HURRICANE IMPACTS ON A RECENTLY NOURISHED CHRONICALLY-ERODING BEACH

Upham Beach, located in southern Pinellas County on the west coast of Florida, is the most rapidly eroding beach nourishment project in the state. Every four years, over 200,000 m³ of sediment is placed in the project area, which is less than 1 km long. After nourishment, the beach typically erodes at a rate of 70 m/yr losing most of the nourished material within 2.5 years. Construction of the July 2004 nourishment project was interrupted by Hurricane Charley, and then after completion of the project in late August, Hurricanes Frances, Ivan, and Jeanne caused significant erosion of the recently placed fill.

To quantify the effects of the hurricanes, beach profiles, spaced every 100 m, and GPS shoreline and dune line surveys were conducted weekly during September 2004. In addition, offshore bathymetry was surveyed at the beginning and end of the month, and an offshore directional wave gauge was deployed, allowing for differentiation between waves from the different hurricanes. Less than one month after project completion, the shoreline of Upham Beach eroded 60 m, a loss of over 60,000 m³ (or 20% of the total amount of beach fill), which is nearly equivalent to a year's worth of erosion based on previous nourishment performance.

The surveys captured pre- and post-storm beach profile and nourishment planform morphologies. Relatively high-energy conditions during the storms resulted in increased cross-shore and longshore transport of the nourished material. Profile equilibration, typically thought to occur on the order of years, occurred within one month. Accelerated planform adjustment also occurred. Overall, the post-nourishment response of a typically rapidly eroding beach was accelerated by nearly an order of magnitude due to the passage of three hurricanes in less than one month.