Coastal Riverbank Armoring

Along an 1800’ length of coastal river shoreline, the property owner estimated that they had lost 10-15’ of property in just five years from erosion. The property owner reached out to an engineering firm south of Charleston, SC for help. Initially, the engineering firm planned to use rock rip rap for the bank stabilization. Due to the size of the project, hundreds of trucks of rip rap would be required. The roads on the property could not handle hundreds of trucks so the rock would need to be transported into the site by barge. Cost estimates for the rock rip rap solution were over $1 million. Additionally, rip rap was not performing well along another section of shoreline at the property. The engineering firm researched other solutions and found Flexamat.

Flexamat is a tied concrete block mat that is packaged in rolls. Rather than requiring hundreds of truckloads of rock, the Flexamat solution only required 8 truckloads of material. Overall, the Flexamat solution was nearly 1/5 the estimates for rock rip rap. A barge was still utilized to transport the material and equipment to the remote site.

This work required a permit by the US Army Corps of Engineers. The engineering firm submitted Flexamat in their design. The design incorporated 102 rolls of 15.5’ wide x 25’ long Flexamat Plus that included a side extension for overlapping adjacent mats. The eroded slope was re-graded utilizing reclaimed earth to a uniform 2:1 slope. Coastal riparian seed was planted under the Flexamat Plus and earth percussion anchors with a cross plate head were incorporated in a diamond pattern along the area exposed to tidal fluctuations.

The installation was smooth and efficient. Within a few weeks, native riparian vegetation was becoming established within the matting.