2007 GSA Denver Annual Meeting (28–31 October 2007)

Paper No. 2
Presentation Time: 8:00 AM-12:00 PM


JACKSON Jr, Chester W., Department of Geology, University of Georgia, Athens, GA 30602, NEAL, William J., Department of Geology, Grand Valley State University, Allendale, MI 49401 and BUSH, David M., Department of Geosciences, University of West Georgia, Carrollton, GA 30118, cwjjr@uga.edu

The term "low cost" applied to engineered shore-hardening and sand-trapping structures is an oxymoron. However, coastal communities with limited resources often opt for perceived solutions to coastal erosion on the basis of cost. Gabions are a case in point. Although the U. S. Army Corps of Engineers discourages the use of gabions on high-energy shorelines, and has documented their failure, Puerto Rico has continued to opt for gabions in the construction of seawalls and revetments. The rock-filled wire cages were chosen to build seawalls and revetments because of their low-cost, and convenience of assembly at the construction site. Without exception (e.g., Balneario de Carolina, Aguada Parque de Colón, Balneario de Rincón, and Playa de Humacao), these structures have failed on Puerto Rico's open-ocean coast as a result of degradation (corrosion and abrasion), rupture of the cages and rock leakage, slumping and collapse during storms, piping, and erosive undercutting. Gabion walls cause the same problems as seawalls (passive and active beach loss), but also contribute to loss of recreational value of beaches due to dangerous exposure of wire and sharp rocks. Their initial low cost is offset by the cost of repair, reconstruction, or ultimately replacement by more costly structures. Ironically, gabion structures have been built on public beaches where no buildings or property were threatened (e.g., Balneario de Rincón). Similarly, other devices are touted as low-cost alternatives to more costly engineering structures (e.g., artificial seaweed, "reefs," geotubes, dewatering devices, fencing, etc.: see http://psds.wcu.edu/1043.asp). In the Great Lakes during times of high water and severe shoreline erosion such devices proliferate, although demonstration projects of such alternative devices generally proved them unsuccessful (e.g., z-walls, longard tubes, sandbag structures).