential pollution sources in parts of Rocky Mount that are near the Tar River. The mapping system includes a legend that tells you what type of pollution source each dot represents. When you’re in the mapping system, you can click on the dot and get a link to more documents about the incident or pollution source. These maps also include census tract data, which are helpful for learning about environmental justice issues, as well as health outcomes for the neighborhoods.

I’ve annotated this map with a few notable places. The blue lines show the location of the Tar River and its tributaries. Notice there was an above ground storage tank leak at some time in the past, right on the river. An unlined landfill — the old Rocky Mount dump — is also right on the Tar. And it’s in a predominantly Black neighborhood that routinely floods.

 

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Source: NC DEQ Community Mapping System