Wave runup and reflection from coastal structures in depth-limited conditions

Abstract

An experimental hydrodynamic study was undertaken to phics. investigate the effects of depth-limited conditions on wave sunup and reflection from coastal structures. The tests were carried out in a two-dimensional wave flume with a mild 1 235 slope installed over much of the length of the flume. A revetment, consisting of an impermeable plywood slope overlaid by a filter and armor stone layer, was located on the mild slope at the far end of the flume. Measurements of the free surface elevations were made at nine locations in the tank and the waterline oscillation along the slope of the revetment was recorded. The water level in the flume was varied to create a range of conditions from those where no waves broke over the sloping foreshore before the toe of the structure to those where the majority of the waves broke before reaching the structure. The results of the wave sunup measurements were compared with existing empirical models of Ahrens and Heimbaugh (1988) and Van der Meer and Janssen (1995). The model of Ahrens and Heimbaugh (1998) was found to overprecise the sunup while the model of Van der Meer and Janssen (1995) was found to underproduce the sunup. A clear trend of increased wave sunup in depth-limited conditions was shown. A new empirical model was proposed that includes the effects of depth-limited conditions on wave sunup through the use of an enhancement factor for depth limited cases. Existing empirical models to predict wave reflection from coastal structures that are based on the surf similarity parameter accurately predicted the general trend of increasing reflection with increasing surf similarity values. However, the parameterization of the reflection coefficient using the surf similarity parameter failed to collapse the data onto a single line. A recent model by Seelig and Ahrens (1995) was shown to accurately predict the reflection coefficient for cases where no wave breaking occurred seaward of the structure. At the shallower water depths where wave breaking occurred seaward of the structure, the model underpredicted the reflection coefficient. The Seelig and Ahrens model was modified to increase its accuracy in depth-limited conditions.