mag

Malaysia Water Research Journal
In flume, the interest study area is marked as 0cm – 250cm with 10cm interval
in Y direction (length of flume). Whilst in X direction the profile is marked from
0cm to 150cm (breadth of flume). Data sample for the first 30cm from both side
walls in the flume is ignored and considered as unstable due to wave reflection
effect. A datum or reference point is fixed at the top corner of flume wall. The
distance between datum and beach surface is remarked as height in Z-axis at
specific points. NEXC Block system is placed fixed along coordinate 0 – 150, 90 –
120 with single layer installation. Beach profile is measured manually each time
before and after simulation to compare the differences, associated to erosion or
accretion. In this paper, all erosion level is measured at the central of wave flume
(x-axis) along the beach profile (y-axis) which is at cross-section 70, 30 – 160 (x, y).
Figure 2 showed the experimental work conducted in wave flume with various
hydrodynamic parameters on a stiff and mild slopes environment. Simulation
equilibrium was set not more than 60 minutes.
Stability of coastal block as a coastal protection structure
The proposed coastal block aims to function as a natural solution to beach
erosion and renourishment. Based on simple conservative economics, the
structure can be used on either semi-permanent to permanent basis, contingent
on the scope of the renourishment project. Coastal blocks work in two ways;
firstly by breaking down the wave energy, therefore lessening erosion impact
to the shore. Secondly, it encourages beach expansion or natural nourishment
by permitting sea water which contains sediment and sand to pass through
the tapered hole. During ebb flow, sediments are trapped behind the structure
and unable to return to the sea. Over the time especially during a calm period,
sediments are accumulated hence expanding the beach naturally. Hence the
design of coastal block must be sufficiently stable against overturning and sliding
failures. The calculation of wave forces on coastal block is according to EM 1110-
2-1100 (Part VI), Goda formula for irregular waves (Goda, 1974; Tanimoto et al.,
1976).
Overturning failure is rotation of wall about its toe due to exceeding of
moment caused due overturning forces to resisting forces. Eq. [1] show the factor
of safety against overturning is given by:
[1]
where,
∑M R
= sum of resisting moment about toe
∑M 0
= sum of overturning moment about toe
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Institut Penyelidikan Hidraulik Kebangsaan Malaysia (NAHRIM)
National Hydraulic Institute of Malaysia (NAHRIM)