St. Lucie Shoal Complex: Regional Sediment Resource or Submerged Storm Breakwater
Nearshore sand shoals have become the predominant sediment resource for beach nourishment projects on the east coast of Florida. Along this coast, the St. Lucie Shoal Complex (SLSC) is comprised of several shoals designated as sediment resources for beach nourishment, many having depths less than 7 meters, at their crests. This group of shoals represents the largest high-quality beach nourishment sediment resource in southeast Florida. Among these shoals, the St. Lucie shoal is the largest and shallowest at the crest. This project explores the current best practice methodologies to explore impacts of excavating sand resources from shallow-crested shoal systems like the SLSC in comparison to those used to previously to demonstrate that assumptions used previously are still viable through a pragmatic use of increased model capabilities and improved datasets. At times, limited modeling capabilities were the problem but, increasingly the sparse data density, both spatially and temporally of regional scale oceanographic datasets, was found as the limiting factor in model accuracy. A brief review of the Wave Information Studies (WIS) hind cast of wave data from the U.S. Army Corps of Engineers (USACE) Coastal and Hydraulics Lab (CHL) indicates that significantly larger wave heights, 13.6 meters at a 14.9 second period, offshore of this area exceed those previously modeled, a 1.4-meter wave at a period of 15 seconds. To examine the potential of sand excavation from the SLSC to alter the local wave regime, the year of 2004, including Hurricanes Frances and Jeanne, was modeled as a worst-case scenario. Shallow crested, relative to their local wave climates, shoals must be evaluated for their wave energy dissipation effects during major storm events. Wave attenuation from the shallowest shoal permitted for use during the strongest conditions (Hurricane Frances), showed a marginal wave reduction of 4%. As the largest high-quality sediment resource in southeast Florida, the SLSC is targeted by several Florida coastal counties for sand excavation. Pragmatic management strategies can help provide a greater benefit for all by reincorporating more of the highest quality beach compatible sediment back into the longshore sediment movement from north to south along the southeast Florida coast. Counties who have downdrift beaches should consider cost sharing as well as mutually beneficial policy changes to encourage the implementation of regional sediment management plans.