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Most guidelines on wave overtopping over coastal structures are based on conditions with waves from one direction only. Here, wave basin tests with oblique wave attack are presented where waves from one direction are combined with waves from another direction. This is especially important for locations where wind waves approach a coastal structure under a specific direction while swell waves approach the coastal structure under another direction. The tested structure was a dike with a smooth and impermeable 1:4 slope. The test programme consisted of four types of wave loading: (1) Wind waves only: “sea” (approaching the structure with an angle of 45°), (2) Wind waves and swell waves from the same direction (45°), (3) Wind waves and swell waves, simultaneously from two different directions (45° and −45°, thus perpendicular to each other), and (4) Wind waves, simultaneously from two different directions (45° and −45°, thus perpendicular to each other). Existing guidelines on wave overtopping have been extended to predict wave overtopping discharges under the mentioned types of wave loading (oblique sea and swell conditions).

Rubble mound breakwaters and revetments typically contain granular filters in one or more layers. The transition from the armour layer to the filter layer, and transitions between other layers within the structure, are normally geometrically tight to prevent material washout. This requires a limited ratio of the material size of the upper layer and neighbouring layer. An alternative is a geometrically open filter where in principle underlayer material can be transported into the upper layer, but if the hydraulic load at this transition between two layers remains low, the transition can be designed such that no or limited transport occurs, see for instance Van Gent and Wolters (2015), Van Gent et al (2015) and Jacobsen et al, (2017). This allows for larger ratios of material sizes, which can reduce the number of filter layers, and relax the material requirements with respect to the width of gradings. This can lead to considerable cost savings. In Van Gent and Wolters (2015) physical model tests for the transition between a layer of rock and an underlayer that consists of sand have been performed and design guidelines have been derived. Here, additional physical model tests are presented to study the influence of the storm duration and water level variations on the response of sand underneath a layer of rock.

Physical model tests were performed to obtain information on the stability of rock slopes with a horizontal berm. This paper is focussed on the rock slope stability of the slope above the berm. By applying a berm the rock size in the upper slope can be significantly smaller than for a straight slope without a berm. The influence of the width of the berm, the level of the berm, and the wave steepness have been investigated. Based on the test results a prediction formula has been derived for 1:2 slopes with various dimensions of the berm.