Many coastal areas have lost thousands of acres of shoreline to erosion. Previous hurricanes have led to vast areas of land just disappearing. Storms, along with the loss of marsh grasses and other vegetation, have taken a toll. To maintain what’s left and bring back what was lost, Arcosa Lightweight aggregate is being used to help in coastal protection and restoration efforts.
Arcosa Lightweight, in collaboration with Industrial Fabrics, has led the development of a perfect solution for coastal protection and restoration applications: large bags encapsulating lightweight aggregates. “These are really great for erosion control," says ARCOSA's Steve Rowe. "We’re working together to promote this concept to engineers looking for a way to protect and restore coastal regions,” he says.
The oversize geotextile fabric bags filled with lightweight aggregate are being used to construct protective berms to keep vital flood control walls safe from the destructive effects of collateral damage caused by hurricane-force storm driven threats. First used in 2002, Rowe says these massive lightweight aggregate filled bags are much lighter than the material that would have been traditionally used: common riprap.
“Normally, they would just build this berm out of ordinary riprap, but because of how soft the soil is all over Southern Louisiana, but especially down below the water, the rock would just sink. "These bags containing rotary kiln produced lightweight aggregate, remain in the proper cross section shape and reduce the mass or load of that berm on the underlying soil by almost half.”"
---- Steve Rowe, Arcosa Lightweight
BAGS BY INDUSTRIAL FABRICS
The oversize aggregate bags were made by Industrial Fabrics, Inc. in Baton Rouge. Equipment to fill the
bags was set up at the Mississippi River port facility owned by 234 Terminal Corp. After each bag was
filled with up to 5 cubic yards of LWA, a hand-held sewing machine was used to seal the top. Once
completed, the bags were then placed, using lifting loops sewn into the bags, onto barges for delivery
directly to the project site.
For a recently completed marsh protection project near Terrebonne Parish, Louisiana, the bag sizes
ranged from four feet containing 1.5 cubic yards of lightweight to seven feet filled with 5 cubic yards
of material. In this particular project, more than 3,000 bags containing 10,000 cubic yards of lightweight
were used to construct the berm. Bags of varying sizes were placed in patterns based upon water
depth and design cross-section, then covered with 250-lb class riprap limestone rock. “By only covering
the tops of the bags with riprap, it’s armored for protection but the overall mass is still reduced
substantially,” says Rowe. “Now, if one of these bags should be punctured, and any material would
happen to escape, the most you would lose is the material in that one bag.”
Rowe says the use of ordinary, heavy riprap could also lead to underwater slope failure and loss of the
berm itself, a destructive issue designers were able to avoid by utilizing LWA-filled geotextile bags. “In
the case of the Algiers Canal project, dredging left the canal bottom deeper than the bottom of the
adjacent berm location. This condition added to the potential for an unstable berm structure,” says Rowe. “The advantage of lightweight aggregate in this particular application is that engineers can protect against or prevent slope failure underneath the berm.”
SELECTED CASE STUDIES
BARATARIA RESTORATION UTILIZES ENCAPSULATED LIGHTWEIGHT AGGREGATE
Louisiana is shrinking. By some estimates, the state loses roughly 16-square miles of coastline every year. Bays and bayous marked on nautical maps for centuries have vanished, washed away by decades of erosion and storm surge. A series of projects hopes to change that.
One such project is called the Barataria Basin Landbridge Shoreline Protection, a restoration campaign conducted by the United States Department of Agriculture Natural Resources Conservation Service (USDA NRCS). The long-term effort is designed to protect vital marshes and wetlands from further damage.
In this coastal preservation project, large bags of geotextile fabric are filled with lightweight aggregate produced at ARCOSA’s Erwinville, Louisiana facility. The bags, armored with rip-rap, help reduce wave energy impacting shorelines and protect adjacent marshes.
ARCOSA LIGHTWEIGHT USED IN MAN-MADE BERM ALONG LOUISIANA COASTLINE
Oversized geotextile bags filled with Arcosa lightweight are being used to protect the shoreline and restore marshes in the Biloxi Wildlife Management Area, a vital coastal ecosystem that protects the city of New Orleans, Louisiana.
The Biloxi Marsh project is located along a 7-mile stretch of the southeastern shoreline of Lake Borgne and the Biloxi Wildlife Management Area.
"The Biloxi Marsh project is a great example of using lightweight aggregate geotextile bags to create a berm," says Jeff Speck, Director of Technical Sales for Arcosa Lightweight. "The first phase of this project was estimated to use about 30,000 cubic yards of material. When this phase was completed, we learned that project used less material than was expected because they had virtually no settlement."
Marshes surrounding Lake Borgne have sustained significant land loss due to wave induced erosion, with approximately 15,640 acres lost between 1932 and 1990 along the 7-mile project reach. In recent years, some areas of the shoreline have receded up to 50 feet per year, greatly endangering the nearly 40,000-acre Biloxi Wildlife Management Area.