AbstractThis paper presents preliminary design guidelines for wave overtopping when circular-shaped roughness elements (ring-type revetment) are placed on the upper slope of a coastal revetment. Such a type of revetment was designed during the tendering phase of the Afsluitdijk reinforcement in 2017 as an innovative and highly effective way of reducing overtopping rates along coastal revetments. The design combines a relatively smooth lower slope (~1 in 2.5), wide storm berm (~1.5x wave height) and the roughened upper slope (~1 in 3) with a specific pattern of circular elements, resulting in a roughness comparable to that of a double layer rubble mound slope with an impermeable core. To effectively reduce overtopping rates, the circular elements require an average height of ~1/10 of the wave height and diameter of ~1/3 of the wave height, as well as a specific placement pattern (staggered pattern and spacing ~1/10 of the wave height).
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