Laboratory Model Studies of Wave Energy Dissipation in Harbors

Wind waves may be amplified in many Great Lakes harbors due to reflection and resonance phenomena. Although the short period waves do not excite the harbors at their fundamental periods, wave amplification in many situations has been sufficient to pose navigational concerns. It is useful to dissipate a portion of the wave energy in order to reduce wave heights to acceptable levels. We have performed numerous laboratory studies at the University of Michigan Hydraulics Laboratory utilizing stone to provide energy dissipation in order to reduce wave activity to an acceptable level. These studies have considered a wide array of stone size and use from large armor stone that would be statically stable under design waves down to much smaller stone confined within gabions. It is likely that a significant portion of this energy dissipation occurs due to fluid motion in the pore spaces. We have systematically varied the stone size in laboratory models for both enclosed harbors and jettied harbor channel entrances. These experiments have indicated that the reduction in wave amplitudes is independent of the stone size. It is therefore concluded that the results of the small-scale laboratory model tests may be applied to estimate prototype harbor behavior for typical Great Lake harbor settings. General results of these studies are discussed with respect to the general effectiveness of different configurations for reducing wave amplitudes.