| An 18 month field monitoring program was conducted to determine the impact of a submerged narrow crested artificial reef, located seaward of the surf zone and immediately adjacent to a tidal inlet, on nearshore beach profile evolution. Observed structure settlement and scour zones adjacent to the structure are analyzed though the use of wind, wave, current, and tidal measurements obtained over two independent time periods, each of one week duration. Complex interactions of wind, wave, and tidal elevation were found to generate a flood dominated current structure in the vicinity of the reef. Due to the complexity of the forcing mechanisms a qualitative analysis of the impact of the structure on nearshore hydrodynamics was performed. The structure was found to reduce the magnitude of the near bottom cross-shore currents. However, structure-induced vertical currents combined with flood dominant tidal currents provides a mechanism to initiate near-structure scour and settlement. In an effort to quantitatively analyze the fluid-structure interactions, a methodology was developed to determine the relative magnitudes of the measured wind, wave, and tidal forcings. The frequency distribution of energy density in the tidal elevation and current records provides insight into nonlinear interactions present in the data set. Decomposing the record into independent forcing terms allowed the development of an empirical model which indicates that linear and nonlinear interactions between the wave amplitude and water depth were found to dominate the forcing of the observed currents. |
