Effects of the bed roughness and beach slope on the non-breaking solitary wave runup height

Abstract

In this study, a series of laboratory experiments were carried out to investigate the effects of bed roughness and beach slope on the non-breaking solitary wave runup height. Experimental measurements reveal that the bottom friction plays different roles in the solitary wave runup process for different beach slopes. Under the same incident wave condition, the maximum runup height on a smooth steel bed was found to be larger than that on a rough sandpaper bed over a 10° beach slope, whereas the same runup heights were observed for the smooth and rough beds over a 45° beach slope. By introducing the runup similarity parameter, quantitative relationships between the maximum runup height and the bed roughness, as well as the beach slope, were analyzed. On the basis of Synolakis (1987), a new empirical model for estimating the non-breaking solitary wave induced runup height was proposed, after incorporating a slope-related enhancement coefficient and a friction-related reduction coefficient. It is found that both the enhancement coefficient (being always larger than unity) and the reduction coefficient (being always smaller than unity) are large under the small relative incident wave height and steep beach slope condition. Influence of the bed roughness is more significant under the small runup similarity parameter condition, under which the runup height monotonically decreases with the increase of the runup similarity parameter for the small bed roughness, whereas it first increases then decreases with the increase of the runup similarity parameter for the large bed roughness. Nevertheless, influence of the bed roughness could be neglected for the large runup similarity parameter condition. These results are consistent with experimental observations. Finally, the present model was validated using a large amount of existing solitary wave runup data with different bed frictions and beach slopes. The good agreement between the model predictions and measured data indicates the reliability and accuracy of the present model.