Guido Wolters

BARDEX II: Bringing the beach to the laboratory - again!

ABSTRACT Masselink, G, Turner, I.L., Conley, D.C., Ruessink, B.G., Matias, A., Thompson, C., Castelle, B. and Wolters, G., 2013. BARDEX II: Bringing the beach to the laboratory – again! Proto-type laboratory experiments are particularly useful in coastal research when forcing parameters are modified in a way that is impossible to achieve in the field, and where installation and maintenance of instrumentation requires absence of waves. In 2008, the Barrier Dynamics Experiment (BARDEX) took place in the Delta Flume, the Netherlands. This project, funded by Hydralab III, focused on the effect of varying wave, sea level and beach groundwater conditions on a gravel beach (D50 = 10 mm). In 2012, a similar project was carried out, referred to as BARDEX II, this time funded by Hydralab IV and on a sandy beach (D50 = 0.42 mm). During the experiment, a 4.5-m high and 70-m wide sandy barrier was constructed in the flume with a lagoon situated to the landward. The barrier was instrumented with a very large number (> 200) of instruments and subjected to a range of wave conditions (Hs = 0.8 m; Tp = 4–12 s) and varying sea and lagoon water levels. Five distinct test series were executed over a 20-day period: series A focused on beach response due to accretionary/erosive wave conditions and a high/low lagoon water level; series B investigated the effect of a lower sea level on nearshore bar dynamics; series C simulated tidal effects; series D addressed the swash/overtopping/overwash threshold; and during series E the beach-barrier system was subjected to an extended period of energetic overwash conditions. This paper will describe the experimental design and the test programme during BARDEX II.

WAVE OVERTOPPING OF RUBBLE MOUND BREAKWATERS WITH CREST ELEMENTS

Crown walls or superstructures on top of permeable breakwaters are often used as a measure in existing structures to counteract insufficient design protection against overtopping. These crest elements, generally located well above the design water level, have been found to effectively decrease the mean overtopping discharge over a dike or rubble mound structure. The current study focusses at investigating the reduction in overtopping which can be expected from crest elements on a permeable breakwater.

MAXIMUM WIND EFFECT ON WAVE OVERTOPPING OF SLOPED COASTAL STRUCTURES WITH CREST ELEMENTS

Wave flume experiments were carried out on wind affected overtopping of rough and smooth sloping coastal structures with crest elements in the low overtopping regime (q* = q/ gHm0 < 2 x 10). The wind influence was modelled by a paddle wheel, a technique which has been shown to be reliable in assessing the maximum effect of wind on overtopping. Rough and smooth sloped coastal structures with slopes of 1:2 and 1:1.5 were tested. The crest of the coastal structure was modelled as a sharp crest using vertical crest elements of varying height. The results show that the mean overtopping discharge for rough and smooth sloping coastal structures under wind influence is in the range of 1.26.3 times the mean overtopping discharge without wind (qw/q 1.2 and 6.3) and thus in the same range as previously published for vertical structures.