Immediate profile and planform evolution of a beach nourishment project with hurricane influences

Abstract

In this study, planform adjustment began during a period of calm weather immediately after nourishment and then the passage of one strong storm caused a substantial portion of the total profile equilibration. Weekly beach profiles, shoreline surveys, and nearshore wave measurements were conducted before, during, and immediately after construction of the 1100-m long Upham Beach nourishment project on the low-energy, west coast of Florida. This project was constructed in three segments: the wide north segment, the central segment, and the narrow south segment. With the exception of the relatively distant passage of Hurricane Charley, calm weather prevailed for 45 days following completion of the south and central segments. Construction of the wide north segment was completed on August 27, 2004. Substantial planform diffusion occurred prior to construction completion via formation of a 300-m long spit extending from the wide north segment. The shoreline orientation was changed abruptly due to this diffusion spit formation, as opposed to the gradual adjustment predicted by most long-term models. Planform adjustment was initiated prior to profile equilibration, and it did not require high-energy conditions. A simple vector sum model for determining the orientation of a potential diffusion spit was developed. This study recommends designing end transitions at the predicted diffusion spit orientation to avoid post-nourishment spit formation during future projects. Profile equilibration occurred rapidly due to the passage of three hurricanes soon after nourishment was complete. Nine days after completion, Hurricane Frances passed by the project area generating high wave conditions ( H sig = 1.7 m) for this region. The steep post-nourishment beach slope of 0.078 was reduced to 0.036, nearly to the equilibrium slope (0.034), due to this storm. Hurricanes Ivan and Jeanne, which were nearly as energetic, passed by the project area within 1 month after Frances and resulted in much less profile slope change. Examination of the ratio of total volume to plan area remaining in the project area also suggested that a substantial portion of the total profile equilibration occurred as a result of Hurricane Frances. This study indicates that profile equilibration can be an event-driven process, which contradicts the concept of longer-term gradual profile equilibration. Both profile and planform adjustment can occur rapidly given the appropriate site conditions and energy levels.