Title: Introduction of environmentally friendly solution for Coast conservation:
Alternative man made structure for rock armours and boulders
C.P. Gunasena, Department of Agric. Engineering, Faculty of Agriculture, University of
Ruhuna, Mapalana, Kamburupitiya, Sri Lanka.
1. To introduce alternative cement structure for rock armours
2. To stop rock blasting for coast conservation
3. To restore Bio-diversity and natural balance around coastal areas as well as inland rocky
4. To create employment opportunities
Naturally there is a balance between land, shore and sea. This balance can be seen very clearly where bays
are located. A bay has a specific shape that can be illustrated as half circle or half of a ellipse.
There is a big impact on coastal areas by water pressure and momentum due to under currents. Due to this
pressure and under currents huge amount of energy brings by waves from the sea to the shore. On the other
hand there is a big resistance to coastal erosion from the land side. Due to ultimate balance of these two
phenomena a bay evolves.
Figure - 1
The occurrence of this balance is illustrated in (Figure -1). At certain bays there are some naturally built
rocky structures, which helps to reduce energy, which carries by the waves.
Figure - 2
Naturally balanced sea beach is illustrated in (Figure - 2). Rocky structures can be seen in the shallow
waters. These structures help to reduce the horizontal component of the energy, which brings by the waves.
These rocky structures are little bit inclined and inclined surface is faced to the sea. Waves that are coming
from the deep sea climb these surfaces and reduce their horizontal component of the energy. This prevents
the erosion of the land side. This is the natural phenomenon and it occurs, where these inclined rocky
structures present in the shallow waters. The shape of these structures was identified and according to that,
shape of the artificial structure was designed.
Figure - 3
When there is no such rocky structures, sea beach get eroded and it shows in the (Figure - 3). Eroded
surface can be more than two to three meters in height. Due to the erosion coconut plantation is also get
damaged in some areas of the island. In order to prevent this types of erosion, certain measures have been
taken by the coast conservation department. Offshore breakwaters and revetments can be constructed to
safeguard the coastal belt.
Figure - 4 Figure - 5
A revetment constructed at a roadside is shows in (Figure - 4). Wave comes from the sea directly hit this
structure and it climbs upward. Some occasion seawater flows in to the road. Return flow (R.F) the
downward movement of the wave generates much higher energy, which course scouring at the bottom of
the structure and revetment will collapse.
A breakwater constructed at offshore is illustrated in the (Figure - 5). In the deep sea huge amount of
energy brings by sea waves. These waves directly hit these breakwaters and without proceeding towards
the shore, it gets reflected backwards. This reflected energy goes some other place and course erosion. It is
obvious that these two methods are at the extremes, when compare to the natural phenomenon. Proposed
structure is illustrated in the (Figure - 6)
Figure - 6
By observing parameters of natural phenomenon this cement structure has been formulated (Figure -6).
Dimensions are not defined. These dimensions have to be adjusted where it is necessary. These structures
can be stacked together as a natural coral reef at a desirable height. It will behave as a natural coral reef and
protect our coastal environment. By using these structures we can re built our nature which is already
destroyed by sand mining and coral mining.
In this method no huge structures are constructed at off shore or any other placeless of the profile of the
sea. Waves are allowed to develop naturally and allow reaching the shore. Energy reduction happens at
near shore. As it happen naturally it happens with these structures too. Sand trapping from return flow will
also occur naturally.
Horizontal component of the force or energy of the waves, which comes from the sea directly, strike the
inclined surface of the structure. (Figure - 6). Then the force, speed and the energy gets reduced due to the
collision with the inclined surface of the structure and waves are allowed to proceed to the shore. This
minimizes the energy of the return flow and it helps to reduce the scouring of the bottom of the structure.
When offshore breakwaters, revetments, groins are concern, due to height of these structures scouring is
obvious at the bottom. There is no mechanism to trap sand particles, which are carried by the return flow of
seawater (Figure -5). By putting off shore breakwaters, groins, and other artificial huge structures,
neighboring areas will bet eroded due to reflecting waves form these structures. Placing these cement
structures in front of these eroding areas, sea erosion can be prevented. Neighboring areas will not get
eroded. Energy reduction will happen in an ordinary way. It also helps to trap sand particles by preventing
along shore and across shore sand movements. Automatically natural balance of the beach will be restored.
Structure arrangement is illustrated in (Figure - 7)
Geographical stability of hill country in Sri Lnaka depends on huge Rocky Mountains. These rocky
mountains are being blasted for rock armours to prevent coastal erosion. This can be a course for earth
slips. We save our coastal belt by destroying our rocky environment. This type of man made cement
structures could be a good solution to conserve our environment.
Hazardous wastes, which are discarded by the factories, can be used to make these structures. It helps to
minimize environmental pollution. Since there is no higher level designing in constructing these concert
blocks, these can be constructed by village masons. It will be an added advantage for the unemployment.