Answer Man: Why is the French Broad River so muddy lately?

Today’s batch of burning questions, my smart-aleck answers and the real deal:

Question: The French Broad River seems awfully muddy recently. I know we have had a bit of rain, but where is all this silt coming from? Is it agricultural or I-26 construction?

My answer: On a positive note, the hundreds of tubers floating down the river every weekend are getting a free mud bath in addition to their float.

Real answer: This is a complex issue with multiple causes, which I will get to in a minute. But first of all, it's important to remember that the French Broad has its headwaters in Transylvania County, then flows through Henderson, Buncombe and Madison counties on its way to Tennessee and ultimately the Gulf of Mexico.

So, while the reader mentioned "a bit of rain" we've been getting lately, that's probably a reference to Buncombe County. But two other counties' runoff feeds the French Broad before it gets to Buncombe.

"We’ve noticed with recent heavy rains in the North Carolina mountains, that tends to put mud in the river," said Doug Outlaw, a meteorologist with the National Weather Service in Greer, South Carolina, which monitors Asheville weather. "Going back to (Aug. 6), that night was another good rain in the headwaters area of the French Broad, with between 1 and 2.5 inches in that headwaters area. So, over the past couple of weeks, there’s been good rain in that area, and that results in some mud flowing into the river."

More: Answer Man: Microplastics in local water? In the French Broad?

As I've noted in a previous Answer Man column, Asheville is typically the driest place in North Carolina, while parts of Transylvania County, about 40 miles away, are the wettest. That's judging by average annual rainfall.

So, the rainfall in Transylvania and Henderson counties, which also have a lot of agriculture, plays a big role in what the river looks like in Buncombe and beyond.

Outlaw noted that in July, Brevard, the county seat of Transylvania, recorded 9.85 inches of rain, while Asheville had 3.89 inches. That's a fair amount in Asheville, but "that's a big contrast to Brevard," Outlaw said.

June was a relatively dry month, with Brevard recording 3.37 inches and Asheville just 1.66 inches.

As of Aug. 16, Asheville (the measuring station is at Asheville Regional Airport) had recorded 1.27 inches of rain, 1.31 inches below normal. Transylvania had recorded 3.5 inches.

More: E. coli in the French Broad River a result of sewage, cattle waste: study

This time of year, Outlaw said, we also tend to get storms that linger longer, "so they kind of rain themselves out." Tropical storms and their remnants can pose particular problems.

In summation, all that rain flows into the French Broad, along with dirt and other runoff, and that causes muddy conditions upstream in Buncombe. And yes, the French Broad flows from south to north, which is unusual.

Now, moving on to the complexity of the issue.

"The story of a muddy French Broad is the story of a death by a thousand cuts," said Anna Alsobrook, watershed outreach coordinator with MountainTrue, an environmental nonprofit based in Asheville. "First, some sediment does enter the river naturally. Erosion is a natural process of river systems."

More from Boyle Column: Boyle column: Is French Broad River drinking, littering getting out of hand?

Boyle Column:Kayaking backwards down the poopy French Broad River

But that accounts for only part of the mud problem.

"Excessive erosion, however, is caused and exacerbated by how we manipulate the land around the river," Alsobrook continued, via email. "As development in our region grows, the amount of impervious surface (surfaces that water cannot penetrate, like roads or sidewalks) also grows. What this means is there is less room for rainwater to penetrate the ground, increasing the amount of stormwater runoff we have and the speed with which it flows.

"This runoff brings in sediments, among other things, from poorly managed land use practices — whether that's development, logging, or agriculture — as well as undermines weaker sections of riverbanks," Alsobrook continued.

We do have tools to mitigate the runoff, with one of the best being "deeper-rooted vegetation near our creeks, streams, and rivers," Alsobrook said, noting this is called a "riparian buffer."

"Tree and shrub roots near rivers act like load-bearing walls of a house," Alsobrook said. "They provide the strength and stability to hold the riverbank up, even during big storms. They also have the added benefit of filtering out potential contaminants that would otherwise be brought into our waterways by stormwater runoff."

Rules are in place that require developers and construction companies to prevent runoff. Alsobrooks says you can report violations to muddywaterwatch.com.

"We can then send it to the appropriate agency to follow up," Alsobrook said.

We'd be remiss in all this in not mentioning the elephant in the room: climate change.

"Climate change is driving more frequent, more intense, and higher volume rain events in the French Broad watershed, which is compounding the impact of stormwater related runoff and erosion issues," Gray Jernigan, central regional director at MountainTrue, said via email.

This is the opinion of John Boyle. To submit a question, contact him at 232-5847 or jboyle@citizen-times.com

This article originally appeared on Asheville Citizen Times: Answer Man: Why is the French Broad River so muddy lately?