How Can We Prevent Catastrophic Flooding?

Visitor Question: I'm finding what happened in Asheville, North Carolina in Hurricane Helene to be truly horrifying. As a minor official in my home community, I want to know what can be done to prevent such an unexpected and overwhelming weather event.

Was there something that should have been done in Asheville that was neglected? Or was this truly just an "act of God" that no one could have done anything to prevent? If we did have such an awful deluge, what measures could we be taking now to minimize the damage to people, buildings, animals, our water system, and our roads and streets?

Editors Reply: I'm going to avoid your questions about whether Asheville should have done something differently and what caused the flooding, since these questions, especially the latter, are well beyond my scope of knowledge.

However, you are correct in intuiting that there are some measures that vulnerable communities should be taking now. First though, it pays to do a bit of research into how vulnerable you actually are. Look at your town's history for clues. Asheville had experienced similar devastation in 1916. Then as now, there was so much rain before the hurricane that the ground was fully saturated, and what we now know is the rainfall from within a hurricane had nowhere to go.

If anything similar has ever happened in your city, study that history as closely as possible and prepare for a repeat occurrence. Actually, prepare for the next time to be far worse.

How would you notify people of the real danger in such a way that they would respond? What do you want them to do, and where do you want them to go if the best course of action would be for them to flee? The more you can educate the population, possibly beginning with the schoolchildren, about the historic event, the more they are likely to believe you when you issue dire warnings shortly before the storm that will cause water to spread everywhere.

Will you have any possible shelters nearby that are of much higher elevation? By "nearby," I don't mean half a mile either. I'm thinking of over in the next county where the geology is quite different. If so, make some contingency plans with those possible shelter locations, including whether and how they can accommodate pets.

We have a general page on flood prevention on this website. That is good general advice, and you should definitely learn about and follow the strategies suggested there. However, they are not sufficient for an extreme flash flood event, which is how I would describe what happened in Asheville.

After assessing your own vulnerability a bit, you should try to engage in some watershed planning with nearby communities and for that matter, communities that are far upstream from where you are located. Poor stormwater management upstream can increase the danger to your own community considerably.

To answer your question, yes, if you learn that there is any historical precedent for flash flooding, your community should find a consultant who is an expert in how to protect your water supply and delivery system in the event of flash flooding. There might be plenty that could be done to keep your drinking water safe, or it might be hopelessly unaffordable and even difficult to impossible physically without redoing the water system as a whole. The community should be presented with an honest picture of the risks and rewards of water system protection so they can make smart decisions about funding any project that makes sense.

As for protecting roads and streets, that too is a difficult and costly proposition. You could explore elevating the surface every time there is a street project, or you could beef up the specifications on the road surface so that even if the street is inundated for a time, it can be scraped and washed down to the good as new. (That has limits too; severe cross-currents and lengthy flooding may undermine a roadway regardless of good specs.)

This topic is so interesting because usually we advise communities to try to maximize groundwater absorption into the soil to prevent flooding in creeks and streams, reduce the need for unnecessary expensive stormwater conveyance structures, and replenish groundwater. In this case though, decreasing the amount of rapid runoff really would not have been a complete solution because the ground was saturated already.

So I am amending our usual advice to say that if your historical research reveals anything remotely similar to an extreme flash flood, you will want to employ a wide variety of approaches, hoping that in combination, they will be enough limit your damage.

In any case, one modest approach that could be helpful is adding to your supply of public space plantings that like to have their feet wet. Trees vary widely in how much moisture they like and will take up, and the same is true of shrubbery and even ground covers and grasses. Armed with some knowledge, your parks and your parkways (the area between the street curb and the sidewalk) could do double or triple duty in helping to absorb more water while also providing beautification benefits. It is rare these days to find a community that has as many plantings as possible in its landscape of public properties.

Certainly address public parking lots and the requirements for private parking lots and driveways in your zoning ordinance or other development regulation. The more permeable pavement (allowing water to soak through the cracks) you can use yourselves as a municipality and require others to use, the better. When journalists interviewing meteorologists say that the ground in Asheville was saturated, I'll go out on a limb to guess that the ground under large parking lots wasn't nearly as saturated. I bet it could have held more.

It also follows that your city could think about reducing the width of streets and converting some of the former paved area to a narrow strip of rain garden on one or both sides of the street.

It would be irresponsible to close this discussion without pointing out that climate scientists have been speaking out about the unquestioned increase in severe storms we are experiencing. Thus many knowledgeable commentators think that the Asheville storm is partly a result of climate change. Larger cities experience an urban heat island effect, but the smaller the city, the less importance you should give to that. To follow up on this line of thinking, you would want to read our climate change planning page.

However, in the face of an immediate threat of extreme flash flooding like the one Asheville suffered, a long-range solution requiring worldwide action seems to us to be an impractical answer to an immediate question. Instead, research similar events in your history, even if smaller and less catastrophic than Asheville.

If you are at risk, take a two-pronged approach: (1) do what you can to increase the capacity of the ground to hold water through reducing impermeable surface and adding water-thirsty landscaping, and (2) make contingency plans for how to limit damage if the worst happens.

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