Seminar Presentation

1. Coastal Processes
Wave Measurements
Usage of Buoys
Soumyaranjan Jena

2. Coastal Processes & Parameters
PROCESSES
● Erosion
● Transportation(Sediment, Pollutants)
● Deposition
PARAMETERS
● Wind
● Wave
● Current
● Tides

4. Classification of Coast
Coasts can be classified based on the energy of waves
1 High Energy coast
● . Large waves (frequently Batter) , Steep slope Sandy beaches
● . Rate of erosion exceeds rate of deposition
2 Low Energy coast
● Rate of deposition exceeds rate of erosion
● Infrequent wave batter, gentle slope, Marshes & Swamps

5. Wave Measurement: WHY & HOW
● Climate change
● Viability of projects, loadings on
ocean structures and ship routing
● To study land feature of coastal
region
● Energy extraction
● To study other important processes
like refraction, shoaling, diffraction,
wave breaking and reflection.
● Wave are measured and analyzed by two
methods;
1. Statistical Analysis (time domain)
2. Spectral Analysis( frequency domain )
● The data is used for wave modelling.eg.
Mike modelling, wavewatch3, SWAN, WAM
● Those models are useful in predicting and
for all those applications

6. Factors influencing wave generation
● Wind speed
● Fetch
● Duration
IMAGE

8. Classification of waves

9. Wave Theories
Shallow water wave theories
● Cnoidal wave theory
● Solitary wave theory
● Stream function theory
Deep water wave theories
● Airy wave theory
● Stokes wave theory

10. Real field waves: Statistical Analysis
● Linear superposition of waves of different
frequencies,direction, phase and
amplitude
● Follows stationary and ergodic process
● Spatial distribution of wave profile is
idealized into time series of sufficient
long, but enough for analysis
● Significant wave height is of most
practical interest among all the wave
heights

11. Spectral Analysis
● Wave spectrum is also a popular method of analyzing a lot
of wave data to find the wave energy vs frequency graph
● Some standard spectrum are
1. Pierson-Moskowitz Spectrum:
2. Bretschneider/ITTC spectrum: Same formula with
3. JONSWAP(Joint North Sea Wave project) spectrum 4. DNV Spectrum

12. Spectral Analysis
The concept of a spectrum is based on work by Joseph Fourier (1768 – 1830), who showed that almost any
function x(t) over the interval (-T / 2 < t < T / 2 ) can be represented as the sum of an infinite series of sine and
cosine functions with harmonic wave frequencies.
In the complex form, we can write the above equation as,
Where Zn is the fourier transform of x(t)

13. Spectral Analysis
Finally the spectrum can be written as
where significant wave height is ,

14. Wave Measurements
● Wave measurements can be made with different types of recorders kept either at the sea surface or
over and below it.
● The airborne devices include the satellite based sensing of the surface using a radar altimeter.
● The floating recorders could be either of electrical resistance gauges, ship borne pressure sensors or
wave rider buoys.
● The submerged category involves the pressure gauges and the echo sounders.
● Out of all above types the wave rider buoy is most commonly employed in routine wave data collection.
WAVE GAUGES
The wave gauge in general works in the principle of resistance, inductance or capacitance. Among these,
resistance type wave gauges are commonly used due to its ruggedness. In general, it comprises of two
parallel electrodes. When immersed in water, the electrodes measure the conductivity of the instantaneous
water volume between them. The conductivity change is proportional to the variation in the water surface
elevation. A set of compensation electrodes mounted at the bottom end of the wave gauge balance the
influence of temperature or salinity changes in the water.

15. Wave Measurements
VELOCITY PROBES
A common methodology adopted for resolving wave directionality is from the measurement of
water particle velocities in two perpendicular horizontal directions. The water particle velocity can be
measured using a velocity probe. This kind of probe works in the principle of mainly acoustics. An ultrasonic
laboratory current meter measures the current by transmitting acoustic signals between pairs of piezoelectric
transducer probes in three orthogonal directions. The transducers are made of, say 4 MHz ceramic elements.
The horizontal axes of the probe use reflector, while, the vertical axis uses a direct signal path. Nowadays,
ADV (Acoustic Doppler Velocimeter) is commonly used which measures three components particle velocity
based on the principle of acoustic scattering.
REMOTE SENSING MEASUREMENTS
In addition, in the real field application, the sea-surface waves are measured over a certain area rather than at
a single point (as using directional buoy) by applying remote sensing methods. There are two techniques:
1. Optical methods following stereophotogrammetry and holography in which aerial photographs form the
basis of analysis.
2. Microwave techniques based on radar observations (space borne Synthetic Aperture Radar, SAR or coastal
land based LIDAR).

16. BUOY SYSTEMS
● can be anchored (stationary) or allowed to drift with ocean currents
● Due to its ease installation, precision in measurement and applicable over a wider range of water depths,
the use of floating buoy, often denoted as “data buoy” for the ocean wave measurements has significantly
increased in the world ocean.
● Generally, buoy systems are divided into three different categories, namely, surface, subsurface and free
drifting buoys.
● The drifters are mainly used for tracking ocean current direction and magnitude.
● The surface floating buoy system is widely being adopted for the wave data collection, because, they can
also be used for the measurement of meteorological parameters, such as characteristics of air
(temperature and pressure), wind (velocity and direction), current (direction and magnitude) and water
(temperature, conductivity and salinity).

17. BUOY SYSTEMS

18. BUOY SYSTEMS

19. BUOY HULL TYPES

20. TYPES ACCORDING TO PATH FOLLOWS

21. Normally used buoys

22. BUOYS on WORLD MAP

23. INDIAN DATA BUOYS

24. Wave control mechanism
Wave control theories:
Hard Engineering
● Break waters
● Gabions
● Groins
● Revetments
● Seawall
● Jetties
Soft Engineering
● Beach Nourishment
● Dune stabilization
● Mangroves
● Coral reefs
● Marsh land
● Reflection
● Refraction
● Scattering
● Wave breaking
● Phase change

25. Thank you