Ask Sam: What Makes For a Very Bad Mud Season?

Apr 19, 2019

Fridays on Morning Edition, Outside/In host Sam Evans-Brown joins the show to answer a burning question from a listener. Here's this week's edition: 

Alison from Wilmot asks: I have not picked up on the conditions that make one mud season worse than another. As I have watched weeks and weeks worth of rainfall through the autumn, before the ground froze, I am now wondering if I should expect to see the fully saturated ground give up its moisture in a longer, slicker, sloppier mud season this spring. My second point is, is there any rhyme or reason to what would make any part of a road sloppier or more rutted?

For this one, I took a field trip up to Conway, New Hampshire (where I can assure you, mud season was in full swing) to meet Russ Lanoie, who has spent many decades maintaining dirt roads, and even distilled his knowledge into a manual called A Ditch in Time.

I spent most of my time up there observing the things that he does to deal with muddy spots (laying down gravel, “cutting” potholes, and digging out ice dams), but I think I can distill what I learned into a few chunky takeaways. The fundamental ingredients of mud season are as follows:

First, the soil is really wet… completely saturated.

Sometimes it was wet in the fall when it started to freeze. Sometimes it rains in the winter and that rain works down into the soil and freezes there. But heck it could be completely dry when frost sets in and as long as there is a good snowpack on top the soil will be wet once it starts to melt.

But the soil can be wet during other times of the year too, right? So why is mud season so muddy?

Ingredient number two is a deep frost.

In the colder parts of New England, the frost line can be more than four feet deep at the end of winter, but as the sun gets higher in the sky..

...you get the final key ingredient: the warmth of spring.

The ground begins to thaw from the top down. The key characteristic of mud season is that all of these dirt roads we’re trying to drive on have a top layer of wet, thawed soil, and a layer of frost underneath that prevents the soil from draining as the snow melts.

“That water’s now all sitting in the top, just waiting for the sun to come warm it up, where it can start making soup,” says Russ.

Oh, and don't forget: the vegetation is still mostly dormant.

To make matters worse, until the perennial plants really wake up from their winter slumber, most of the vegetation that surrounds the roads isn't actively taking water up through its roots, helping to dry the soil out. That process really gets kicking toward the end of April and into the month of May.

And not only that, but the roads can’t drain properly

Russ Lanoie digs out an ice dam in order to create a place for spring rains to drain.
Credit Sam Evans-Brown / NH Public Radio

Dirt roads get hammered with sand from plow trucks. Russ says that he scraped over ninety yards of sand off the roads of a single development that he maintains.

The sand then gets scraped flat by plow trucks, which eliminates the “crown” of the road. (A crown is what we call it when the center of a road is slightly higher than the edges, so that water runs off into the ditches on either side.)

To make matters worse, drainage ditches are often full of snow during mud season, and places where the water “wants” to run off can be blocked with ice dams.

All of this contributes to water lingering on the road, and as Russ points out “potholes are water and traffic.”

If you take all these ingredients together, you realize that a longer, more miserable mud season is much more about the weather in the winter and spring than in the fall. The soil will be saturated by snowmelt regardless, so the real wild card is how long it takes for the frost to disappear. In fact, while a soaking spring rain can make for some spectacular mud pits, it also carriess a lot of latent heat that can soak down into the soil and beat back the frost line. 

"The rain helps to dry things out" is one of Russ' maxims. 

In sum: the worst mud seasons tend to be a result of long, cold winters with a lot of snow, followed by a chilly spring that allows the frost to hold on for longer and keeps the plants from budding out.

So then why are some spots worse than others?

Russ doesn’t have a magic formula for knowing where the mud will pop up. “A place that’s been fine for twenty years all of the sudden will have a soupy spot start up, and it makes absolutely no sense,” he says.

Obviously anywhere that the lay of the land funnels melt water down into a low spot will probably be bad. But almost any spot can be muddy, and Russ attributes that to the mystery of what’s underneath.

“You don’t know what somebody did years ago, under that road, to stabilize it,” he says, “If there’s a lot of rock and it’s well supported, that can be just as good as a road through a very dry area.”

American road construction standards have varied over time. Modern roads are often built with systems of curbs and catchment basins to direct water away from the road bed. Or they are built with a layer of geotextile fabric (to keep the gravel from migrating down into the soil) covered by as much as a foot of various gravel sizes.

But maybe you live on a road where they just pulled out the stumps, threw down a bit of gravel and called it a road. That’s what makes mud season an adventure!