| Summary: | The problem of coastal erosion has gained widespread and serious attention
from government and society, as a direct result their impact cause losses both
material and casualties. Submerged breakwater of geotextile tube (geotube) type is
an alternative to coastal protection structure against erosion. This research aims
to determine the effect of gap width variation to the waves characteristic
(transmission and piling-up), rip-current, sedimen transport pattern and stable
shore profile behind submerged breakwater.
The Research carried out with physical model in the Hydraulics laboratory
of Civil and Environmental Engineering, UGM. Physical model of submerged
breakwater was conducted with variations of gap 25 cm, 50 cm and 125 cm. while
the other parameter (Rc / hs = 0), Ho = 8,9 cm, To = 1,4 sec sediment variety are
Krakal Beach (D50 = 0,8 mm), Gs = 2650 kg/m
3
. The model wave basin with
dimension 9 m x 7 m, the initial slope of sand behind structure at surfzone is 1 :
5,88 and constant regular wave deploy until sand profile behind structure
approaching stable condition. Data analysis use software Microsoft Excel and
Surfer 9.
Results of the research showed that the effect of increasing gap width
between segmen geotube: wave transmission has increased, piling-up has
decreased, deviate value between rip-current analysis and measured rip-current
has increased however head loss coefficient (Cv) has decreased, the area of sand
movement behind structure has increasingly widespread, beach slope on the
surfzone has decreased, errosion profile behind the structure and the gap have
increased. Maximum gap width when submerged breakwater has the function to
maintain acretion at Lo/Lg � 23,577 and Lg/Lb � 0,44.
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