| Summary: | Longshore current is formed when the breaking wave direction make a certain angle to shore line. The longshore current in the surf zone may cause longshore sediment transport. Longshore the sediment transport can cause coastal erotion. One of the solution to overcome this kind of erotion is use groins as coastal protection. Therefore impermeable atructure in groins must be changed by permeable structure that can passed by longshore current but still can reduce the velocity of longshore current.
This reseacrh utilize two model of permeable groins, double peermeable groins with diameter (dt) 1,25cm and 1,5cm. sSpace between groins pile (a) 0,7cm and 1cm, length of groins (L) 50cm and the length between two structure groins (b) 0,5m, 1m, 1,5m. The equipments are wave generator, ADV (Accoustic Dopler Velocimeter). wave probe, gauge and camera. this research also utilize fix bed without sediment as sea bed. Longshore current verocity and wave height are collected in this reseacrh. This research location is in hydraulic laboratory of civil engineering, Gajhah Mada University.
The result show that be longshore current is derected in occurence with the breaking wave direction. Current rose also shows that dominant current direction is directed in ocurence with the breaking wave direction. The current velocity decreases after pass permeable groins structure. The reduction of longshore current velocity is calsulated base on the difference of current velocity with (Vg) and without groins (Vo). The reduction increase when the ratio of the length of eeach groins structure (b) with the groins length (L) decrease while the reduction coefficient increase wwhen the ratio of the length of each groins structure (b) with the groins length (L) increase. The reduction of longshore current velocity increase when permeability of groins decrease while reduction coeffeicient of longshore current velocity increase when permeability of groins increase.
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