186
R.H. Charlier and Chr. P. De Meyer
Mud coasts, common in the tropics, constitute a somewhat particular case.
Destruction has been generally man-induced.
The 860 km (533 mi) east coast of Peninsular Malaysia consists of a straight
sandy coast in the north while the southern half is comprised of a series of large
and small hook - and spiral-shaped bays. The west coast, 1,100 km (682 mi)
long, is made up of low elevation coastal plains formed from a deep marine clay
stratum. The 1,800 km (1,116 mi) coastline of Sabah is characterized by rugged
formation, and many bays of a variety of sizes and shapes, sandy beaches and
mud coast, a situation similar in 1,040 km (645 mi) coastline of Sarawak.
Large tracts of the mangrove fringed coastline of the west coast of peninsular
Malaysia have been reclaimed for agricultural development through construction
of coastal embankments (coastal bunds or dykes) to prevent tidal flooding.
Hinterland drainage is regulated through a series of tidal control gates. Bands, at
least 400 m from the seaward edge of the mangrove area, are protected against
waves by mangrove buffer, but the protection is lost when mangroves vanishes
due to erosion. [Midum and Lee, 1989, Mud coast protection - Malaya : Coast.
Zone '89 1, 806-820].
There are two conceivable approaches to effecting coastal protection in
mangrove-fringed coasts, to wit stabilizing the eroding scarp by means of
revetment aligned approximately parallel to and positioned at adequate distance
seaward of the threatened bund. Eventually supplemented with replanting of
mangroves in the intervening space, if site condition permits, and direct bund
protection of the threatened bund with surface armoring to develop a functional
reveted structure.
The first approach is in effect a composite scheme in which the escarpment
protection acts to absorb/expend the energy of the incoming waves by triggering
off early wave breaking, while the mangroves filter the smaller secondary waves
passing unbroken over the escarpment crown of reformed waves regenerated
landward of the escarpment. Here, the minimum width of the mangrove thicket
required to effectively attenuate the secondary/reformed waves is 50 m (164 ft).
The second approach is used when the eroding shoreline has encroached very
close to the bund line. The mangrove tree trunks, their protruding roots and the
dense underbush throughout the mangrove thicket acts as a wave filter. Waves up
to 1 m (3.28 ft) are completely attenuated by mangrove thickets 30 to 50 m (98 to
164 ft) wide. Where mangroves have been severely denuded, direct bund
revetment remains the only feasible option short of bund retreat. The bund
protection comprises two layers of armor rocks with individual weight heavy
enough to remain stable under the action of the breaking waves. Below the cover
layer are smaller rocks forming the secondary layer. Further down, a geotextile
layer forms the separator between the rock mass and the in situ ground.
R.H. Charlier and Chr. P. De Meyer
Mud coasts, common in the tropics, constitute a somewhat particular case.
Destruction has been generally man-induced.
The 860 km (533 mi) east coast of Peninsular Malaysia consists of a straight
sandy coast in the north while the southern half is comprised of a series of large
and small hook - and spiral-shaped bays. The west coast, 1,100 km (682 mi)
long, is made up of low elevation coastal plains formed from a deep marine clay
stratum. The 1,800 km (1,116 mi) coastline of Sabah is characterized by rugged
formation, and many bays of a variety of sizes and shapes, sandy beaches and
mud coast, a situation similar in 1,040 km (645 mi) coastline of Sarawak.
Large tracts of the mangrove fringed coastline of the west coast of peninsular
Malaysia have been reclaimed for agricultural development through construction
of coastal embankments (coastal bunds or dykes) to prevent tidal flooding.
Hinterland drainage is regulated through a series of tidal control gates. Bands, at
least 400 m from the seaward edge of the mangrove area, are protected against
waves by mangrove buffer, but the protection is lost when mangroves vanishes
due to erosion. [Midum and Lee, 1989, Mud coast protection - Malaya : Coast.
Zone '89 1, 806-820].
There are two conceivable approaches to effecting coastal protection in
mangrove-fringed coasts, to wit stabilizing the eroding scarp by means of
revetment aligned approximately parallel to and positioned at adequate distance
seaward of the threatened bund. Eventually supplemented with replanting of
mangroves in the intervening space, if site condition permits, and direct bund
protection of the threatened bund with surface armoring to develop a functional
reveted structure.
The first approach is in effect a composite scheme in which the escarpment
protection acts to absorb/expend the energy of the incoming waves by triggering
off early wave breaking, while the mangroves filter the smaller secondary waves
passing unbroken over the escarpment crown of reformed waves regenerated
landward of the escarpment. Here, the minimum width of the mangrove thicket
required to effectively attenuate the secondary/reformed waves is 50 m (164 ft).
The second approach is used when the eroding shoreline has encroached very
close to the bund line. The mangrove tree trunks, their protruding roots and the
dense underbush throughout the mangrove thicket acts as a wave filter. Waves up
to 1 m (3.28 ft) are completely attenuated by mangrove thickets 30 to 50 m (98 to
164 ft) wide. Where mangroves have been severely denuded, direct bund
revetment remains the only feasible option short of bund retreat. The bund
protection comprises two layers of armor rocks with individual weight heavy
enough to remain stable under the action of the breaking waves. Below the cover
layer are smaller rocks forming the secondary layer. Further down, a geotextile
layer forms the separator between the rock mass and the in situ ground.