Plastic may be the future for rice trunks
By Tommy Howard,
thoward@gtowntimes.com
August 18, 2006
Geese, ducks and other waterfowl really don’t care about technology, modern or ancient. They just want a source of food and water as they wend their way along the migratory flyways of the Eastern Seaboard.
For the people who have impoundments and other managed wetlands from old water sources, such as the rice fields that cover the Santee River Delta and much of Georgetown County, rice trunks are effective water control devices.
With the construction of the Santee Cooper hydroelectric project in the late 1930s, however, the increased salinity in the North and South Santee Rivers caused a lot of problems. Trees and other vegetation that couldn’t tolerate more salt in the water died off. Fish and other marine life that lived in fresh or brackish water died or moved on.
New aquatic life and organisms that could tolerate higher salinity levels entered the canals and rice fields, including marine borers.
Bob Joyner, wildlife biologist with the South Carolina Department of Natural Resources at the 20,000-acre Tom Yawkey Wildlife Center, says the small worms eat up the timbers of the old rice trunks within a few years. That causes problems with how to effectively and efficiently provide the means to control the water level in the rice fields.
The cost for labor and materials is high, and environmental concerns are paramount.
Electricity brings saline environment
Santee Cooper lakes, dams, canal and hydroelectric plant were built from 1939 to 1942. Electricity was first delivered in February 1942, with customers in Berkeley, Georgetown and Horry counties benefiting from that electric power.
In the 1980s, the U.S. Army Corps of Engineers built its rediversion project or canal to put more fresh water back into the Santee River and reduce the flow of water and silt into Charleston Harbor.
In the mid to late 1940s, Joyner said, “All hell broke loose with salt water from the ocean.”
Before that project was built, you could plant within a half-mile of the ocean. He has a letter someone wrote years ago stating the Santee River brought “so much fresh water that you could drink water from the mouth of the Santee River.”
“Within a month or so of the diversion,” Joyner said, “vegetation began to die. With salt water came marine borers.”
Need for change
The cypress logs that did the job for centuries just don’t last as long in the salt-water environment. In fresh water, Joyner said, cypress can endure for 30 or so years. In a saline environment, even treated wood just doesn’t have the staying power needed.
Over time, the lumber and building products industry has tried creosote on wood, pressure treating and CCA (Chromated Copper Arsenate). While each of these methods works, they also have drawbacks. The Environmental Protection Agency (EPA) said some of those chemicals shouldn’t be used. While docks, piers and rice trunks made of those materials don’t have to be removed before their time, no new structures can be built with those materials.
What to do?
Recycle plastic milk jugs.
That’s the primary ingredient of Trimax Building Products engineered or structural lumber.
Joyner learned that the man-made plastic lumber can be made to specifications. Trimax is reinforced with fiberglass to give it greater strength and durability.
For more on the product, visit Trimax Building Products’s website, www.trimaxbp.com
The first rice trunks built of Trimax were installed at the Yawkey Center in 2001. They’ve held up well, Joyner said, and more will be built as needed.
Staff at the Yawkey Center learned that galvanized nails and bolts lose their rust resistance as they are hammered into the wood or Trimax, so they have changed to using stainless steel nails, pegs, threaded rods, bolts, nuts and washers.
Before making that change, he said, some of the wood and coated wood products would last, but the rusting hardware would eventually lose its hold and the timbers would come loose and fall into the water.
Plastic benefits
Trimax doesn’t absorb water, is resistant to ultraviolet rays, and doesn’t warp, crack or split. The material — which can be extruded into just about any desired shape and size of lumber — can be cut, drilled and worked like wood. You can make mortise and tenon joints to hold the lumber together.
The marine borers or worms don’t like to eat milk jugs and fiberglass, so that’s not a problem either.
While he doesn’t speak for the company, Joyner said rice trunks and other marine structures built with Trimax should last about 50 years. That’s considerably longer than the 15 to 30 years that other materials would provide.
Even though the initial cost of Trimax is maybe 20 to 25 percent higher than wood, Joyner believes the longer life and environmental benefits outweigh the cost factor.
The product is a little more dense than CCA-treated material, Joyner said, but it will still float.
“It does have more flex in it than treated wood, but not so much that you can’t build from it.”
“We’ve been quite pleased with it,” he added.
As DNR staff has built several rice trunks, they have found that boards three inches thick by 10 inches wide are the best choice for their application. They are stronger than 2x10 boards.
The material costs from a third to a half more than CCA material, but lasts two to three times longer. Since it’s inert, there’s nothing to get into the environment, Joyner said.
Looking back
Joyner showed an old map compiled by the U.S. Coast and Geodetic Survey in 1893. It showed about 44,000 acres of rice plantation lands along the North and South Santee Rivers.
“It probably took 140 to 150 years to clear all that land and get it into cultivation,” he said.
“In order to manage all that land, you had to have trunks.” There were probably 100 different plantations along those two rivers, he said, in addition to the others in the rest of Georgetown County.
Winyah Bay is formed by the confluence of the Waccamaw, Great and Little Pee Dee, Black and Sampit rivers. The Santee River Delta is about six to eight miles south of the mouth of Winyah Bay along the Atlantic Ocean.
“This was probably the richest agricultural area in the world at that time,” Joyner said.
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