Short duration bores in the coastal zone are generated by wave breaking in shallow water and mild foreshore conditions. In storm weather situations and for sea level rise scenarios, these bores approach the dike and interact with previously overtopped or reflected bores. Combined laser scanner and video measurements were used to study the complex and turbulent bore interaction processes. Five bore interaction patterns were distinguished as (1) regular bore pattern; (2) collision bore pattern; (3) plunging breaking bore pattern; (4) sequential overtopping bore pattern, and (5) catch-up bore pattern. Video images of the bore running up the wall and motion tracking of the leading edge were used to obtain a time series of the run-up water at the wall. The impact loads of the bore hitting the wall on the promenade were studied based on the signal of a vertical array of 13 pressure sensors installed over the wall height. Three impact types were distinguished and classified as (1) impulsive impact type; (2) dynamic impact type; and (3) quasi-static impact type. The majority of ~2/3 of the total number of impacts were comprised of the quasi-static impact type.

Overtopping wave loads on vertical structures on top of a dike have been investigated in several small scale experiments in the past. A large-scale validation for a mild foreshore situation is still missing. Hence the WALOWA experimental campaign was carried out to address this topic. In the present paper the objectives of the WALOWA project are outlined in detail, the model and measurement set-up described and the test program presented. Furthermore, preliminary results featuring a single 1000 irregular waves test of the test program are highlighted. This includes the study of the mild and sandy foreshore evolution by comparing profiles before and after the test execution. The profile measurements are obtained with a mechanical profiler. The wave parameters offshore and at the dike toe are numerically simulated using a SWASH model. The numerical results are validated against the measurements. Finally, the force and pressure time series of the waves impacting against the wall are processed and filtered. The load cell measurements and the time series of integrated pressures are compared to each other and for each impact event the maximum force is derived.