8
Coastal Engineering: Theory and Practice
the near shore, it usually steepen while its length reduces resulting in the
waves breaking. The rnost widely adopted criteria for the wave to break are
listed below.
(1) When horizontal particle velocity at the crest exceeds the celerity of
the wave.
(2) When vertical particle accélération is greater than accélération due to
gravity.
(3) When crest angle is less than 120°.
(4) When the wave steepness, H/L> 0.142 tanh kd and for deep waters
tanh kd will become 1.
(5) When wave height is greater than 0.78d.
The characteristics of the beaches dépend also on the type of wave
breaking, which in turn, dépend on the wave steepness and the beach slope.
It is characterised as per the parameter, M = tan/3/^/Hq/Lq. The breaker
types namely spilling, plunging, surging and collapsing dictâtes the extent
of mixing of sédiments in the breaker zone.
When waves of low steepness waves break over beaches of mild slopes,
spilling breakers are generated in which case N\ is less than 0.5. Breaking is
graduai and is by continuous spilling of foam down the front face sometimes
called as “white water”. Such breakers are expected to move fine sédiments
on to the beach. Plunging breakers occur when waves of medium steep
break over beach of medium steepness. The waves at breaking curl over.
The breaking is instant and N\ = 0.5 to 3.3. The beaches are characterized
by well mixed sédiments as they are churned due to the turbulence induced
during breaking. Surging breakers occur with the steepest waves breaking
over steep slopes. The base of the wave surges up the beach generating
considérable foam. It builds up as if to form the plunging type. For this
type of breaker N\ > 3.3. A fourth category of breaking waves called as
"Collapsing breakers” that would be in between the plunging and surging
breakers.
1.2.5 Reflection
\\ hen waves strike vertical imperméable obstructions its amplitude will be
twice (standing waves) inducing larger forces as well as a large velocity gradient along the vertical plane. This velocity gradient in turn will accelerate
scour at the toe of the structure and may lead to its instability. This could
be avoided by designing suitable toe protection. It is wise to avoid such
Coastal Engineering: Theory and Practice
the near shore, it usually steepen while its length reduces resulting in the
waves breaking. The rnost widely adopted criteria for the wave to break are
listed below.
(1) When horizontal particle velocity at the crest exceeds the celerity of
the wave.
(2) When vertical particle accélération is greater than accélération due to
gravity.
(3) When crest angle is less than 120°.
(4) When the wave steepness, H/L> 0.142 tanh kd and for deep waters
tanh kd will become 1.
(5) When wave height is greater than 0.78d.
The characteristics of the beaches dépend also on the type of wave
breaking, which in turn, dépend on the wave steepness and the beach slope.
It is characterised as per the parameter, M = tan/3/^/Hq/Lq. The breaker
types namely spilling, plunging, surging and collapsing dictâtes the extent
of mixing of sédiments in the breaker zone.
When waves of low steepness waves break over beaches of mild slopes,
spilling breakers are generated in which case N\ is less than 0.5. Breaking is
graduai and is by continuous spilling of foam down the front face sometimes
called as “white water”. Such breakers are expected to move fine sédiments
on to the beach. Plunging breakers occur when waves of medium steep
break over beach of medium steepness. The waves at breaking curl over.
The breaking is instant and N\ = 0.5 to 3.3. The beaches are characterized
by well mixed sédiments as they are churned due to the turbulence induced
during breaking. Surging breakers occur with the steepest waves breaking
over steep slopes. The base of the wave surges up the beach generating
considérable foam. It builds up as if to form the plunging type. For this
type of breaker N\ > 3.3. A fourth category of breaking waves called as
"Collapsing breakers” that would be in between the plunging and surging
breakers.
1.2.5 Reflection
\\ hen waves strike vertical imperméable obstructions its amplitude will be
twice (standing waves) inducing larger forces as well as a large velocity gradient along the vertical plane. This velocity gradient in turn will accelerate
scour at the toe of the structure and may lead to its instability. This could
be avoided by designing suitable toe protection. It is wise to avoid such