Granite Geek: Repairing New Hampshire's At-Risk Culverts

Feb 24, 2016

As average rainfall increases, the culvert becomes an increasingly important part of our infrastructure. These pipes that run under roads allow easy passage for creeks and streams too small to merit actual bridges, but poorly-constructed or undersized culverts could pose huge transportation problems in the event of heavy rains. David Brooks, a reporter for The Concord Monitor and writer at Granitegeek.org, spoke with NHPR's Peter Biello. 

You were inspired to write about culverts here in New Hampshire because the state is looking at improving many of them in the state. So, what problems are they trying to avoid?

The problems they’re trying to avoid is basically, they get blown out by overly heavy rains, by flooding, which happens every now and then and when it happens it’s really bad. The issue—I’ve always been attracted to writing about culverts because they’re so incredibly boring.

I was going to say, why, why would you be attracted to something so boring?

Well, because there’s something appealing about trying to find the interesting in the mundane, and you can’t get much more mundane than a culvert. On a road near me, a culvert failed and so it took them a year to get to it, because you’ve got to have the budget, the annual budget and all that stuff. So, for a year, everyone had to drive miles out of their way—it was a bad thing. And there’s a bigger issue actually about culverts: they’re kind of the front line for climate change for us here, in central New Hampshire, at least. The Seacoast has other issues, of course.

Culverts are likely to be the one piece of infrastructure that you’re really going to see get hurt by climate change, because climate change is increasing the number of extreme precipitation events, lots of heavy rains that cause flooding, or droughts on the other side. And culverts have been sized, over the years, I mean road agents and towns have learned, you know, I need a culvert this big on this creek and I need a culvert that big on this creek. And, all of a sudden, the creek here or there is having twice the cubic feet per minute that it used to two times a year, and that’s going to start eating away the soil around the culvert and next thing you know, hey, presto it’s gone.

So, that’s the issue. And this was actually, I was prodded by a project that’s taking place within the Piscataqoug watershed, eleven towns, the water district. They actually, they’re trying to set up a model that would help prioritize which culverts need repair.

Tell us about the prioritization. How do they determine which culverts need the most urgent attention?

Well, it’s a function of a number of things. One is, you know, what condition is the culvert in? Most culverts, frankly, are metal pipes— if you’re lucky it’s got concrete around it— most of them are just metal pipes surrounded by dirt with the pavement up on top. That’s kind of what differentiates a culvert from a bridge: the bridge, the traffic travels directly over the deck of the bridge, as compared to over dirt that’s been put on top of the culvert. And so if, you know, the pipe is already collapsing, or last year it already backed up three times because it couldn’t handle the flow, that gives you a certain number of points on whether it needs to be replaced or not.

And other factors are obviously how important the road is. You don’t want to have a culvert blow out that now you can’t get to the fire station. And to complicate it, but make it more interesting, there are environmental issues with culverts, which, frankly, was driving a lot of the research before even the climate change came along.

Environmental issues, meaning, what the culverts do for fish?

What they do for aquatic life in general. A culvert is a way for the water to pass through, but it’s a way also for everything that lives in the creek or the stream to pass through, and there’s generally a lot more stuff in these little creeks than we think. I actually know somebody who used to go into the deep woods in part of the Piscataqoug watershed and find trout living in these creeks that you didn’t even know was a creek. But it doesn’t work if culverts sort of divide up the creek into pieces.

So, if a culvert is just a pipe that’s too high up, so it’s above the bed of the stream, then the fish can’t move up and down the stream, and neither can any other life that has to sort of climb into the bed and back down again. And so if you have a couple of culverts on a stream, which is not at all uncommon, and each one of them is crummy, you’ve basically divided the stream up into these little unconnected segments. And the amount of life that they can support, the ecosystem they can support, is much less because you’ve chopped it up. It’s sort of like a dam on the Merrimack, it’s very kind of similar. The dams on the Merrimack prevent the fish from moving up and down. Well, culverts on a creek can do the same thing.

So part of the idea is to replace culverts that are blocking movement of life up and down the waterway. And if at the same time you make them more resilient to higher waters, because they won’t get blocked by sediment. A lot of sediment gets moved around when there’s heavy rain. That can clog up a culvert, and the water backs up and starts flowing over the road and then washes away the pavement, hey presto. Then, if you can do both at once, make it easier for the fish and make it safer in case of heavy rains, then that’s obviously a good thing to do.

And the economic argument you present in your column this week is that it costs less to build a good culvert now than to have to pay for cleanup when a poorly constructed culvert fails.

Of course that’s an easy argument to make, but you know, if you were going before a town hall meeting and you were saying, you know, we want, I don’t know, $100,000 to replace this culvert, and somebody stands up and says, "What are you talking about? The last time we replaced it, it only cost $30,000." You’re saying, "Well this time instead of metal pipe we want to put in a larger pipe with a flatbed that’s lower, because it’s better for the fish." That’s a tough thing to sell at town meetings. So this economic argument is correct, you know, in the objective sense, but it’s sometimes a little hard to pitch when you’ve got to pay the tax bill.