Overtaking and runup of double solitary waves on a gentle slope*

The overtaking interaction of the double solitary waves over a plane slope is studied experimentally. The slope of the plane beach is 1:20. For the cases of the double solitary waves of different amplitude ratios and different relative wave crest distances, the time series of the surface elevation and waterline movement are measured by wave gauges and recorded by high-speed cameras respectively. Three categories of overtaking solitary wave interactions are reproduced in the wave flume. Analyzing the measured runups, it turns out that the maximum runup amplification coefficient, defined as the ratio of the maximum runup to the larger amplitude of the double solitary waves, is dependent of the relative distance between two peaks of the incident waves. There is a peak in the curve of the maximum runup amplification coefficient versus the relative distance. The mechanism of generating the peak value is that the violent plunging breaking does not appear by the overtaking collision of two solitary waves near the breaking point on the slope.