Runup of landslide-generated waves breaking on steep slopes captured using digital imagery and hydrochromic paint

Runup of landslide-generated waves is an important natural hazard in coastal regions, and can result in major damage to the natural and built environment. Past work has investigated the runup of non-breaking waves, whereas, in contrast, little data is available on the runup of waves at the point of breaking prior to interaction with the opposing shore. In the present study, impulse waves were generated in a series of laboratory flume experiments by releasing a range of different slide source volumes of highly mobile slide material (water) into different reservoir depths, to observe the runup of breaking and non-breaking waves at the point of arrival at steep slopes ranging from 25° to 45°. Water surface characteristics including the maximum wave amplitude were measured using wave probes and digital imagery was obtained using high-speed cameras. The maximum runup, and the cross-slope variability in runup, of each wave was captured using hydrochromic paint, which changes colour on contact with water. The experimental results indicate that in the near-field the runup of breaking waves is dependent on the wave amplitude relative to the water depth, and is nearly independent of the slope angle. Statistical analysis of the runup observations for breaking and non-breaking waves indicate that the variability of runup across the width of the slope increases with increasing incident relative wave amplitude. These observations, combined with runup data from previous studies, are used to develop a new semi-empirical equation for the maximum runup of breaking and non-breaking waves. The formulation is valid over an extended range of relative wave amplitudes, relevant for near-field runup that has been documented in major field cases. The experimental observations in the present study provide, for the first time, a comprehensive dataset of runup for impulse waves involving breaking and no breaking on arrival at a slope. •Novel large-scale experiments reveal differences in runup for waves that are breaking or not breaking on arrival at a slope.•A new technique is developed using paint that changes colour in contact with water to quantify spatial variability of runup.•A new equation for runup of breaking and non-breaking waves improves predictions over an extended range of conditions.