4. Coastal Erosion and Protection Measures Including Case Studies
99
Table 4.1. Causes for Coastal érosion.
Nature
Man-made
Rise in sea level
Construction of dams, dykes and other
Coastal structures.
Protruding headlands, reefs or rocks
into the sea
Groins, breakwaters, jetties etc.
Tidal entrances and river mouths
causing interruption of free passage of
sédiments along the shore, natural
protection of tidal entrances
Manmade entrances causing interruption of
littoral drift. This includes construction
jetties.
Shoreline geometry causing rapid
increase of drift quantity
Fills protruding in the océan to an extent
that they change local shoreline geometry
radically.
Removal of beach material by wind
drift
Removal of material from beaches for
construction and other purposes.
Removal of beach material by sudden
outbursts of flood waters
Digging or dredging of new inlets, channels
and entrances offshore dumping of materials.
4.4 Strategy for Coastal Protection
Prior to planning of protection measures, one has to understand the basic
behaviour of waves in moving the sédiments and its interaction with sédiments that décidés the zone of érosion and accression. The block diagram
shown in Fig. 4.2, clearly explains the conditions under which a coast could
be stable or otherwise.
Whenever érosion occurs, there are some guidelines to be followed. Coping érosion along a sandy coast is different from coping érosion along muddy
coast, mangrove coast, and coast with clay or rock. The following are the
suggested procedures:
• Verify if the érosion is temporary due to seasonal effect.
• Work out the cost of different alternatives. The costs should include not
only maintenance, construction etc. but also in terms of loss of cultural
values, impact on safety and the needs of the local public, etc.
• Fund/resources to combat érosion in a sustainable way.
Only after ascertaining the above basic resources and needs, proceed as
follows:
• If fund/resources are available, then combat érosion permanently by
proper planning.
99
Table 4.1. Causes for Coastal érosion.
Nature
Man-made
Rise in sea level
Construction of dams, dykes and other
Coastal structures.
Protruding headlands, reefs or rocks
into the sea
Groins, breakwaters, jetties etc.
Tidal entrances and river mouths
causing interruption of free passage of
sédiments along the shore, natural
protection of tidal entrances
Manmade entrances causing interruption of
littoral drift. This includes construction
jetties.
Shoreline geometry causing rapid
increase of drift quantity
Fills protruding in the océan to an extent
that they change local shoreline geometry
radically.
Removal of beach material by wind
drift
Removal of material from beaches for
construction and other purposes.
Removal of beach material by sudden
outbursts of flood waters
Digging or dredging of new inlets, channels
and entrances offshore dumping of materials.
4.4 Strategy for Coastal Protection
Prior to planning of protection measures, one has to understand the basic
behaviour of waves in moving the sédiments and its interaction with sédiments that décidés the zone of érosion and accression. The block diagram
shown in Fig. 4.2, clearly explains the conditions under which a coast could
be stable or otherwise.
Whenever érosion occurs, there are some guidelines to be followed. Coping érosion along a sandy coast is different from coping érosion along muddy
coast, mangrove coast, and coast with clay or rock. The following are the
suggested procedures:
• Verify if the érosion is temporary due to seasonal effect.
• Work out the cost of different alternatives. The costs should include not
only maintenance, construction etc. but also in terms of loss of cultural
values, impact on safety and the needs of the local public, etc.
• Fund/resources to combat érosion in a sustainable way.
Only after ascertaining the above basic resources and needs, proceed as
follows:
• If fund/resources are available, then combat érosion permanently by
proper planning.