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Development 101: Stormwater regulations and 'impervious surfaces'

A retention pond in Brunswick County that had a stand of pine trees until crews cut them down in January 2023 in the name of pond maintenance.
A retention pond in Brunswick County that had a stand of pine trees until crews cut them down in January 2023 in the name of pond maintenance.

In the last part of our series on the logistics of development, WHQR News Director Ben Schachtman interviews Reporter Kelly Kenoyer about stormwater.

Want the big picture? Development 101: A look at the how the process works in the Cape Fear region

Ben Schachtman: Alright, Kelly, it’s our last deep dive on development, and you wanted to tell me about stormwater. That makes sense, given that this is a flat, marshy, storm-prone area.

Kelly Kenoyer: And we have special soil in certain parts that just doesn’t drain. So yeah, stormwater is a major issue developers have to deal with — both in terms of not causing flooding, and in mitigating the pollution of nearby watersheds.

BS: So how do developers deal with that?

KK: Well, first, developers have to make sure that the flow of water currently coming to and from their property is unchanged by their construction. Here’s County Engineer Tim Lowe:

Tim Lowe: “So we get a set of calculations from the engineer showing that what what the rate was leaving the property before it was developed. And their their design is supposed to show that it doesn't leave any faster than it did before.”

KK: And that’s supposed to be the case for a 25-year storm. Staff at the city and county also check on the impact of a 50 and 100-year storm to make sure there aren’t any unexpected problems.

BS: Alright, so what does that actually mean, though? We hear these terms all the time, but I think they’re easily misunderstood.

KK: It basically means there is a probable recurrence of a storm that size once in every 25 years — it’s a benchmark for what you can reasonably expect in terms of a sizeable storm.

BS: So what was Florence? When we got 30 inches of rain?

KK: That was a 1,000-year storm, and Lowe said you just can’t design to that standard. But for your more common storms, the idea is that neighbors won’t see any change to the flow of water in their streams or on their land. That’s why so many developments built retention ponds. And I think it’s worth noting that this is a relatively new component of the design process, at least according to local developer, McKay Siegel with East West Partners.

McKay Siegel “We didn't even have a stormwater review process until the late 80s. So anything that was built before that, you know, likely was either not graded correctly, or was not considered, you know, where's this water gonna run out to? How are the ditches gonna work? I mean, a ditch network was pretty much as far as we got, and by the way, clean your ditches out!”

BS: I’ve seen places where the old ditch network had basically failed, because it got clogged with debris and no one was really responsible for it — although the county’s new stormwater utility does tackle that now. So, let’s also talk about ‘impermeable surfaces’ — that’s something we hear about a lot these days.

KK: Yeah, that’s mostly asphalt, concrete, and rooftops — they can cause flooding because water just streams over them and doesn’t get absorbed — and they also collect pollution, like motor oil or debris from tires that run off into local watersheds. There are ways to mitigate those problems, with rain barrel collection systems or permeable road and parking lot surfaces, but not all of those are particularly common. Current code in many parts of the city looks a lot more closely at that impermeable surface ratio, rather than the density of units, when determining what is allowed to be built. Sometimes, developers are allowed to build more impervious surfaces if they mitigate them with specific strategies, like rain gardens, which stop pollution from going into the watershed. The flow rates are also partially determined by the type of plant coverage on the property, because trees drain a lot more water than grasses, which take in way more water than concrete.

BS: And those strategies can make a huge difference when a major storm does hit — or even an afternoon cloudburst, which causes flooding in some of our less-well-designed developments.

In any case, I hope this series has been helpful for people who want to understand what’s actually going on when a new development comes to town. That doesn’t mean you have to like it, but a lot of times we hear complaints from residents based on an incomplete understanding of the process. Basically, we encourage people to get involved – but, be informed, too.

KK: It can be kind of challenging to look at development as a regular resident: it’s not your day job, after all, while county and city staff and developers look at this every single day. But the best way to learn about what might go in next door is to attend a community meeting if a developer puts one on, or read a staff report if there’s a planned rezoning hearing. That way, you can avoid a surprise when they break ground next door. And you’ll know exactly what to expect in terms of its impact on you.

BS: And of course, you can always send us your questions.

KK: Even if I don’t know what’s happening with that development, I can send you to the right government staffer.

BS: Alright, well, thank you for your reporting this week!

KK: You’re welcome!

Kelly Kenoyer is an Oregonian transplant on the East Coast. She attended University of Oregon’s School of Journalism as an undergraduate, and later received a Master’s in Journalism from University of Missouri- Columbia. Contact her on Twitter @Kelly_Kenoyer or by email: KKenoyer@whqr.org.