The Associated Press
Clark Alexander spent three years studying the question: Do boat docks built over coastal marshes do less environmental harm if they’re riddled with holes to let sunlight pass through to marsh grasses beneath them?
The researcher for the Skidaway Institute of Oceanography in Savannah concluded that, during most of the year, docks made from open grating still block almost as much light as those built of solid wood. Now conservation groups are using Alexander’s work to challenge a rule by federal and state agencies that gives homeowners on the Georgia coast permission to build larger docks if they use grating for the walkways.
The Savannah Riverkeeper and the Center for a Sustainable Coast filed a lawsuit July 23 asking a U.S. District Court judge to throw out the perk, saying Alexander’s research debunks the assumption that docks filled with holes have environmental benefits. The U.S. Army Corps of Engineers, which issued its latest permitting rules for Georgia docks last year, said its conclusion that grating is less harmful to marshes also has a scientific source: the same 2012 dock study by Alexander.
So far, the scientist at the center of the legal battle hasn’t taken sides.
“I can see people using the data in both ways,” Alexander said.
Alexander began looking more closely at boat docks a decade ago when he served on the state committee assigned to protect Georgia’s 590 square miles of tidal salt marsh. That’s amounts to about a third of the total saltwater marsh on the East Coast. Tall marsh grasses form a critical part of the food chain that allows fish, shrimp and crabs to thrive.
They’re also an obstacle for waterfront homeowners trying to cross from backyards on the marsh to their boats in open water. Some coastal Georgia homes have boat docks up to 2,000 feet long. The Southern Environmental Law Center, which filed the lawsuit on behalf of the environmental groups, estimates that more than 2,300 single-family docks were built in coastal Georgia from 1996 to 2011.
Most private docks in Georgia are approved through general permits issued by the state Department of Natural Resources. They require minimal government review as long as plans adhere to restrictions issued by the U.S. Army Corps of Engineers.
“Right now it’s fairly easy to get a dock in Georgia, and there’s not a lot of science out there on the impacts of docks,” said Nate Hunt, an attorney for the Southern Environmental Law Center. “When we have new scientific evidence, it must inform state and federal agencies’ regulations.”
Billy Birdwell, spokesman for the Army Corps’ Savannah District, declined to comment on the lawsuit. But he said the agency is making rules based on science, particularly the research done by Alexander.
The agency’s rules say coastal Georgia docks generally must be no more than 3,000 square feet to avoid closer scrutiny. But from 2007 until last year, homeowners could build their docks 50 percent larger if they used open grating. When Alexander published findings last year saying docks blocked most sunlight with or without holes in their decks, the Corps cut that perk in half.
“It went from a 50-percent credit down to a 25-percent credit,” Birdwell said. “That’s a significant reduction.”
Alexander’s prior research focused on the shadows that boat docks cast onto the marsh grasses below. He found that the density of marsh grasses tends to thin out by half under the shade from a dock. The same shady conditions reduce the amount of carbon in the marsh — essential foodstuff for the bottom of the food chain — by about 30 percent.
He turned to studying whether marshes fared better under docks made with grating after manufacturers began making the hole-filled walkways with fiberglass, plastic and metal rather than wood and advertising their environmental benefits.
Starting in 2008, Alexander set up “mock docks” 20-feet long on the upland grasses at the Skidaway Institute. One was solid wood, while others were made from different types of grating sold by manufacturers. Sensors measured the intensity of sunlight both on top of and underneath the docks. He recorded those findings daily for two years. That gave him time to capture the effects of all four seasons. He also rotated the docks at regular intervals between north-to-south and east-to-west to see how their orientation affected light penetration.
“In a nutshell, what we found out is basically that alternative materials do allow extra light to penetrate through the dock, but only in the summertime season when the sun is highest in the sky,” Alexander said. “When the angle of the sun is low in the sky during the fall, winter and spring, there really is no extra light you get beneath these docks.”
At best, Alexander’s study found that docks with holes allowed 25 percent more light beneath them than solid docks, but only on certain summer days. Essentially, he said, the government permitting agencies decided to base their 25-percent credit for dock size on his study’s best seasonal result rather than the overall findings.
Spokeswomen for agencies in Florida, South Carolina and North Carolina said their states don’t give any special credits for docks built with open grating. Now the courts will decide whether Georgia’s credit stands up to science.