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Malaysia Water Research Journal
sliding failures. Vertical distribution of pressure due to wave force acting on sea
block is measured based on wave velocity and state (peak or trough) and water
level (Hanbin GU et al., 2003).
There are three available designs of NEXC Block with different face angles;
namely 30°, 45° and 60°. Due to technical, engineering and financial justification,
the 45° angle is selected and suited in the physical experiment and site
installations. Actual dimension of NEXC Block is 1.2m x 1.2m x 1.2m and each unit
weighs approximately 2,500kg, made of reinforced concrete grade 40 which is
suitable with marine environment. A laboratory scale model weighs about 5kg
each and was found sufficiently strong and stable in providing protection against
a downscaled wave and water level impacts in 2D wave flume simulations.
4 DISCUSSION ON LABORATORY DATA SAMPLING AND ANALYSIS
Figure 3 depicted the beach profiling on erosion-accretion analysis of
selected simulations. No structure simulations as presented in Figure 3a shows
that erosion occurred along the unprotected beach. Higher water level led to
erosion farther landward. Higher wave magnitude caused greater erosion level
or scarp height. Combination of high water and large wave magnitude caused
catastrophic impact; total sand loss along the exposed shore. Rate of erosion is
quicker and higher at a steeper slope and higher water levels conditions, until it
reaches equilibrium. Data and information from this simulation is used as control
and reference to the simulations with proposed coastal structure.
Figure 3b illustrated the erosion-accretion profile after simulations with NEXC
Block are completed. It is found that with NEXC Block installation, erosion is
controlled to occur only at the face of the structure, thus the backside of system
is protected. Erosion was generally occurred at all water level scenarios MLLW,
MSL and MHHW with Hs 0.2m. The protected beach at the backside of installation
was found safe with the installation of NEXC Block. The system were also found
stable against overturning and sliding failures.
It is also found that lower water level with lower wave magnitude encouraged
sediment accumulation at the structure face. This was found in simulation with
MLLW 0.9m and Hs 0.1m. In a longer calm period or outside monsoon season,
the accumulation process is repeated until the sediments are returned to the
beach and trapped behind the structure installation, resulted of a natural beach
nourishment.
Even though erosion is controlled to occur only at the face of the structure,
this has led to scouring problem at the toe of structure. Scour is found maximum
when water level is at the structure level; within wave breaking zone. Wave
impact on structure caused wave overtopping and sediment deposition near
structure toe. Higher water level which submerging the structure minimized the
impact of toe scouring. However due to higher water level reaching farther
landward, it left the area unprotected hence erosion is found more landward.
Nevertheless the structure managed to block and control the sediment from
moving farther seaward from land.
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Institut Penyelidikan Hidraulik Kebangsaan Malaysia (NAHRIM)
National Hydraulic Institute of Malaysia (NAHRIM)