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Coastal Engineering: Theory and Practice
effects. They steepen due to the shallowing of the bottom depth contours
and finally break. When the incoming wave from deep water breaks, its
energy is dissipated along the surf zone width and when this width is insufficient or less to dissipate the energy the remaining energy is spent in eroding
the sédiments. These eroded materials either get suspended in the littoral
currents or gets deposited in the nearshore bottom forming an offshore
bar. When the offshore bar becomes large enough to facilitate breaking of
incoming waves, the energy contained in them gets dissipated in the surf
zone. The above said process of shore érosion due to the attack of storms
is illustrated in Fig. 4.1. In addition, at locations dominated by alongshore
currents moving the sédiments, man-made or natural barriers in the near
shore obstruct the free passage that would lead to advance of the shoreline on the updrift side and érosion along the shoreline on the downdrift
side.
□ EROSION
ES ACCRETION
NORMAL WAVE
ACTION
INITIAL ATTACK OF
STORM WAVES
MHW-MEAN HIGH WATER
MLW - MEAN LOW WATER
STORM WAVE ATTACK
OF FOREDUNE
AFTER STORM
ATTACK(NORMAL WAVE
ATTACK)
Fig. 4.1 Schematic diagram of storm wave attack on beach and dune.
4.3 Causes for Coastal Erosion
The broad classification of the causes for érosion due to nature anc
man-made obstructions are brought out in Table 4.1.