Tons of Sediment Runoff Are Reduced Through Erosion Control Projects

 

Island Resources Foundation’s Kevel Lindsay, left, and Sediment Scientist Dr. Carlos Ramos, right, on a recent trip to St. John.

Unpaved roads are not uncommon on St. John, but what many residents may not realize is these roads are the primary source of the more than 300,000 pounds of sediment being washed into the island’s bays.
Dr. Carlos Ramos is aiming to study just how much sediment the roads contribute to the island’s waters — and he is going to do something about reducing that sediment, which distresses coral reefs and other marine life.

Ramos, who began doing work on St. John in 1997 for his dissertation with the Watershed Sciences program at Colorado State University, is currently working on the Fish Bay Watershed in conjunction with the Island Resources Foundation, which is being funded by the Gulf of Mexico Foundation and the National Fish and Wildlife Foundation.

As part of his study in the late 1990s, Ramos and his colleagues set up 40 sediment traps across the island, from Maho Bay, to Cinnamon Bay to Bordeaux Mountain.

Those 40 traps collected 600,000 pounds of dirt over a two-year period, and by creating a model that predicts erosion rates, it was discovered that the slope of an unpaved road and how often that road is graded affect sediment runoff.

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Unpaved roads and construction sites in Fish Bay, left center, contribute heavily to the thousands of pounds of sediment that are washed into the bay.

Graded Roads Produce More Sediment
“Basically, we set up silt fences that are supposed to be set up on every construction site,” said Ramos. “If you install them right, they catch a lot of sediment. We discovered that roads that are graded at least once every two years erode at a much faster rate than roads that are used often, but not graded frequently.”

Roads that are graded often produce anywhere from 60 to 600 tons of sediment per hectare, or 10,000 square meters, per year, while roads that are not graded produce approximately 40 percent less, or 25 to 250 tons per hectare per year, according to Ramos.

By comparison, a natural hill slope contributes only 0.01 tons of sediment per hectare per year, Ramos added.

By implementing erosion control measures such as cement swales, Ramos, in partnership with the Friends of the V.I. National Park and Maho Bay Camps, was able to reduce sediment from the road to Maho Bay Camps, he said.

Maho Sediment Reduced
“The Maho Bay road used to be one of the worst roads on St. John as far as sediment production,” said Ramos. “One 230-meter segment of the road was producing 28 tons of sediment per year, which was draining into the Francis Bay wetland. We constructed five cemented swales and a ditch to improve the road drainage.”

Data was collected after these measures were implemented.

“We continued to collect data, and the final outcome was that we reduced sediment yields by 70 percent,” said Ramos. “Now, the road produces eight tons of sediment per year.”

Ramos and his colleagues also studied the Lameshur Bay watershed, which yields about 30 tons of sediment into the coastal waters every year.

Erosion Control For Fish Bay
“Lameshur is perceived as an undisturbed watershed, because it’s mostly within the National Park,” he said. “Thirty tons per year is not very significant when compared to other study areas.”

The Cinnamon Bay watershed drops about 50 tons of sediment per year, while Fish Bay, which Ramos will be focusing on in his next erosion control project, yields a staggering 230 tons of sediment per year — almost six times higher than sediment yields under natural conditions.

“This is one of the first studies ever done in the dry tropics, and we didn’t have a good grasp as to how much sediment would be coming off naturally, so it’s a bit hard to compare this figure to the rest of the world,” said Ramos, who will act as project manager in the efforts to reduce the sediment that is washed into Fish Bay. “Our studies do show that land disturbance is causing a significant increase in the amount of sediment entering St. John’s coastal waters.”

The erosion control project will begin with an assessment of the area.

“First, we want to do a watershed assessment, to find out where the problem segments are,” said Ramos. “The outcome becomes our first step toward erosion control.”

Control Runoff With Gravel, Ditches
Area maps will be taken to homeowners associations in the area, and the VINP, and suggestions for improvements will be discussed.

“We will make some initial suggestions as to what should be done on the roads,” said Ramos. “The idea is to work with the community.”

Although paving the roads may be the best solution, the funds for such a project are not available, according to Ramos.

“We don’t have enough money to pave the roads, so the rationale behind this will be just controlling the road drainage, which proved to be effective at Maho Bay,” he said. “We will probably use gravel on some of the roads, and build some ditches. Once these things are implemented, we will start monitoring how much sediment is coming from the roads and compare it to the data I collected before.”

Keep Sediment Out Of Oceans
Controlling sediment runoff is important to marine life, especially coral reefs, which have suffered due to high water temperatures and bleaching episodes in the last two years.

“Sediment can prevent sunlight from entering the water,” he said. “The sediment may cause the coral to be more prone to disease or even bleaching.”

Ramos’ work will be an improvement for the Fish Bay Watershed, according to Rafe Boulon, chief of resource management with for VINP, which is collaborating with Ramos on the project.

“Ramos has been working on best management practices, and ways to reduce the sediment without paving the roads, which is costly,” said Boulon. “But, if people want to protect the environment, it will take a lot of money. Unfortunately, anything you do to protect the environment from damages that we humans have wrought costs us humans some money.”

“The main goal is for us to keep sediment out of the ocean, and whatever is done at this point will be an improvement,” Boulon added.

Chuck Pishko, a member of the Estate Fish Bay Homeowners Association who met with Ramos on a recent visit to St. John, hopes Ramos’ work will improve water quality in the bay, he said.

New Construction Produces Sediment
“He has been really diligent about the area,” said Pishko. “ I hope his work will protect the reefs and improve water quality. What you end up doing is fixing the worst segments, then the next segment becomes the worst one.”

In addition to reducing sediment produced by unpaved roads, construction sites must also be monitored, said Pishko.

“New construction is a problem you have to be diligent on all the time,” he said. “People just have to be aware of what they’re doing. Everybody has a tendency to want to clear cut their land, and that’s probably the silliest thing you could do, because then you have nothing to hold the silt back.”

Ramos welcomes anyone interested in helping with the erosion control project, he said.

“We’re open for any information and collaboration that anybody can provide,” said Ramos. “We are directly working with the Fish Bay community, because they live there, but anyone is welcome to help.”

Those interested in helping with the project should contact Ramos at 787-587-0416 or [email protected]