3.gelombang

Hydrographic Science and Engineering Working Group
Faculty of Earth Science and Technology
Institute of Technology, Bandung
WAVESWAVES
Dr. rer nat. Wiwin Windupranata
coastal environmental survey windupranata@2010

WHY STUDY WAVES ?WHY STUDY WAVES ?

ShippingShipping

Coastal ConstructionsCoastal Constructions

Offshore ConstructionsOffshore Constructions

Beach Erosion and SedimentBeach Erosion and Sediment
TransportTransport

RecreationsRecreations

FUNDAMENTAL PRINCIPLESFUNDAMENTAL PRINCIPLES

Wave ParametersWave Parameters
Wave Period = Time it Takes a Wave Crest to Travel one
Wavelength (units of time)
Wave Frequency = Number of Crest per Unit Time Passing A Fixed
Location (units of 1/time)
Wave Speed = Distance a Wave Crest Travels per Unit Time (units
of distance/time)

Wave SpectrumWave Spectrum

Wave ClassificationWave Classification

Most of the waves present on the ocean’s
surface are wind-generated waves.
Wave ClassificationWave Classification
Size and type of wind-generated waves are controlled by Wind
velocity, Wind duration, Fetch, and Original state of sea surface
As wind velocity increases wave length, period and height increase,
but only if wind duration and fetch are sufficient
Significant wave height is the average wave height of the highest
1/3 of the waves present and is a good indicator of potential for
1/3 of the waves present and is a good indicator of potential for
wave damage

Addition of WavesAddition of Waves
Constructive
Destructive
Mixed

Ideal WavesIdeal Waves
Propagate Energy notPropagate Energy notPropagate Energy notPropagate Energy not
Water MassWater Mass

Wave MovementWave Movement
Note that the water molecules in the crest of the wave move in
the same direction as the wave, but molecules in the trough
move in the opposite direction

Wave MovementWave Movement
Note the importance of the
relationship between
wavelength and depth in
determining wave type.

Wave RegionsWave Regions

Deep-Water Waves (Bottom Depth > L/2)
– Speed is a Function of Wavelength Only
– Waves with Longer Wavelength move faster than Waves
Wave SpeedsWave Speeds
– Waves with Longer Wavelength move faster than Waves
with Shorter Wavelength
Shallow-Water Waves (Bottom Depth < L/20)
– Speed is a Function of Depth Only
– Waves (of any Wavelength) Travel Slower in Shallower
Water
Intermediate region (L/20 < Depth < L/2)
– Speed is a Function of Wavelength and Depth Only

Wave Speed as a Function ofWave Speed as a Function of
WavelengthWavelength

Wave Speed as a Function ofWave Speed as a Function of
Water DepthWater Depth

Wind speed - wind must be moving faster than the
Factors Affecting Wind WaveFactors Affecting Wind Wave
DevelopmentsDevelopments
Wind speed - wind must be moving faster than the
wave crests for energy transfer to continue
Wind duration - winds that blow for a short time will
not generate large waves
Fetch - the uninterrupted distance over which the wind
Fetch - the uninterrupted distance over which the wind
blows without changing direction

Factors Affecting Wind WaveFactors Affecting Wind Wave
DevelopmentsDevelopments

Wind Wave DevelopmentsWind Wave Developments
Wind waves are gravity waves formed by the transfer of wind energy
into water. Wind forces convert capillary waves to wind waves.

Lateral Spreading of Wave EnergyLateral Spreading of Wave Energy
from a Storm Sourcefrom a Storm Source
(95% of Energy Contained Within ±45o of Storm Direction)

The Importance of FetchThe Importance of Fetch

FetchFetch is the area of contact between the wind and the wateris the area of contact between the wind and the water
and is where windand is where wind--generated waves begingenerated waves begin
SeasSeas is the term applied when the fetch has a chaotic jumbleis the term applied when the fetch has a chaotic jumble
Life History of Ocean WavesLife History of Ocean Waves
SeasSeas is the term applied when the fetch has a chaotic jumbleis the term applied when the fetch has a chaotic jumble
of new wavesof new waves
WavesWaves continue to grow until the sea is fully developed orcontinue to grow until the sea is fully developed or
becomes limited bybecomes limited by fetch restrictionfetch restriction oror wind durationwind duration
Wave interferenceWave interference is the momentary interaction betweenis the momentary interaction between
waves as they pass through each other. Wave interference canwaves as they pass through each other. Wave interference can
be constructive or destructivebe constructive or destructive
be constructive or destructivebe constructive or destructive
Because celerity increases as wave length increases, longerBecause celerity increases as wave length increases, longer
waves travel faster than short waveswaves travel faster than short waves

WaveWave
InterferenceInterference

Wave TransformationsWave Transformations

WaveWave
TransformationsTransformations
Wave separation, or dispersion, is a
function of wavelength. Waves with
the longest wavelength move the
the longest wavelength move the
fastest and leave the area of wave
formation sooner. The smooth
undulation of ocean water caused
by wave dispersion is called swell.
The process known as a wave train.

The shallower the water, the greater the interactionThe shallower the water, the greater the interaction
between the wave and the bottom alters the wavebetween the wave and the bottom alters the wave
between the wave and the bottom alters the wavebetween the wave and the bottom alters the wave
properties, eventually causing the wave to collapseproperties, eventually causing the wave to collapse
Celerity decreases as depth decreases
Wave length decreases as depth decreases
Wave height increases as depth decreases
Troughs become flattened and wave profile becomes extremely
asymmetrical
asymmetrical
Period remains unchanged. Period is a fundamental property of
a wave
Refraction is the bending of a wave into an area where it
travels more slowly

Wave steepness (stability) is a ratio of wave heightWave steepness (stability) is a ratio of wave height
divided by wave lengthdivided by wave length
divided by wave lengthdivided by wave length
wave stability = H/Lwave stability = H/L
In shallow water, wave height increases and wave length
decreases
When H/L is larger than or equals to 1/7 (H/L ≥ 1/7), the
When H/L is larger than or equals to 1/7 (H/L ≥ 1/7), the
wave becomes unstable
There are three types of breakers:, Spilling breakers,
Plunging breakers, and Surging breakers

Spilling waves occur on gradually sloping ocean bottoms.
The crest of a spilling wave slides down the face of the wave as it
Waves Approaching ShoreWaves Approaching Shore
The crest of a spilling wave slides down the face of the wave as it
breaks on shore
Plunging waves break violently against the shore, leaving an air-filled
tube, or channel, between the crest and foot of the wave.
Plunging waves are formed when waves approach a shore over a
steeply sloped bottom
Surging waves occur on a very steep sloped bottom where the beach
slope exceeds wave steepness.
The wave does not really curl and break but runs up against the shore
while producing foam and large surges of water

Wave refraction - the slowing and bending of waves
in shallow water
in shallow water
Wave diffraction - propagation of a wave around an
obstacle
Wave reflection - occurs when waves “bounce back”
from an obstacle they encounter. Reflected waves
from an obstacle they encounter. Reflected waves
can cause interference with oncoming waves,
creating standing waves

Waves RefractionWaves Refraction
Bending of shallowBending of shallow--water wavewater wave
fronts due to change in bottomfronts due to change in bottom
depthdepth
The leading edge of a wave frontThe leading edge of a wave front
enters shallower water and slowsenters shallower water and slows
while the remaining frontwhile the remaining front
while the remaining frontwhile the remaining front
continues at higher speedcontinues at higher speed
The net result is a rotation ofThe net result is a rotation of
wave fronts toward being parallelwave fronts toward being parallel
with bottom depth contours.with bottom depth contours.

Waves RefractionWaves Refraction
Consequence of
wave refraction:
Focusing of wave
energy on
energy on
headlands
Defocusing of
wave energy on
bays

Waves DiffractionWaves Diffraction
Propagation of wave around an obstaclePropagation of wave around an obstacle

Waves ReflectionWaves Reflection
Wave reflection - occurs when waves “bounce back” from an
obstacle they encounter.obstacle they encounter.
When approaching a steep solid object, waves are bounced
back, creating a confused sea or interfering waves
Sometimes part of the energy is absorbed and the remaining
energy is reflected
Reflected waves can cause interference with oncoming waves,
Reflected waves can cause interference with oncoming waves,
creating standing waves

Waves ReflectionWaves Reflection

Storm surge is the rise in sea level resulting from lowStorm surge is the rise in sea level resulting from low
atmospheric pressure associated with storms and theatmospheric pressure associated with storms and the
Storm SurgeStorm Surge
atmospheric pressure associated with storms and theatmospheric pressure associated with storms and the
accumulation of water driven shoreward by the windsaccumulation of water driven shoreward by the winds
Water is deeper at the shore area, allowing waves to
progress farther inland
Storm surge is especially severe when superimposed
upon a high tide
upon a high tide

Standing WavesStanding Waves
Standing waves or seiches consist of a water surfaceStanding waves or seiches consist of a water surface
“seesawing” back and forth“seesawing” back and forth
A node is an imaginary line across the surface which experiences
no change in elevation as the standing wave oscillates. It is the
line about which the surface oscillates
Antinodes are where there is the maximum displacement of the
surface as it oscillates and are usually located at the edge of the
basin
Geometry of the basin controls the period of the standing wave
Geometry of the basin controls the period of the standing wave
A basin can be closed or open
Standing waves can be generated by storm surges

Resonance amplifies the displacement at the nodes and occurs whenResonance amplifies the displacement at the nodes and occurs when
the period of the basin is similar to the period of the forcethe period of the basin is similar to the period of the force
producing the standing waveproducing the standing wave

Internal WavesInternal Waves
Waves that occur at the boundaries of water layers
with different densities are called internal waves.

Internal waves form within the water column on theInternal waves form within the water column on the
pycnoclinepycnocline
pycnoclinepycnocline
Because of the small density difference between the water massesBecause of the small density difference between the water masses
above and below theabove and below the pycnoclinepycnocline, wave properties are different, wave properties are different
compared to surface wavescompared to surface waves
Internal waves display all the properties of surface progressiveInternal waves display all the properties of surface progressive
waves including reflection, refraction, interference, breaking, etcwaves including reflection, refraction, interference, breaking, etc
Any disturbance to theAny disturbance to the pycnoclinepycnocline can generate internal waves,can generate internal waves,
Any disturbance to theAny disturbance to the pycnoclinepycnocline can generate internal waves,can generate internal waves,
including: flow of water related to the tides, flow of water massesincluding: flow of water related to the tides, flow of water masses
past each other, storms, or submarine landslidespast each other, storms, or submarine landslides

Thin Layers of Phytoplankton Oscillating with an Internal Wave
Formed along the Continental Shelf

Tsunamis were previously called tidal waves, but areTsunamis were previously called tidal waves, but are
unrelated to tidesunrelated to tides
TsunamiTsunami
unrelated to tidesunrelated to tides
Tsunamis consist of a series of long-period waves characterized by
very long wave length (up to 100 km) and high speed (up to 760
km/hr) in the deep ocean
Because of their large wave length, tsunamis are shallow-water to
intermediate-water waves as they travel across the ocean basin
They become a danger when reaching coastal areas where wave
They become a danger when reaching coastal areas where wave
height can reach 10 m
Tsunamis originate from earthquakes, volcanic explosions, or
submarine landslides

TsunamiTsunami

Longshore Current andLongshore Current and
Sediment TransportSediment Transport

Longshore Current andLongshore Current and
Sediment TransportSediment Transport
Along-Shore Sediment Transport Obstructed by Groins

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