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

Paper No. 1
Presentation Time: 8:00 AM-12:00 PM


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

Puerto Rico's high population density (400/km2) and associated development, concentrated in the coastal zone, results in communities that are highly-to-extremely vulnerable to coastal hazards. In 1995 we classified the island's shoreline vulnerability as 6.2% extreme-hazard, 61.1% high-hazard, 20.4% moderate-hazard, and 2.3% low-hazard. Tsunamis pose the greatest extreme risk (e.g., 1867 tsunami struck southeast coast; 1918 tsunami did extensive damage to northwest coast). The island is in the zone of westward-moving Atlantic hurricanes, and has a history of severe impact from such storms (e.g., Hurricane Hugo, 1989, $1 billion in property damage; San Ciriaco hurricane of 1899 left over 3,300 dead). The north and west sides of the island face the large Atlantic fetch and experience winter storms that cause local shoreline retreat. Far-traveled winter-storm swell severely impacted the northern coast in November 1962, January 1963, December 1967, January 1988, as well as the "Perfect Storm" of 1991 (Halloween Nor'easter). The sea-level rise may not be perceived as a significant problem, but flooding of low-lying coastal mangroves, wetlands, and developments at low elevations will increase, and erosion of wave-cut bluffs will accelerate (e.g., southern Municipios of Arroyo and Guayama). Anthropomorphic effects have seriously modified coastal processes to create high-to-extreme risk zones. Examples include removal of protective dunes and beach-sediment by sand mining (e.g., Piñones, Caribe Playa Seabeach Resort, and Camuy), and erosional impacts due to marinas (e.g., erosion rates of 3 m/yr in Rincón area due to Punta Ensenada marina). Communities have taken the wrong course in shoreline erosion control by emplacing shore-hardening structures along over 50 coastal stretches (e.g., seawalls at San Juan Harbor and Arecibo; groins in Ensenada de Boca Vieja), and utilizing poor construction designs in such structures (e.g., extensive use of gabions). Beach profiling reveals that beaches narrow and disappear in front of these structures (e.g., no dry beach in front of 55% of seawalls surveyed). Mitigation must come though prohibiting construction in high-risk zones, encouraging wider adoption of set-back principles (e.g., as at Villa Palmira), relocation after storms, and better public education.