Environmental Engineering Reference
In-Depth Information
N
INDIA
S 9
S 8
S 7
S 1
S 10
S 11
S 6
S 2
S 12
S 3
S 4
S 5
Bay of Bengal
Fig. 1.13 Map showing the major estuaries of Indian
Sundarbans;
freshwater and have become tide-fed in nature;
S 7 - S 12
are in the eastern Indian Sundarbans (adjacent to Bangla-
desh Sundarbans), which receive certain volume of
freshwater through creeks and inlets from the Bangladesh
Sundarbans part
are the sampling stations.
S 1 - S 4 are in the western Indian Sundarbans, where the
salinity is relatively low due to Farakka barrage discharge;
S 5 and
the
red circles
S 6 are in the central sector of Indian Sundarbans,
where the rivers have lost
their connections with
In a wave train, there is a regular succession
of crests and troughs (Fig. 1.20 ). The horizontal
distance between successive crests is the wave-
length (L), while the wave height (H) is the
vertical distance from a crest to a trough.
The period (T) is the time for passage of two
successive wave crests passed through a
This causes elliptical-shaped orbits. Wave size
and speed depend on wind speed, wind duration
and distance of water over which the wind blows.
Theoretically, a wave
'
s height cannot exceed
0.14 of its wavelength. If this is exceeded, white
caps and breaking waves are formed.
Ocean surface waves can be classi
xed
point and is usually expressed in seconds. Wave
speed (V) can be calculated by V = L/T.
At the surface, water moves in circular verti-
cal orbits with a diameter equal to the wave
height. Away from the surface, orbital motion
decreases, and orbits become smaller. At a depth
of half a wavelength (L/2), orbital motion
essentially vanishes. Thus, wave-generated water
movements only occur near the surface. Where
the water depth is less than half a wavelength, the
bottom interferes with the water motion. Water
particles near the bottom cannot move vertically.
ed in
several ways. The most common way is by the
period of the waves (Table 1.5 ).
a. The shortest period waves under this classi
-
cation are the capillary waves. When the wind
starts to blow on the ocean surface, capillary
waves are generated. They seem just like a
ne
structure of small ripples of nearly capillary
dimension. They basically contribute the larg-
est amount of energy from the wind to the ocean
water. Their wavelength is up to 1.74 cm.
b. Ultra-gravity wave is another type of wave
with periods between 0.1 and 1 s.
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